Monello Ryan J, Powers Jenny G, Hobbs N Thompson, Spraker Terry R, O'Rourke Katherine I, Wild Margaret A
National Park Service, Biological Resource Management Division, Fort Collins, CO 80525, USA.
J Wildl Dis. 2013 Apr;49(2):270-8. doi: 10.7589/2011-12-362.
A reliable antemortem test is needed to understand the ecology of chronic wasting disease (CWD) in elk (Cervus elaphus nelsoni). We measured the ability of antemortem biopsy samples from the rectal mucosa to detect the abnormal prion protein associated with CWD (PrP(CWD)), the relationship between test results from the obex and rectal biopsies at varying stages of CWD progression, and the prevalence of CWD in free-ranging elk from Rocky Mountain National Park, Colorado, USA. We sampled and placed radio collars on 136 adult female elk in the winter of 2007-08. Elk with biopsy samples found positive for PrP(CWD) by immunohistochemistry (IHC) were euthanized and the obex and retropharyngeal lymph nodes were examined with IHC. We resampled, euthanized, and necropsied 20, 25, and 34 of the remaining study elk in each of the three following winters, respectively. Sensitivity of rectal biopsy samples increased in an asymptotic fashion with follicle count and was maximized at 85% (95% credible limits [CL]=60, 98) in the beginning of the study, when a greater proportion of elk were in a detectable stage of prion infection. However, maximum sensitivity was reduced to 72% (CL=46, 94) when we included resampled elk, which included recently infected elk that were initially negative using rectal biopsies and IHC. Test results were similar between rectal biopsies and the obex, but the earliest stages of prion infection were only detected by using retropharyngeal lymph nodes. Minimum CWD prevalence was estimated to be 9.9% (CL=5.7, 15.7) using rectal biopsies, but this rose to 12.9% (CL=8.0, 19.1) when we included four elk that were likely misdiagnosed at initial capture. Our results indicate rectal biopsies can provide a useful research tool for CWD in elk populations, but should be used with caution because they can miss individuals in early stages of infection and underestimate prevalence. Prevalence estimates from this population are the highest reported to date in elk and indicate that under appropriate conditions, CWD may be able to affect the dynamics of high-density elk populations.
需要一种可靠的生前检测方法来了解美洲赤鹿（Cervus elaphus nelsoni）慢性消耗病（CWD）的生态学。我们测量了直肠黏膜生前活检样本检测与CWD相关的异常朊病毒蛋白（PrP(CWD)）的能力、在CWD进展的不同阶段延髓和直肠活检的检测结果之间的关系，以及美国科罗拉多州落基山国家公园自由放养的美洲赤鹿中CWD的患病率。2007 - 2008年冬季，我们对136只成年雌性美洲赤鹿进行了采样并佩戴无线电项圈。通过免疫组织化学（IHC）检测发现活检样本中PrP(CWD)呈阳性的美洲赤鹿被实施安乐死，并对延髓和咽后淋巴结进行IHC检查。在接下来的三个冬季，我们分别对剩余研究美洲赤鹿中的20只、25只和34只进行了重新采样、安乐死和尸检。直肠活检样本的敏感性随着卵泡计数呈渐近式增加，在研究开始时达到最大值85%（95%可信区间[CL]=60, 98），此时处于朊病毒感染可检测阶段的美洲赤鹿比例更高。然而，当我们纳入重新采样的美洲赤鹿（包括最初直肠活检和IHC检测为阴性的近期感染美洲赤鹿）时，最大敏感性降至72%（CL=46, 94）。直肠活检和延髓的检测结果相似，但朊病毒感染的最早阶段仅通过咽后淋巴结检测到。使用直肠活检估计CWD的最低患病率为9.9%（CL=5.7, 15.7），但当我们纳入四只在初次捕获时可能被误诊的美洲赤鹿后，患病率升至12.9%（CL=8.0, 19.1）。我们的结果表明，直肠活检可为美洲赤鹿种群中的CWD提供一种有用的研究工具，但应谨慎使用，因为它们可能会遗漏感染早期的个体并低估患病率。该种群的患病率估计是迄今为止美洲赤鹿中报道的最高值，表明在适当条件下，CWD可能会影响高密度美洲赤鹿种群的动态。
