Abstract.To compare the genetic susceptibility of elk (Cervus elaphus nelsoni) with various alleles of the PRNP gene, which encodes the normal cellular prion protein, to chronic wasting disease (CWD), eight 8-monthold elk calves of 3 genotypes (2 132MM, 2 132LM, and 4 132LL) were orally dosed with CWD-infected brain material from elk. During postinoculation (PI) month 23, both 132MM elk had lost appetite, developed clinical signs of weight loss and central nervous system (CNS) dysfunction, and were euthanized. Two other elk (both 132LM) developed similar clinical signs of disease and were euthanized during PI month 40. All 4 affected elk had microscopic lesions of spongiform encephalopathy (SE), and PrP res , the disease-associated form of the prion protein, was detected in their CNS and lymphoid tissues by use of immunohistochemical (IHC) and Western blot (WB) techniques. These findings indicate that elk with MM and LM at codon 132 are susceptible to orally inoculated CWD. All 4 LL elk are alive at PI year 4 and are clinically normal, which suggests that 132LL elk may have reduced susceptibility to oral infection with CWD-infected material or may have prolonged incubation time.
Background: A large multistate outbreak of equine herpesvirus myeloencephalopathy (EHM) occurred in May 2011 among horses that participated in a competitive event.Objective: To identify EHM risk factors among horses with a common exposure venue. Animals: A total of 123 horses: 19 horses with EHM, 14 equine herpesvirus-1 cases with no reported neurologic signs, and 90 control horses.Methods: EHM case survey data were compared with data from EHV-1 cases with no neurologic signs and healthy controls using univariable and multivariable methods.Results: Significant factors associated with higher risk for EHM compared with EHV-1 cases with no neurologic signs were (1) greater number of biosecurity risks at the event, (2) female sex, (3) increasing number of classes competed in at the event, and (4) an interaction between sex and number of classes competed in. In the EHM versus controls comparison, in addition to sex and biosecurity risks, factors associated with higher EHM risk included EHV-1 vaccination in the 5 weeks before the event and increasing number of events attended in April 2011; zinc dietary supplementation was associated with decreased risk. An interaction between sex and the number of events attended in April 2011 also was significant.Conclusions and Clinical Importance: Findings from this study suggest that dietary zinc supplementation may be associated with decreased risk of EHM. Several factors were associated with increased risk of EHM. Additional investigations of factors associated with risk of EHM are warranted to evaluate the importance of these factors in this complex disease of horses.
Abstract. Preclinical diagnostic tests for transmissible spongiform encephalopathies have been described for mule deer (Odocoileus hemionus), using biopsy tissues of palatine tonsil, and for sheep, using lymphoid tissues from palatine tonsil, third eyelid, and rectal mucosa. The utility of examining the rectal mucosal lymphoid tissues to detect chronic wasting disease (CWD) was investigated in Rocky Mountain elk (Cervus elaphus nelsoni), a species for which there is not a live-animal diagnostic test. Postmortem rectal mucosal sections were examined from 308 elk from two privately owned herds that were depopulated. The results of the postmortem rectal mucosal sections were compared to immunohistochemical staining of the brainstem, retropharyngeal lymph nodes, and palatine tonsil. Seven elk were found positive using the brainstem (dorsal motor nucleus of the vagus nerve), retropharyngeal lymph nodes, and palatine tonsil. Six of these elk were also found positive using postmortem rectal mucosal sections. The remaining 301 elk in which CWD-associated abnormal isoform of the prion protein (PrP CWD ) was not detected in the brainstem and cranial lymphoid tissues were also found to be free of PrP CWD when postmortem rectal mucosal sections were examined. The use of rectal mucosal lymphoid tissues may be suitable for a live-animal diagnostic test as part of an integrated management strategy to limit CWD in elk.
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.
We monitored a herd of fallow deer (Dama dama) for evidence of prion infection for 7 yr by periodic postmortem examination of animals from the herd. The fallow deer were exposed to the chronic wasting disease (CWD) agent from mule deer by living in a paddock considered contaminated with infectivity from its history of housing CWD infected deer and, after the first year of the study, by comingling with infected mule deer (Odocoileus hemionus). At least 8 of 12 mule deer serving as sentinels for prion transmission and 25 additional mule deer serving as sources of infectivity developed clinical CWD or were otherwise confirmed to be infected with CWD via lymphoid tissue immunohistochemistry (IHC). In contrast, none of the 41 exposed fallow deer showed clinical signs suggestive of CWD, IHC staining of disease-associated prion in lymphoid or brain tissues, or evidence of spongiform degeneration in sections of brain stem at the level of the obex when sampled 18 mo to 7 yr after entering the mule deer paddock. The absence of clinical disease and negative IHC results in fallow deer housed in the same contaminated paddock for up to 7 yr and almost continuously exposed to CWD-infected mule deer for up to 6 yr suggests a species barrier or other form of resistance preventing fallow deer infection by the CWD agent or delaying progression of the disease in this species.
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