Ehrlichia spp. in cervids from California

Genetic diversity of Anaplasma bacteria: Twenty years later

The genus Anaplasma (family Anaplasmataceae, order Rickettsiales) includes obligate intracellular alphaproteobacteria that multiply within membrane-bound vacuoles and are transmitted by Ixodidae ticks to vertebrate hosts. Since the last reclassification of Anaplasmataceae twenty years ago, two new Anaplasma species have been identified. To date, the genus includes eight Anaplasma species (A. phagocytophilum, A. marginale, A. centrale, A. ovis, A. bovis, A. platys, A. odocoilei, and A. capra) and a large number of unclassified genovariants that cannot be assigned to known species. Members of the genus can cause infection in humans and a wide range of domestic animals with different degrees of severity. Long-term persistence which, in some cases, is manifested as cyclic bacteremia has been demonstrated for several Anaplasma species. Zoonotic potential has been shown for A. phagocytophilum, the agent of human granulocytic anaplasmosis, and for some other Anaplasma spp. that suggests a broader medical relevance of this genus. Genetic diversity of Anaplasma spp. has been intensively studied in recent years, and it has been shown that some Anaplasma spp. can be considered as a complex of genetically distinct lineages differing by geography, vectors, and host tropism. The aim of this review was to summarize the current knowledge concerning the natural history, pathogenic properties, and genetic diversity of Anaplasma spp. and some unclassified genovariants with particular attention to their genetic characteristics. The high genetic variability of Anaplasma spp. prompted us to conduct a detailed phylogenetic analysis for different Anaplasma species and unclassified genovariants, which were included in this review. The genotyping of unclassified genovariants has led to the identification of at least four distinct clades that might be considered in future as new candidate species.

Parallelisms and Contrasts in the Diverse Ecologies of the Anaplasma phagocytophilum and Borrelia burgdorferi Complexes of Bacteria in the Far Western United States

Anaplasma phagocytophilum and Borrelia burgdorferi are two tick-borne bacteria that cause disease in people and animals. For each of these bacteria, there is a complex of closely related genospecies and/or strains that are genetically distinct and have been shown through both observational and experimental studies to have different host tropisms. In this review we compare the known ecologies of these two bacterial complexes in the far western USA and find remarkable similarities, which will help us understand evolutionary histories and coadaptation among vertebrate host, tick vector, and bacteria. For both complexes, sensu stricto genospecies (those that infect humans) share a similar geographic range, are vectored mainly by ticks in the Ixodes ricinus-complex, utilize mainly white-footed mice (Peromyscus leucopus) as a reservoir in the eastern USA and tree squirrels in the far west, and tend to be generalists, infecting a wider variety of vertebrate host species. Other sensu lato genospecies within each complex are generally more specialized, occurring often in local enzootic cycles within a narrow range of vertebrate hosts and specialized vector species. We suggest that these similar ecologies may have arisen through utilization of a generalist tick species as a vector, resulting in a potentially more virulent generalist pathogen that spills over into humans, vs. utilization of a specialized tick vector on a particular vertebrate host species, promoting microbe specialization. Such tight host-vector-pathogen coupling could also facilitate high enzootic prevalence and the evolution of host immune-tolerance and bacterial avirulence.

Diversity of rickettsial pathogens in Columbian black-tailed deer and their associated keds (Diptera: Hippoboscidae) and ticks (Acari: Ixodidae)

Cervids host multiple species of ixodid ticks, other ectoparasites, and a variety of rickettsiae. However, diagnostic test cross-reactivity has precluded understanding the specific role of deer in rickettsial ecology. In our survey of 128 Columbian black-tailed deer (Odocoileus hemionus columbianus (Richardson)) and their arthropod parasites from two northern Californian herds, combined with reports from the literature, we identified four distinct Anaplasma spp. and one Ehrlichia species. Two keds, Lipoptena depressa (Say) and Neolipoptena ferrisi Bequaert, and two ixodid ticks, Ixodes pacificus Cooley and Kohls and Dermacentor occidentalis Marx, were removed from deer. One D. occidentalis was PCR-positive for E. chaffeensis; because it was also PCR-positive for Anaplasma sp., this is an Anaplasma/Ehrlichia co-infection prevalence of 4.3%. 29% of L. depressa, 23% of D. occidentalis, and 14% of deer were PCR-positive for Anaplasma spp. DNA sequencing confirmed A. bovis and A. ovis infections in D. occidentalis, A. odocoilei in deer and keds, and Anaplasma phagocytophilum strain WI-1 in keds and deer. This is the first report of Anaplasma spp. in a North America deer ked, and begs the question whether L. depressa may be a competent vector of Anaplasma spp. or merely acquire such bacteria while feeding on rickettsemic deer.

Alpha proteobacteria of genusAnaplasma(Rickettsiales: Anaplasmataceae): Epidemiology and characteristics ofAnaplasmaspecies related to veterinary and public health importance

TheAnaplasmaspecies are important globally distributed tick-transmitted bacteria of veterinary and public health importance. These pathogens, cause anaplasmosis in domestic and wild animal species including humans.Rhipicephalus, Ixodes, DermacentorandAmblyommagenera of ticks are the important vectors ofAnaplasma.Acute anaplasmosis is usually diagnosed upon blood smear examination followed by antibodies and nucleic acid detection. All age groups are susceptible but prevalence increases with age. Serological cross-reactivity is one of the important issues amongAnaplasmaspecies. They co-exist and concurrent infections occur in animals and ticks in same geographic area. These are closely related bacteria and share various common attributes which should be considered while developing vaccines and diagnostic assays. Movement of susceptible animals from non-endemic to endemic regions is the major risk factor of bovine/ovine anaplasmosis and tick-borne fever. Tetracyclines are currently available drugs for clearance of infection and treatment in humans and animals. Worldwide vaccine is not yet available. Identification, elimination of reservoirs, vector control (chemical and biological), endemic stability, habitat modification, rearing of tick resistant breeds, chemotherapy and tick vaccination are major control measures of animal anaplasmosis. Identification of reservoirs and minimizing the high-risk tick exposure activities are important control strategies for human granulocytic anaplasmosis.

Opening the black box of Anaplasma phagocytophilum diversity: current situation and future perspectives

Anaplasma phagocytophilum is a zoonotic obligate intracellular bacterium known to be transmitted by ticks belonging to the Ixodes persulcatus complex. This bacterium can infect several mammalian species, and is known to cause diseases with variable symptoms in many domestic animals. Specifically, it is the causative agent of tick-borne fever (TBF), a disease of important economic impact in European domestic ruminants, and human granulocytic anaplasmosis (HGA), an emerging zoonotic disease in Asia, USA and Europe. A. phagocytophilum epidemiological cycles are complex and involve different ecotypes, vectors, and mammalian host species. Moreover, the epidemiology of A. phagocytophilum infection differs greatly between Europe and the USA. These different epidemiological contexts are associated with considerable variations in bacterial strains. Until recently, few A. phagocytophilum molecular typing tools were available, generating difficulties in completely elucidating the epidemiological cycles of this bacterium. Over the last few years, many A. phagocytophilum typing techniques have been developed, permitting in-depth epidemiological exploration. Here, we review the current knowledge and future perspectives regarding A. phagocytophilum epidemiology and phylogeny, and then focus on the molecular typing tools available for studying A. phagocytophilum genetic diversity.

Anaplasma phagocytophilum--a widespread multi-host pathogen with highly adaptive strategies

The bacterium Anaplasma phagocytophilum has for decades been known to cause the disease tick-borne fever (TBF) in domestic ruminants in Ixodes ricinus-infested areas in northern Europe. In recent years, the bacterium has been found associated with Ixodes-tick species more or less worldwide on the northern hemisphere. A. phagocytophilum has a broad host range and may cause severe disease in several mammalian species, including humans. However, the clinical symptoms vary from subclinical to fatal conditions, and considerable underreporting of clinical incidents is suspected in both human and veterinary medicine. Several variants of A. phagocytophilum have been genetically characterized. Identification and stratification into phylogenetic subfamilies has been based on cell culturing, experimental infections, PCR, and sequencing techniques. However, few genome sequences have been completed so far, thus observations on biological, ecological, and pathological differences between genotypes of the bacterium, have yet to be elucidated by molecular and experimental infection studies. The natural transmission cycles of various A. phagocytophilum variants, the involvement of their respective hosts and vectors involved, in particular the zoonotic potential, have to be unraveled. A. phagocytophilum is able to persist between seasons of tick activity in several mammalian species and movement of hosts and infected ticks on migrating animals or birds may spread the bacterium. In the present review, we focus on the ecology and epidemiology of A. phagocytophilum, especially the role of wildlife in contribution to the spread and sustainability of the infection in domestic livestock and humans.

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.

Differences in prevalence of Borrelia burgdorferi and Anaplasma spp. infection among host-seeking Dermacentor occidentalis, Ixodes pacificus, and Ornithodoros coriaceus ticks in northwestern California

Previous studies revealed that the Pacific Coast tick (Dermacentor occidentalis) is infected occasionally with the agents of Lyme disease (Borrelia burgdorferi) or human granulocytic anaplasmosis (Anaplasma phagocytophilum) and that it is an inefficient experimental vector of B. burgdorferi. The relationship of the pajahuello tick (Ornithodoros coriaceus) to each of these bacterial zoonotic agents has not been reported. The primary bridging vector of both bacterial zoonotic agents to humans is the western black-legged tick (Ixodes pacificus). Because of the spatial and temporal overlap of D. occidentalis and O. coriaceus populations with those of I. pacificus in natural foci of B. burgdorferi and A. phagocytophilum in northwestern California, we conducted field and laboratory studies to determine if the Pacific Coast tick or the pajahuello tick potentially may serve as secondary vectors of either bacterium. Our findings reconfirmed that wild-caught D. occidentalis ticks are infected infrequently with B. burgdorferi or A. phagocytophilum, but some adult ticks from dense woodlands or chaparral were found to contain 2 important veterinary pathogens for the first time (Anaplasma bovis, A. ovis). The high prevalence of A. bovis infection (4.3%, n=185 ticks) within chaparral-derived ticks suggests that D. occidentalis could be an efficient vector of this rickettsia. Experimental attempts to transmit borreliae or Anaplasma spp. that may have been present in >100 wild-caught D. occidentalis adults to naïve rabbits were unsuccessful. Anaplasma spp. were not detected in O. coriaceus, but one (4.3%) of 23 nymphs was infected with B. bissettii. This finding and an antecedent report of a B. burgdorferi-like spirochete from the same tick species demonstrate that O. coriaceus sometimes acquires and transstadially passes Lyme disease group spirochetes. I. pacificus nymphs inhabiting a woodland nidus of B. burgdorferi and A. phagocytophilum had a 5-fold higher prevalence of borreliae than adult ticks from the same generational cohort. In contrast to the results of preceding studies carried out at the same site, none of the nymphal or adult ticks was PCR-positive for A. phagocytophilum. This suggests that the distribution of this rickettsia is highly focal or variable from year-to-year within this particular woodland.

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.

Transovarial transmission of Francisella-like endosymbionts and Anaplasma phagocytophilum variants in Dermacentor albipictus (Acari: Ixodidae)

Dermacentor albipictus (Packard) is a North American tick that feeds on cervids and livestock. It is a suspected vector of anaplasmosis in cattle, but its microbial flora and vector potential remain underevaluated. We screened D. albipictus ticks collected from Minnesota white-tailed deer (Odocoileus virginianus) for bacteria of the genera Anaplasma, Ehrlichia, Francisella, and Rickettsia using polymerase chain reaction (PCR) gene amplification and sequence analyses. We detected Anaplasma phagocytophilum and Francisella-like endosymbionts (FLEs) in nymphal and adult ticks of both sexes at 45 and 94% prevalences, respectively. The A. phagocytophilum and FLEs were transovarially transmitted to F1 larvae by individual ticks at efficiencies of 10-40 and 95-100%, respectively. The FLEs were transovarially transmitted to F2 larvae obtained as progeny of adults from F1 larval ticks reared to maturity on a calf, but A. phagocytophilum were not. Based on PCR and tissue culture inoculation assays, A. phagocytophilum and FLEs were not transmitted to the calf. The amplified FLE 16S rRNA gene sequences were identical to that of an FLE detected in a D. albipictus from Texas, whereas those of the A. phagocytophilum were nearly identical to those of probable human-nonpathogenic A. phagocytophilum WI-1 and WI-2 variants detected in white-tailed deer from central Wisconsin. However, the D. albipictus A. phagocytophilum sequences differed from that of the nonpathogenic A. phagocytophilum variant-1 associated with Ixodes scapularis ticks and white-tailed deer as well as that of the human-pathogenic A. phagocytophilum ha variant associated with I. scapularis and the white-footed mouse, Peromyscus leucopus. The transovarial transmission of A. phagocytophilum variants in Dermacentor ticks suggests that maintenance of A. phagocytophilum in nature may not be solely dependent on horizontal transmission.

Prevalence and geographic distribution of Dirofilaria immitis, Borrelia burgdorferi, Ehrlichia canis, and Anaplasma phagocytophilum in dogs in the United States: results of a national clinic-based serologic survey

We evaluated a comprehensive national database that documents canine infection with, or exposure to, four vector-borne disease agents, Dirofilaria immitis, Borrelia burgdorferi, Ehrlichia canis, and Anaplasma phagocytophilum in order to assess geographic trends in rates of positive tests. While the percent positive test results varied by agent in different regions of the United States, with D. immitis antigen and antibodies to E. canis more commonly identified in dogs from the South (3.9% and 1.3%, respectively), and antibody to B. burgdorferi and A. phagocytophilum found more frequently in dogs from the upper Midwest and Northeast (4.0-6.7% and 5.5-11.6%, respectively), evidence of at least one agent was found in dogs from every state considered. Furthermore, each organism also appeared to occur in endemic foci within larger areas of relatively low prevalence. Relocation of infected or previously exposed dogs from endemic regions likely accounts for some of the unexpected geographic distribution seen, although local transmission in previously under-recognized areas of endemicity could also be occurring. Although data were only available from the 48 contiguous states (Alaska and Hawaii were not included), taken together, our results suggest that these disease agents may be present over a wider geographic area, and thus pose greater animal and public health risks, than is currently recognized. Dogs can serve as sentinels to identify the presence of vector-borne disease agents of both veterinary and public health significance.

Co-phylogenetic analysis of Anaplasma phagocytophilum and its vectors, Ixodes spp. ticks

The coevolutionary history of Ixodes spp. ticks, the obligately tick-transmitted bacterial pathogen Anaplasma phagocytophilum, and its various rodent reservoir hosts world-wide is not known. According to coevolution theory, the most recently evolved of tick-bacterial complexes could have difficulty maintaining A. phagocytophilum in nature, because transmissibility has not been efficiently maximized. This study was intended to examine the phylogeographic history of I. ricinus-subgroup ticks and A. phagocytophilum, provide an estimate for the date of the divergence of A. marginale and A. phagocytophilum, and evaluate whether there is correspondence between tick and Anaplasma spp. trees. Analysis of Ixodes spp. ticks showed a New World clade consisting of I. scapularis and I. pacificus, European I. ricinus as a sister group to this clade, and Asian I. persulcatus as basal. Of the three A. phagocytophilum genes evaluated, the most resolution was provided by the ankA gene. ankA sequences formed an Old World clade with eastern North America strains as a sister clade. California strains were highly diverse and did not form a clade. Base substitution rates were very comparable along both A. marginale and A. phagocytophilum lineages. Based on 16S rDNA analysis, maximum and minimum divergence times of A. phagocytophilum and A. marginale were calculated to be 78,296,703 and 43,415,708 years, respectively. If A. phagocytophilum did closely coevolve with specific I. ricinus-subgroup tick species, then A. phagocytophilum strains could have specialized on local tick species and optimized local infectivity in the Old World and eastern US. However, lack of absolute resolution of tick trees and conflicting prevalence data (with low prevalence in Asia and western North America) preclude us from inferring a tight coevolutionary relationship of tick species from this phylogeographic analysis.

Use of real-time quantitative PCR targeting the msp2 protein gene to identify cryptic Anaplasma phagocytophilum infections in wildlife and domestic animals

Anaplasma phagocytophilum is an emerging pathogen throughout much of the Holarctic, where Ixodes spp. tick vectors occur. This organism was expected to be present at study sites in Humboldt County, north-western California, based on the presence of appropriate tick vectors, seropositivity in sentinel hosts, and previously reported human infections. However, despite high seroprevalence suggesting circulating A. phagocytophilum, active infections in dogs and wildlife (including suspected reservoir species) were rare using published polymerase chain reaction (PCR) protocols. This finding was possible if the published PCR protocol lacked sensitivity for strains in the study areas. We report a new TaqMan-PCR (TM-PCR) assay targeting the msp2 gene that has greater sensitivity and specificity for diverse A. phagocytophilum strains from this region. The new assay detected as few as one plasmid copy and a range of genetically diverse strains of A. phagocytophilum. Specificity was confirmed by failure to amplify targets of closely related bacteria. Application of the TM-PCR to samples from northern California confirmed PCR-positivity in 94 woodrats (71%; n=134), three (4%; n=80) bears, and seven (7%; n=97) domestic dogs. The msp2 TM-PCR protocol appears to be more sensitive for use in assays of samples from parts of western North America and possibly in other regions where populations are genetically diverse or divergent from eastern United States strains of A. phagocytophilum.

Evidence of tick-borne organisms in mule deer (Odocoileus hemionus) from the western United States

Free-ranging mule deer (MD; Odocoileus hemionus) from Arizona and California were tested for evidence of infection with several tick-borne pathogens, including species of Ehrlichia, Anaplasma, Babesia, and Borrelia. Of 125 mule deer tested from Arizona, 29 (23%) and 11 (9%) had antibodies reactive to E. chaffeensis and A. phagocytophilum by indirect immunofluorescent antibody testing, respectively; none of the six MD tested from California were seropositive. Using a commercial competitive ELISA kit, antibodies reactive to Anaplasma spp. were detected in 19 (15%) MD from Arizona and four of six (67%) MD from California. Polymerase chain reaction (PCR) testing for tick-borne pathogens was conducted on blood samples from 29 MD from Arizona and 11 MD from California. Twenty-two of 29 (75.9%) MD from Arizona had PCR evidence of infection with at least one tick-borne pathogen. We detected an Anaplasma sp. in 19 of 29 (65.5%) MD and a Babesia sp. in 10 of 29 (34%) MD. Sequencing of these amplicons indicated that the Anaplasma sp. was the same that had previously been detected in MD from California and the Babesia sp. was similar to one previously detected in a reindeer (Rangifer tarandus tarandus) from California. All of the California MD had evidence of infection with a tick-borne pathogen. Two different species of Anaplasma spp. were detected in MD from California, eight of of 11 MD were infected with an Anaplasma sp., and three of 11 MD were infected with A. ovis. This is the first report of a mule deer naturally infected with A. ovis. Ten of 11 MD from California were infected with a Babesia-like organism previously associated with human disease, and a single MD was PCR positive for Borrelia coriaceae, which has been associated with epizootic bovine abortion. Together, these data suggest that MD in northern Arizona and eastern California are exposed to several pathogens of human and veterinary importance.

GIS-facilitated spatial epidemiology of tick-borne diseases in coyotes (Canis latrans) in northern and coastal California

Ixodes pacificus is the main tick vector for transmission of Anaplasma phagocytophilum and Borrelia burgdorferi to large vertebrates in California. The present study was undertaken in I. pacificus-infested counties in California to examine spatial and temporal relationships among A. phagocytophilum and B. burgdorferi-exposed coyotes with vegetation type and climate. The overall A. phagocytophilum and B. burgdorferi seroprevalences were 39.5% (N=215) and 18.9% (N=148), respectively, with no association with sex. PCR for A. phagocytophilum and B. burgdorferi was negative in all blood and kidney samples. Increased seroprevalence was a positive function of rainfall. Ehrlichial seropositivity was increased in blue-oak foothill pine, montane hardwood, and redwood vegetation regions, and decreased in coastal sagebrush and cropland. Increased exposure to B. burgdorferi occurred in blue oak woodland.

Isolation of an Anaplasma sp. organism from white-tailed deer by tick cell culture

We used tick cell culture to isolate a bacterium previously referred to as the "white-tailed deer (WTD) agent" from two captive fawns inoculated with blood from wild WTD (Odocoileus virginianus). Buffy coat cells were added to ISE6 tick cell cultures and incubated at 34 degrees C, and 8 days later, Anaplasma-like inclusions were demonstrated in Giemsa-stained culture samples. The microbes became established and could be continuously passaged in tick cells. The identity of a culture isolate designated WTD76 was verified as the WTD agent by using specific PCR primers and by DNA sequencing. Comparison with sequences available in GenBank indicated that the isolate was most closely related first to Anaplasma platys and second to Anaplasma phagocytophilum, supporting its placement in the genus Anaplasma. Transmission electron microscopy of this Anaplasma sp. organism in tick cell cultures revealed large inclusions filled with pleomorphic and rod-shaped bacteria. Tick cells infected with the Anaplasma sp. organism were used to successfully infect a naive deer, thereby proving the infectivity of the isolate for deer.

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.

Acarologic risk of exposure to emerging tick-borne bacterial pathogens in a semirural community in northern California

An acarologic study was conducted in a semirural community in northern California to determine the relative abundance of, and the prevalence of infection with, three emerging bacterial pathogens in the western black-legged tick (Ixodes pacificus). These included the agents causing Lyme disease (Borrelia burgdorferi), human granulocytic ehrlichiosis [Ehrlichia phagocytophila (formerly Ehrlichia equi)], and human monocytic ehrlichiosis (Ehrlichia chaffeensis). The study area in Sonoma County consisted of two properties each with four residents and an uninhabited adjacent comparison area. Six of the eight residents had been either physician-diagnosed or serodiagnosed previously with Lyme disease, and, of these, one also had been serodiagnosed with human monocytic ehrlichiosis. Direct immunofluorescent/culture assays and bacterial species-specific polymerase chain reaction assays were used to test whole ticks individually for presence of B. burgdorferi and Ehrlichia spp., respectively. Overall, 6.5% of the nymphal (n = 589) and 1.6% of the adult ticks (n = 318) from the same generational cohort were found to contain B. burgdorferi. In contrast, none of 465 nymphs and 9.9% of 202 adults were infected with E. phagocytophila. Excised tissues from another 95 adult ticks yielded a comparable E. phagocytophila infection prevalence of 13.7%. E. chaffeensis was not detected in either nymphal or adult ticks. Using a combination of culture and polymerase chain reaction assays, coinfection of I. pacificus adults with B. burgdorferi and E. phagocytophila was demonstrated for the first time. The marked disparity in the infection prevalence of these pathogens in nymphal and adult ticks suggests that their maintenance cycles are inherently different.

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.

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.

Susceptibility of cattle to infection with Ehrlichia equi and the agent of human granulocytic ehrlichiosis

OBJECTIVE

To determine susceptibility of cattle to infection with Ehrlichia equi and the agent of human granulocytic ehrlichiosis (HGE).

DESIGN

Experimental disease and prevalence survey.

ANIMALS

6 cattle, 2 horses, and 2,725 serum samples from healthy cattle.

PROCEDURE

2 cattle and 1 horse were inoculated with E equi, 2 cattle and 1 horse were inoculated with the HGE agent, and 2 cattle served as sham-inoculated controls; inoculated animals were evaluated via clinical, hematologic, serologic, and real-time polymerase chain reaction tests. Prevalence of antibodies against E equi in 2,725 healthy cattle was determined by use of an indirect immunofluorescent technique.

RESULTS

No abnormal clinical or hematologic findings or inclusion bodies within granulocytes were observed in the cattle after inoculation, and results of all polymerase chain reaction tests were negative. Seroconversion in inoculated cattle developed 10 to 12 days after inoculation (reciprocal titers, 160). Both horses developed clinical signs of ehrlichiosis. Five of 2,725 (0.18%) cattle were seropositive for E equi, with titers ranging from 20 to 80. All seropositive cattle originated from the same tick-rich region in the Sierra Nevada foothills.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that cattle are not susceptible to infection with E equi or the agent of HGE and that prevalence of exposure to E equi in healthy cattle is low. Therefore, E equi and the agent of HGE are likely of negligible importance for cattle in North America.

Association of Ixodes pacificus (Acari: ixodidae) with the spatial and temporal distribution of equine granulocytic ehrlichiosis in California

This study was conducted to determine if the biology of certain ticks associated with horses regulates the spatial and temporal distribution of equine granulocytic ehrlichiosis (EGE) in California north of Monterey County. We compared the spatial and temporal distribution of EGE cases with the seasons of activity and life histories of ticks that infest horses. Spatially, cases collected from equine veterinarians clustered around each other in a manner different from the way in which control cities of practice were distributed, with foci limited to the Sierra Nevada and coastal foothills. Cases also clustered seasonally: most were diagnosed between November and April. The spatial and temporal pattern of EGE cases closely parallels the well-characterized life history and distribution of Ixodes pacificus Cooley & Kohls, but not other ticks commonly associated with horses. Building on previous studies, there is compelling evidence that this tick has the vectorial capacity to transmit Ehrlichia equi to horses. Based on the life history and distribution of I. pacificus in relation to EGE cases, we reason that this tick is the only biologically plausible vector of E. equi in California, and provide evidence for a tightly linked association between I. pacificus and the epidemiology of EGE.