Ehrlichiosis and Anaplasmosis Subcommittee Report to the Tick-Borne Disease Working Group

Disclaimer

Information and opinions in this report do not necessarily reflect the opinions of the Working Group, the U.S. Department of Health and Human Services, or any other component of the federal government. Readers should not consider the report or any part of it to be guidance or instruction regarding the diagnosis, care, or treatment of tick-borne diseases or to supersede in any way existing guidance. All subcommittee members actively participated in the development of this report. Members voted to approve submission of the report to the Working Group and on the wording of each of the possible actions contained in the report. The vote to submit the report indicates general agreement with the content of the document, but it does not necessarily indicate complete agreement with each and every statement in the full report.

Background

Ehrlichiosis and anaplasmosisare important human health threats caused by Ehrlichia species and Anaplasma phagocytophilum, respectively. These tick-borne bacterial infections were mentioned in the first Tick-Borne Disease Working Group report but were not the subject of focused discussion. They differ from Lyme disease in many ways. Importantly, ehrlichiosis and anaplasmosis have much higher fatality rates than Lyme disease, despite a lower prevalence in humans and tick vectors, and are significantly under-recognized by primary care physicians in the United States. In addition, all three infections have distinctive clinical presentations.

The primary pathogens causing ehrlichiosis and anaplasmosis are Ehrlichia chaffeensis and Anaplasma phagocytophilum, respectively. Ehrlichia chaffeensis causes human monocytic ehrlichiosis (HME) and is transmitted to humans by the lone star tick, Amblyomma americanum, while A. phagocytophilum causes human granulocytic anaplasmosis (HGA) and is transmitted by the black-legged (deer) tick, Ixodes scapularis. Additional Ehrlichia species have also been recognized and will be covered in this report. All of the species were recognized after the identification of Borrelia burgdorferi in 1981, and thus less is known about these important pathogens.

The incidence of anaplasmosis and ehrlichiosis is rising in the United States. Compared to the documented four-fold increase in Lyme disease between 2004 and 2016 (Rosenberg, 2018), the number of ehrlichiosis cases reported to U.S. Centers for Disease Control and Prevention (CDC) also rose four-fold from 338 in 2004 to 1,377 in 2016 (Madison-Antenucci et al. 2020). The increase in the number of lone star tickslikely explains the increased human exposure and incidence of disease observed in the Southeast and South-Central U.S. A similar spread of lone star ticks into new regions of the North, New England including Maine; West; and Midwest, including Ohio, Illinois, Iowa, Kansas, and Nebraska has been observed, suggest an expanding human risk and reporting of HME. HGA cases based on CDC data have also increased; reported cases have increased even faster than Lyme disease, eightfold, from 537 cases in 2004 to 4151 cases in 2016; a 39% increase was documented between 2016 and 2017 alone (Centers for Disease Control and Prevention [CDC], 2019a). As with the lone star tick, the black-legged tick has shown significant expansion of its geographic range in the United States, resulting in expanded human risk of HGA. Unfortunately, the CDC data do not capture the true incidence of disease since these are based upon passive surveillance systems which suffer from important limitations. Passive surveillance requires physician awareness and consideration of these diseases in their diagnosis, performance of appropriate laboratory testing, and submission of case report forms to CDC. None of these activities are performed at a satisfactory rate. Studies using active surveillance methods show significantly higher incidence rates (ten to fiftyfold higher).

Despite the increasing numbers of HME and HGA cases, clinical awareness of these diseases is low. For example, a survey of U.S. patients revealed that only 1.4% were familiar with ehrlichiosis, compared with more than 50% for Lyme disease. Lack of consideration of the diagnosis of ehrlichiosis is prevalent in regions endemic for lone star ticks, and this likely contributes to underdiagnosis. In North Carolina, over 90% of ticks humans encounter are lone star ticks, and yet physicians were twice as likely to test for Lyme disease (66%) than ehrlichiosis (36%) (Boyce et al., 2018). Retrospective testing for ehrlichiosis in those not tested revealed that 20.2% of patients in this study were positive for Ehrlichia.

Finally, HME and HGA have significant case fatality rates (2.7% and 0.3% respectively). Given that many cases of these infections may be misdiagnosed or undiagnosed, these rates are likely higher than reported.

The following aspects of ehrlichiosis and anaplasmosis were discussed and summarized: etiology, surveillance, disease presentation and management, diagnosis, treatment, and pathogenesis. Key needs were identified based on important gaps in our understanding of disease. These knowledge gaps arise from incomplete studies assessing active disease surveillance, a lack of practitioner awareness in endemic areas, and lingering pathogenesis questions.

Methods

Membership – In establishing the subcommittee, the co-chairs made a deliberate effort to ensure diversity among the group by including - university researchers, government scientists, public health professionals, physicians, and patient advocates. In addition to including members from different stakeholder groups, subcommittee members were also selected to represent different regional perspectives due to the regionality of these illnesses. The subcommittee members and a brief description of their qualifications to serve are included in Table 1. Except for one co-chair and one member, all remaining subcommittee members were non-federal participants. The subcommittee was supported by a science writing team; and a federal officer, Debbie Seem, RN, MPH; throughout their deliberations.

Table 1: Members of the Ehrlichiosis and Anaplasmosis Subcommittee.

Members	Type	Stakeholder Group	Expertise
Co-Chair Dennis M. Dixon, PhD, Chief, Bacteriology and Mycology Branch, National Institute of Allergy and Infectious Diseases, National Institutes of Health, U.S. Department of Health and Human Services (HHS); Rockville, MD	Federal	Scientist	Microbiologist with over 40 years of experience spanning academia, industry (sabbatical), state government (clinical laboratory) and federal government.
Co-Chairs David Hughes Walker, MD, Professor, Department of Pathology, The Carmage and Martha Walls Distinguished University in Tropical Diseases; Executive Director, University of Texas Medical Branch Center for Biodefense and Emerging Infectious Diseases; Galveston, TX	Public	Scientist	48 years of experience in vector-borne zoonotic diseases including 29 years of research on ehrlichiosis with emphasis on pathogenesis, immunity, and diagnosis. Co-discoverer of human anaplasmosis. Funded by NIH for research on rickettsial diseases since 1979.
John A. Branda, MD, Associate Professor of Pathology, Harvard Medical School; and Clinical Laboratory Director and Research Investigator, Clinical Microbiology Laboratories, Massachusetts General Hospital; Cambridge, MA	Public	Scientist and Health Care Provider	Specialist in medical microbiology with over 15 years of clinical and research laboratory experience in the diagnosis of tick-borne infectious diseases.
Stephen Clark, PhD, Retired Associate Professor Emeritus, University of Connecticut School of Medicine; Farmington, CT	Public	Patient and Patient Advocate	Patient with an Anaplasma infection. Relayed experience with the infection, treatment, and recovery.
J. Stephen Dumler, MD, Professor and Chairperson, Department of Pathology, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, U.S. Department of Defense (DoD); Bethesda, MD	Federal	Scientist and Health Care Provider	Over 40 years’ experience with tick-borne disease including co-discoverer of human anaplasmosis, rickettsial diseases, Lyme disease, and other vector-borne infections. Board certified in Anatomic and Clinical Pathology, with special emphasis in Medical Microbiology and Parasitology. Continuously funded by NIH since 1996 for work on tick-borne infections.
Harold W. Horowitz, MD, Professor of Clinical Medicine, Weill Cornell Medicine; and Chief of Service, Infectious Diseases Hospital Epidemiologist, New York-Presbyterian Brooklyn Methodist Hospital; New York, NY	Public	Scientist and Health Care Provider	20 years’ experience in describing the clinical presentation, laboratory evaluation, and natural history of individual tick-borne diseases and co-infection in New York State.
Bobbi S. Pritt, MD, MSc, Professor of Laboratory Medicine and Pathology; Medical Director, Clinical Parasitology Laboratory; and Co-Director, Vector-borne Diseases Laboratory Services, Mayo Clinic; Rochester, MN	Public	Scientist and Health Care Provider	12 years’ experience overseeing molecular testing of specimens from patients suspected of having a tick-borne disease. Led collaborative efforts with state and national health laboratories to characterize two novel tick-borne pathogens (Borrelia mayonii and Ehrlichia muris eauclairensis).
Daniel J. Sexton, MD, FACP, FIDSA, Professor of Medicine, Division of Infectious Diseases, Duke University Medical Center; Durham NC	Public	Scientist and Health Care Provider	Over 40 years’ research and clinical experience with spotted fever rickettsioses and other vector-borne diseases with an emphasis on their epidemiology and clinical features both in the United States and Australia.
Gregory (Greg) A. Storch, MD, Ruth L. Siteman Professor of Pediatrics, Washington University School of Medicine; St. Louis, MO	Public	Scientist and Health Care Provider	Pediatric infectious disease clinician with more than 35 years’ experience caring for children with monocytic ehrlichiosis and other tick-borne infections, and expertise in molecular diagnostic tests for ehrlichiosis.

Meetings – Initial discussions between the co-chairs yielded a framework for the report that draws upon the scientific conventions used in peer reviewed research publications: an introduction of the topic, a summary of recent history, then current research and findings. The topics for focus and the approach to summarizing the topics were discussed in 11 bi-weekly conference calls with the full subcommittee from July 18, 2019 through January 10, 2020. Conference calls were complemented with email exchanges to arrive at the topics for focus and the selection of subject matter experts for summarizing the topics. Consensus was gained in group conference calls when key milestones were met. The technical writer summarized the calls; summaries were reviewed by co-chairs and circulated to subcommittee members. An overview of these meetings is presented in Table 2.

Table 2: Overview of Ehrlichiosis and Anaplasmosis Subcommittee Meetings, 2019.

Meeting No.	Date	Present	Topics Addressed
1	July 17, 2019	John Branda, Dennis Dixon (Co-Chair), Harold Horowitz, Bobbi Pritt, Greg Storch, David Walker (Co-Chair) Jennifer Gillissen (contractor support), Christina Li (contractor support), Sarah Miers, NIH	Introduction of members to each other; review of subcommittee report outline, milestones, and deliverables; and discussion of proposed topics to be addressed, including potential speakers.
2	July 31, 2019	John Branda, Stephen Dumler, Harold Horowitz, Bobbi Pritt, David Walker (Co-Chair) Debbie Seem (TBDWG support), Jennifer Gillissen (contractor support), Christina Li (contractor support), Samuel Perdue, NIH	Introduction of new members to the subcommittee; two presenters provided PowerPoint presentations and answered questions from subcommittee members; discussion of proposed topics to be addressed and potential speakers. The presenters and their topics included in order of presentation: David H Walker, MD, and J. Stephen Dumler, MD: Overview of Ehrlichiosis and Anaplasmosis.
3	August 14, 2019	Stephen Clark, Dennis Dixon (Co-Chair), Stephen Dumler, Harold Horowitz, Bobbi Pritt, Greg Storch, David Walker (Co-Chair) Debbie Seem (TBDWG support), Jennifer Gillissen (contractor support), Melinda T. Hough (contractor support), Sarah Miers, NIH	Two presenters provided PowerPoint presentation and answered questions from subcommittee members. The presenters and their topics included in order of presentation: J. Stephen Dumler, MD: Treatment of Human Monocytic Ehrlichiosis; and Harold W. Horowitz, MD: Treatment of Human Granulocytic Anaplasmosis.
4	August 28, 2019	John Branda, Stephen Clark, Stephen Dumler, Harold Horowitz, Bobbi Pritt, Daniel Sexton, Greg Storch, David Walker (Co-Chair) Debbie Seem (TBDWG support), Jennifer Gillissen (contractor support), Melinda T. Hough (contractor support), Samuel Perdue, NIH	Three presenters provided PowerPoint presentations and answered questions from subcommittee members. The presenters and their topics included in order of presentation: Bobbi S. Pritt, MD: Epidemiology and Surveillance; Paige Armstrong, MD, MHS: Surveillance for Anaplasmosis and Ehrlichiosis in the United States; and Jeannine Petersen, PhD: Nationwide Metagenomic Surveillance for Tick-Borne Pathogens.
5	September 25, 2019	John Branda, Harold Horowitz, Daniel Sexton, Greg Storch, David Walker (Co-Chair) Debbie Seem (TBDWG support), Jennifer Gillissen (contractor support), Melinda T. Hough (contractor support), Sarah Miers, NIH	Five presenters provided PowerPoint presentations and answered questions from subcommittee members. The presenters and their topics included in order of presentation: John A. Branda, MD: Clinical Diagnosis of Anaplasmosis; Daniel J. Sexton, MD: Ehrlichiosis – Clinical Features, Unanswered Questions; Harold W. Horowitz, MD: Diagnosis of Human Granulocytic Anaplasmosis; and David H. Walker, MD, and Jere W. McBride, PhD: Laboratory Diagnosis of Human Monocytic Ehrlichiosis.
6	October 9, 2019	John Branda, Stephen Clark, Dennis Dixon (Co-Chair), Stephen Dumler, Bobbi Pritt, David Walker (Co-Chair) Debbie Seem (TBDWG support), Jennifer Gillissen (contractor support), Melinda T. Hough (contractor support), Samuel Perdue, NIH	Subcommittee members reviewed the key points and potential actions of the following presentations: Overview of Ehrlichiosis and Anaplasmosis; and Clinical Diagnosis of Anaplasmosis. The subcommittee also discussed the Results and Potential Actions draft process.
7	October 23, 2109	John Branda, Stephen Clark, Stephen Dumler, Harold Horowitz, Daniel Sexton, Greg Storch, David Walker (Co-Chair) Debbie Seem (TBDWG support), Jennifer Gillissen (contractor support), Melinda T. Hough (contractor support), Samuel Perdue, NIH	Subcommittee members reviewed the key points and potential actions of the following presentations: Ehrlichiosis Features, Unanswered Questions; and Treatment of Human Monocytic Ehrlichiosis. The subcommittee also discussed the Results and Potential Actions draft process.
8	November 6, 2019	Stephen Clark, Dennis Dixon (Co-Chair), Harold Horowitz, Bobbi Pritt, Greg Storch Jennifer Gillissen (Public), Melinda T. Hough (Writer)	Subcommittee members reviewed the key points and potential actions of the following presentation: Epidemiology and Surveillance of Ehrlichiosis and Anaplasmosis. The subcommittee also discussed the Results and Potential Actions draft process.
9	November 20, 2019	John Branda, Stephen Dumler, Harold Horowitz, Daniel Sexton, Greg Storch, David Walker (Co-Chair) Debbie Seem (TBDWG support), Jennifer Gillissen (contractor support), Melinda T. Hough (contractor support), Samuel Perdue, NIH	Subcommittee members reviewed and condensed the identified potential actions down to 27 for consideration.
10	December 04, 2019	John Branda, Stephen Clark, Dennis Dixon (Co-Chair), Stephen Dumler, Bobbi Pritt, Daniel Sexton, Greg Storch Debbie Seem (TBDWG support), Jennifer Gillissen (contractor support), Melinda T. Hough (contractor support), Samuel Perdue, NIH, Sarah Miers, NIH	Subcommittee members reviewed and condensed the previously identified 27 potential actions down to 10 for consideration.
11	December 18, 2019	John Branda, Stephen Dumler, Daniel Sexton, Greg Storch, David Walker (Co-Chair) Jennifer Gillissen (contractor support), Melinda T. Hough (contractor support), Samuel Perdue, NIH	Subcommittee members reviewed outstanding Potential Actions language and agreed a timeline for full subcommittee comment, voting, and submission.
12	January 15, 2020	John Branda, Stephen Clark, Dennis Dixon (Co-Chair), Stephen Dumler, Harold Horowitz, Bobbi Pritt, Daniel Sexton, Greg Storch, David Walker (Co-Chair) Jim Berger (DFO), Jennifer Gillissen (contractor support), Cat Thomson (contractor support), Samuel Perdue, NIH	Subcommittee members reviewed the complete draft report and resolved outstanding questions and suggestions for revision. Three members agreed to work directly with the support writer via email to submit final revisions and ready the report for submission.

Over the course of the meetings, PowerPoint presentations were given both by outside subject matter experts, who were suggested by subcommittee members, and by subcommittee members themselves who are known experts in the field. These presentations, coupled with current literature, provided important content and background information for the report. The list of presentation topics and presenters is shown in Table 3.

Table 3: Presenters to the Ehrlichiosis and Anaplasmosis Subcommittee.

Meeting No.	Presenter	Topics Discussed	Ok to Share?
2	David H. Walker, MD; and J. Stephen Dumler, MD.	Overview of Ehrlichiosis and Anaplasmosis	Yes
3	J. Stephen Dumler, MD; and Harold W. Horowitz, MD.	Treatment of Human Monocytic Ehrlichiosis; and Treatment of Human Granulocytic Anaplasmosis.	Yes
4	Bobbi S. Pritt, MD; Paige Armstrong, MD, MHS; and Jeannine Petersen, PhD.	Epidemiology and Surveillance; Surveillance for Anaplasmosis and Ehrlichiosis in the United States; and Nationwide Metagenomic Surveillance for Tick-Borne Pathogens.	Yes
5	John A. Branda, MD; Daniel J. Sexton, MD; Harold W. Horowitz, MD; and David H. Walker, MD, and Jere W. McBride, PhD.	Clinical Diagnosis of Anaplasmosis; Ehrlichiosis – Clinical Features, Unanswered Questions; Diagnosis of Human Granulocytic Anaplasmosis; Laboratory Diagnosis of Human Monocytic Ehrlichiosis.	Yes

Report Development – Subcommittee meetings that were held from July through October focused on developing a deep understanding of the needs based on subject matter expert presentations. Meetings from October through January focused on drafting and discussing various sections of the report.

Throughout the course of the subcommittee’s discussions efforts were made to encourage a diversity of views and opinions. When disagreements occurred, efforts were made to discuss the differences, arriving at compromises when possible. For any points of impasse, the opportunity was provided for written minority views. Members voted by email to accept each section of the report, the Potential Actions, and ultimately the final report, which was submitted on January 17, 2020. All votes taken by the subcommittee are summarized in Table 4.

Table 4: Votes Taken by the Ehrlichiosis and Anaplasmosis Subcommittee.

Meeting or Date	Motion	Result	Minority Response
12/18/2019 & 01/09/2020	Results > Epidemiology & Surveillance > Vote on Potential Action One: Determine the true number of human cases per year (incidence) and full clinical spectrum, clinical manifestations, and potential complications of human monocytic ehrlichiosis (HME) and human granulocytic anaplasmosis (HGA). Actions that accomplish this include: • Enhance the system of case detection and reporting to capture the true incidence of infections and the specific agents that are causing the infections. Active surveillance is recommended for endemic regions. • Support expanded participation among health departments in newly available electronic surveillance data submission through Message Mapping Guides, part of CDC’s National Notifiable Diseases Surveillance System Modernization Initiative. • Establish a program to fund standardized tick surveillance and testing for pathogens using well-validated molecular methods that are capable of detecting pathogens to the genus and species level across all states in disease-endemic areas.	Outcome: Passed—all present in favor; none opposed; none abstained; none absent (9/0/0/0)	No
12/18/2019 & 01/09/2020	Results > Epidemiology and Surveillance > Vote on Potential Action Two: Support clinical education for primary medical caregivers (family medicine, primary internal medicine, pediatrics, emergency medicine, and physician’s assistants) and public awareness of ehrlichiosis and anaplasmosis to reduce morbidity and mortality through prevention; early, accurate diagnosis; and appropriate treatment.	Outcome: Passed—all present in favor; none opposed; none abstained; none absent (9/0/0/0)	No
12/18/2019 & 01/09/2020	Results > Clinical Features > Vote on Potential Action Three: Establish studies to identify risk factors for severe illness including the presence or absence of specific co-morbidities, patient characteristics (age, gender, and race), immune impairment/underlying medical condition, and genetic host factors.	Outcome: Passed—all present in favor; none opposed; none abstained; none absent (9/0/0/0)	No
12/18/2019 & 01/09/2020	Results > Clinical Features > Vote on Potential Action Four: Determine the impact of co-infection with other tick-borne pathogens, including emerging tick-borne viruses, in patients with ehrlichiosis or anaplasmosis, and how these co-infections are related to variations in clinical features and disease severity.	Outcome: Passed—7 present in favor; none opposed; 2 abstained; none absent (7/0/2/0)	No
12/18/2019 & 01/09/2020	Results > Clinical Features > Vote on Potential Action Five: Develop an organized and concerted public health approach to the prevention of ehrlichiosis and anaplasmosis that includes public and provider education and outreach.	Outcome: Passed—7 present in favor; 2 opposed; none abstained; none absent (7/2/0/0)	Yes; Minority Response: Two subcommittee members opposed this recommendation stating that it overlaps with Potential Actions One and Two consequently a separation potential action is not needed.
12/18/2019 & 01/09/2020	Results > Laboratory Diagnosis > Vote on Potential Action Six: Develop and evaluate diagnostic test(s), such as nucleic acid amplification tests (NAAT) or rapid immunoassays, that can be used in routine clinical laboratories, local clinical laboratories, and eventually as point-of-care tests that are sensitive and specific for the diagnosis of ehrlichioses and anaplasmosis during the early-acute disease state. Encourage development of these tests as in vitro diagnostics approved by the FDA.	Outcome: Passed—all present in favor; none opposed; none abstained; none absent (9/0/0/0)	No
12/18/2019 & 01/09/2020	Results > Treatment > Vote on Potential Action Seven: Identify alternative antimicrobial treatments for i) doxycycline contraindications and/or hesitancy to prescribe (e.g., pregnant women, children under 8 years of age, and those with known allergies or co-infections), ii) broad spectrum coverage for potential bloodstream infections, and iii) acceptable alternatives during possible supply shortages of primary therapeutics.	Outcome: Passed—all present in favor; none opposed; none abstained; none absent (9/0/0/0)	No
12/18/2019 & 01/09/2020	Results > Treatment > Vote on Potential Action Eight: Optimize duration of treatment to minimize the risk of adverse reactions to doxycycline and effects on healthy microbiomes, as well as address patients at risk for severe disease or complications (e.g., HIV or immunomodulatory therapies).	Outcome: Passed—all present in favor; none opposed; none abstained; none absent (9/0/0/0)	No
12/18/2019 & 01/09/2020	Results > Treatment > Vote on Potential Action Nine: Investigate adjunctive therapies, such as corticosteroids, etoposide, anakinra, or novel host-directed signaling pathways to address severe disease, including hemophagocytic lymphohistiocytosis (HLH).	Outcome: Passed—7 present in favor; 1 opposed; 1 abstained; none absent (7/1/1/0)	Yes; Minority Response: One subcommittee member opposed this recommendation stating that these the recommendations belong in an HLH study. The rarity of this in ehrlichiosis will make such a study extremely difficult as a stand-alone. That said, the idea is good.
12/18/2019 & 01/09/2020	Results > Overarching Theme > Vote on Potential Action Ten: Develop approaches for incorporating data mining and artificial intelligence into health care systems for real-time identification of characteristic signs, symptoms, exposures and laboratory findings of ehrlichiosis and anaplasmosis at the point of patient presentation. Data analytics and systems should be able to access and analyze available clinical and laboratory information within the electronic medical record and provide guidance to clinicians for patient assessment, formulating a differential diagnosis and recommending confirmatory laboratory testing, taking into account local disease prevalence and patient travel history.	Outcome: Passed—all present in favor; none opposed; none abstained; none absent (9/0/0/0)	No
01/17/2020 Vote via email	To approve the Background section of the report for submission to the Working Group	Outcome: Passed— all voted yes; none opposed; none abstained; none absent (9/0/0/0)	No
01/17/2020 Vote via email	To approve the Background and Methods section of the report for submission to the Working Group	Outcome: Passed— all voted yes; none opposed; none abstained; none absent (9/0/0/0)	No
01/17/2020 Vote via email	To approve the full draft report including Background, Methods, Priority Actions, Potential Actions, and Appendices; and send it to the Working Group for consideration.	Outcome: Passed— all voted yes; none opposed; none abstained; none absent (9/0/0/0)	No

A PowerPoint briefing on subcommittee progress and accomplishments was presented virtually to the larger Tick-Borne Diseases Working Group on September 12, 2019. A final PowerPoint briefing outlining key findings was presented to the larger HHS Tick-Borne Diseases Working Group on January 29, 2020. Both briefings were initially drafted by the subcommittee co-chairs and the reviewed, revised, and approved by the entire subcommittee.

Results

Background

There are three Ehrlichia species and one Anaplasma species that cause human diseases in the U.S. (Biggs et al., 2016). E. chaffeensis is the causative agent of human monocytic ehrlichiosis (HME), Ehrlichia ewingii, and Ehrlichia muris eauclairensis are responsible for related and emerging ehrlichioses. Anaplasma phagocytophilum is the causative agent of human granulocytic anaplasmosis (HGA).

Changes in the incidence and geographic distribution of HME have been driven by populations of white tailed-deer and lone star ticks. The lone star tick range has been spreading north and west driving increases in disease incidence (Molaei, Little, Williams & Stafford, 2019). In Missouri, 9% of lone star ticks carry E. chaffeensis and 5% carry E. ewingii (Gaines et al., 2014; Hudman & Sargentini, 2018). Similar prevalence in ticks has been recorded in other endemic regions suggesting high human exposure rates. HME incidence is underreported by an estimated fiftyfold. The incidence of HME in endemic regions was determined through active surveillance to be 10-100/100,000 in exposed populations versus 0.5/100,000 in the general population based on a CDC study (Olano et al., 2003).

The incidence of HGA is increasing at a rate higher than any other tick-borne disease in the last 20 years. Similar to HME, the incidence and geographic distribution of HGA has been driven by populations of the reservoir host(s) and expansion of the range of the tick vector, Ixodes scapularis (Eisen, 2018). The actual incidence of disease is estimated to be elevenfold greater than currently captured by passive reporting based on studies using active surveillance methods (Bakken & Dumler, 2015; Bakken et al., 1996; IJdo et al., 2000; CDC, 2018).

Both HME and HGA are frequently confused with other tick-borne diseases or febrile illnesses making diagnostic considerations and testing more complex (Biggs et al., 2016). Clinical presentation with a febrile illness during summer months in an endemic region is often suspected to be Lyme disease or Rocky Mountain spotted fever (RMSF) before HME or HGA. Underreporting and misdiagnosis are the two most common problems associated with these diseases. Seroprevalence studies of HME and HGA indicate underreporting, misdiagnosis, subclinical infection, or stimulation of antibodies by other agents (cross-reactivity).

HME often presents with a spectrum of non-specific symptoms ranging from an acute onset fever with constitutional symptoms similar to an RMSF- or toxic shock syndrome (TSS)- like multisystem disease. Some patients develop meningoencephalitis or acute respiratory distress syndrome (ARDS) that can be fatal (Biggs et al., 2016). Immunocompromised patients often develop overwhelming Ehrlichia infection.

Similar to HME, HGA infections present with a spectrum of less severe non-specific symptoms. There is little evidence for central nervous system involvement, and the case fatality rate (0.3%) is lower based on passive surveillance. (Dahlgren, Heitman, Drexler, Massung & Behravesh, 2015; CDC, 2019a). Seven to nine percent of patients will develop severe complications including sepsis, disseminated intravascular coagulation (DIC), and inflammatory syndromes; seven percent will be admitted to the intensive care unit (ICU) (Dahlgren et al., 2015; Dumler, Madigan, Pusterla & Bakken, 2007). Data on HGA in immunocompromised patients does not exist as extensively as for HME. Ehrlichia ewingii infection occurs more often in immunocompromised patients (Biggs et al., 2016). Ehrlichia muris eauclairensis infections are primarily reported in Wisconsin and Minnesota and are clinically milder, requiring up to four days hospitalization, with no reported deaths (Johnson et al., 2015).

Priority One. Gaps in the Epidemiology and Surveillance of Ehrlichiosis and Anaplasmosis.

Summary

Reported cases of both ehrlichiosis and anaplasmosis markedly increased over the past 20 to 30 years. Passive surveillance underestimates the prevalence of tick-borne infections since it relies on multiple factors.Standardized tick surveillance and testing do not exist. Broad-range microbial detection methods employing next generation sequencing show great promise for national level surveillance of known pathogens and the potential to detect novel pathogens.

Issue

More robust incidences of HME and HGA should be determined.

Evidence and Findings

National reporting data collected by the CDC, based on passive surveillance methods, show that ehrlichiosis cases increased fourfold: 338 in 2004 to 1,377 in 2016 (Madison-Antenucci et al. 2020). The majority of these cases, 7,309 (98%) from 2013 to 2017, have been attributed to E. chaffeensis infection (Adams et al., 2015; CDC, 2018). In 2017, four states (Missouri, Arkansas, New York, and Virginia) accounted for more than 50% of all reported cases of ehrlichiosis (CDC, 2019b). Egizi, Fefferman and Jordan (2017) found in New Jersey that the incidence of lone star ticks (A. americanum) carrying E. chaffeensis is nearly the same as the incidence of blacklegged ticks (I. scapularis) carrying B. burgdorferi, the causative agent of Lyme disease, despite a markedly higher rate of reported Lyme disease cases, suggesting equivalent human infection risk but underdiagnosis of HME.

Anaplasmosis cases increased eightfold between 2004 (537 cases) and 2016 (4151 cases) - more than any other tick-borne infection in the U.S. over that timespan (Madison-Antenucci et al. 2020).. Anaplasmosis is most frequently reported from the Upper Midwestern and Northeastern U.S. Eight states (Vermont, Maine, Rhode Island, Minnesota, Massachusetts, Wisconsin, New Hampshire, and New York) account for 90% of all reported cases (CDC, 2019a).

Passive surveillance underestimates the prevalence of tick-borne infections since it relies on multiple factors including a state’s definition of reportable diseases and voluntary physician/health care system reporting. It also excludes asymptomatic, subclinical, and undiagnosed cases, since these do not come to the attention of health care providers. Evidence of disease underestimation can be seen by comparing data collected using active surveillance methods to those collected using passive surveillance methods. An active: passive surveillance ratio of 11 (i.e., multiply passive surveillance data by a factor of 11 to estimate the actual number of cases) was calculated for A. phagocytophilum based on multiple published studies using active surveillance methods (Bakken et al., 1996; IJdo et al., 2000; CDC, 2018; J.S. Dumler & B. Pritt, personal communication, August 28, 2019). Similarly, a prospective study of E. chaffeensis infection in a typical setting of lone star tick-white tailed deer ecology revealed fiftyfold higher incidence than the passive surveillance data (Olano, Masters, Hogrefe, & Walker, 2003).

Data from studies using active surveillance (e.g., prospectively testing symptomatic patients) or surveillance of ticks or reservoir hosts are available for some populations. However, there are significant limitations on their utility including:

Serologic testing suffers from cross reactivity among Ehrlichia species, and to a lesser extent, between A. phagocytophilum and Ehrlichia species.
Older serologic studies relied on laboratory-developed methods that are not universally comparable between performing laboratories. Assays used different methodology (e.g., indirect fluorescent immunoassays (IFA) vs. enzyme immunoassays (EIA)) and antigens.

Surveillance for A. phagocytophilum-infected tick and reservoir host populations is confounded by the fact that many nucleic acid amplification tests (NAAT) do not differentiate between non-pathogenic (AP-variant-1; found widely in deer and I. scapularis) and human pathogenic A. phagocytophilum strains

Depending on the population studied (e.g., symptomatic vs. asymptomatic or different age groups), published human seroprevalence rates vary and may reach as 35% in some regions (Marshall et al., 2002; Leiby et al., 2002; Aguero-Rosenfeld et al., 2002; Bakken 1998).

The relatively high prevalence of these infections is corroborated by data from reference laboratories offering NAATs for the agents of infection. In symptomatic human populations, positivity rates for these assays can exceed 10% (Mayo Clinic unpublished data, 2018; Harris et al., 2016; Schotthoefer et al., 2013). This is remarkable considering that asymptomatic patients, those who did not seek medical care, and those whose blood was not submitted for testing, are not represented by these studies.

The best data available detecting A. phagocytophilum and Ehrlichia species in ticks is listed in Table 5 (Steiert & Gilfoy, 2002; Wright, Gaff & Hynes, 2014; Pritt et al., 2011; Murphy et al., 2017; Magnarelli et al., 1995). Although the detection of these organisms in ticks does not necessarily correlate with the rates of human infections, it provides insight into the risk of disease transmission via tick bite.

Table 5. Incidence of Pathogen Prevalence in Ticks.

Causative agent	Prevalence in Ticks
E. chaffeensis	0.0% to 9.8%
E. ewingii	0.0% to 8.2%
E. muris eauclairensis	0.9% to 2.9% (only in Minnesota and Wisconsin)
A. phagocytophilum	1.5 to 50.0%

Broad-range bacterial assays employing next generation sequencing show great promise for national level surveillance of known pathogens and the potential to detect novel pathogens.CDC has designed and optimized such an assay for screening clinical specimens for known and novel pathogens from patients with suspected tick-borne diseases. Use of this and similar assays in private and public health settings would greatly expand nationwide capabilities for actively detecting tick-borne pathogens.

Priority Two. Gaps in the Clinical Features of Ehrlichiosis and Anaplasmosis.

Ehrlichiosis

Summary

Ehrlichioses are primarily seasonal illnesses transmitted by a tick bite in endemic areas. As the geographic range of ticks continues to expand, and patients travel more frequently, increasing numbers of cases will occur in previously non-endemic areas. Transmission has also been reported by blood transfusion and organ donation (Regan et al., 2013; Sachdev, Joshi, Cox, Amorosos & Palekar, 2014). Patients typically present with a broad spectrum of non-specific, constitutional symptoms, many do not recall a tick bite, thereby complicating diagnosis and treatment (Biggs et al., 2016). In a small proportion of patients, HME is associated with hemophagocytic lymphohistiocytosis (HLH), which further confounds diagnosis.

Issue

Our knowledge of the frequency and full range of non-specific, atypical features is fragmentary. Understanding these features as well as the contribution of co-infections, the possible contribution of E. chaffeensis to HLH progression, and the true number of asymptomatic and sub-clinical cases is needed to improve patient diagnosis and treatment.

Evidence and Findings

Clinical Presentation – Ehrlichioses usually occur in the late spring and early summer in endemic regions. Onset is typically characterized by an acute fever accompanied by non-specific, constitutional symptoms such as myalgias and headache following the bite of an infected tick; although many patients do not recall a tick bite. Children often present with non-specific gastrointestinal symptoms. A diffuse erythema resembling the rash of toxic shock syndrome has been reported in up to 30% of cases; more commonly in children than adults (Hamburg, Storch, Micek & Kollef, 2008; Schutze et al., 2007; CDC, 2019c). Although rarely present, petechial rashes can occur. Neurological symptoms, including altered mental status associated with abnormal cerebrospinal fluid (CSF), have also been reported. A 1996 study from the University of Missouri found eight out of 15 patients had abnormal CSF samples (Ratnasamy, Everett, Roland, McDonald & Caldwell, 1996). Due to these varied, non-specific symptoms, many patients do not seek medical attention and clinicians find it difficult to diagnose.

Thrombocytopenia and/or leukopenia are usually found during the initial clinical presentation. In later stages of the illness, lymphopenia may be replaced by atypical lymphocytosis (CDC, 2019c). HME can cause severe thrombocytopenia; if severe enough petechial rash may appear. Liver damage including a mild elevation of AST, ALT, alkaline phosphatase, or LDH occur in more than 80% of cases (CDC, 2019c). An acute febrile illness, in an endemic region, accompanied by thrombocytopenia, leukopenia, and abnormal liver function tests are suggestive of, but not specific for, ehrlichiosis.

Risk factors associated with severe disease include older age, a delay in treatment, and compromised immunity (e.g., HIV/AIDS or organ recipients). Anecdotal evidence suggests that children who were previously treated with sulfonamides are at a greater risk for severe illness. DeSilva, Hogan, Fritz and Hunstad (2017) found that in more than half of the cases of ehrlichiosis diagnosed at St. Louis Children’s Hospital during a multi-year period, children were taking trimethoprim-sulfamethoxazole, often for acne or cutaneous infections, at the time of ehrlichiosis onset (G.A. Storch, poster personal communication, May 6-9, 2017).

Ehrlichia infection is a possible contributor to HLH, a syndrome where the immune system overreacts to multiple potential causes. The clinical manifestations of HME often overlap with HLH as the disease progresses, including a rise in ferritin levels (Otrock, Gonzalez & Eby, 2015; Kaplan, Swat & Singer, 2016). Additional research identifying the differences between HLH and HME will help clinicians understand if the observed rises in ferritin are a result of true HLH, or an indicator of the natural course of the immune response to Ehrlichia species, and ensure patients receive the correct treatments in a timely manner.

Asymptomatic and Subclinical Infections – Asymptomatic and subclinical cases may also occur but have not been documented (Olano et al., 2003). Transfusion-associated ehrlichiosis, especially associated with E. ewingii, has occurred with transfusion of blood from asymptomatic, infected donors (Regan et al., 2013). There is an urgent need for prospective studies that would detect both symptomatic and asymptomatic infections.

E. ewingii and E. muris eauclairensis – The range of clinical symptoms caused by E. ewingii and E. muris eauclairensis are less well understood than HME.

Anaplasmosis

Summary

Anaplasmosis is primarily a seasonal illness transmitted by a tick bite in endemic areas. As the geographic range of ticks continues to expand, and patients travel more frequently, increasing numbers of cases will occur. From 2013 to 2017, the incidence of anaplasmosis has doubled based on passive surveillance (CDC, 2019a). Transmission has also been reported by blood transfusion from asymptomatic, infected donors and from mother to fetus (Goel et al., 2017). Patients typically present with a broad spectrum of non-specific, constitutional symptoms; many do not recall a tick bite. Co-infections with other tick-borne pathogens, such as B. burgdorferi and Babesia microti, have been reported; but their frequency remains unknown.

Issue

A full understanding of the spectrum of disease, including the frequency and full range of non-specific symptoms, should be determined.

Evidence and Findings

Clinical Presentation – Anaplasmosis usually occurs in the late spring and early summer in endemic regions as a consequence of an Ixodes species tick bite; many patients do not recall a tick bite (Weil, Baron, Brown & Drapkin, 2012). Due to an expansion of the Ixodes tick range, new populations may be at risk. A. phagocytophilum resides in tick salivary glands, but how long a tick must remain attached to transmit the illness has not been clearly established (Telford, 1996; Sukuraman, 2006; Bakken et al., 1996; Aguero-Rosenfeld et al., 1996; Weil et al., 2012; Wormser et al., 2013). Onset is typically characterized by the acute onset of non-specific, constitutional symptoms such as fever, often with sweats and/or chills; malaise, fatigue, myalgias, and headache within a week of being bitten by an infected tick (Bakken et al., 1996; Aguero-Rosenfeld et al., 1996; Weil et al., 2012; Wormser et al., 2016). Children often present with abdominal pain (Sigurjonsdottir, Feder & Wormser, 2016). Due to these varied, non-specific symptoms, many patients do not seek medical attention and clinicians may not consider HGA in the differential diagnosis. If patients are not treated relatively early in disease, hospitalization occurs in a significant percentage (Bakken et al., 1996; Aguero-Rosenfeld et al., 1996; Weil et al., 2012).

Patients often present with characteristic laboratory abnormalities. Laboratory results depend on the timing of sample collection and are not consistent from patient to patient. Approximately 80% of patients are thrombocytopenic and/or leukopenic at the time of initial clinical presentation (Bakken et al., 2001). Thrombocytopenia develops within a few days of symptom onset, whereas leukopenia typically develops after four to five days of illness (Bakken et al., 2001). Leukopenia is caused by lymphopenia, then followed by neutropenia as lymphocyte counts start to recover. As lymphopenia resolves, it may be replaced by atypical lymphocytosis. Liver damage including a mild elevation of AST, ALT, alkaline phosphatase, or LDH can occur (Weil et al., 2012). A recovered patient member of the subcommittee noted his primary symptom was jaundice, which is a rare presentation. His illness went undiagnosed due to this non-specific clinical presentation underscoring how the diversity of clinical presentations associated with the illness makes a definitive diagnosis difficult.

Risk factors associated with a more severe presentation of HGA include older age (typically over 40 years of age), male, those who report frequent outdoor activity and/or a recent tick bite, a delay in treatment, and compromised immunity (e.g., HIV/AIDS or organ recipients) (Bakken et al., 1996; Aguero-Rosenfeld et al., 1996; Weil et al., 2012).

Asymptomatic and Subclinical Infections – Asymptomatic and subclinical infections probably occur on the basis of high rates of seroprevalence and may be more common than symptomatic disease. In addition, transfusion-associated HGA has occurred from asymptomatic, infected donors (Goel et al., 2017).

Priority Three. Gaps in The Laboratory Diagnosis of Ehrlichiosis and Anaplasmosis.

Ehrlichiosis

Summary

Acute disease diagnosis of HME often relies on disease suspicion in endemic areas or among those who have traveled to such areas. Blood smear detection of E. chaffeensis is extremely insensitive because there are few infected monocytes in the peripheral blood. Clinical diagnosis is usually confirmed by detection of Ehrlichia-specific antibodies in patient sera using serology or NAAT. Identifying the specific pathogen by serology is difficult due to a lack of standardization between laboratories and false positives due to cross-reactive antibodies stimulated by conserved bacterial proteins or related organisms (e.g., Ehrlichia canis, E. ewingii, E. muris eauclairensis, and A. phagocytophilum) (Luo, Mitra & McBride, 2018). Molecular diagnostic methods, such as NAAT, are specific and sensitive for the detection of E. chaffeensis, particularly prior to development of reactive antibodies that occurs by two- or three-weeks post-disease onset. Whenever possible, NAAT should be used for the diagnosis of acute ehrlichiosis. Point of care testing remains to be developed.

Issue

Develop sensitive, species-specific, standardized diagnostic tests to complement currently available serology and multiplex NAAT assays.

Evidence and Findings

General Clinical Laboratory Assays and Microscopy – Characteristic immune cell and liver function abnormalities, although suggestive of HME, are non-specific. Blood smear is not sensitive for the diagnosis of HME.

IFA Serology – Diagnosis of HME by serology requires patients to produce reactive antibodies against Ehrlichia species which occurs in the second and third week of illness. Due to its insensitivity during the initial stages of illness and an inability to distinguish among related species, especially E. chaffeensis and E. ewingii cross-reactive antibodies, serology is not useful for the diagnosis of acute illness.

Nucleic acid amplification tests (NAAT) – NAAT performed on whole blood is relatively sensitive for the diagnosis of HME in the acute disease stage prior to doxycycline treatment. However, there are no assays or point-of-care testing for HME that are cleared or approved by the U.S. Food and Drug Administration (FDA).

Potential Novel Diagnostics - The development of point-of-care and reference laboratory diagnostic assays based on antigen or antibody detection is currently being investigated. During infection, Ehrlichia release proteins into the blood stream that induce an immune response. Several Ehrlichia tandem repeat proteins (TRP32 and TRP120) have recently been molecularly characterized from sera of patients with acute HME (Luo et al., 2018). TRPs are immunoreactive and species-specific thereby presenting novel candidates for immunodiagnostic assays, suggesting that such approaches might be beneficial in the future for point-of-care testing.

Market Incentives – The traditional endemic regions where HME occurs are likely to expand as the geographic distribution of ticks increases. Due to the perception of HME as a regional illness with limited profitability, the enthusiasm for industry to develop FDA-approved, in vitro, diagnostic tests are limited at present. Market incentives may be required to drive innovation in the future.

Anaplasmosis

Summary

Acute disease diagnosis of HGA often relies on disease suspicion in endemic areas or among those who have traveled in endemic areas. A specific diagnosis is often confirmed through one of several techniques. Immediate, clinical diagnosis can be made by buffy coat examination of white blood cells. Abnormalities in whole blood counts, such as thrombocytopenia or leukopenia, and liver function tests are suggestive of HGA, but non-specific due their similarities with HME and other tick-borne diseases. A suspected diagnosis of HGA is confirmed retrospectively using serology. Use of CDC surveillance serology cut-off values on a single serum sample is non-specific for acute infection.Molecular diagnostic tests, such as NAAT, are the methods of choice for early diagnosis.

Issue

Develop sensitive, species-specific, standardized diagnostic tests to complement currently available serology and NAAT.

Evidence and Findings

Complete blood count and chemistry studies – Characteristic peripheral blood cell and liver function abnormalities, although suggestive of HGA, are non-specific.

Microscopy – Buffy coat examination of neutrophils from the white blood cell layer of a spun, anticoagulated blood sample for the intracellular Anaplasma organisms (morulae) is approximately 50% sensitive as a point-of-care diagnostic in early, acute disease (Silaghi et al., 2017). Experienced technicians are required to detect the morulae, and results can be erroneous owing to misinterpretation of observations.

IFA Serology – The sensitivity and specificity of serology depends on the timing of sample collection and may not be diagnostic during the acute disease. Diagnosis of HGA by serology requires patients to produce antibodies and is relatively sensitive 10-14 days after disease onset, especially if the patient is acutely ill. The titer value for a serodiagnosis during the acute disease has not been adequately established. Serology is problematic due to cross-reactivity and the fact that titers remain positive for a prolonged period of time, suggesting that some patients with low titers are demonstrating either non-specific results or old, cured disease (Bakken, Haller, Riddell, Walls & Dumler, 2002; Aguero-Rosenfeld et al., 2000).

Nucleic acid amplification tests (NAAT) – NAAT performed on whole blood is extremely sensitive for the diagnosis of HGA early in disease and prior to doxycycline treatment. However, there are no FDA-approved or cleared NAATs or point-of-care tests for HGA.

Potential Novel Diagnostics - Culture-based diagnostic testing is and will likely remain in the research domain. A rapid point-of-care assay would make real-time diagnosis accessible.

Market Incentives – The endemic regions in which HGA traditionally occurs are likely to expand as the geographic distribution of ticks increases. Due to the perception as a regional illness with limited profitability, the enthusiasm of industry to develop FDA-approved, in vitro, diagnostic tests are limited currently. Market incentives may be required to drive innovation in the future.

Priority Four. Gaps in the Treatment of Ehrlichiosis and Anaplasmosis.

Ehrlichiosis

Summary

No clinical trials have been conducted for the use of any antimicrobial agent for the treatment of HME in humans. Patients who have not received doxycycline upon admission have increased risk of severe outcomes including admission to the ICU, mechanical ventilation, longer hospital stays, and longer illnesses (Hamburg et al., 2008). In vivo studies demonstrate the clinical efficacy of doxycycline; however, clinical failures have occurred with its use (Ismail, Walker, Ghose & Tang, 2012; Sosa-Gutierrez et al., 2016; Esbenshade, Esbanshade, Domm, Williams & Frangoul, 2010; Fishbein, Dawson & Robinson, 1994; Dumler, Sutker & Walker, 1993). Doxycycline remains the antibiotic of choice, however, newer antimicrobial agents remain to be tested against E. chaffeensis.

Issue

The optimal duration of doxycycline therapy, the impact of patient demographics and clinical condition (e.g., immunocompromised, children, or pregnant women) and co-infections on treatment outcome, and potential alternatives to doxycycline need to be determined.

Evidence and Findings

Doxycycline is the antibiotic of choice for the treatment of E. chaffeensis infections in humans, but the optimal duration of therapy remains to be determined. Studies have found that suspected HME cases treated with doxycycline at the time of emergency department or hospital admission show remarkable improvement including (Hamburg et al., 2008; Eng et al., 1990; Schutze & Jacobs, 1997; Fishbein et al., 1994; Fishbein et al., 1989):

Lower rate of ICU transfer (0% vs. 40%; p<0.001);
Decreased requirement for mechanical ventilation (0% vs. 27%; p<0.001);
Decreased hospital stays (4 days vs. 12 days; p<0.001); and
Decreased length of illness (9 days vs. 21 days; p=0.001).

At least three in vitro susceptibility studies of a limited range of antimicrobial drugs have been conducted, but these may exclude newer antimicrobial agents. (Branger, Rolain & Raoult, 2004; Brouqui and Raoult, 1992; Rolain, Maurin, Bryskier & Raoult, 2000). Ehrlichia chaffeensis is susceptible to doxycycline, rifampin, and thiamphenicol in vitro at concentrations considered achievable in human blood (Brouqui and Raoult, 1992; Rolain, Maurin, Bryskier & Raoult, 2000). Ehrlichia chaffeensis is not susceptible in vitro to a range of commonly used antimicrobial agents including: aminoglycosides, cephalosporins and other beta-lactams, fluoroquinolones, macrolides, and cotrimoxazole. Remarkably, E. chaffeensis is not susceptible in vitro to chloramphenicol or telithromycin (Branger et al., 2004; Brouqui and Raoult, 1992; Rolain et al., 2000). This gap in the spectrum of drugs that can be used complicates treatment for children and pregnant women. Resistance has been reported to ciprofloxacin, a quinolone antibiotic (Maurin, Abergel & Raoult, 2001). Further studies suggest fluoroquinolone resistance is caused by a point mutation in the quinolone resistance determining region of gyrA (Maurin et al., 2001).

No randomized controlled clinical trials to evaluate efficacy of therapy for HGA have been conducted. Current recommendations for treatment are derived from prospective and retrospective case series and case reports, and strongly support the use of doxycycline (or tetracycline) in both adults and children. Alternatives with less evidence for successful treatment include rifampin when considering infection in pregnancy or when tetracycline antibiotics are contraindicated (e.g. with allergy) (Bakken and Dumler, 2016; Kimberlin, Long, Brady & Jackson, 2018, pp323-327).

A non-comprehensive analysis of treatment outcomes extracted from case series and case reports has insufficient power to provide evidence for significant differences in treatment outcomes between any two antimicrobial agent classes, except for death in those treated with doxycycline vs. no treatment (p=0.001) (J.S. Dumler, personal communication, August 28, 2019).

Information on the kinetics of PCR clearance after starting doxycycline therapy is lacking and would be useful. A clinical question is whether a “test-of-cure” PCR should be obtained at the end of therapy.

Anaplasmosis

Summary

No clinical trials have been conducted for the use of any antimicrobial agent for the treatment of HGA in humans. In case studies, doxycycline has proven remarkably effective for the treatment. There are limited data of successful treatment using rifampin (Klein, Nelson & Goodman, 1997; Horowitz et al., 2001; Krause, Corrow, & Bakken, 2003). Several newer antimicrobial agents, such as eravacycline, omadacycline, and delafloxacin, have yet to be tested in vitro for activity against A. phagocytophilum.

Issue

The optimal duration of doxycycline therapy, the impact of patient demographics and clinical condition (e.g., immunocompromised, children, or pregnant women) and co-infection on treatment outcome, and potential alternatives to doxycycline need to be determined.

Evidence and Findings

Doxycycline is the antibiotic of choice for the treatment of HGA, but the optimal duration of therapy remains to be determined. Patients suspected of having HGA in endemic regions are often treated with doxycycline; rapid improvement as a result of treatment is frequently used as diagnostic confirmation. In vitro testing has confirmed the susceptibility of A. phagocytophilum to doxycycline and rifampin (Klein et al., 1997; Horowitz et al., 2001). Clinical failures or relapses following doxycycline treatment are rare. Despite in vitro susceptibility to quinolones, treatment failures have been reported (Klein et al., 1997; Horowitz et al., 2001; Wormser et al., 2006). No macrolides have been found to be effective in in vitro studies to date (Klein et al., 1997; Horowitz et al., 2001).

Potential Actions

Potential actions were presented and discussed by subcommittee members. The wording of potential actions here were voted on by subcommittee members, and results are presented here.

Epidemiology and Surveillance

Determine the true number of human cases per year (incidence) and full clinical spectrum, clinical manifestations, and potential complications of human monocytic ehrlichiosis (HME) and human granulocytic anaplasmosis (HGA). Actions that accomplish this include:
- Enhance the system of case detection and reporting to capture the true incidence of infections and the specific agents that are causing the infections. Active surveillance is recommended for endemic regions.
- Support expanded participation among health departments in newly available electronic surveillance data submission through Message Mapping Guides, part of CDC’s National Notifiable Diseases Surveillance System Modernization Initiative.
- Establish a program to fund standardized tick surveillance and testing for pathogens using well-validated molecular methods that are capable of detecting pathogens to the genus and species level across all states in disease-endemic areas.

Vote on Potential Action One:

Number in Favor	Number Opposed	Number Abstained	Number Absent
9	0	0	0

Minority Response: One subcommittee member agreed with this recommendation but noted that although inferred perhaps by the notion of “system of case detection,” active surveillance might be best coordinated through a multicentered study team such as the ACTG study group for HIV. Such a group would be useful to study the panoply of tick-borne disease, in particular co-infection (incidence, clinical manifestations, etc.) that has been sparsely addressed.

Support clinical education for primary medical caregivers (family medicine, primary internal medicine, pediatrics, emergency medicine, and physician’s assistants) and public awareness of ehrlichiosis and anaplasmosis to reduce morbidity and mortality through prevention; early, accurate diagnosis; and appropriate treatment.

Vote on Potential Action Two:

Number in Favor	Number Opposed	Number Abstained	Number Absent
9	0	0	0

Clinical Features

Establish studies to identify risk factors for severe illness including the presence or absence of specific co-morbidities, patient characteristics (age, gender, and race), immune impairment/underlying medical condition, and genetic host factors.

Vote on Potential Action Three:

Number in Favor	Number Opposed	Number Abstained	Number Absent
9	0	0	0

Determine the impact of co-infection with other tick-borne pathogens, including emerging tick-borne viruses, in patients with ehrlichiosis or anaplasmosis, and how these co-infections are related to variations in clinical features and disease severity.

Vote on Potential Action Four:

Number in Favor	Number Opposed	Number Abstained	Number Absent
7	0	2	0

Minority Response: One subcommittee member abstained with this recommendation noting that although inferred perhaps by the notion of “system of case detection,” this might be best coordinated through a multicentered study team such as the ACTG study group for HIV. Such a group would be useful to study the panoply of tick-borne disease, in particular co-infection (incidence, clinical manifestations, etc.) that has been sparsely addressed.

Develop an organized and concerted public health approach to the prevention of ehrlichiosis and anaplasmosis that includes public and provider education and outreach.

Vote on Potential Action Five:

Number in Favor	Number Opposed	Number Abstained	Number Absent
7	2	0	0

Minority Response: One subcommittee member agreed with this recommendation but noted that options for the prevention of ehrlichiosis and anaplasmosis are few and of limited efficacy. However, an organized and concerned public health approach is warranted to educate the public about the need to seek treatment if they become ill after a tick bite and also to educate providers of the clinical features and spectrum and treatment of these two diseases.

Minority Response: Two subcommittee members opposed this recommendation stating that it overlaps with Potential Actions One and Two consequently a separation potential action is not needed.

Laboratory Diagnosis

Develop and evaluate diagnostic test(s), such as nucleic acid amplification tests (NAAT) or rapid immunoassays, that can be used in routine clinical laboratories, local clinical laboratories, and eventually as point-of-care tests that are sensitive and specific for the diagnosis of ehrlichioses and anaplasmosis during the early-acute disease state. Encourage development of these tests as in vitro diagnostics approved by the FDA.

Vote on Potential Action Six:

Number in Favor	Number Opposed	Number Abstained	Number Absent
9	0	0	0

Treatment

Identify alternative antimicrobial treatments for i) doxycycline contraindications and/or hesitancy to prescribe (e.g., pregnant women, children under 8 years of age, and those with known allergies or co-infections), ii) broad spectrum coverage for potential bloodstream infections, and iii) acceptable alternatives during possible supply shortages of primary therapeutics.

Vote on Potential Action Seven:

Number in Favor	Number Opposed	Number Abstained	Number Absent
9	0	0	0

Optimize duration of treatment to minimize the risk of adverse reactions to doxycycline and effects on healthy microbiomes, as well as address patients at risk for severe disease or complications (e.g., HIV or immunomodulatory therapies).

Vote on Potential Action Eight:

Number in Favor	Number Opposed	Number Abstained	Number Absent
9	0	0	0

Minority Response: One subcommittee member agreed with this recommendation but noted that currently these studies are not feasible due to methodological barriers to human clinical research on patients including relatively few cases, many of which present with diverse symptoms as well as difficulties with informed consent and follow-up. Research studies focused on answering questions about duration of treatment for even common infections such as cellulitis, staphylococcal bacteremia, and meningitis have been remarkably few in number and the results of such studies are often inconclusive.

Investigate adjunctive therapies, such as corticosteroids, etoposide, anakinra, or novel host-directed signaling pathways to address severe disease, including hemophagocytic lymphohistiocytosis (HLH).

Vote on Potential Action Nine:

Number in Favor	Number Opposed	Number Abstained	Number Absent
7	1	1	0

Minority Response: One subcommittee member agreed with this recommendation but noted there are currently no good human models for HLH or HME. Studies involving humans with HLH designed to investigate adjunctive therapies are not feasible due to their rarity and difficulties with informed consent.

Minority Response: One subcommittee member opposed this recommendation stating that these the recommendations belong in an HLH study. The rarity of this in ehrlichiosis will make such a study extremely difficult as a stand-alone. That said, the idea is good.

Overarching Theme

Develop approaches for incorporating data mining and artificial intelligence into health care systems for real-time identification of characteristic signs, symptoms, exposures and laboratory findings of ehrlichiosis and anaplasmosis at the point of patient presentation. Data analytics and systems should be able to access and analyze available clinical and laboratory information within the electronic medical record and provide guidance to clinicians for patient assessment, formulating a differential diagnosis and recommending confirmatory laboratory testing, taking into account local disease prevalence and patient travel history.

Vote on Potential Action Ten:

Number in Favor	Number Opposed	Number Abstained	Number Absent
9	0	0	0

References

Adams D., Fullerton K., Jajosky R., Sharp, P., Onweh, D., Schley, A., . . . Kugeler, K. (2015). Summary of notifiable infectious diseases and conditions - United States, 2013. MMWR: Morbidity and Mortality Weekly Reports. 62(53), 1–122. doi:10.15585/mmwr.mm6253a1.

Aguero-Rosenfeld, M.E., Donnarumma, L., Zentmaier, L., Jacob, J., Frey, M., Noto, R., . . . Wormser, G.P. (2002). Seroprevalence of antibodies that react with Anaplasma phagocytophila, the agent of human granulocytic ehrlichiosis, in different populations in Westchester County, New York. Journal of Clinical Microbiology, 40(7), 2612-2615. doi:10.1128/jcm.40.7.2612-2615.2002.

Aguero-Rosenfeld, M.E., Horowitz, H.W., Wormser, G.P., McKenna, D.F., Nowakowski, J., Munoz, J., Dumler, J.S. (1996). Human granulocytic ehrlichiosis: a case series from a medical center in New York State. Annals of Internal Medicine, 125(11), 904-908. doi:10.7326/0003-4819-125-11-199612010-00006.

Aguero-Rosenfeld, M.E., Kalantarpour, F., Baluch, M., Horowitz, H.W., McKenna, D.F., Raffalli, J.T., . . . Wormer, G.P. (2000). Serology of culture-confirmed cases of human granulocytic ehrlichiosis. Journal of Clinical Microbiology, 38(2), 635-638. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/10655359

Bakken, J.S., Aguero-Rosenfeld, M.E., Tilden, R.L., Wormser, G.P., Horowitz, H.W., Raffilli, J.T., . . . Dumler, J.S. (2001). Serial measurements of hematologic counts during the active phase of human granulocytic ehrlichiosis. Clinical Infectious Diseases, 32(6), 862-870. doi:10.1086/319350.

Bakken, J.S. & Dumler, S.J. (2015). Human granulocytic anaplasmosis. Infectious Disease Clinics of North America, 29(2), 341-355. doi:10.1016/j.idc.2015.02.007.

Bakken, J.S. & Dumler, J.S. (2016). Ehrlichia and Anaplasma species. In Yu, V., Weber, R., & Raoult, D. (Eds.), Antimicrobial Therapy and Vaccines, 3rd Edition. New York, NY: Apple Tree Productions, LLC.

Bakken, J.S., Haller, I., Riddell, D., Walls, J.J., & Dumler, J.S. (2002). The serological response of patients infected with the agent of human granulocytic ehrlichiosis. Clinical Infectious Diseases, 34(1), 22-27. doi:10.1086/323811.

Bakken J.S., Krueth J., Wilson-Nordskog C., Tilden, R.L., Asanovich, K., & Dumler, J.S. (1996). Clinical and laboratory characteristics of human granulocytic ehrlichiosis. JAMA, 275(3), 199-205. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/8604172

Bakken JS, Goellner P, Van Etten M, Boyle DZ, Swonger OL, Mattson S, Krueth J, Tilden RL, Asanovich KM, Walls J, Dumler JS. (1998). Seroprevalence of human granulocytic ehrlichiosis (HGE) and risk factors associated with infection among residents in northwestern Wisconsin. Clin Infect Dis; 27:1491-1496.

Biggs, H.M., Behravesh, C.B., Bradley, K.K., Dahlgren, F.S., Drexler, N.A., Dumler, J.S., . . . Traeger, M.S. (2016). Diagnosis and management of tick-borne rickettsial diseases: Rocky Mountain spotted fever and other Spotted Fever group rickettsioses, ehrlichioses, and anaplasmosis – United States. MMWR: Morbidity and Mortality Weekly Reports, 65(2), 1-44. doi:10.15585/mmwr.rr6502a1.

Boyce, R.M., Sanfilippo, A.M., Boulos, J.M., Cleinmark, M., Schmitz, J., & Meshnick, S. (2018) Ehrlichia infections, North Carolina, USA, 2016. Emerging Infectious Diseases, 24(11), 2087-2090. doi:10.3201/eid2411.180496.

Branger, S., Rolain, J.M., & Raoult, D. (2004). Evaluation of antibiotic susceptibilities of Ehrlichia canis, Ehrlichia chaffeensis, and Anaplasma phagocytophilum by Real-Time PCR. Antimicrobial Agents and Chemotherapy, 48(12), 4822-4828. doi:10.1128/AAC.48.12.4822-4828.2004.

Brouqui, P. & Raoult, D. (1992). In vitro antibiotic susceptibility of the newly recognized agent of ehrlichiosis in humans, Ehrlichia chaffeensis. Antimicrobial Agents and Chemotherapy, 36(12), 2799-2803. doi:10.1128/aac.36.12.2799.

Centers for Disease Control and Prevention. (2018). National Notifiable Diseases Surveillance System, 2017 Annual Tables of Infectious Disease Data. Retrieved from https://www.cdc.gov/nndss/infectious-tables.html

Centers for Disease Control and Prevention. (2019a). Anaplasmosis – Epidemiology and Statistics. Retrieved from https:// https://www.cdc.gov/anaplasmosis/stats/index.html

Centers for Disease Control and Prevention. (2019b). Ehrlichiosis – Epidemiology & Statistics. Retrieved from https://www.cdc.gov/ehrlichiosis/stats/index.html

Centers for Disease Control and Prevention. (2019c). Ehrlichiosis – Signs & Symptoms. Retrieved from https://www.cdc.gov/ehrlichiosis/symptoms/index.html

Dahlgren, F.S., Heitman, K.N., Drexler, N.A., Massung, R.F., & Behravesh, C.B. (2015). Human granulocytic anaplasmosis in the United States from 2008 to 2012: a summary of national surveillance data. American Journal of Tropical Medicine and Hygiene, 93(1), 66-72. doi:10.4269/ajtmh.15-0122.

Dumler, J.S., Madigan, J.E., Pusterla, N., & Bakken, J.S. (2007). Ehrlichioses in humans: epidemiology, clinical presentation, diagnosis, and treatment. Clinical Infectious Diseases, 45(Suppl1), S45-51. doi:10.1086/518146.

Dumler, J.S., Sutker, W.L., & Walker, D.H. (1993). Persistent infection with Ehrlichia chaffeensis. Clinical Infectious Diseases, 17(5), 903-905. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/8286638

Egizi, A., Fefferman, N.H., & Jordan, R.A. (2017). Relative risk for ehrlichiosis and Lyme disease in an area where vectors for both are sympatric, New Jersey, USA. Emerging Infectious Diseases, 23(6), 939-945. doi:10.3201/eid2306.160528.

Eisen, R.J. (2018). The blacklegged tick, Ixodes scapularis: an increasing public health concern. Trends in Parasitology, 34(4), 295-309. doi:10.1016/j.pt.2017.12.006.

Eng, T.R., Harkess, J.R., Fishbein, D.B., Dawson, J.E., Greene, C.N., Redus, M.A., Satalowich, F.T. (1990). Epidemiologic, clinical, and laboratory findings of human ehrlichiosis in the United States, 1988. JAMA, 264(17), 251-2258. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/2214103

Esbenshade, A., Esbenshade, J., Domm, J., Williams, J., & Frangoul, H. (2010). Severe ehrlichia infection in pediatric oncology and stem cell transplant patients. Pediatric Blood & Cancer, 54(5), 776-778. doi:10.1002/pbc.22392.

Fishbein, D.B., Dawson, J.E., & Robinson, L.E. (1994). Human ehrlichiosis in the United States, 1985 to 1990. Annals of Internal Medicine, 120(9), 736-743. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/8147546

Fishbein, D.B., Kemp, A., Dawson, J.E., Greene, N.R., Redus, M.A., & Fields, D.H. (1989). Human ehrlichiosis: prospective active surveillance in febrile hospitalized patients. The Journal of Infectious Diseases, 160(5), 803-809. doi:10.1093/infdis/160.5.803.

Gaines, D.N., Operario, D.J., Stroup, S., Stromdahl, E., Wright, C., Gaff, H., . . . Houpt, E. (2014). Ehrlichia and Spotted Fever group Rickettsiae surveillance in Amblyomma americanum in Virginia through use of a novel six-plex Real-Time PCR assay. Vector Borne and Zoonotic Disease, 14(5), 307-316. doi:10.1089/vbz.2013.1509.

Goel, R., Westblae, L.F., Kessler, D.A., Sfeir, M., Slavinski, S., Backenson, B., . . . Cushing, M.M. (2018). Death from transfusion-transmitted anaplasmosis, New York, USA, 2017. Emerging Infectious Diseases, 24(8), 1548-1550. doi:10.3201/eid2408.172048.

Hamburg, B.J., Storch, G.A., Micek, S.T., & Kollef, M.H. (2008). The importance of early treatment with doxycyline in human ehrlichiosis. Medicine (Baltimore), 87(2), 53-60. doi:10.1097/MD.0b013e318168da1d.

Harris, R.M., Couturier, B.A., Sample, S.C., Coulter, K.S., Casey, K.K., & Schlaberg R. (2016). Expanded geographic distribution and clinical characteristics of Ehrlichia ewingii infections, United States. Emerging Infectious Diseases, 22(5):862-5. doi:10.3201/eid2205.152009.

Horowitz, H.W., Hsieh, T.C., Aguero-Rosenfeld, M.E., Kalantarour, F., Chowdhury, I., Wormser, G.P., Wu, J.M. (2001). Antimicrobial susceptibility of Ehrlichia phagocytophila. Antimicrobial Agents & Chemotherapy, 45(3), 786-787. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/11181361

Hudman, D.A. & Sargentini, M.J. (2018). Prevalence of tick-borne pathogens in Northeast Missouri. Missouri Medicine, 115(2), 162-168. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/30228710

IJdo, J.W., Meek, J.I., Cartter, M.L., Magnarelli, L.A., Wu, C., Tenuta, S.W., . . . Ryder, R.W. (2000). The emergence of another tick-borne infection in the 12-town area around Lyme, Connecticut: human granulocytic ehrlichiosis. The Journal of Infectious Diseases, 181(4), 1388-1393. doi:10.1086/315389.

Ismail, N., Walker, D.H., Ghose, P., & Tang, Y.W. (2012). Immune mediators of protective and pathogenic immune responses in patients with mild and fatal human monocytotropic ehrlichiosis. BMC Immunology, 13, 26. doi:10.1186/1471-2172-13-26.

Johnson, D.K., Schiffman, E., Davis, J.P., Neitzel, D., Sloan, L.M., Nicholson, W.L., . . . Pritt, B. (2015). Human infection with Ehrlichia muris–like pathogen, United States, 2007–2013. Emerging Infectious Diseases, 21(10), 1794-1799. doi:10.3201/eid2110.150143.

Kaplan, R.M., Swat, S.A., & Singer, B.D. (2016). Human monocytic ehrlichiosis complicated by hemophagocytic lymphohistiocytosis and multi-organ dysfunction syndrome. Diagnostic Microbiology and Infectious Disease, 86(3), 327-328. doi:10.1016/j.diagmicrobio.2016.08.007.

Kimberlin, D.W., Long, S.S., Brady, M.T., & Jackson, M.A. (Eds.). (2018). Ehrlichia, Anaplasma, and related infections. 2018. In Red Book 2018: Report of the Committee on Infectious Diseases, 31st Edition (pp. 323-327). Itasca, IL: American Academy of Pediatrics.

Klein, M.B., Nelson, C.M., & Goodman, J.L. (1997). Antibiotic susceptibility of the newly cultivated agent of human granulocytic ehrlichiosis: promising activity of quinolones and rifamycins. Antimicrobial Agents & Chemotherapy, 41(1), 76-79. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/8980758

Krause, P. J., Corrow, C. L., Bakken, J. S. (2003). Successful treatment of human granulocytic ehrlichiosis in children using rifampin. Pediatrics, 112(3 Pt 1), e252-3. doi: 10.1542/peds.112.3.e252

Leiby, D.A., Chung, A.P., Cable, R.G., Trouern-Trend, J., McCullough, J., Homer, M.J., . . . Persing, D.H. (2002). Relationship between tick bites and the seroprevalence of Babesia microti and Anaplasma phagocytophila (previously Ehrlichia sp.) in blood donors. Transfusion, 42(12), 1585-91. doi:10.1046/j.1537-2995.2002.00251.x.

Luo, T., Mitra, S., & McBride, J.W. (2018). Ehrlichia chaffeensis TRP75 interacts with host cell targets involved in homeostasis, cytoskeleton organization, and apoptosis regulation to prevent infection. mSphere. 3(2):e00147-18. doi:10.1128/mSphere.00147-18.

Madison-Antenucci, S., Kramer, L. D., Gebhardt, L. L., & Kauffman, E. (2020). Emerging Tick-Borne Diseases. Clinical Microbiology Reviews, 33(2), e00083-18. doi: 10.1128/CMR.00083-18

Magnarelli, L. A., Stafford 3rd, K. C., Mather, T. N., Yeh, M. T., Horn, K. D., & Dumler, J. S. (1995). Hemocytic rickettsia-like organisms in ticks: serologic reactivity with antisera to Ehrlichiae and detection of DNA of agent of human granulocytic ehrlichiosis by PCR. Journal of Clinical Microbiology, 33(10), 2710-4.) PMC228561

Marshall, G.S., Jacobs, R.F., Schutze, G.E., Paxton, H., Buckingham, S.D., DeVincenzo, J.P., . . . Tick-Borne Infections in Children Study Group. (2002). Ehrlichia chaffeensis seroprevalence among children in the southeast and south-central regions of the United States. Archives of Pediatric and Adolescent Medicine, 156(2):166-70. doi:10.1001/archpedi.156.2.166.

Maurin, M., Abergel, C., & Raoult, D. (2001). DNA gyrase-mediated natural resistance to fluoroquinolones in Ehrlichia spp. Antimicrobial Agents and Chemotherapy, 45(7), 2098-2105. doi:10.1128/AAC.45.7.2098-2105.2001.

Molaei, G., Little, E.A.H., Williams, S.C., & Stafford, K.C. (2019). Bracing for the worst – range expansion of the lone star tick in the Northeastern United States. The New England Journal of Medicine, 381(23), 2189-2192. doi:10.1056/NEJMp1911661.

Murphy, D.S., Lee, X., Larson, S.R., Johnson, D.K., Loo, T., & Paskewitz, S.M. (2017). Prevalence and distribution of human and tick infections with the Ehrlichia muris-like agent and Anaplasma phagocytophilum in Wisconsin, 2009-2015. Vector Borne and Zoonotic Diseases, 17(4), 229-236. doi:10.1089/vbz.2016.2055.

Olano, J.P., Masters, E., Hogrefe, W., & Walker DH. (2003). Human monocytotropic ehrlichiosis, Missouri. Emerging Infectious Diseases, 9(12):1579-86. doi:10.3201/eid0912.020733.

Otrock, Z.K., Gonzalez, M.D., & Eby, C.S. (2015). Ehrlichia-induced hemophagocytic lymphohistiocytosis: a case series and review of literature. Blood Cells, Molecules, and Disease, 55(3), 191-193. doi:10.1016/j.bcmd.2015.06.009.

Pritt, B.S., Sloan, L.M., Johnson, D.K., Munderloh, U.G., Paskewitz, S.M., McElroy, K.M., . . . Eremeeva, M.E. (2011). Emergence of a new pathogenic Ehrlichia species, Wisconsin and Minnesota, 2009. The New England Journal of Medicine, 365(5):422-9. doi:10.1056/NEJMoa1010493.

Ratnasamy, N., Everett, E.D., Roland, W.E., McDonald, G., & Caldwell, C.W., (1996). Central nervous system manifestations of human ehrlichiosis. Clinical Infectious Diseases, 23(2), 314-319. doi:10.1093/clinids/23.2.314.

Regan, J., Matthias, J., Green-Murphy, A., Stanek, D., Bertholf, M., Pritt, B.S., . . . Whittle, J.P. (2013). A confirmed Ehrlichia ewingii infection likely acquired through platelet transfusion. Clinical Infectious Diseases, 56(12), e105-107. doi:10.1093/cid/cit177.

Rolain, J.M., Maurin, M., Bryskier, A., & Raoult, D. (2000). In vitro activities of telithromycin (HMR 3647) against Rickettsia rickettsii, Rickettsia conorii, Rickettsia africae, Rickettsia typhi, Rickettsia prowazekii, Coxiella burnetii, Bartonella henselae, Bartonella quintana, Bartonella bacilliformis, and Ehrlichia chaffeensis. Antimicrobial Agents and Chemotherapy, 44(5), 1391-1393. doi:10.1128/aac.44.5.1391-1393.2000.

Rosenberg, R., Lindsey, N. P., Fischer, M., Gregory, C. J., Hinckley, A. F., Mead, P. S., . . . Petersen, L. R. (2018). Vital Signs: Trends in Reported Vectorborne Disease Cases - United States and Territories, 2004-2016. MMWR Morbidity and Mortality Weekly Report, 67(17), 496-501. doi: 10.15585/mmwr.mm6717e1.

Sachdev, S.H., Joshi, V., Cox, E.R., Amoroso, A., & Palekar, S. (2014). Severe life-threatening Ehrlichia chaffeensis infections transmitted through solid organ transplantation. Transplant Infectious Diseases, 16(1), 119-124. doi:10.1111/tid.12172.

Schotthoefer, A.M., Meece, J.K., Ivacic, L.C., Bertz, P.D., Zhang, K., Weiler, T., . . . Fritsche, T.R. (2013). Comparison of a real-time PCR method with serology and blood smear analysis for diagnosis of human anaplasmosis: importance of infection time course for optimal test utilization. Journal of Clinical Microbiology, 51(7), 2147-2153. doi:10.1128/JCM.00347-13.

Schutze, G.E., Buchingham, S.C., Marshall, G.S., Woods, C.R., Jackson, M.A., Patterson, L.E., . . . Tick-borne Infections in Children Study (TICS) Group. (2007). Human monocytic ehrlichiosis in children. The Pediatric Infectious Disease Journal, 26(6), 475-479. doi:10.1097/INF.0b013e318042b66c.

Schutze, G.E. & Jacobs, R.F. (1997). Human monocytic ehrlichiosis in children. Pediatrics, 100(1), E10. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/9200384

Sigurjonsdottir, V.K., Feder, H.M. JR., & Wormser, G.P. (2017). Anaplasmosis in pediatric patients: case report and review. Diagnostic Microbiology and Infectious Disease, 89(3), 230-234. doi:10.1016/j.diagmicrobio.2017.08.003.

Silaghi, C., Santos, A.S., Gones, J., Christova, I., Matei, I.A., Walder, G., . . . Dumler, J.S. (2017). Guideline for the direct detection of Anaplasma spp. in diagnosis and epidemiological studies. Vector Borne and Zoonotic Diseases, 17(1), 12-22. doi:10.1089/vbz.2016.1960.

Sosa-Gutierrez, C.G., Solorzano-Santos, F., Walker, D.H., Torres, J., Serrano, C.A., & Gordillo-Perez, G. (2016). Fatal monocytic ehrlichiosis in woman, Mexico, 2013. Emerging Infectious Diseases, 22(5), 871-874. doi:10.3201/eid2205.151217.

Steiert, J.G. & Gilfoy, F. (2002). Infection rates of Amblyomma americanum and Dermacentor variabilis by Ehrlichia chaffeensis and Ehrlichia ewingii in Southwest Missouri. Vector Borne and Zoonotic Disease, 2(2), 53-60. doi: 10.1089/153036602321131841.

Sukumaran, B., Narasimhan, S., Anderson, J. F., DePonte, K., Marcantonio, N., Krishnan, M. N., . . . Fikrig E. (2006). An Ixodes scapularis protein required for survival of Anaplasma phagocytophilum in tick salivary glands. Journal of Experimental Medicine, 203(6), 1507-17.doi: 10.1084/jem.20060208

Telford, 3rd, S. R., Dawson, J. E., Katavolos, P., Warner, C. K., Kolbert, C. P., Persing, D. H. (1996). Perpetuation of the agent of human granulocytic ehrlichiosis in a deer tick-rodent cycle. Proceedings of the National Academy of Sciences in the United States of America, 93(12):6209-14. doi: 10.1073/pnas.93.12.6209

Weil, A.A., Baron, E.L., Brown, C.M., & Drapkin, M.S. (2012). Clinical findings and diagnosis in human granulocytic anaplasmosis: a case series from Massachusetts. Mayo Clinical Proceedings, 87(3), 233-239. doi:10.1016/j.mayocp.2011.09.008.

Wormser, G.P., Aguero-Rosenfeld, M.E., Cox, M.E., Nowakowski, J., Nadelman, R.B., Holmgren, D., . . . Horowitz, H.W. (2013). Differences and similarities between culture-confirmed human granulocytic anaplasmosis and early Lyme disease. Journal of Clinical Microbiology 51(3), 954-958. doi:10.1128/JCM.02929-12.

Wormser, G.P., Filozov, A., Telford, S.R. III, Utpat, S., Kamer, R.S., Liveris, D., . . . Aguero-Rosenfeld, M.E. (2006). Dissociation between inhibition and killing by levofloxacin in human granulocytic anaplasmosis. Vector Borne and Zoonotic Diseases, 6(4), 388-394. doi:10.1089/vbz.2006.6.388.

Wormser, G.P., Sudhindra, P., Lopez, E., Patel, L., Rezai, S, Brumbaugh, A.D., . . . Visintainer, P. (2016). Fatigue in patients with erythema migrans. Diagnostic Microbiology and Infectious Disease, 86(3), 322-326. doi:10.1016/j.diagmicrobio.2016.07.026.

Wright, C.L., Gaff, H.D., & Hynes, W.L. (2014). Prevalence of Ehrlichia chaffeensis and Ehrlichia ewingii in Amblyomma americanum and Dermacentor variabilis collected from Southeastern Virginia, 2010-2011. Ticks and Tick-Borne Disease, 5(6):978-82. doi:10.1016/j.ttbdis.2014.07.023.