EVALUATION OF A TEST AND CULL STRATEGY FOR REDUCING PREVALENCE OF CHRONIC WASTING DISEASE IN MULE DEER ( ODOCOILEUS HEMIONUS).

We evaluated a test and cull strategy for lowering chronic wasting disease (CWD) prevalence in a naturally-infected, free-ranging mule deer ( Odocoileus hemionus) herd wintering in the town of Estes Park, Colorado, US and in nearby Rocky Mountain National Park. We tested 48-68% of the estimated number of adult (≥1 yr old) deer annually for 5 yr via tonsil biopsy immunohistochemistry (IHC), collecting 1,251 samples from >700 individuals and removing IHC-positive deer. Among males, CWD prevalence during the last 3 yr of selective culling was lower (one-sided Fisher's exact test P=0.014) than in the period prior. In contrast, CWD prevalence among females before culling and after culling were equivalent ( P=0.777). Relatively higher annual testing of males (mean 77%) compared to females (mean 51%) might have contributed to differences seen in responses to management. A more intensive and sustained effort or modified spatial approach might have reduced prevalence more consistently in both sexes. Limitations of this technique in wider management application include cost and labor as well as property access and animal tolerance to repeated capture. However, elements of this approach could potentially be used to augment harvest-based disease management.

Survival patterns in white-tailed and mule deer after oral inoculation with a standardized, conspecific prion dose.

We orally inoculated white-tailed deer (Odocoileus virginianus) and mule deer (Odocoileus hemionus) with a standardized, conspecific prion dose and collected biologic samples throughout the disease course. Mule deer (PRNP genotype 225SS) and PRNP genotype 96GG white-tailed deer succumbed along similar trajectories, but 96GS- and 96SS-genotype individuals tended to survive longer.

Salivary prions in sheep and deer.

Scrapie of sheep and chronic wasting disease (CWD) of cervids are transmissible prion diseases. Milk and placenta have been identified as sources of scrapie prions but do not explain horizontal transmission. In contrast, CWD prions have been reported in saliva, urine and feces, which are thought to be responsible for horizontal transmission. While the titers of CWD prions have been measured in feces, levels in saliva or urine are unknown. Because sheep produce ~17 L/day of saliva, and scrapie prions are present in tongue and salivary glands of infected sheep, we asked if scrapie prions are shed in saliva. We inoculated transgenic (Tg) mice expressing ovine prion protein, Tg(OvPrP) mice, with saliva from seven Cheviot sheep with scrapie. Six of seven samples transmitted prions to Tg(OvPrP) mice with titers of -0.5 to 1.7 log ID50 U/ml. Similarly, inoculation of saliva samples from two mule deer with CWD transmitted prions to Tg(ElkPrP) mice with titers of -1.1 to -0.4 log ID50 U/ml. Assuming similar shedding kinetics for salivary prions as those for fecal prions of deer, we estimated the secreted salivary prion dose over a 10-mo period to be as high as 8.4 log ID50 units for sheep and 7.0 log ID50 units for deer. These estimates are similar to 7.9 log ID50 units of fecal CWD prions for deer. Because saliva is mostly swallowed, salivary prions may reinfect tissues of the gastrointestinal tract and contribute to fecal prion shedding. Salivary prions shed into the environment provide an additional mechanism for horizontal prion transmission.

Asymptomatic deer excrete infectious prions in faeces.

Infectious prion diseases-scrapie of sheep and chronic wasting disease (CWD) of several species in the deer family-are transmitted naturally within affected host populations. Although several possible sources of contagion have been identified in excretions and secretions from symptomatic animals, the biological importance of these sources in sustaining epidemics remains unclear. Here we show that asymptomatic CWD-infected mule deer (Odocoileus hemionus) excrete CWD prions in their faeces long before they develop clinical signs of prion disease. Intracerebral inoculation of irradiated deer faeces into transgenic mice overexpressing cervid prion protein (PrP) revealed infectivity in 14 of 15 faecal samples collected from five deer at 7-11 months before the onset of neurological disease. Although prion concentrations in deer faeces were considerably lower than in brain tissue from the same deer collected at the end of the disease, the estimated total infectious dose excreted in faeces by an infected deer over the disease course may approximate the total contained in a brain. Prolonged faecal prion excretion by infected deer provides a plausible natural mechanism that might explain the high incidence and efficient horizontal transmission of CWD within deer herds, as well as prion transmission among other susceptible cervids.

Evaluation of intramuscular butorphanol, azaperone, and medetomidine and nasal oxygen insufflation for the chemical immobilization of white-tailed deer, Odocoileus virginianus.

Chemical immobilization of wildlife often includes opioids or cyclohexamines. These substances are problematic as a result of their required storage, handling, and record-keeping protocols. A potentially useful alternative sedation protocol includes a combination of butorphanol, azaperone, and medetomidine (BAM: 0.43 mg/kg butorphanol, 0.36 mg/kg azaperone, 0.14 mg/kg medetomidine). One risk of wildlife immobilization with any drug combination is hypoxemia. This may be of particular importance when using an alpha 2 agonist such as medetomidine because of its powerful vasoconstrictive effect. In this prospective study, the BAM combination was evaluated for chemical immobilization of white-tailed deer. Additionally, selected physiologic parameters associated with BAM immobilization, including oxygen saturation via pulse oximetry and arterial blood gas measurement, with and without nasal insufflation of oxygen at a relatively low flow of 3 L/min, were evaluated. The BAM combination resulted in a predictable onset of sedation, with a mean induction time to lateral recumbency of 9.8 +/- 3.6 min. All deer recovered smoothly within a range of 5-20 min after reversal with intramuscular administration of naltrexone, atipamazole, and tolazoline (NAT). Clinically relevant decreases in arterial partial pressure of oxygen (PaO2) and oxygen saturation (SpO2) were observed in animals not receiving supplemental oxygen, while both parameters significantly improved for oxygen-supplemented deer. Pulse oximetry with this protocol was an unreliable indicator of oxygen saturation. In this study, altitude, recumbency, hypoventilation, butorphanol- and medetomidine-specific effects, as well as the potential for alpha 2 agonist-induced pulmonary changes all may have contributed to the development of hypoxemia. Overall, capture of white-tailed deer with the BAM/NAT protocol resulted in excellent chemical immobilization and reversal. Because the BAM combination caused significant hypoxemia that is unreliably detected by pulse oximetry but that may be resolved with nasal oxygen insufflation, routine use of oxygen supplementation is recommended.

PrPCWD in rectal lymphoid tissue of deer (Odocoileus spp.).

The utility of rectal lymphoid tissue sampling for the diagnosis of chronic wasting disease (CWD) infections in mule deer (Odocoileus hemionus) and white-tailed deer (Odocoileus virginianus) was evaluated. CWD-associated prion protein (PrP(CWD)) deposits were observed in the rectal mucosa from 19 orally inoculated mule deer by 381 days post-inoculation (p.i.); similarly, 45 out of 50 naturally infected mule deer had PrP(CWD) in their rectal mucosa. In orally inoculated white-tailed deer, the presence of glycine (G) or serine (S) at codon 96 of the native PrP (denoted 96GG, 96GS or 96SS) appeared to influence the temporal patterns of PrP(CWD) deposition: nine out of 11 infected 96GG individuals had PrP(CWD) in their rectal mucosa by 342 days p.i., whereas only three out of seven infected 96GS individuals had PrP(CWD) in their rectal mucosa by 381 days p.i. and none of three 96SS individuals had PrP(CWD) in their rectal mucosa by 751 days p.i. These findings support further evaluation of rectal mucosa sampling in CWD surveillance.