Persistent Ehrlichia chaffeensis infection in white-tailed deer

Four white-tailed deer (Odocoileus virginianus) were inoculated intravenously with a deer-origin isolate (15B-WTD-GA) of Ehrlichia chaffeensis. The course of infection was monitored using indirect fluorescent antibody (IFA), polymerase chain reaction (PCR), and culture over a 9 m period. All deer became rickettsemic within 24 days post inoculation (DPI), and all developed antibody titers >1:64 to E. chaffeensis by 17 DPI. Titers in all deer fell below 1:64 during 87 to 143 DPI. One deer exhibited a second period of seropositivity (peak titer of 1:256) from 207 to 271 DPI but was culture and PCR negative during this period. Rickettsemia was confirmed by reisolation of E. chaffeensis as late as 73 to 108 DPI in three deer. Positive PCR results were obtained from femur bone marrow of one deer and from rumenal lymph node of another (leer at 278 DPI. None of the deer developed clinical signs, hematologic abnormalities, or gross or microscopic lesions attributable to E. chaffeensis. Two uninoculated control deer were negative on all tests through 90 DPI at which time they were removed from the study. Herein we confirm that white-tailed deer become persistently infected with E. chaffeensis, have initial rickettsemias of several weeks duration and may experience recrudescence of rickettsemia, which reaffirm the importance of deer in the epidemiology of E. chaffeensis.     

Ehrlichia chaffeensis in archived tissues of a white-tailed deer.

White-tailed deer (Odocoileus virginianus) play an integral role in the natural history of Ehrlichia chaffeensis, the causative agent of human monocytic ehrlichiosis (HME). Paraffinized tissues from a white-tailed deer submitted as a diagnostic case to the Southeastern Cooperative Wildlife Disease Study (Athens, Georgia, USA) in October of 198.5 and originally described as infected with an unidentified rickettsial organisim were re-examined by specific nested polymerase chain reaction (PCR) for evidence of infection with Ehrlichia spp. Ehrlichia chaffeensis was identified from the bone marrow and inguinal lymph node of this deer based on amplification of a characteristic sequence-confirmed 16S rDNA fragment from these tissues. Parallel PCR tests on the same samples were negative for 16S rDNA fragments of the agent of human granulocytic ehrlichiosis (HGE) and for an Ehrlichia-like organism widely distributed in white-tailed deer populations. This report describes detection of E. chaffeensis in archived tissue from a deer collected before the index case of human monocytic ehrlichiosis was established.     

Transmission of Ehrlichia chaffeensis from lone star ticks (Amblyomma americanum) to white-tailed deer (Odocoileus virginianus)

Amblyomma americanum is an aggressive ixodid tick that has been implicated as a vector for several bacterial agents. Among these is Ehrlichia chaffeensis, which causes human monocytic (or monocytotropic) ehrlichiosis. In this study, experimental tick transmission of E. chaffeensis from infected lone star ticks to deer was revisited, and the question of whether it would be possible to re-isolate the organism from deer was asked, because this had not been done previously. Here, we were able to transmit a wild strain of E. chaffeensis from acquisition-fed lone star ticks to white-tailed deer. Ehrlichia chaffeensis was re-isolated from one white-tailed deer on multiple days during the infection and from another deer on one day during the infection. Peak rickettsemias for E. chaffeensis-infected deer were 17 DPI with acquisition-fed ticks and 14 DPI with needle-inoculated deer. This study supports the role of the lone star tick and white-tailed deer as vector and reservoir host for E. chaffeensis, demonstrating culture re-isolation of E. chaffeensis in deer infected by experimental tick transmission for the first time.     

Experimental infection of white-tailed deer (Odocoileus virginianus) with Ehrlichia chaffeensis by different inoculation routes

The infection dynamics of the tick-transmitted organism Ehrlichia chaffeensis were investigated in white-tailed deer (Odocoileus virginianus) using different routes of inoculation. Six deer were each inoculated with 5.4 x 10(6) DH82 cells infected with E. chaffeensis (Arkansas strain) by three different routes: intravenous (n = 2), subcutaneous (n = 2), and intradermal (n = 2). Two control deer were inoculated with uninfected cells. Infections were monitored for 54 days and were continued in one deer from each E. chaffeensis inoculated group for an additional 31 days. All deer inoculated with E. chaffeensis seroconverted (> or = 1: 64) and became 16S rDNA polymerase chain reaction and/or cell culture positive by post-inoculation day 15. There was no apparent (difference in susceptibility to infection between deer inoculated by different routes for the first 50 days based on detection of E. chaffeensis infection by PCR assay of blood or culture isolation. These results demonstrate infection of (deer by intradermal and subcutaneous routes for the first time.     

Clinical and biological aspects of infection caused by Ehrlichia chaffeensis

Ehrlichia chaffeensis is an obligatory intracellular bacterium that infects the monocyte-macrophage. E. chaffeensis, which is transmitted to humans by ticks primarily from infected deer, causes human monocytic ehrlichiosis, an acute febrile systemic illness. This paper reviews current knowledge of clinical and biological aspects of infections caused by E. chaffeensis.     

Parasitism among white-tailed deer and domestic sheep on common range

Parasitism was studied in white-tailed deer (Odocoileus virginianus) and domestic sheep (Ovis aries) which shared a common range in eastern West Virginia. Of 30 species of internal parasites, 11 were found in deer and 22 in sheep. Five parasites, Sarcocystis sp., Cysticercus tenuicollis, Oesophagostomum venulosum, Cooperia punctata, and Gongylonema pulchrum, occurred in both deer and sheep. An index of similarity of 17.2 suggests that the parasite faunas of these hosts are distinct, and that it is unlikely that white-tailed deer are reservoirs of common parasites of domestic sheep in the southern Appalachian region.     

Susceptibility of red and gray foxes to infection by Ehrlichia chaffeensis

Red foxes (Vulpes vulpes) and gray foxes (Urocyon cinereoargenteus) were evaluated for their susceptibility to experimental infection with Ehrlichia chaffeensis, the causative agent of human monocytotropic ehrlichiosis. Two red foxes and three gray foxes were inoculated intravenously with E. chaffeensis (15B-WTD-GA strain) and were monitored at 7, 14, 21, and 28 days post inoculation (DPI) for evidence of infection using an indirect fluorescent antibody (IFA) assay, light microscopy, polymerase chain reaction (PCR), and cell culture methods. One red fox and one gray fox served as negative controls. Red foxes were susceptible to infection based on reisolation of E. chaffeensis from blood at 7 and 14 DPI, seroconversion by 7 DPI, and positive PCR assays on spleen and lymph nodes at 28 DPI. Morulae were not found in circulating leukocytes and clinical signs or lesions of ehrlichiosis were not observed. In contrast, gray foxes were refractory to infection based on negative results on all culture, PCR, serologic, and microscopic examinations. These findings imply that red foxes, but not gray foxes, are potential vertebrate reservoirs for E. chaffeensis. These findings also illustrate the need to verify serologic evidence of E. chaffeensis infection among wild animals.     

Spatial heterogeneity of mitochondrial DNA and allozymes among populations of white-tailed deer and mule deer.

A white-tailed deer (Odocoileus virginianus) population in northeastern Minnesota and a mule deer (O. hemionus) population in the Bridger Mountains Montana, have previously been shown to be spatially subdivided into contiguous subpopulations. We assessed the degree of genetic differentiation among subpopulations and tested the hypothesis that differentiation will be greater for mitochondrial DNA (mtDNA) than for nuclear-encoded allozymes. Differentiation of the white-tailed deer subpopulations was significant for two allozyme loci but not for mtDNA, and the overall degree of differentiation was low. Gene flow, recent founding of the subpopulations, and polygamous breeding structure may all have contributed to this pattern. Greater differentiation was evident among disjunct populations than between the contiguous subpopulations of white-tailed deer. The contiguous mule deer subpopulations were significantly differentiated for mtDNA and one allozyme locus. Differentiation was greater for mtDNA than for allozymes. These results are consistent with demographic data that indicate mule deer males disperse more than do females. Disjunct mule deer populations may be similar or dramatically different in mtDNA haplotype frequencies that do not necessarily vary with geographic distance. Current and historical gene flow and breeding structure will influence population genetic patterns.     

The developmental cycle of Ehrlichia chaffeensis in vertebrate cells

Ehrlichia chaffeensis, an obligatory intracellular bacterium, has two forms in mammalian cells: small dense-cored cells (DC) with dense nucleoid and larger reticulate cells (RC) with uniformly dispersed nucleoid. We have determined by electron microscopy that DC but not RC attaches to and enters into the host cells and RC but not DC multiples inside the host cells. Analysis of outer membrane protein expression by confocal microscopy showed that RC expressed the 28 kDa outer membrane protein (p28), the intermediate form, which were transforming from RC to DC, expressed both gp120 and p28, and the mature DC expressed gp120 only. The TCID50 of DC is 6 log10 higher than RC. We conclude that E. chaffeensis has a developmental cycle, in which the DC attaches to and enters into the host cells, and transforms into RC and the RC multiplies by binary fission for 48 h and then matures into DC at 72 h.     

Geographic occurrence of Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae) infesting white-tailed deer in North Carolina

A state-wide survey to determine the occurrence and comparative numbers of ticks infecting white-tailed deer (Odocoileus virginianus) was conducted in North Carolina (USA). One thousand six hundred twenty nine deer were examined in 60 of 100 counties; with the exception of one county in the piedmont region, all tick-infested deer occurred in the coastal plain. Ixodes scapularis (46%) and Amblyomma americanum (53%) were the most prevalent species encountered and accounted for more than 98% of the 4,286 ticks collected. Some specimens of Dermacentor albipictus and Amblyomma maculatum also were collected.     

Natural and experimental infection of white-tailed deer (Odocoileus virginianus) from the United States with an Ehrlichia sp. closely related to Ehrlichia ruminantium

An Ehrlichia sp. (Panola Mountain [PM] Ehrlichia sp.) closely related to Ehrlichia ruminantium was recently detected in a domestic goat experimentally infested with lone star ticks (LSTs, Amblyomma americanum) collected from Georgia, USA. The infected goat exhibited pyrexia and mild clinical pathologic abnormalities consistent with ehrlichiosis. At least two other Ehrlichia species (Ehrlichia chaffeensis and Ehrlichia ewingii) are maintained in nature by a cycle involving LSTs as the primary vector and white-tailed deer (Odocoileus virginanus) as a known or suspected reservoir. To investigate the possibility that white-tailed deer are potential hosts of the PM Ehrlichia sp., whole blood samples collected from 87 wild deer from 2000 to 2002 were screened with a species-specific nested PCR assay targeting the citrate synthase gene. In addition, two laboratory-raised white-tailed deer fawns were each infested with 120 wild-caught LST adults from Missouri, USA, and blood samples were periodically collected and tested for the PM Ehrlichia sp. Of 87 deer tested from 20 locations in the southeastern United States, three (3%) deer from Arkansas, North Carolina, and Virginia were positive for the PM Ehrlichia sp. Wild-caught ticks transmitted the PM Ehrlichia sp. to one of two deer fawns, and colony-reared nymphal LSTs acquired the organism from the deer, maintained it transstadially as they molted to adults, and transmitted the PM Ehrlichia sp. to two na?ve fawns. These findings indicate that white-tailed deer are naturally and experimentally susceptible to infection with an Ehrlichia sp. closely related to E. ruminantium and are able to serve as a source of infection to LSTs.     

Out-of-season breeding of captive white-tailed deer

Although techniques to induce out-of-season breeding in deer with exogenous hormones are documented, a successful technique has not been developed for use with white-tailed deer (Odocoileus virginianus). The efficacy of using a combined treatment of melatonin, progesterone, and pregnant mare serum gonadotropin to advance seasonal estrus in captive white-tailed deer was tested. First estrus of 12 treated does (n = 16) occurred at least 57 days sooner than did those of 4 non-treated controls (mid-November). Previous estrus dates were known for 11 does, suggesting that their estrus was advanced by 37 to 119 days (X = 82 days). At first estrus, 12 does were bred to untreated bucks that had velvet-covered or recently polished antlers, resulting in a conception rate of 75%. Two does conceived when bred at second or third estrus. Two does failed to conceive when bred at first estrus and displayed no estrous cycling that year, but conceived out-of-season in subsequent years. These data document that this technique is useful for inducing successful, out-of-season breeding of captive white-tailed deer. Furthermore, we demonstrate that some bucks at our facility have adequate fertility and libido to impregnate does during midsummer.     

Geospatial analysis of giant liver flukes among moose: effects of white-tailed deer

Natural infections of giant liver flukes (Fascioloides magna) occur primarily in cervids and bovids. In northeastern North America, a common definitive host for giant liver flukes is the white-tailed deer (Odocoileus virginianus). Giant liver flukes cannot reproduce in moose (Alces alces) and eventually die, but only after causing extensive tissue damage in the liver. We used data on the occurrence of giant liver flukes in adult moose collected between 1972 and 2000 from northeastern Minnesota, USA. These data were recorded by 93 km² sampling units (square grid of 9.66 km on each side). Sample sizes varied between 0 and 45 adult moose examined per sampling unit. We fitted a second-order global polynomial model to adjust for trends in the occurrence of flukes across the study area, modeled the de-trended data using a circular semi-variogram model, and finally kriged our data, arriving at a predicted response surface for the occurrence of liver flukes in moose. Correlational analyses indicated that the occurrence of liver flukes in moose was influenced more by the density of white-tailed deer based on rates of hunter harvest (r?=?0.54) than was the proportion of wetland habitats (r?=?0.25). Ordinary least-squares multiple regression (R _adj?=?0.29, AIC_c?=?795.3) documented a strong relationship between the occurrence of liver flukes in moose and population density of white-tailed deer (p?<?0.001) but a weaker relationship for wetland habitats (p?=?0.16). A geographically weighted multiple regression produced a stronger relationship (R _adj?=?0.60, AIC_c?=?765.7). Disease maps, as we developed here, are a useful geospatial tool that has relevance for understanding disease processes in moose that may be extended to other mammals.     

Detection of antibodies reactive with Ehrlichia chaffeensis in the raccoon

Antibodies reactive with Ehrlichia chaffeensis were detected in raccoon (Procyon lotor) serum samples by using an indirect immunofluorescence assay. Samples from 411 raccoons trapped in the southeastern United States from 1977 to 1999 were tested. Serologically reactive samples with reciprocal titers of > or =16 were detected from 83 raccoons (20%) from 13 of 16 counties in eight states, indicating that raccoons are commonly exposed to E. chaffeensis. Samples collected as early as 1977 were positive. A polymerase chain reaction assay specific for E. chaffeensis failed to detect the presence of ehrlichial DNA in serum samples from 20 representative seroreactive raccoons. Because of serologic cross-reactivity among antigens derived from different Ehrlichia spp., additional immunologic, molecular, or culture-based studies will be required to confirm E. chaffeensis infections of raccoons in the southeastern United States.