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Biomedical subjects

D E Stallknecht

Publications and source records attributed to D E Stallknecht.

At least 37 records · Page 2Linked to original sources
PubMed1998

Evaluation of two oral baiting systems for wild rodents.

Tetracycline hydrochloride (TC)-treated peanut butter or rodent chow baits were distributed during March 1990, on separate 0.53 ha sites in Oglethorpe County, Georgia (USA). Rodents were trapped on a control site prior to bait distribution and on two baited sites 6 days post-distribution. Cleaned skulls from euthanized mammals were grossly examined for TC fluorescence using an ultraviolet (UV) light. Mandibles were sectioned and examined for TC fluorescence using an ultraviolet light microscope. All 21 cotton rats (Sigmodon hispidus), four eastern harvest mice (Rithrodontomys humulis), and two golden mice (Ochrotomys nuttalli) captured on the control site were negative for TC fluorescence. On the peanut butter bait site, mandible sections from 29 of 32 (91%) cotton rats, three of three (100%) eastern harvest mice, two of three (66%) golden mice, zero of five (0%) white-footed mice (Peromyscus leucopus), one of three (33%) short-tailed shrews (Blarina brevicauda), and zero of two (0%) least shrews (Cryptotis parva) were positive for TC. Results from the rodent chow bait site indicated that 18 of 25 (72%) cotton rats, zero of three (0%) eastern harvest mice, two of seven (29%) golden mice, zero of four (0%) white-footed mice, and zero of four (0%) least shrews were positive for TC fluorescence in mandible sections. These results suggest that a large portion of a free-ranging small rodent population can be administered biological markers or vaccines using baits.

Animal Feed↗
PubMed1998

Lack of seroreactivity to Ehrlichia chaffeensis among rodent populations.

A retrospective serosurvey for antibodies to Ehrlichia chaffeensis was conducted on eight species of wild rodents (Mus musculus, Oryzomys palustris, Peromyscus leucopus, Rattus norvegicus, Reithrodontomys humulis, Sciurus carolinensis, Sciurus niger, and Sigmodon hispidus) from the southeastern United States. Serum samples (n = 281) collected between 1973 and 1993 were evaluated using an indirect fluorescent antibody test. All samples, screened at a dilution of 1:32, were negative for antibodies to E. chaffeensis. Sixty-three percent of the rodents tested were from areas where E. chaffeensis has been confirmed or is strongly suspected to be endemic. These data suggest limited or no involvement of rodents in the epidemiology of E. chaffeensis.

Animals↗
PubMed1998

Natural coinfection of a white-tailed deer (Odocoileus virginianus) population with three Ehrlichia spp.

The ticks Amblyomma americanum and Ixodes scapularis, strongly implicated vectors of Ehrlichia chaffeensis and the human granulocytic ehrlichiosis (HGE) agent, respectively, commonly are found on white-tailed deer (Odocoileus virginianus). As deer can be infected with E. chaffeensis, the HGE agent, and another Ehrlichia-like organism, a deer population parasitized by both tick species in coastal Georgia was tested for evidence of Ehrlichia spp. infection using serologic, molecular, and culture techniques. Antibodies to both E. chaffeensis (geometric mean titer = 111) and Ehrlichia equi, surrogate antigen for the HGE agent, (geometric mean titer = 1,024) were detected by indirect fluorescent antibody testing. Nested polymerase chain reaction employing species-specific primers demonstrated sequence-confirmed 16S rDNA fragments of 3 distinct Ehrlichia spp. in this population: E. chaffeensis (1/5), the HGE agent (3/5), and an Ehrlichia-like organism previously described from white-tailed deer (5/5). Ehrlichia chaffeensis was isolated in culture from the inguinal lymph node of a single deer. An Ehrlichia-type morula was identified in a neutrophil of 1 deer on examination of blood smears. This work provides the first evidence of the HGE agent in a nonhuman host in the southeastern United States and documents infection with both E. chaffeensis and the HGE agent in a single deer population, thereby supporting the importance of white-tailed deer in the natural history of the human ehrlichioses agents.

Animals↗
PubMed1997

Cell-mediated immune response and IL-2 production in white-tailed deer experimentally infected with hemorrhagic disease viruses.

Hemorrhagic disease, caused by various serotypes of two closely related orbivirus serogroups, the epizootic hemorrhagic disease viruses (EHDV) and the bluetongue viruses (BTV), is a major cause of morbidity and mortality in white-tailed deer (WTD) in the United States. Despite the importance of hemorrhagic disease in WTD, little is known about host defense mechanisms triggered by infection with either causative virus or how that immune response is modulated by challenge with closely related orbiviruses, as can occur under natural conditions. Initial experimental data from our laboratory showed WTD infected with EHDV serotype 2 (EHDV-2) had responded serologically but often became lymphopenic and had a reduced lymphocyte proliferative response in vitro to T-cell mitogens, suggesting possible suppression of cell-mediated immunity. The primary objective of this study was to more closely examine cell-mediated immunity of WTD when experimentally infected with EHDV-2 and subsequently challenged with BTV serotype 10 (BTV-10). The cell-mediated response was evaluated via in vitro lymphocyte proliferation and interleukin-2 (IL-2) production assays, and in vivo delayed type hypersensitivity tests. Deer infected with either EHDV-2 or BTV-10 responded similarly in all assays. Infected deer had decreased lymphocyte counts between post-infection days (PID) 6 and 10, with concurrent diminished lymphocytic response to concanavalin A in lymphocyte proliferation assays and phytohemagglutinin in delayed, type hypersensitivity tests. However, IL-2 production by peripheral blood lymphocytes of infected deer was comparable with that of non-infected control deer as measured using a IL-2-dependent bovine cell line (BT2). This suppression of T-cell proliferation, but not IL-2 production suggests selective inhibition of T-cells probably via altered signal transduction for either expression of the IL-2 receptor or for IL-2 receptor signal-induced T-cell proliferation.

Animals↗
PubMed1997

Isolation of Ehrlichia chaffeensis from wild white-tailed deer (Odocoileus virginianus) confirms their role as natural reservoir hosts.

Field and experimental studies have implicated white-tailed deer (Odocoileus virginianus) as probable reservoir hosts for Ehrlichia chaffeensis, the causative agent of human monocytic ehrlichiosis, but natural infection in deer has not been confirmed through isolation of E. chaffeensis. Thirty-five white-tailed deer collected from three Amblyomma americanum-infested populations in Georgia were examined for evidence of E. chaffeensis infection by serologic, molecular, cell culture, and xenodiagnostic methods. Twenty-seven deer (77%) had E. chaffeensis-reactive indirect fluorescent-antibody assay titers of > or = 1:64; and the blood, spleens, or lymph nodes of seven (20%) deer were positive in a nested PCR assay with E. chaffeensis-specific primers. E. chaffeensis was isolated in DH82 cell cultures from the blood of five (14%) deer, including two deer that were PCR negative. Combination of culture and PCR results indicated that six (17%) deer were probably rickettsemic and that nine (26%) were probably infected. Restriction digestion of PCR products amplified from deer tissues and cell culture isolates resulted in a banding pattern consistent with the E. chaffeensis 16S rRNA gene sequence. The sequences of all PCR products from deer tissues or cell culture isolates were identical to the sequence of the Arkansas type strain of E. chaffeensis. Xenodiagnosis with C3H mice inoculated intraperitoneally with deer blood, spleen, or lymph node suspensions was unsuccessful. When viewed in the context of previous studies, these findings provide strong evidence that E. chaffeensis is maintained in nature primarily by a tick vector-vertebrate reservoir system consisting of lone star ticks and white-tailed deer.

Animals↗
PubMed1997

Experimental vesicular stomatitis in swine: effects of route of inoculation and steroid treatment.

An enzootic focus of vesicular stomatitis virus New Jersey serotype (VSV-NJ) exists on Ossabaw Island, Georgia. Many questions regarding the epizootiology of this virus at this focus still exist, but evidence suggests that the vector for this virus is a phlebotomine sand fly (Lutzomyia shannoni), with feral swine serving as a potential source of virus for the sand fly and for other swine via contact transmission. We conducted 2 experimental trials in domestic swine using VSV-NJ isolated from a sand fly from Ossabaw Island to determine if route of inoculation or immunosuppression via steroid administration affected the development of disease, viremia, viral shedding, or the neutralizing antibody response. In a third trial, we studied the potential for contact transmission among swine using this isolate. Virus isolations were made from nasal cavity or palatine tonsil of the soft palate, and VSV-NJ neutralizing antibodies developed when pigs were inoculated intradermally in the apex of the snout, ear, or coronary band, intravenously, intranasally, or via scarification of the apex of the snout or coronary band. Vesicles developed only in pigs inoculated in the apex of the snout or coronary band, and these vesicles were at the site of inoculation. Steroid treatment did not potentiate the development of secondary vesicles and did not prolong the period of virus shedding from VSV-NJ-infected swine. Contact transmission, as determined by shedding of virus from the tonsil of the soft palate and the development of VSV-NJ neutralizing antibodies, occurred in pigs in contact with animals inoculated in the apex of the snout but not in contact animals exposed to pigs inoculated intradermally in the coronary band or intranasally. These trials show that contact transmission can occur and VSV-NJ can be shed without the development of clinical disease (i.e., vesicle formation). Viremia was never detected in any of the experimental pigs, suggesting that swine may not be a good amplifying host for VSV-NJ.

Animals↗
PubMed1997

Development and use of specific polymerase reaction for the detection of an organism resembling Ehrlichia sp. in white-tailed deer.

The role of white-tailed deer (Odocoileus virginianus) in the epidemiology of Ehrlichia chaffeensis and the agent of human granulocytic ehrlichiosis (HGE) is not fully understood, and diagnostic procedures may be complicated by the recent detection of 16S rDNA sequence from an Ehrlichia sp.-like organism in wild deer. A specific forward primer (DGA) and an Ehrlichia spp. reverse primer (GA1UR) were constructed to amplify this new, distinct Ehrlichia sp.-like 16S rDNA. The DGA primer, a forward primer specific for E. chaffeensis (DCH), and a forward primer specific for the E. phagocytophila genogroup (GE9f) were each used with GA1UR in nested polymerase chain reactions to amplify 16S rDNA sequences from control samples containing the deer Ehrlichia sp.-like organism, E. chaffeensis, or the HGE agent. Primer pairs DGA/GA1UR and DCH/GA1UR specifically amplified 16S rDNA sequences from the corresponding target organism, whereas GE9f/GA1UR amplified 16S rDNA sequence from both the HGE agent and the deer Ehrlichia sp.-like organism. With a nested PCR using DGA/GA1UR and DCH/GA1IUR on DNA extracted from white blood cells from 62 deer from 10 populations in four U.S. states, we observed a high prevalence (65%) of 16S rDNA sequences of the deer Ehrlichia sp.-like organism, and a low prevalence (5%) of the E. chaffeensis sequence. In this field survey, E. chaffeensis-reactive antibodies detected by indirect fluorescence assays were associated (P < 0.001) with PCR evidence of the deer Ehrlichia sp.-like organism, but not E. chaffeensis. Infestations of Amblyomma americanum also were associated (P < 0.001) with PCR evidence of the deer Ehrlichia sp.-like organism. The potential for serologic cross-reactions and non-specific PCR products arising from the deer Ehrlichia sp.-like organism should be considered when evaluating the role of deer and their ticks in the epidemiology of ehrlichial pathogens of humans.

Animals↗
PubMed1997

In vitro replication of epizootic hemorrhagic disease and bluetongue viruses in white-tailed deer peripheral blood mononuclear cells and virus-cell association during in vivo infections.

In vitro and in vivo infections were conducted to determine if the epizootic hemorrhagic disease (EHD) and bluetongue (BT) viruses would replicate in peripheral blood mononuclear (PBM) cells of white-tailed deer (Odocoileus virginianus). All of the North American EHD and BT viruses (EHD virus serotypes 1 and 2, and BT virus serotypes 2, 10, 11, 13, and 17) replicated in vitro in cultures of white-tailed deer PBM cells. However, this replication appeared to be monocyte-dependent and was not enhanced by lymphocyte blastogenesis induced by the addition of concanavalin A. In white-tailed deer infected with either EHD virus serotype 2 or BT virus serotype 10, virus could be isolated consistently from PBM cells only from post-infection day 4 through 8, although they remained viremic through post-infection day 21. In deer, highest viral titers were associated with the erythrocyte fraction, and in no cases did viral titers detected in the platelet, PBM cell or polymorphonuclear cell fractions approach titers observed in whole blood. In the in vitro infections of white-tailed deer erythrocytes, the EHD and BT viruses were associated with pits in the erythrocyte membrane. This association may be important in the long-term viremia observed in deer.

Animals↗
PubMed1997

Host defense responses associated with experimental hemorrhagic disease in white-tailed deer.

Our objectives were to examine the immunity conferred by epizootic hemorrhagic disease virus serotype 2 (EHDV-2) infection in white-tailed deer (Odocoileus virginianus) and determine if this immunity was protective during challenge with homologous (EHDV-2) or heterologous (bluetongue virus serotype 10; BTV-10) virus. Trials were conducted in the fall of 1992 and 1993. In the first experiment, naive white-tailed deer were infected intradermally and subcutaneously with EHDV-2 and monitored via physical examinations, complete blood counts, alpha and beta interferon (IFN) assays, viral isolation, and serology. Infected deer had a wide range of clinical signs in response to infection. Eleven of the 16 deer had body temperature elevations > or = 0.5 C between post-infection day (PID) 4 and 8. Infected deer had decreased lymphocyte counts between PID 6 and 10 that returned to normal levels by PID 17. Severely lymphopenic animals had the most severe clinical signs; five of 10 deer with lymphocyte counts less than 1000 cells/microliters succumbed to the infection. Viremia was detected in all 16 EHDV-2 infected animals by PID 4, and peak viremias occurred between PID 4 and PID 10. Three deer remained viremic until PID 56, the study endpoint. Interferon was first detected between PID 2 and 6. Peak alpha and beta IFN levels coincided with peak viremia in 11 deer. Precipitating and neutralizing antibodies were detected in infected deer by PID 10. In the second experiment, convalescent deer were challenged subcutaneously and intradermally with either EHDV-2 or BTV-10 and similarly monitored. Virus was detected in the blood of all four deer challenged with BTV-10, but viremia was not detected in three EHDV-2-challenged deer. Temperature fluctuations, blood cell parameter changes, and IFN and antibody responses seen in BTV-10-challenged deer were similar to those seen in the initial experiment. Deer challenged with EHDV-2 had mildly increased temperatures, but minimal IFN response and lymphocyte alterations.

Acute Disease↗
PubMed1997

Natural history of Ehrlichia chaffeensis (Rickettsiales: Ehrlichieae) in the piedmont physiographic province of Georgia.

The roles of wild mammals and ticks in the epidemiology of Ehrlichia chaffeensis at a suspected endemic site were investigated using serologic testing, culture, and polymerase chain reaction (PCR) supported by restriction endonuclease analysis and DNA sequencing. Antibodies reactive to E. chaffeensis (> or = 1:64) were detected in 92% of white-tailed deer (Odocoileus virginianus), 21% of raccoons (Procyon lotor), and 8% of opossums (Didelphis virginianus), but not in 8 other species of mammals. Of 7 species of ticks found by host and environmental sampling, Amblyomma americanum was the dominant species, accounting for greater than 99% of all ticks collected. Deer, raccoons, and opossums were the only species parasitized by all life stages of A. americanum, and A. americanum was the only tick parasitizing deer. A nested PCR protocol incorporating E. chaffeensis-specific primers detected E. chaffeensis DNA in blood, lymph nodes, or spleen from 54% of deer examined. The nested PCR detected E. chaffeensis DNA in 6 of 50 (12%) individual adult A. americanum collected from the environment, in 14 of 79 (18%) pools representing 402 adult A. americanum collected from the environment, and in 7 of 25 (28%) pools of mixed stages of A. americanum collected from deer. Although no Ehrlichia spp. were isolated in culture, sequencing of representative amplicons from deer and ticks confirmed PCR products as E. chaffeensis. These data provide strong evidence that white-tailed deer and lone star ticks are the primary reservoir and vector of E. chaffeensis, respectively. The same PCR protocol, incorporating primers specific for an Ehrlichia-like organism of white-tailed deer, detected this organism in blood, lymph nodes, or spleen from 96% of these deer. The Ehrlichia-like organism of deer was detected by PCR from 0 of 50 individual ticks, 7 of 79 (9%) pools, and 1 of 25 (4%) pools of A. americanum collected from deer. Sequencing of representative amplicons from deer and ticks confirmed PCR products as Ehrlichia-like organism of deer. These data suggest that the Ehrlichia-like organism of deer is present in both the deer and lone star ticks populations at this location.

Animals↗
PubMed1996

Experimental infection of Culicoides lahillei (Diptera: Ceratopogonidae) with epizootic hemorrhagic disease virus serotype 2 (Orbivirus: Reoviridae).

To evaluate the vector competence of Culicoides lahillei Lutz for epizootic hemorrhagic disease (EHD) viruses, wild-caught females were allowed to feed on 4 viremic white-tailed deer, Odocoileus virginianus Zimmermann, experimentally infected with EHD virus serotype 2 (EHDV-2). Colonized C. variipennis sonorensis (Coquillett) were included as a positive control. Virus was not isolated from 13 C. lahillei tested 4-15 d after feeding on deer with viremias of 3.0 or <2.1 log10 tissue culture infectious dose50 (TCID50) virus per milliliter of blood. Virus was isolated from 6 of 69 (8.7%) C. lahillei tested 4-15 d after feeding on deer with viremias of 5.3 or 6.0 TCID50 virus per milliliter of blood. The average amount of EHDV-2 ingested in the blood meal ranged from <log10 1.5 to log10 1.9 TCID50 per C. lahillei. Titers of EHDV-2 in C. lahillei that tested positive 4-15 d after feeding peaked at log10 2.7 TCID50 EHDV per fly. Replication of EHDV-2 also occurred in control C. variipennis. This report of infection of C. lahillei with an EHD virus serotype indicates that C. lahillei may be a vector of EHD viruses.

Animals↗
PubMed1996

Site-specific geographic association between Amblyomma americanum (Acari: Ixodidae) infestations and Ehrlichia chaffeensis-reactive (Rickettsiales: Ehrlichieae) antibodies in white-tailed deer.

Serum samples from white-tailed deer, Odocoileus virginianus Zimmermann, collected from 1982 through 1992 from the southeastern United States were tested for antibodies reactive to Ehrlichia chaffeensis Anderson, Dawson, Jones, & Wilson, the causative agent of human ehrlichiosis. Results were compared between areas based on known infestations of the lone star tick, Amblyomma americanum L., a suspected vector of E. chaffeensis. One hundred and twenty-five of 300 (41.7%) deer tested positive (> or = 1:128) for E. chaffeensis-reactive antibodies by fluorescent antibody analysis. Thirty of 30 (100%) collection areas known to be lone star tick infested contained deer that tested positive for E. chaffeensis-reactive antibodies, corresponding to 121/150 (80.7%) of deer examined. A few deer, 4/150 (2.7%) of those examined, from 2 of 30 (6.7%) areas where lone star ticks were not detected were positive for E. chaffeensis-reactive antibodies. This site-specific geographic association between A. americanum and the presence of E. chaffeensis-reactive antibodies in deer provides strong evidence that A. americanum is a natural vector of E. chaffeensis or a closely related species among white-tailed deer.

Animals↗
PubMed1996

Culicoides (Diptera:Ceratopogonidae) collected during epizootics of hemorrhagic disease among captive white-tailed deer.

To help determine specific vectors of epizootic hemorrhagic disease (EHD) and bluetongue (BT) viruses for white-tailed deer, Odocoileus virginianus Zimmermann, in the southeastern United States, Culicoides sp. midges were collected during epizootics of hemorrhagic disease among captive white-tailed deer in Georgia, Mississippi, and North Carolina. Culicoides variipennis (Coquillett), a confirmed vector of EHD and BT viruses, was present in low numbers in light-trap collections made at all sites. Collections from deer made in Georgia and North Carolina yielded only a single specimen of C. variipennis. Other Culicoides species present in far greater numbers during the epizootics included C. lahillei Lutz, C. paraensis (Goeldi), and C. stellifer (Coquillett) C. lahillei warrants particular attention as a potential vector because its readily feeds on white-tailed deer and was by far the predominant species collected from deer during the epizootics.

Animals↗
PubMed1996

Monitoring of Culicoides spp. at a site enzootic for hemorrhagic disease in white-tailed deer in Georgia, USA.

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) were monitored at a Georgia (USA) site where epizootic hemorrhagic disease (EHD) and bluetongue (BT) viruses are enzootic among white-tailed deer (Odocoileus virginianus). Collections were made using a captive white-tailed deer and light traps from June 1993 through November 1994. We collected 210,482 females from the captive deer during morning and evening periods. Predominant species were C. lahillei (73%), C. stellifer (16%), C. biguttatus (6%), C. niger (3%), C. spinosus (2%), and C. paraensis (0.2%). Other species were C. venustus, C. obsoletus/sanguisuga, C. haematopotus, C. guttipennis, and C. arboricola, which together represented < 0.1% of the specimens collected. No C. variipennis, a known vector of EHD and BT viruses, were collected from the deer. An estimated 953,299 females were collected in 695 light-trap nights. The most common species in light-trap collections were C. spinosus (45%), C. biguttatus (27%) and C. stellifer (24%). Culicoides variipennis was rare in the light-trap samples, representing < 0.01% of the total collections. There was serological evidence from hunter-killed deer that local deer were infected with EHD and BT viruses during the study, particularly during 1994. A primary suspect vector was C. lahillei, which attacked the bait deer in large numbers during the summer and early fall of both 1993 and 1994. Based on their seasonality, relative abundance, and host-seeking activity, C. stellifer and C. spinosus also were considered as possible vectors. However, virus isolation attempts on 113,716 Culicoides, including 62,530 C. lahillei and 32,769 C. stellifer, were negative.

Animals↗
PubMed1996

Hemorrhagic disease in white-tailed deer in Texas: a case for enzootic stability.

Although antibodies to viruses in both the epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV) sero-groups have been reported from white-tailed deer (Odocoileus virginianus) in Texas (USA), there are few reports of hemorrhagic disease (HD) in these populations. To understand the extent and diversity of exposure to the North American EHDV and BTV serotypes in these deer populations, we serologically tested 685 white-tailed deer collected from November 1991 through March 1992 throughout their range in Texas. Overall, 574 (84%) of deer had antibodies to EHDV or BTV. Prevalence estimates varied according to ecological region, from 57% in the Gulf Prairies to 100% in the northwest Edwards Plateau. Based on serum neutralization tests, the deer had evidence of previous exposures to multiple EHDV and BTV serotypes, with evidence of exposure to two to five serotypes detected in each ecological region. The apparent lack of HD in relation to this high antibody prevalence cannot be explained, but may be related to enzootic stability in which a near perfect host-virus relationship exists.

Age Distribution↗
PubMed1996

Ehrlichia-like 16S rDNA sequence from wild white-tailed deer (Odocoileus virginianus).

The reservoir hosts of Ehrlichia chaffeensis, etiologic agent of human ehrlichiosis are unknown. Initially, white-tailed deer (WTD) were serologically implicated as possible reservoirs of E. chaffeensis. Subsequent studies showed that WTD were susceptible to infection with E. chaffeensis and that deer-to-deer transmission by a tick vector, Amblyomma americanum, is possible under experimental conditions. To determine if wild WTD were infected with E. chaffeensis, whole blood was collected from 10 deer from Oklahoma and Georgia. All 10 deer had antibodies reactive to E. chaffeensis. Whereas E. chaffeensis was not isolated, restriction enzyme mapping and sequencing of the 16S rDNA gene revealed that a unique Ehrlichia-like agent was present. All 10 deer appeared to be infected with the same agent. We suspect that A. americanum is the vector of this new agent based upon the previously published temporal association between the appearance of E. chaffeensis seropositive WTD and A. americanum. However, the taxonomic and antigenic relationships, geographic distribution, epidemiology, and zoonotic potential of this agent are yet to be determined.

Animals↗