Human Ehrlichiosis Research Articles

Proposal to reclassify Ehrlichia muris as Ehrlichia muris subsp. muris subsp. nov. and description of Ehrlichia muris subsp. eauclairensis subsp. nov., a newly recognized tick-borne pathogen of humans.

We have previously described a novel taxon of the genus Ehrlichia (type strain WisconsinT), closely related to Ehrlichia muris, that causes human ehrlichiosis among patients with exposures to ticks in the upper midwestern USA. DNA from this bacterium was also detected in Ixodes scapularis and Peromyscus leucopus collected in Minnesota and Wisconsin. To determine the relationship between the E. muris-like agent (EMLA) and other species of the genus Ehrlichia phenotypic, genotypic and epidemiologic comparisons were undertaken, including sequence analysis of eight gene loci (3906 nucleotides) for 39 EMLA DNA samples and the type strain of E. muris AS145T. Three loci were also sequenced from DNA of nine strains of E. muris from mouse spleens from Japan. All sequences from E. muris were distinct from homologous EMLA sequences, but differences between them were less than those observed among other species of the genus Ehrlichia. Phenotypic comparison of EMLA and E. muris revealed similar culture and electron microscopic characteristics, but important differences were noted in their geographic distribution, ecological associations and behavior in mouse models of infection. Based on these comparisons, we propose that type strain WisconsinT represents a novel subspecies, Ehrlichia murissubsp. eauclairensis,subsp. nov. This strain is available through the Centers for Disease Control and Prevention Rickettsial Isolate Reference Collection (CRIRC EMU002T) and through the Collection de Souches de l'Unité des Rickettsies (CSURP2883 T). The subspecies Ehrlichia murissubsp. muris subsp. nov. is automatically created and the type strain AS145T is also available through the same collections (CRIRC EMU001T, CSUR E2T). Included is an emended description of E. muris.

Genetic profiling for Anaplasma and Ehrlichia species in ticks collected in the Eastern Cape Province of South Africa

BackgroundAnaplasma and Ehrlichia are emerging tick-borne pathogens that cause anaplasmosis and ehrlichiosis in humans and other animals worldwide. Infections caused by these pathogens are deadly if left untreated. There has been relatively no systematic survey of these pathogens among ticks in South Africa, thus necessitating this study. The presence of Anaplasma and Ehrlichia species were demonstrated by PCR in ticks collected from domestic ruminants at some selected communities in the Eastern Cape of South Africa. The ticks were identified by morphological characteristics and thereafter processed to extract bacterial DNA, which was analyzed for the presence of genetic materials of Anaplasma and Ehrlichia.ResultsThree genera of ticks comprising five species were identified. The screening yielded 16 positive genetic materials that were phylogenetically related to Ehrlichia sequences obtained from GenBank, while no positive result was obtained for Anaplasma. The obtained Ehrlichia sequences were closely related to E. chaffeensis, E. canis, E. muris and the incompletely described Ehrlichia sp. UFMG-EV and Ehrlichia sp. UFMT.ConclusionThe findings showed that ticks in the studied areas were infected with Ehrlichia spp. and that the possibility of transmission to humans who might be tick infested is high.

Clinical Features of PCR Confirmed Human Ehrlichiosis and Anaplasmosis in an Endemic Area of the Northeast United States

Clinical Features of PCR Confirmed Human Ehrlichiosis and Anaplasmosis in an Endemic Area of the Northeast United States

Occurrence of Amblyomma americanum (Acari: Ixodidae) and Human Infection With Ehrlichia chaffeensis in Wisconsin, 2008-2015.

Because of the increasing incidence of human ehrlichiosis in Wisconsin, we assessed reports of human infections by Ehrlichia chaffeensis and the distribution of its vector, the lone star tick (Amblyomma americanum (L.)). From 2008 through 2015, 158 probable and confirmed human cases of E. chaffeensis infections were reported to the Wisconsin Department of Health Services. Five cases without travel history outside of Wisconsin were confirmed as E. chaffeensis by polymerase chain reaction. Surveillance for the vector occurred from 2008 through 2015 and was based on active and passive methods, including examination of white-tailed deer, collections from live-trapped small mammals, submissions of ticks removed from wild and domestic animals through the Wisconsin Surveillance of Animals for Ticks (SWAT) program, digital or physical submissions by the public to the University of Wisconsin Insect Diagnostic or Medical Entomology laboratories, and active tick dragging. More than 50 lone star ticks (46 adults, 6 nymphs, and 1 larva) were identified. Lone star ticks were more commonly found in south central Wisconsin, particularly in Dane County, where discovery of more than one life stage in a single year indicates possible establishment.

Ehrlichioses: An Important One Health Opportunity.

Ehrlichioses are caused by obligately intracellular bacteria that are maintained subclinically in a persistently infected vertebrate host and a tick vector. The most severe life-threatening illnesses, such as human monocytotropic ehrlichiosis and heartwater, occur in incidental hosts. Ehrlichia have a developmental cycle involving an infectious, nonreplicating, dense core cell and a noninfectious, replicating reticulate cell. Ehrlichiae secrete proteins that bind to host cytoplasmic proteins and nuclear chromatin, manipulating the host cell environment to their advantage. Severe disease in immunocompetent hosts is mediated in large part by immunologic and inflammatory mechanisms, including overproduction of tumor necrosis factor α (TNF-α), which is produced by CD8 T lymphocytes, and interleukin-10 (IL-10). Immune components that contribute to control of ehrlichial infection include CD4 and CD8 T cells, natural killer (NK) cells, interferon-γ (IFN-γ), IL-12, and antibodies. Some immune components, such as TNF-α, perforin, and CD8 T cells, play both pathogenic and protective roles. In contrast with the immunocompetent host, which may die with few detectable organisms owing to the overly strong immune response, immunodeficient hosts die with overwhelming infection and large quantities of organisms in the tissues. Vaccine development is challenging because of antigenic diversity of E. ruminantium, the necessity of avoiding an immunopathologic response, and incomplete knowledge of the protective antigens.

Ehrlichia chaffeensis TRP120 Activates Canonical Notch Signaling To Downregulate TLR2/4 Expression and Promote Intracellular Survival.

ABSTRACTEhrlichia chaffeensis preferentially targets mononuclear phagocytes and survives through a strategy of subverting innate immune defenses, but the mechanisms are unknown. We have shown E. chaffeensis type 1 secreted tandem repeat protein (TRP) effectors are involved in diverse molecular pathogen-host interactions, such as the TRP120 interaction with the Notch receptor-cleaving metalloprotease ADAM17. In the present study, we demonstrate E. chaffeensis, via the TRP120 effector, activates the canonical Notch signaling pathway to promote intracellular survival. We found that nuclear translocation of the transcriptionally active Notch intracellular domain (NICD) occurs in response to E. chaffeensis or recombinant TRP120, resulting in upregulation of Notch signaling pathway components and target genes notch1, adam17, hes, and hey. Significant differences in canonical Notch signaling gene expression levels (>40%) were observed during early and late stages of infection, indicating activation of the Notch pathway. We linked Notch pathway activation specifically to the TRP120 effector, which directly interacts with the Notch metalloprotease ADAM17. Using pharmacological inhibitors and small interfering RNAs (siRNAs) against γ-secretase enzyme, Notch transcription factor complex, Notch1, and ADAM17, we demonstrated that Notch signaling is required for ehrlichial survival. We studied the downstream effects and found that E. chaffeensis TRP120-mediated activation of the Notch pathway causes inhibition of the extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK) pathways required for PU.1 and subsequent Toll-like receptor 2/4 (TLR2/4) expression. This investigation reveals a novel mechanism whereby E. chaffeensis exploits the Notch pathway to evade the host innate immune response for intracellular survival.

Hacker within! Ehrlichia chaffeensis Effector Driven Phagocyte Reprogramming Strategy.

Ehrlichia chaffeensis is a small, gram negative, obligately intracellular bacterium that preferentially infects mononuclear phagocytes. It is the etiologic agent of human monocytotropic ehrlichiosis (HME), an emerging life-threatening tick-borne zoonosis. Mechanisms by which E. chaffeensis establishes intracellular infection, and avoids host defenses are not well understood, but involve functionally relevant host-pathogen interactions associated with tandem and ankyrin repeat effector proteins. In this review, we discuss the recent advances in our understanding of the molecular and cellular mechanisms that underlie Ehrlichia host cellular reprogramming strategies that enable intracellular survival.

Comparative speed of kill of sarolaner (Simparica) and afoxolaner (NexGard) against induced infestations of Amblyomma americanum on dogs.

BackgroundThe lone star tick, Amblyomma americanum, infests dogs and cats in North America and is the vector of the pathogens that cause monocytic and granulocytic ehrlichiosis in dogs and humans. A parasiticide’s speed of kill is important to minimize the direct and deleterious effects of tick infestation and especially to reduce the risk of transmission of tick-borne pathogens. In this study, speed of kill of a novel orally administered isoxazoline parasiticide, sarolaner (Simparica™ chewable tablets), against A. americanum on dogs was evaluated and compared with afoxolaner (NexGard®) for 5 weeks following a single oral dose.MethodsBased on pretreatment tick counts, 24 dogs were randomly allocated to treatment with sarolaner (2 to 4 mg/kg), afoxolaner (2.5 to 6.8 mg/kg) or a placebo. Dogs were examined and live ticks counted at 8, 12, and 24 h after treatment and subsequent re-infestations on Days 7, 14, 21, 28, and 35. Efficacy was determined at each time point relative to counts for placebo dogs.ResultsA single oral dose of sarolaner provided 100 % efficacy within 24 h of treatment, and consistently provided >90 % efficacy against subsequent weekly re-infestations with ticks to Day 28. Significantly more live ticks were recovered from afoxolaner-treated dogs than from sarolaner-treated dogs at 24 h after infestation from Day 7 through Day 35 (P ≤ 0.0247). At 24 h, efficacy of afoxolaner declined to less than 90 % from Day 14 to the end of the study. There were no adverse reactions to treatment.ConclusionsIn this controlled laboratory evaluation, sarolaner had a faster speed of kill against A. americanum ticks than afoxolaner. The rapid and consistent kill of ticks by sarolaner within 24 h after a single oral dose over 28 days, suggests this treatment will provide highly effective and reliable control of ticks over the entire treatment interval, and could help reduce the risk of transmission of tick-borne pathogens by A. americanum.

Prevalence of antibodies against Ehrlichia spp. and Orientia tsutsugamushi in small mammals around harbors in Taiwan.

BackgroundTick-borne ehrlichiosis and mite-borne scrub typhus represent important emerging zoonotic rickettsial diseases. Although scrub typhus has been recognized by the Taiwanese public health system, information on ehrlichial infections is scarce in Taiwan. In this study, the risk of spread of ectoparasites on rodents through aerial and marine transportation was assessed in international and domestic harbors. Here, we report the first systematic surveillance of seroprevalence against Ehrlichia spp. in small mammals on the main island of Taiwan.MethodsIn total, 1648 small mammals were trapped from 8 international ports, 18 domestic fishing harbors, and 7 local public health centers around Taiwan from November 2004 to December 2008. Sera were analyzed using indirect immunofluorescence assays to detect IgG antibodies against Ehrlichia chaffeensis and Orientia tsutsugamushi. A serum titer of ≧1:80 was considered positive.ResultsAntibodies against Ehrlichia spp. and O. tsutsugamushi were detected in 3.28 % and 4.92 % of small mammals active around harbors, respectively. The seropositive rate against Ehrlichia was higher in northern Taiwan from 2005 to 2008. However, O. tsutsugamushi infections increased in southern Taiwan during this period. The serological evidence of ehrlichial and O. tsutsugamushi infections in all international ports were included in the study. No significant differences were found among the seropositive rates of Ehrlichia spp. and O. tsutsugamushi in small mammals trapped between international and local harbors.ConclusionsThe overall prevalence of Ehrlichia spp. and O. tsutsugamushi infections in small mammals active around harbors was 3.28 % and 4.92 %, respectively. The results provided serological evidence supporting the potential risks of transporting pathogens through air and maritime traffic. This study highlights serious issues of the emergence and spread of rickettsial diseases in Taiwan. The incidence of human ehrlichiosis requires further investigation.

Natural Focality of Lyme Borreliosis, Granulocytic Anaplasmosis, and Monocytic Ehrlichiosis in Humans in the Republic of Tatarstan

Objective of the study is to investigate natural focality of Ixodidae tick borreliosis, granulocytic anaplasmosis, monocytic ehrli-chiosis in humans in the Republic of Tatarstan. Materials and methods. Utilized were the data from tick studies conducted between 2010–2015. Applying immune-enzymatic analysis, investigated were the blood sera from residents (donors) of Kazan and municipal districts of the Republic of Tatarstan for the presence of specific antibodies to borreliosis, ehrlichiosis, and anaplasmosis pathogens. Results and conclusions. For the first time ever, the data on spontaneous carriage of Ehrlichiosis pathogens in Ixodidae ticks have been obtained. The information received is an indicative of the active circulation of Borrelia, Ehrlichia and Anaplasma in the territory of the region and of necessity to expand the research on the “novel” for the Republic nosological forms of natural-focal infections.

Development of Structure-Based Vaccines for Ehrlichiosis.

The obligate intracellular bacterium Ehrlichia chaffeensis that resides in mononuclear phagocytes is the etiologic agent of human monocytotropic ehrlichiosis (HME). HME is an emerging and often life-threatening zoonotic, tick-transmitted infectious disease in the USA. Lack of early diagnosis and treatment of HME are the main factors that lead to severe and fatal disease. Ehrlichia also causes diseases in companion animals and domesticated ruminants. E. chaffeensis and E. canis cause canine ehrlichioses in dogs, whereas E. ruminantium causes heartwater in cattle, sheep, and goats. As yet there are no commercially available vaccines to protect against these pathogens. This chapter describes a protocol to develop a structure-based vaccine for Ehrlichia based on the antigenic proteins P28-19 and Ehrlichia Hsp60.

Undetermined Human Ehrlichiosis and Anaplasmosis in the United States, 2008-2012: A Catch-All for Passive Surveillance.

Human ehrlichiosis and anaplasmosis are potentially severe illnesses endemic in the United States. Several bacterial agents are known causes of these diseases: Ehrlichia chaffeensis, Ehrlichia ewingii, Ehrlichia muris-like agent, Panola Mountain Ehrlichia species, and Anaplasma phagocytophilum. Because more than one agent may be present in one area, cases of human ehrlichiosis and anaplasmosis may be reported as "human ehrlichiosis/anaplasmosis undetermined" when the available evidence does not suggest an etiology to the species level. Here, we present a brief summary of these undetermined cases with onset of symptoms from 2008 to 2012 reported to two passive surveillance systems in the United States. The reported incidence rate during this time was 0.52 cases per million person-years. Many cases (24%) had positive polymerase chain reaction results. Enhanced surveillance in an area where several of these etiologic agents are endemic may provide a better understanding of the epidemiology of ehrlichiosis and anaplasmosis in the United States.

Increasing Incidence of Ehrlichiosis in the United States: A Summary of National Surveillance of Ehrlichia chaffeensis and Ehrlichia ewingii Infections in the United States, 2008-2012.

Human ehrlichiosis is a potentially fatal disease caused by Ehrlichia chaffeensis and Ehrlichia ewingii. Cases of ehrlichiosis are reported to Centers for Disease Control and Prevention through two national surveillance systems: Nationally Notifiable Diseases Surveillance System (NNDSS) and Case Report Forms. During 2008-2012, 4,613 cases of E. chaffeensis infections were reported through NNDSS. The incidence rate (IR) was 3.2 cases per million person-years (PYs). The hospitalization rate (HR) was 57% and the case fatality rate (CFR) was 1%. Children aged < 5 years had the highest CFR of 4%. During 2008-2012, 55 cases of E. ewingii infection were reported through NNDSS. The national IR was 0.04 cases per million PY. The HR was 77%; no deaths were reported. Immunosuppressive conditions were reported by 26% of cases. The overall rate for ehrlichiosis has increased 4-fold since 2000. Although previous literature suggests E. ewingii primarily affects those who are immunocompromised, this report shows most cases occurred among immunocompetent patients. This is the first report to show children aged < 5 years with ehrlichiosis have an increased CFR, relative to older patients. Ongoing surveillance and reporting of tick-borne diseases are critical to inform public health practice and guide disease treatment and prevention efforts.

PS-142 Safety Of Empiric Outpatient Treatment Of Suspected Tick Borne Illness In The Paediatric Emergency Department

<h3>Background/Aims</h3> Rocky Mountain spotted fever (RMSF) and human Ehrlichiosis are common tick-borne infections in the United States and many patients may be treated as outpatients with doxycycline. However, bacterial meningitis presents with similar symptoms. We evaluated whether empiric outpatient treatment for possible tick-borne illness resulted in cases of inadequately treated bacterial meningitis. <h3>Methods</h3> We performed a review of all patients seen in our tertiary children’s hospital emergency department (PED) from May to August of 2004–2013 who had a diagnosis consistent with possible tick-borne infection. Clinical and laboratory characteristics of all patients who returned to the PED within two weeks were collected from the electronic medical record. <h3>Results</h3> 718 patients were discharged from the PED during our study period and 43 (6.0%) returned to the PED within 2 weeks. There were no cases of bacterial meningitis and no deaths among patients who returned to the PED. 27/43 children (63%) were discharged with doxycycline. 11/43 children (26%) underwent lumbar puncture (LP) at their initial visit; 3/43 patients (7.0%), all of whom returned with neck pain, had an LP at their return visit and all three were diagnosed with viral meningitis. 16/43 patients (37%) were admitted after their second visit, with an average length of stay of 2.7 days. <h3>Conclusion</h3> Empiric treatment of suspected tick-borne illness in our PED did not result in any cases of unrecognised bacterial meningitis. Further prospective studies may identify low risk children who may be discharged from the PED without extensive laboratory testing.

Co-circulation of multiple species of Rickettsiales bacteria in one single species of hard ticks in Shenyang, China

Bacteria in the order Rickettsiales include some of the most important zoonotic (re)emerging pathogens for animals and humans. In 2012, a total of 1267 adult Haemaphysalis longicornis ticks were collected from domestic animals (cattle and sheep) in Shenyang of Liaoning Province, China. These ticks were grouped into 181 pools (each pool with 6–7 ticks). Rickettsiales agents were identified in 93 (51.38%) tick pools using PCR targeting rrs (16S rRNA). In addition to 16S rRNA gene sequences, gltA and groEL gene sequences were also recovered from these positive samples. Phylogenetic analyses of these sequences revealed the presence of five species of Rickettsiales bacteria in a single tick species (H. longicornis) in nature in Shenyang, including Rickettsia japonica, Rickettsia raoultii, Anaplasma centrale, Anaplasma bovis, and a potentially novel A. phagocytophilum variant. Additionally, two Candidatus Ehrlichia spp. (Ehrlichia sp. Yonaguni138, Candidatus Ehrlichia shimanensis) were also identified in these ticks, with the highest prevalence of Ehrlichia sp. Yonaguni138 (73/181, 40.3%). Notably, these agents except the novel A. phagocytophilum variant had close evolutionary relationships with those previously identified in northeastern Asian countries including Korea, Japan, and Russia, indicating a geographic clustering pattern. Our data also reinforce the need for vigilance in recognition and prevention of rickettsiosis, ehrlichiosis, and anaplasmosis in humans and animals in this region.

Primer caso de ehrlichiosis monocítica humana reportado en Colombia

First case of human monocytic ehrlichiosis reported in Colombia Abstract Human ehrlichiosis is an infection that is neither suspected or recognized in our country. Certain epidemiologic clues should arouse suspicion for this entity when the symptoms are suggestive. We present a case of a young soldier with clear risk factors for zoonotic infection, with fever, a petechial rash, thrombocytopenia, hepatitis and multiple organ failure, for whom a diagnosis of Ehrlichia chaffeensis was confirmed by serology after ruling out common infections and other infections caused by vectors. There are important limitations in documenting these cases, because there is no mandatory public reporting and a significant proportion of these cases are asymptomatic, leading to

An animal model of a newly emerging human ehrlichiosis.

Human ehrlichioses are emerging life-threatening diseases transmitted by ticks. Animal models have been developed to study disease development; however, there is no valid small animal model that uses a human ehrlichial pathogen. The objective of this study was to develop a mouse model for ehrlichiosis with the newly discovered human pathogen, Ehrlichia muris-like agent (EMLA). Three strains of mice were inoculated with different doses of EMLA by the intravenous, intraperitoneal, or intradermal route and evaluated for clinical and pathologic changes during the course of infection. EMLA infected C57Bl/6, BALB/c, and C3H/HeN mice and induced lethal or persistent infection in a route- and dose-dependent manner. The clinical chemistry and hematologic changes were similar to those of human infection by Ehrlichia chaffeensis or EMLA. Bacterial distribution in tissues differed after intradermal infection, compared with the distribution after intravenous or intraperitoneal injection. Lethal infection did not cause remarkable pathologic changes, but it caused fluid imbalance. EMLA infection of endothelium and mononuclear cells likely plays a role in the severe outcome. The EMLA mouse model mimics human infection and can be used to study pathogenesis and immunity and for development of a vector transmission model of ehrlichiosis.

Detection of bacterial agents in Amblyomma americanum (Acari: Ixodidae) from Georgia, USA, and the use of a multiplex assay to differentiate Ehrlichia chaffeensis and Ehrlichia ewingii.

Amblyomma americanum, the lone star tick, is the most common and most aggressive human biting tick in the Southeastern United States. It is known to transmit the agents of human ehrlichioses, Ehrlichia chaffeensis and Ehrlichia ewingii. In addition, it carries agents of unspecified pathogenicity to humans, including Rickettsia amblyommii, Borrelia lonestari, and the newly emerging Panola Mountain Ehrlichia (PME). Surveillance of these ticks for recognized or emerging pathogens is necessary for assessing the risk of human infection. From 2005 to 2009, we surveyed A. americanum ticks from four locations in the state of Georgia. Ticks (1,183 adults, 2,954 nymphs, and 99 larval batches) were tested using a multiplex real-time polymerase chain reaction (PCR) assay designed to detect and discriminate DNA from Rickettsia spp., E. chaffeensis, and E. ewingii. This assay was capable of detecting as few as 10 gene copies of the aforementioned agents. Ticks were also tested for PME and B. lonestari by nested PCR. The prevalence of infection ranged from 0 to 2.5% for E. chaffeensis, 0 to 3.9% for E. ewingii, 0 to 2.2% for PME, 17 to 83.1% for R. amblyommii, and 0 to 3.1% for B. lonestari. There were 46 (4.1%) individual adults positive for two agents, and two females that were each positive for three agents. Two larval batches were positive for both B. lonestari and R. amblyommii, indicating the potential for transovarial transmission of both agents from a single female. Although infrequent in occurrence, the dynamics of coinfections in individual ticks should be explored further, given the potential implications for differential diagnosis and severity of human illness.

Mixed cryoglobulinemia and secondary membranoproliferative glomerulonephritis associated with ehrlichiosis.

Ehrlichiosis is a tick-borne disease with diverse clinical presentations, ranging in severity from a flu-like illness with fever and myalgias to a serious systemic disease with multisystem organ failure. Nephrotic syndrome has been reported previously in two cases of human ehrlichiosis. A kidney biopsy revealed minimal change disease in one of those patients. Herein, we present the case of a 40-year-old man with ehrlichiosis who developed nephrotic syndrome, cryoglobulinemia, and secondary membranoproliferative glomerulonephritis (MPGN). The patient originally presented with shortness of breath, diffuse myalgias, headache, and lower extremity edema. He subsequently developed acute kidney injury and underwent kidney biopsy which showed MPGN and acute tubular injury. A tick-borne disease panel was positive for IgM and IgG to Ehrlichia chaffeensis. Serum testing revealed type 3 mixed cryoglobulinemia with no evidence of hepatitis C infection. The cryoprecipitate contained IgM and IgG antibodies to E. chaffeensis. Cryoglobulinemia is frequently associated with infections, particularly hepatitis C; however, our case is the first to describe ehrlichiosis associated with cryoglobulinemia and secondary MPGN.

Rickettsiae and Ehrlichiae Within a City Park: Is the Urban Dweller at Risk?

Tick-borne diseases, such as spotted fever rickettsioses and ehrlichioses, are potentially severe and life-threatening infections. The incidences of these infections increase during warm weather months as ticks become active. Clinicians often consider outdoor activities in rural areas to be a risk factor for exposure to ticks and the pathogens they carry, but are those who live, work, and play within an urban environment excluded from this risk? In this study, we collected ticks from two urban parks in Little Rock, AR, to assess the presence of rickettsiae and ehrlichiae within an urban setting. A total of 273 ticks were collected during July, 2011. Amblyomma americanum was the predominant tick species, with 255 (93%) of those collected. The remaining 18 (7%) were Dermacentor variabilis. Ticks were separated and pooled into groups for further testing. Forty-two of the 43 (98%) A. americanum pools demonstrated molecular evidence for the presence of rickettsiae. None of the D. variabilis contained rickettsiae. Restriction enzyme fragment length polymorphism analysis and DNA sequencing revealed Rickettsia amblyommii to be the species present. One A. americanum pool from park A demonstrated the presence of Ehrlichia chaffeensis, the pathogen responsible for human monocytotropic ehrlichiosis. These results indicate that tick-borne pathogens are not limited to rural or suburban areas.