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Biomedical subjects

W R Davidson

Publications and source records attributed to W R Davidson.

At least 37 records · Page 2Linked to original sources
PubMed1997

Mycoplasmas in wild turkeys living in association with domestic fowl.

One hundred and nineteen Merriam's wild turkeys (Meleagris gallopavo merriami) and 31 domestic chickens coexisting on a ranch in west-central Colorado (USA) were surveyed for mycoplasmosis by serologic and cultural methods. Although no clinical signs were apparent in any wild turkeys tested, 51 (43%) had positive rapid plate agglutination (RPA) reactions for M. gallisepticum (MG) and/or M. synoviae (MS); 37% of 56 adults and 48% of 63 subadults were classified as positive reactors to MG and/or MS. No turkeys tested in 1992 (n = 61) and 17 (29%) of 58 turkeys tested in 1993 were RPA-positive for M. meleagridis (MM). Hemagglutination inhibition (HI) test results were negative for MG, MS and MM as were most enzyme-linked immunosorbent assay (ELISA) test reactions (MG = 99%, MS = 93%, MM = 87%). Immunoblotting showed mild to moderate reactivity to MG proteins in 49% of 41 samples tested. Most chickens were strongly positive for MS by RPA (81%), HI (58%) and ELISA (87%); 48% also were positive for MG by RPA but all were MG-negative by HI and ELISA. No pathogenic mycoplasmas were isolated from either group of birds. Mycoplasma gallopavonis was commonly identified from the wild turkeys, and M. gallinaceum was isolated from both the chickens and wild turkeys. In a transmission study conducted in 1994, disease-free domestic turkeys failed to seroconvert when co-housed with wild turkeys from this population that were RPA-positive for MG. Collectively, the results of this study were inconclusive regarding the status of pathogenic mycoplasmas within this wild turkey population.

Agglutination Tests↗
PubMed1997

Winter mortality of common loons in Florida coastal waters.

Diagnostic findings are presented for 434 common loons (Gavia immer) found sick or dead on Florida beaches from 1970 through 1994, primarily during the months of December to April. The most commonly recognized problem was an emaciation syndrome (66%), followed by oiling (18%), aspergillosis (7%), trauma (5%) and miscellaneous disease entities (1%). The cause-of-death for 3% of the birds was not determined. Many of the carcasses examined (n = 173) were obtained during an epizootic which occurred from January to March of 1983 in which more than 13,000 loons were estimated to have died. An emaciation syndrome, characterized by severe atrophy of pectoral muscles, loss of body fat and hemorrhagic enteritis, was the primary finding in this epizootic. It was postulated to have a complex etiologic basis involving synergistic effects and energy costs of migration, molting and replacement of flight feathers, food resource changes, salt-loading, intestinal parasitism, environmental contaminants, and inclement weather.

Animals↗
PubMed1997

Use of the hand-held dental X-ray machine during joint operation, NATO exercise Display Determination-92.

The hand-held dental X-ray machine is a 30-pound, battery-powered X-ray machine capable of use in military medicine, humanitarian missions, and training exercises. The machine was developed for dental radiology, but with the attachment of a medical collimator, the equipment can also be used for medical exams. In 1992, the machine was tested under field conditions in a NATO joint exercise in Bolayir, Turkey. The hand-held dental X-ray machine was found easier to use than the currently deployed Siemens dental X-ray unit and than produced radiographs of equal quality.

Adult↗
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

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

Parelaphostrongylus tenuis on Wassaw Island, Georgia: a result of translocating white-tailed deer.

Meningeal worms (Parelaphostrongylus tenuis) were found in each of five white-tailed deer (Odocoileus virginianus) examined from Wassaw Island, Chatham County, Georgia, in September 1993. This represents the first reported occurrence of the parasite on a southeastern barrier island and extends its geographic distribution approximately 140 km beyond the nearest known infected mainland deer population. According to an anecdotal account, six white-tailed deer were imported from Pennsylvania and released on Wassaw Island in 1905 or shortly thereafter. Based on its absence elsewhere along the southeastern coast from North Carolina to Louisiana and its high prevalence in Pennsylvania, the enzootic focus of P. tenuis on Wassaw Island was attributed to translocation of infected deer.

Animals↗
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↗
PubMed1995

Temporal association of Amblyomma americanum with the presence of Ehrlichia chaffeensis reactive antibodies in white-tailed deer.

From 1981 through 1993, tick infestations and serum antibodies reactive to Ehrlichia chaffeensis, the causative agent of human ehrlichiosis, were monitored among white-tailed deer (Odocoileus virginianus) at Whitehall Experimental Forest, Clarke County, Georgia (USA). Neither ticks nor E. chaffeensis antibodies were detected during the first two years of the study. Infestations of the lone star tick (Amblyomma americanum), a suspected vector of E. chaffeensis, first were noted on deer in 1983. Prevalence and intensity of A. americanum sharply increased from 1985 to 1989, and prevalence was 100% from 1990 to 1993. Antibodies reactive to E. chaffeensis were first detected in 7% of deer sampled in 1986. Antibody prevalence increased to 21% in 1987 and was 100% from 1988 to 1993. This temporal association between the establishment of A. americanum and the appearance of E. chaffeensis antibodies provides evidence to support the concept that A. americanum could be a natural vector of E. chaffeensis. The high prevalence of antibodies among all age classes of deer also reaffirms that white-tailed deer may be sensitive natural sentinels for monitoring the distribution of E. chaffeensis.

Animals↗
PubMed1995

Toxoplasmosis in wild turkeys: a case report and serologic survey.

Toxoplasmosis was diagnosed in a free-ranging wild turkey (Meleagris gallopavo) from West Virginia (USA) in June 1993. Gross findings included emaciation, splenomegaly, multifocal necrotizing hepatitis and splenitis, and crusting dermatitis on the head and neck. Histologically, multifocal necrosis with mononuclear inflammation was present in kidney, liver, spleen, heart, lungs, and pancreas. Toxoplasma gondii was confirmed in sections of liver by avidin-biotin immunohistochemical analysis. Subsequently, a retrospective serosurvey of wild turkeys for T. gondii antibodies was conducted using turkey sera collected between 1984 and 1989. An antibody prevalence of 10% was detected in 130 birds from 21 locations in the southeastern United States. While wild turkeys in the Southeast have T. gondii antibodies, this is only the second natural case of fatal toxoplasmosis reported; it appears that wild turkeys infrequently develop clinical disease when infected with T. gondii.

Animals↗
PubMed1995

An assessment of the role of white-tailed deer in the epizootiology of anaplasmosis in the southeastern United States.

The role of white-tailed deer (Odocoileus virginianus) in the epizootiology of anaplasmosis in the southeastern United States was examined through retrospective and prospective serosurveys and by experimental infection studies. No serum antibody reactive to Anaplasma marginale was detected with an indirect fluorescent antibody (IFA) assay from any of 1,376 free-ranging deer sampled from 1968 through 1990 from 13 states and Puerto Rico. Thirty-one additional deer from three bovine anaplasmosis enzootic premises also were negative by IFA and Giemsa-stained blood films. Three captive deer given A. marginale intravenously developed antibodies 38 to 41 days post-inoculation (DPI) and remained seropositive for the duration of the study (161 to 287 DPI). At 42 DPI, rickettsemias of approximately 0.0001% infected erythrocytes were observed in all three deer using a DNA probe; low rickettsemias (maximum 0.01%) persisted through 56, 63, and 87 DPI, respectively. One deer had a recrudescent infection from 126 to 146 DPI (maximum rickettsemia 0.001%). We believe that white-tailed deer in the southeastern United States, even though susceptible to A. marginale infection, are not exposed naturally, even at enzootic sites. Furthermore, white-tailed deer did not develop rickettsemias sufficient to support mechanical transmission by biting flies, which is believed to be the primary means of anaplasmosis transmission in this region.

Anaplasma↗
PubMed1994

Seasonal and annual abundance of Amblyomma americanum (Acari: Ixodidae) in central Georgia.

Seasonal and annual changes in the abundance of Amblyomma americanum (L.) larvae, nymphs, and adults were monitored over a 5-yr period in the Piedmont physiographic region of Georgia. Tick abundance was monitored with cloth drags (all life stages) and CO2-baited cloth panels (nymphs and adults) monthly during March through September from 1987 through 1991. Larvae appeared in substantial numbers in July and were most numerous in August and September. Small numbers of unfed larvae apparently overwintered each year based on their presence during March, April, or May. Nymphs were most numerous from April through June and declined to much lower numbers by August and September. Adults were most numerous from March through May and virtually disappeared by August. These seasonal patterns were similar to those reported for A. americanum at other southeastern locations. Each life stage exhibited similar trends of annual abundance with an increase in 1988 followed by a relatively steady decline to levels equivalent to or below initial 1987 values by 1991. Major environmental variables that potentially could have influenced annual abundance were identified from Haile & Mount's (1987) computerized model of A. americanum population dynamics. Habitat type, host density, and day length were constants and rationally could be excluded as causes of annual variations in abundance; weather and host-finding rate were presumed to have been primarily responsible for these annual differences.

Animals↗
PubMed1994

Influence of annual and biennial prescribed burning during March on the abundance of Amblyomma americanum (Acari: Ixodidae) in central Georgia.

A 5-yr study to evaluate the influence of annual and biennial prescribed burning in March on the abundance of Amblyomma americanum (L.) was conducted on Oconee Wildlife Management Area in the Piedmont physiographic region of Georgia. Tick abundance on plots embedded in larger burned and unburned areas were monitored with cloth drags and CO2-baited cloth panels monthly during March through September from 1987 through 1991. Annual and biennial prescribed burning from 1988 to 1991 significantly reduced the abundance of larvae, nymphs, and adults but did not alter their seasonal trends of abundance. Annual burning more consistently suppressed all life stages than biennial burning. The magnitude of tick suppression tended to increase with successive burns, especially with the annual burning regime. The order of vulnerability to direct incineration appeared to be overwintered larvae > adults > nymphs; however, only overwintered larvae were highly vulnerable. Consistent reductions in larvae during June-September following burning were associated with reduced litter depths and presumably lowered habitat suitability. During years of fire omission, the abundance of larvae on biennially burned plots increased to levels equal to or exceeding those on unburned plots. Based on cloth drag sampling, mean percentage control during 1988-1991 for larvae, nymphs, and adults, respectively, was 80, 75, and 70% on annually burned plots and 48, 73, and 65% on biennially burned plots. Frequent late-winter prescribed burning, which is commonly used to achieve wildlife habitat management objectives, could be an effective and economical component of an integrated A. americanum control program in habitats ecologically suited to regimes of frequent fire.

Animals↗
PubMed1994

Susceptibility of white-tailed deer (Odocoileus virginianus) to infection with Ehrlichia chaffeensis, the etiologic agent of human ehrlichiosis.

Although more than 320 cases of human ehrlichiosis have been diagnosed in 27 states since 1986, the reservoir host or hosts remain unknown. Since antibodies reactive to Ehrlichia chaffeensis, the etiologic agent of human ehrlichiosis, have been found in white-tailed deer (Odocoileus virginianus), we experimentally evaluated the susceptibilities of four white-tailed deer to infection with E. chaffeensis and Ehrlichia canis, a closely related species. A fifth deer served as a negative control. Isolation and nested PCR amplification results from peripheral blood indicated that E. chaffeensis circulated for at least 2 weeks. The deer developed antibodies to E. chaffeensis by day 10 after inoculation, but there was no indication of clinical disease. Immunohistochemical staining identified E. chaffeensis within macrophage-type cells in lymph nodes. The deer inoculated with E. canis did not become infected and did not seroconvert. These results indicate that white-tailed deer can support an E. chaffeensis infection with resulting rickettsemia of at least 2 weeks. The resistance to infection and the absence of seroconversion upon exposure to E. canis indicate that antibody responses previously detected among wild deer are not E. canis cross-reactions. The role of deer as competent reservoirs in the life cycle of E. chaffeensis remains to be explored with suspected tick vectors.

Animals↗
PubMed1993

Echocardiographic assessment of atrial septal defects.

Echocardiography has become the method of choice for the assessment of patients with a known or suspected atrial septal defect. The majority of patients with defects can be identified by this method. In patients with inconclusive transthoracic studies, transesophageal echocardiography is useful for identification or exclusion of a defect. Echocardiography is useful for quantification of left-to-right shunting, identification of associated anomalies, and estimation of pulmonary pressure. Cardiac catheterization can be reserved for patients who require measurement of pulmonary vascular resistance, those who have a significant risk of coronary artery disease, and those with complex congenital heart disease.

Blood Flow Velocity↗
PubMed1993

Echocardiographic evaluation of size, function, and mass of normal and hypertrophied rat ventricles.

The noninvasive evaluation of cardiac structure and function in small animals would provide a means for investigators to repeatedly evaluate treatment effects at various stages of experimental protocols. In this study, commercially available echocardiographic and Doppler equipment was utilized to evaluate hypertrophied (HYP) and normal (SH) rat hearts. Surgically induced renovascular hypertension was used to produce a 35% increase in left ventricular (LV) weight in HYP relative to SH hearts. A commercially available echocardiographic system with integral Doppler capabilities and a 7.5-mHz single-crystal mechanical transducer was used to obtain parasternal long- and short-axis images of HYP and SH hearts in anesthetized animals. HYP hearts were found to have normal systolic function, as evidenced by preserved LV systolic and diastolic dimensions and volumes as well as fractional shortening and ejection fraction. HYP hearts demonstrated a 62% increase in their echocardiographically measured LV posterior wall thicknesses and a 44% increase in calculated ventricular mass. Both parameters were reliable in predicting the presence and degree of left ventricular hypertrophy. Doppler flow velocities through the aortic root and pulmonic valve did not differ between groups, again suggesting preserved LV systolic performance. These results indicate that two-dimensional echocardiography provides a useful means to noninvasively evaluate cardiac structure and function in rats.

Animals↗
PubMed1993

Evaluation of fox-chasing enclosures as sites of potential introduction and establishment of Echinococcus multilocularis.

Following detection of Echinococcus multilocularis in red foxes (Vulpes vulpes) illegally imported into South Carolina (USA) for release in fox-chasing enclosures, a survey for E. multilocularis was conducted in four enclosures in Georgia (USA) and six enclosures in South Carolina. Survey methods included examination of potential small mammal intermediate hosts (n = 390) for E. multilocularis larvae, examination of fox and coyote (Canis latrans) scats (n = 59) for taeniid eggs, and examination of one possible canine definitive hosts for adult E. multilocularis. All intermediate and definitive hosts examined were negative for E. multilocularis and taeniid eggs were not recovered from fox and coyote fecal samples. Thus, E. multilocularis may not yet be established in fox-chasing enclosures in Georgia and South Carolina. Despite the failure to demonstrate E. multilocularis in the fox-chasing enclosures surveyed, translocation of wild canids from known enzootic regions should be discouraged because E. multilocularis is known to be ecologically adaptable and because contact with potentially infected definitive hosts during translocation is a public health risk.

Animals↗
PubMed1992

Ischemia-induced depressed systolic thickening is transiently augmented by remote coronary occlusion.

To determine if ischemia-induced depressed myocardial thickening can be augmented by remote coronary occlusion, posterior wall function (pulsed Doppler crystal) was measured before and after left anterior descending coronary artery occlusion in the presence of reduced circumflex coronary artery flow (of sufficient severity to reduce resting function) in an anesthetized open-chest canine preparation in which the circumflex was pump-perfused with carotid arterial blood. Left anterior descending coronary occlusion elicited an immediate significant increase in posterior bed thickening fraction (TF%) (3.7 +/- 1.5 to 5.9 +/- 1.3%), but by 135 sec TF% had again deteriorated. The transient increase in thickening was not caused by increased flow to the posterior bed (microspheres, n = 3), nor was it related to a Frank-Starling mechanism (echocardiography, n = 3). Despite an ischemic-induced reduction in systolic shortening, systolic thickening can be transiently augmented by remote coronary occlusion. The etiology may be related to systolic unloading.

Animals↗