Serologic evidence of a natural infection of white-tailed deer with the agent of human granulocytic ehrlichiosis in Wisconsin and Maryland

Anaplasma odocoilei sp. nov. (family Anaplasmataceae) from white-tailed deer (Odocoileus virginianus)

Recently, an undescribed Anaplasma sp. (also called Ehrlichia-like sp. or WTD agent) was isolated in ISE6 tick cells from captive white-tailed deer. The goal of the current study was to characterize this organism using a combination of experimental infection, morphologic, serologic, and molecular studies. Each of 6 experimentally inoculated white-tailed deer fawns (Odocoileus virginianus) became chronically infected (100+ days) with the Anaplasma sp. by inoculation of either infected whole blood or culture. None of the deer showed evidence of clinical disease, but 3 of the 6 deer evaluated had multiple episodes of transient thrombocytopenia. Light microscopy of Giemsa-stained, thin blood smears revealed tiny, dark, spherical structures in platelets of acutely infected deer. Anaplasma sp. was detected in platelets of inoculated deer by polymerase chain reaction, transmission electron microscopy, immunohistochemistry, and in situ hybridization. Five of 6 deer developed antibodies reactive to Anaplasma sp. antigen, as detected by indirect fluorescent antibody testing. Phylogenetic analyses of 16S rRNA, groESL, and gltA sequences confirmed the Anaplasma sp. is related to A. platys. Two attempts to transmit the Anaplasma sp. between deer by feeding Amblyomma americanum, a suspected tick vector, were unsuccessful. Based on its biologic, antigenic, and genetic characteristics, this organism is considered a novel species of Anaplasma, and the name Anaplasma odocoilei sp. nov. is proposed with UMUM76(T) (=CSUR-A1) as the type strain.

Prevalence and molecular characterization of Anaplasmataceae agents in free-ranging Brazilian marsh deer (Blastocerus dichotomus)

Anaplasmataceae organisms comprise a group of obligate intracellular gram-negative, tick-borne bacteria that can infect both animals and humans. In the present work we investigate the presence of Ehrlichia, Anaplasma, and Neorickettsia species in blood samples from Brazilian marsh deer (Blastocerus dichotomus), using both molecular and serologic techniques. Blood was collected from 143 deer captured along floodplains of the Paraná River, near the Porto Primavera hydroelectric power plant. Before and after flooding, marsh deer were captured for a wide range research program under the financial support of São Paulo State Energy Company (CESP), between 1998 and 2001. Samples were divided into four groups according to time and location of capture and named MS01 (n=99), MS02 (n=18) (Mato Grosso do Sul, before and after flooding, respectively), PX (n=9; Peixe River, after flooding), and AGUA (n=17; Aguapeí River, after flooding). The seroprevalences for Ehrlichia chaffeensis and Anaplasma phagocytophilum were 76.76% and 20.2% in MS01, 88.88% and 5.55% in MS02, 88.88% and 22.22% in PX, and 94.12% and 5.88% in AGUA, respectively. Sixty-one animals (42.65% of the total population) were PCR-positive for E. chaffeensis PCR (100.0% identity based on 16S rRNA, dsb, and groESL genes). Seventy deer (48.95% of the total population) were PCR-positive for Anaplasma spp. (99.0% of identity with A. platys, and in the same clade as A. phagocytophilum, A. bovis, and A. platys based on 16S rRNA phylogenetic analysis). Our results demonstrate that Brazilian marsh deer are exposed to E. chaffeensis and Anaplasma spp. and may act as reservoirs for these rickettsial agents, playing a role in disease transmission to humans and other animals.

Clinical presentation of 26 anaplasma phagocytophilum-seropositive dogs residing in an endemic area

Anaplasma (A.) phagocytophilum, the etiological agent of canine granulocytic anaplasmosis, is capable of inciting moderate to severe clinical disease in a variety of mammals and is endemic in the upper midwest. The purpose of this study was fourfold: to describe the range of clinical signs in dogs seropositive to A. phagocytophilum; to examine the prevalence of immune-mediated hemolytic anemia (IMHA) in this population; to evaluate whether specific clinical signs were associated with coexposure to Borrelia (B.) burgdorferi in actively infected dogs; and to determine whether clinical response to doxycycline was complete in treated dogs. Medical records of dogs seropositive for A. phagocytophilum were reviewed retrospectively. Peripheral blood smears were also reviewed retrospectively for granulocytic Anaplasma morulae. Lethargy (81%), inappetence (58%), and lameness (50%) were the most common clinical signs, followed by fever (46%). Thrombocytopenia was the most common laboratory abnormality, and IMHA was diagnosed in three dogs. Dogs that were thrombocytopenic and had antibodies to both A. phagocytophilum and B. burgdorferi had a median platelet count of 51,000/μL (range 20,000 to 171,000/μL), which was significantly lower than the count in dogs with antibodies only to A. phagocytophilum (P=0.04). Some dogs had an apparent relapse of clinical signs after an appropriate course of doxycycline. Testing for A. phagocytophilum by polymerase chain reaction, serum antibody assays, and/or blood smear evaluation should be considered in dogs with IMHA, cough, or epistaxis and that reside in A. phagocytophilum-endemic areas. If moderate to severe thrombocytopenia is present, testing for concurrent B. burgdorferi infection may be warranted.

Natural history of Ehrlichia chaffeensis: vertebrate hosts and tick vectors from the United States and evidence for endemic transmission in other countries

Ehrlichia chaffeensis, an intracellular gram-negative zoonotic bacterium, is the causative agent of human monocytotropic ehrlichiosis (HME). In humans, the disease can range from a mild, non-specific illness with few to no clinical signs to a moderately severe to fatal disease, especially those with compromised immune systems. E. chaffeensis is maintained in a complex cycle involving white-tailed deer (WTD; Odocoileus virginianus) as a primary reservoir and the lone star tick (LST; Amblyomma americanum) as a primary vector. Numerous other species are naturally exposed to E. chaffeensis and disease has been documented in some domestic animals and wildlife including domestic dogs and ring-tailed lemurs. The organism has been found throughout the natural range of the LST and as the tick continues to expand its range, the geographic range of risk for E. chaffeensis infections will likely continue to expand. Recent data have indicated that E. chaffeensis, or a closely related organism, has been found in many species of ticks and vertebrate hosts in numerous countries.

Anaplasma phagocytophilum in central and western Wisconsin: a molecular survey

Anaplasma phagocytophilum is an obligate intracellular bacterium that is transmitted to humans through the bite of Ixodes spp. ticks, and causes a febrile disease known as human granulocytic anaplasmosis. The presence of A. phagocytophilum in Wisconsin white-tailed deer blood and in deer ticks was assessed using PCR and DNA sequencing. Sampling sites in the western part of the state (Buffalo County) and central region (Waushara, Waupaca, and Green Lake counties) were used. In Buffalo County, 5.6% of deer and 8.9% of ticks were infected. At Hartman Creek State Park (Waupaca County), 11.5% of ticks were infected, while the observed prevalence in deer from counties to the south of the park (Waushara and Green Lake) reached 19-26%. Based on 16S rRNA sequences, A. phagocytophilum strains associated and not associated with human infections were identified. Furthermore, two novel A. phagocytophilum variants were found in deer blood samples. Transmission of Lyme disease has been documented in both the Western and Central regions we sampled, and the presence of A. phagocytophilum in naturally occurring tick populations could present an additional risk of disease to humans that enter tick habitats.

Characterization of Anaplasma phagocytophilum major surface protein 5 and the extent of its cross-reactivity with A. marginale

Major surface protein 5 (Msp5) of Anaplasma marginale is highly conserved in the genus Anaplasma and the antigen used in a commercially available competitive enzyme-linked immunosorbent assay (cELISA) for serologic identification of cattle with anaplasmosis. This study analyzes the degrees of conservation of Msp5 among various isolates of Anaplasma phagocytophilum and the extent of serologic cross-reactivity between recombinant Msp5 (rMsp5) of Anaplasma marginale and A. phagocytophilum. The msp5 genes from various isolates of A. phagocytophilum were sequenced and compared. rMsp5 proteins of A. phagocytophilum and A. marginale were used separately in an indirect ELISA to detect cross-reactivity in serum samples from humans and dogs infected with A. phagocytophilum and cattle infected with A. marginale. Serum samples were also tested with a commercially available competitive ELISA that uses monoclonal antibody ANAF16C1. There were 100% sequence identities in the msp5 genes among all of the A. phagocytophilum isolates from the United States and a horse isolate from Sweden. Sheep isolates from Norway and dog isolates from Sweden were 99% identical to one another but differed in 17 base pairs from the United States isolates and the horse isolate. Serologic cross-reactivity was identified when serum samples from cattle infected with A. marginale were reacted with rMsp5 of A. phagocytophilum and when serum samples from humans and dogs infected with A. phagocytophilum were reacted with rMsp5 of A. marginale in an indirect-ELISA format. Serum samples from dogs or humans infected with A. phagocytophilum did not cross-react with rMsp5 of A. marginale when tested with the commercially available cELISA. These results suggest that rMsp5 of A. phagocytophilum is highly conserved among United States and European isolates and that serologic distinction between A. phagocytophilum and A. marginale infections cannot be accomplished if rMsp5 from either organism is used in an indirect ELISA.

Evaluation of white-tailed deer (Odocoileus virginianus) as natural sentinels for Anaplasma phagocytophilum

Anaplasma phagocytophilum, the causative agent of human granulocytotropic anaplasmosis, can infect white-tailed deer (WTD; Odocoileus virginianus), and this species is a crucial host for adult Ixodes scapularis, the primary vector of A. phagocytophilum. The goal of this study was to determine the geographic distribution of A. phagocytophilum among WTD across a 19 state region and to evaluate the utility of WTD as natural sentinels. Serologic testing using the indirect fluorescent antibody (IFA) assay was conducted on WTD serum samples and molecular and xenodiagnostic tests were performed to confirm serologic results. The surveillance system was assessed through examination of vital attributes including WTD age and gender associations with serologic status, sample size adequacy for accurate infection status classification, and presence of the vector, I. scapularis. Six hundred thirty-three of 2,666 (24%) WTD in 17 states tested positive for antibodies (>or=128) when tested by IFA assay. Testing for p44 and/or 16S rRNA gene targets identified 73 (16%) PCR positive WTD among 458 animals tested, all of which originated from seropositive populations. Attempts to culture A. phagocytophilum from WTD were unsuccessful; however, xenodiagnostic mice inoculated with blood from 3 WTD became infected. Seroprevalence did not differ by deer age or gender; however, WTD<or=0.75 years old had a higher prevalence of PCR positivity. Using seroprevalence data, a sample size of 6-9 animals per population was projected to be adequate for identifying seropositive populations. The presence of I. scapularis was significantly associated with A. phagocytophilum antibodies in WTD. Collectively, the results of this study demonstrate that WTD would be suitable natural sentinels for this emerging zoonotic pathogen.

Detection of Anaplasma phagocytophilum and Babesia odocoilei DNA in Ixodes scapularis (Acari: Ixodidae) collected in Indiana

The blacklegged tick, Ixodes scapularis Say, first reported in Indiana in 1987, has now been detected in more than half of Indiana's counties. The first case of human granulocytic ehrlichiosis (human anaplasmosis) in Indiana was reported in 2002. We now report the detection of Anaplasma phagocytophilum and Babesia odocoilei (Emerson and Wright 1968) in I. scapularis ticks collected in northern Indiana. Using polymerase chain reaction analysis, 41 of 193 adult ticks (21.2%) collected from deer were positive for A. phagocytophylum, and 22 (11.4%) were positive for Babesia sp. Restriction fragment analysis of 12, and sequencing of another five of the amplified products identified these parasites as B. odocoilei. Five ticks (2.6%) were coinfected. Eight of 68 questing adult ticks (11.8%) were positive for A. phagocytophilum; seven (10.3%) were positive for Babesia sp. Six of the latter seven positive samples were determined to be B. odocoilei by restriction fragment analysis and sequencing of two samples. None of 39 pools of nymphs was positive for Babesia sp. Three of 15 ticks (20%) collected from a dog were positive for A. phagocytophilum and three ticks (20%) were positive for Babesia sp. One was confirmed as B. odocoilei. One tick was coinfected. This is the first report of the presence of these two agents in ticks in Indiana.

Anaplasma phagocytophilum in white-tailed deer

We examined the reservoir potential of white-tailed deer for Anaplasma phagocytophilum. Results suggest that white-tailed deer harbor a variant strain not associated with human infection, but contrary to published reports, white-tailed deer are not a reservoir for strains that cause human disease. These results will affect surveillance studies of vector and reservoir populations.

Potential Vertebrate Reservoir Hosts and Invertebrate Vectors ofAnaplasma marginaleandA. phagocytophilumin Central Spain

Organisms in the genus Anaplasma are obligate intracellular pathogens that multiply in both vertebrate and invertebrate hosts. The type species, A. marginale, causes bovine anaplasmosis and only infects ticks and ruminants. A. phagocytophilum causes human and animal granulocytic anaplasmosis, and genetically closely related strains show a wide host range, including ticks, ruminants, rodents, equids, canids, birds, and humans. Recent reports demonstrated that A. marginale and A. phagocytophilum co-exist in geographic areas and that concurrent infections occur in ruminants and ticks. In this study, we characterized A. marginale and A. phagocytophilum infections in wild and domestic animals, and ticks collected in central Spain by serology, PCR, and sequence of 16S rRNA genotypes. Species tested included humans, cattle, dogs, rodents, Iberian red deer, European wild boar, birds, and ticks. Species of hematophagous Diptera were analyzed as potential mechanical vectors of Anaplasma spp. A. marginale was detected in tabanids, ticks, cattle, and deer, while A. phagocytophilum was detected in ticks, deer, cattle, and birds. Concurrent infections of the two Anaplasma were found in cattle and deer. These results illustrate the complexity of the epizootiology of A. marginale and A. phagocytophilum in regions where both pathogens co-exist and share common reservoir hosts and vectors. The increasing contact between wildlife, domestic animals, and human populations increases the risk of outbreaks of human and bovine anaplasmosis, and the difficulty of implementing surveillance and control measures.

Experimental infection of white-tailed deer with Anaplasma phagocytophilum, etiologic agent of human granulocytic anaplasmosis

Serologic and molecular evidence of Anaplasma phagocytophilum has been demonstrated in white-tailed deer (WTD; Odocoileus virginianus), and deer are an important host for the tick vector Ixodes scapularis. In this study, we describe experimental infection of WTD with A. phagocytophilum. We inoculated four WTD with a human isolate of A. phagocytophilum propagated in tick cells. Two additional deer served as negative controls. All inoculated deer developed antibodies (titers, > or =64) to A. phagocytophilum, as determined by an indirect fluorescent antibody test, between 14 and 24 days postinfection [p.i.]), and two deer maintained reciprocal titers of > or =64 through the end of the 66-day study. Although morulae were not observed in granulocytes and A. phagocytophilum was not reisolated via tick cell culture of blood, 16S reverse transcriptase nested PCR (RT-nPCR) results indicated that A. phagocytophilum circulated in peripheral blood of three deer through at least 17 days p.i. and was present in two deer at 38 days p.i. Femoral bone marrow from one deer was RT-nPCR positive for A. phagocytophilum at 66 days p.i. There was no indication of clinical disease. These data confirm that WTD are susceptible to infection with a human isolate of A. phagocytophilum and verify that WTD produce detectable antibodies upon exposure to the organism. Because adults are the predominant life stage of I. scapularis found on deer and because adult I. scapularis ticks do not transmit A. phagocytophilum transovarially, it is unlikely that WTD are a significant source of A. phagocytophilum for immature ticks even though deer have a high probability of natural infection. However, the susceptibility and immunologic response of WTD to A. phagocytophilum render them suitable candidates as natural sentinels for this zoonotic tick-borne organism.

Restricted changes in major surface protein-2 (msp2) transcription after prolonged in vitro passage of Anaplasma phagocytophilum

Background

Anaplasma phagocytophilum strains often vary in Msp2 expression, a situation assumed to be related to immune evasion. However, Msp2 is also an adhesin, and little is known about the role of endogenous msp2 transcriptional changes in the absence of immune selection. Thus, Msp2 profiles and msp2 transcripts of low passage A. phagocytophilum Webster strain, initially comprised of a single abundant msp2 transcript, were re-examined after ≥ 20 in vitro passages without immune selection.

Results

Using an Msp2 monoclonal antibody, immunoblots revealed an unchanged dominant band and several weak bands that appeared with passage. Similarly, msp2 transcript diversity changed, with a decrease in the initially abundant low passage transcript and appearance of a newly abundant and several minor msp2 transcripts with high passage. BLASTN search of the A. phagocytophilum HZ strain genome revealed ≥ 52 msp2 paralogs.

Conclusions

Msp2 expression and msp2 transcription modulate even without immune selective pressures. However, the limited diversity of msp2 transcripts in the absence of immune pressure suggests selection for Msp2 by specific functions beyond that of immune evasion, in spite of a large genomic reservoir for Msp2 diversity.

Evaluation of a PrototypeEhrlichia chaffeensisSurveillance System using White-Tailed Deer (Odocoileus virginianus) as Natural Sentinels

The natural history of Ehrlichia chaffeensis, the causative agent of human monocytotropic ehrlichiosis, includes the lone star tick (LST, Amblyomma americanum) as a vector and white-tailed deer (WTD; Odocoileus virginianus) as both a natural reservoir of E. chaffeensis and a major host of LST. The goal of the current study was to implement and evaluate a prototype surveillance system to delineate the geographic distribution of E. chaffeensis using WTD as natural sentinels. To accomplish this goal, serologic testing using the indirect immunofluorescent antibody (IFA) test was performed on WTD serum samples, and to confirm serologic results, polymerase chain reaction (PCR) assays and culture isolation were conducted. Considerations relevant to the applicability of a surveillance system utilizing WTD were analyzed (e.g., age and gender relationships to serologic status, adequacy of sample sizes needed to distinguish between uninfected and infected populations, presence of LST, and ability to detect stability and spread of E. chaffeensis in WTD populations). Of 3275 WTD serologically tested, 549 (47%) from 17 of 18 states had antibodies reactive to E. chaffeensis (IFA titer > or = 1:128). No difference between age groups or gender was noted with serologic testing, thus these variables would not be a concern for a surveillance system using WTD. Significantly more deer in younger age groups (< or = 1.5 yr) were PCR and culture positive, and 46% of 122 seropositive WTD populations were confirmed positive by PCR or culture isolation. A significant association between LST infestation and E. chaffeensis seroreactivity was noted. Furthermore, the surveillance system was able to detect stability of E. chaffeensis within WTD populations and also spread to new populations, both of which were associated with LST status. These data clearly demonstrate that WTD are useful as natural sentinels for this emerging human pathogen, and establish a prototypical framework for a WTD surveillance system.

Canine borreliosis

A guild of organisms carried by the same vector (Ixodes ticks) in Lyme-endemic areas may be confounding the understanding of Lyme disease in dogs. A new diagnostic method, the C6 peptide test for Lyme, and serology and PCR testing for Ehrlichia, Babesia, and Bartonella species will help to sort out seroprevalence and symptomatology caused by exposure to these agents or by coinfections. In addition, Rickettsia, Leptospira, Mycoplasma species, and more could be involved in dogs diagnosed with a "doxycycline-responsive" disease. The author does not recommend treating asymptomatic Borrelia carrier dogs, but does recommend screening them for proteinuria and for exposure to other agents. A positive Lyme titer is a marker of exposure to Ixodes ticks and the agents they carry. The risk/benefit of vaccination will be understood better as the symptomatology and immunopathogenesis of Lyme disease are defined. Meanwhile, tick control is highly recommended for all dogs in Lyme-endemic areas.

Analysis of genetic identity of North American Anaplasma phagocytophilum strains by pulsed-field gel electrophoresis

Biological and geographic heterogeneity of anthropozoonosis caused by Anaplasma phagocytophilum is poorly understood. Seven North American A. phagocytophilum strains were compared by PFGE. The average genome size was 1.58 Mbp, and restriction patterns were identical. New World strains of A. phagocytophilum have a large genome and a high degree of genetic uniformity.

Molecular characterization of Anaplasma phagocytophilum and Borrelia burgdorferi in Ixodes scapularis ticks from Pennsylvania

Ixodes scapularis ticks were collected in 2000 and 2001 from two areas in Pennsylvania and tested for the presence of Anaplasma phagocytophilum and Borrelia burgdorferi by PCR and DNA sequencing. Of the ticks collected from northwestern and southeastern Pennsylvania, 162 of 263 (61.6%) and 25 of 191 (13.1%), respectively, were found to be positive for B. burgdorferi. DNA sequencing showed >99% identity with B. burgdorferi strains B31 and JD1. PCR testing for A. phagocytophilum revealed that 5 of 263 (1.9%) from northwestern Pennsylvania and 76 of 191 (39.8%) from southeastern Pennsylvania were positive. DNA sequencing revealed two genotypes of A. phagocytophilum, the human granulocytic ehrlichiosis (HGE) agent and a variant (AP-Variant 1) that has not been associated with human infection. Although only the HGE agent was present in northwestern Pennsylvania, both genotypes were found in southeastern Pennsylvania. These data add to a growing body of evidence showing that AP-Variant 1 is the predominant agent in areas where both genotypes coexist.

PCR detection and serological evidence of granulocytic ehrlichial infection in roe deer (Capreolus capreolus) and chamois (Rupicapra rupicapra)

The role of wild mammals, such as roe deer (Capreolus capreolus) and chamois (Rupicapra rupicapra), in the epidemiology of granulocytic ehrlichiae in Switzerland was investigated. We tested blood samples for Ehrlichia phagocytophila genogroup 16S rRNA gene sequences by PCR and for immunoglobulin G antibodies against granulocytic ehrlichiae by indirect fluorescent-antibody assay (IFA). Overall means of 60.9% of 133 roe deer serum samples and 28.2% of 39 chamois serum samples were seroreactive by IFA. PCR results were positive for 18.4% of 103 roe deer serum samples as well. None of the 24 chamois blood samples tested were positive by PCR. Partial 16S rRNA gene and groESL heat shock operon sequences of three roe deer samples tested showed strong degrees of homology (> or =99.7 and > or =98.6%, respectively) with the sequences of granulocytic ehrlichiae isolated from humans. These results confirm that chamois, and particularly roe deer, are commonly infected with granulocytic ehrlichiae and provide evidence that these wild mammals are potential reservoirs for granulocytic ehrlichiae in Switzerland.

Genetic variability and stability of Anaplasma phagocytophila msp2 (p44)

Anaplasma (Ehrlichia) phagocytophila's major immunodominant surface protein antigen, Msp2 (P44, 44-kDa antigen), is encoded by a family of paralogous genes characterized by conserved sequences flanking a hypervariable region. The antigenic profiles of most strains of A. phagocytophila are different, and the differences are principally related to Msp2 expression. To date, multiple unique msp2 gene paralogs have been found in A. phagocytophila isolates, but the overall number in the genome of a single strain is not yet known. Changes in msp2 expression may be related to antigenic variability; thus, we examined the minimal complement of msp2 genes or pseudogenes in two strains of A. phagocytophila and the number of transcriptionally active msp2 gene paralogs during low-passage, steady-state, in vitro propagation. Of 15 BDS strain clones, 1 had a hypervariable region identical to the region in a clone obtained from a BDS strain genomic library previously prepared from organisms after only two horse passages. When 124 Webster strain clones were examined, 18 unique hypervariable regions were identified. Of 64 Webster strain cDNA clones, 56 (87.5%) were derived from a single gene, and transcripts from six additional msp2 genes were also identified. The sequences of several hypervariable regions that were > or = 97% similar to regions present in other strains were identified by performing a BLAST analysis of sequences deposited in the GenBank database. These findings suggest that antigenic variability results from transcription of one or a few of the multiple paralogs and not from genetic instability that results in random accumulated mutations, although the possibility that gene recombination plays a role cannot be eliminated. The predominant Msp2 pattern in vitro is determined by transcription from a single gene.

Spatial distribution of seropositivity to the causative agent of granulocytic ehrlichiosis in dogs in California

OBJECTIVE

To assess spatial and temporal patterns of seroprevalence among dogs in California to the causative agent of granulocytic ehrlichiosis (GE).

SAMPLE POPULATION

Sera of 1,082 clinically normal dogs from 54 of 59 counties in California in 1997 to 1998.

PROCEDURES

Serum-specific IgG reactivity to Ehrlichia equi was assessed by use of an immunofluorescent antibody assay, using E. equi-infected horse neutrophils as substrate. Data were analyzed, using a geographic information system. Spatial analysis of seroprevalence included first order Bayesian analysis of seroprevalence and second order analysis of clustering by K-function and Cuzick-Edwards tests. Monthly seroprevalence among dogs was examined by use of regression on monthly densities of Ixodes pacificus adults and nymphs.

RESULTS

Seroprevalence among dogs to E. equi was 8.68%. Data were seasonally bimodal with highest prevalence in winter (when adult ticks were abundant) and a secondary peak in late spring (corresponding to nymphal ticks). Humboldt County had the highest seroprevalence (47.3%), and other northern coast range counties had seroprevalence from 15 to 30%.

CONCLUSIONS AND CLINICAL RELEVANCE

The patchy distribution of exposure to Ehrlichia organisms is a subset of the distribution of the tick vector. This may reflect enzootic cycles or climatic or historical factors that limited the range of the disease. Dogs, horses, and humans from north coast range counties in California are at increased risk of GE. These data provide a background for assessing risk of infection in horses and dogs, depending on geographic location. Dogs may be sentinels for assessing risk of GE in humans.

Human granulocytic ehrlichiosis

Human granulocytic ehrlichiosis is a recently recognized tick-borne infectious disease, and to date >600 patients have been identified in the United States and Europe. Most patients have presented with a non-specific febrile illness occurring within 4 weeks after tick exposure or tick bite. The risk for serious illness or death increases with advancing age and delayed onset of therapy. Routine laboratory testing may reveal reduced white blood cell and platelet concentrations and mildly elevated hepatic transaminase activity in peripheral blood. A high index of suspicion is necessary to arrive at a timely clinical diagnosis. Patients suspected of having human granulocytic ehrlichiosis (HGE) should be treated with a tetracycline-class antibiotic while awaiting the outcome of confirmatory laboratory testing.

PCR detection of granulocytic ehrlichiae in Ixodes ricinus ticks and wild small mammals in western Switzerland

The presence of granulocytic ehrlichiae was demonstrated by PCR in Ixodes ricinus ticks and wild small mammals in Switzerland in two areas of endemicity for bovine ehrlichiosis. Six ticks (three females and three nymphs) (1.4%) of 417 I. ricinus ticks collected by flagging vegetation contained ehrlichial DNA. A total of 201 small mammals from five species, wood mouse (Apodemus sylvaticus), yellow-necked mouse (Apodemus flavicollis), earth vole (Pitymys subterraneus), bank vole (Clethrionomys glareolus), and common shrew (Sorex araneus), were trapped. The analysis of I. ricinus ticks [corrected] collected on 116 small mammals showed that nine C. glareolus voles and two A. sylvaticus mice hosted infected tick larvae. In these rodents, granulocytic ehrlichia infection was also detected in blood, spleen, liver, and ear samples. Further examinations of 190 small mammals without ticks or with noninfected ticks showed the presence of ehrlichial DNA in spleen and other tissues from six additional C. glareolus, three A. flavicollis, and one S. araneus mammals. This study suggests that A. sylvaticus, A. flavicollis, S. araneus, and particularly C. glareolus are likely to be natural reservoirs for granulocytic ehrlichiae. Partial 16S rRNA gene sequences of granulocytic ehrlichiae from ticks and rodents showed a high degree of homology (99 to 100%) with granulocytic ehrlichiae isolated from humans. In contrast, groESL heat shock operon sequence analysis showed a strong divergence (approximately 5%) between the sequences in samples derived from rodents and those derived from samples from questing ticks or from other published ehrlichia sequences. Dual infections with granulocytic ehrlichia and Borrelia burgdorferi were found in ticks and small mammals.

Tick-borne diseases

Tick-transmitted infectious agents have assumed increased importance as causes of human disease in the United States. During the past two decades, Lyme borreliosis, ehrlichiosis, and babesiosis have emerged as newly described tick-borne infectious diseases of significance for pediatricians and pediatric neurologists. In fact, the highest rates of infection for Lyme disease and Rocky Mountain spotted fever (RMSF), by decade of age, are in childhood. As such, tick-borne infectious disease are of considerable public health concern, particularly for children residing in endemic regions. RMSF and human ehrlichioses can be life-threatening but are also eminently treatable when recognized early. Delays in diagnosis and treatment can lead to adverse outcomes. This article reviews the clinical and epidemiological features of Lyme borreliosis, RMSF, and ehrlichiosis, important causes of neurological illness among children, and summarizes current therapeutic and preventive strategies.

Infection with agents of human granulocytic ehrlichiosis, lyme disease, and babesiosis in wild white-footed mice (Peromyscus leucopus) in Connecticut

White-footed mice, Peromyscus leucopus, were captured in southern Connecticut during 1997 and 1998 to determine the prevalence of infections caused by granulocytic Ehrlichia sp., Borrelia burgdorferi, and Babesia microti. Of the 50 mice captured and recaptured, 25 of 47 (53.2%) and 23 of 48 (47.9%) contained antibodies to the BDS or NCH-1 Ehrlichia strains, respectively, as determined by indirect fluorescent antibody (IFA) staining methods. The majority (83.3%) of 48 mice also contained antibodies to B. burgdorferi, as determined by enzyme-linked immunosorbent assay. Moreover, 20 of 26 (76.9%) contained antibodies to B. microti by IFA staining methods. In nested PCR tests using the 16S rRNA gene, the DNA of the human granulocytic ehrlichiosis (HGE) agent was detected in 17 of 47 mice (36.2%), but only 4 (23.5%) of these 17 mice were PCR positive at each capture. Antibody-positive reactions to granulocytic Ehrlichia sp. organisms were detected in 17 of 23 (73. 9%) of the PCR-positive mice. The sequences from PCR products from nine positive blood samples were identical to the HGE agent. Ehrlichia spp. were cultured from three of five mice captured in April 1998, including one that was PCR positive in April 1997. In addition, 2 of 14 larval Ixodes scapularis pools, which were attached to two PCR-positive mice, contained DNA of the HGE agent. A high percentage of white-footed mice are infected or have been infected naturally by the HGE agent with low-level persistent infection or frequent reinfection in some individual mice. However, the changes noted in the presence of DNA and antibodies in repeated blood and serum samples from individual mice over several months of field collection suggests that infection with granulocytic Ehrlichia is transient in most wild P. leucopus.