Saturday, September 06, 2008

Chronic wasting disease in a Wisconsin white-tailed deer farm 79% INFECTION RATE

Contents: September 1 2008, Volume 20, Issue 5

Journal of Veterinary Diagnostic Investigation Vol. 20 Issue 5, 698-703 Copyright © 2008 by the American Association of Veterinary Laboratory Diagnosticians


Case Reports

Chronic wasting disease in a Wisconsin white-tailed deer farm

Delwyn P. Keane1, Daniel J. Barr, Philip N. Bochsler, S. Mark Hall, Thomas Gidlewski, Katherine I. O'Rourke, Terry R. Spraker and Michael D. Samuel Correspondence: 1Corresponding Author: Delwyn Keane, University of Wisconsin, Wisconsin Veterinary Diagnostic Laboratory, 445 Easterday Lane, Madison, WI 53706.

In September 2002, chronic wasting disease (CWD), a prion disorder of captive and wild cervids, was diagnosed in a white-tailed deer (Odocoileus virginianus) from a captive farm in Wisconsin. The facility was subsequently quarantined, and in January 2006 the remaining 76 deer were depopulated. Sixty animals (79%) were found to be positive by immunohistochemical staining for the abnormal prion protein (PrPCWD) in at least one tissue; the prevalence of positive staining was high even in young deer. Although none of the deer displayed clinical signs suggestive of CWD at depopulation, 49 deer had considerable accumulation of the abnormal prion in the medulla at the level of the obex. Extraneural accumulation of the abnormal protein was observed in 59 deer, with accumulation in the retropharyngeal lymph node in 58 of 59 (98%), in the tonsil in 56 of 59 (95%), and in the rectal mucosal lymphoid tissue in 48 of 58 (83%). The retina was positive in 4 deer, all with marked accumulation of prion in the obex. One deer was considered positive for PrPCWD in the brain but not in the extraneural tissue, a novel observation in white-tailed deer. The infection rate in captive deer was 20-fold higher than in wild deer. Although weakly related to infection rates in extraneural tissues, prion genotype was strongly linked to progression of prion accumulation in the obex. Antemortem testing by biopsy of recto–anal mucosal-associated lymphoid tissue (or other peripheral lymphoid tissue) may be a useful adjunct to tonsil biopsy for surveillance in captive herds at risk for CWD infection.


Title: Chronic wasting disease in a Wisconsin captive white-tailed deer farm


Keane, Delwyn - U OF WIS, WIS VET DIAG LA Barr, Daniel - U OF WIS, WIS VET DIAG LA Bochsler, Philip - U OF WIS, WIS VET DIAG LA Hall, S - USDA, APHIS, VS, NVSL Gidlewski, Thomas - USDA, APHIS, VS O`rourke, Katherine Spraker, Terry - CO STATE UNIVERSITY Samuel, Michael - US GEOLOGIC SERVICE

Submitted to: Journal of Veterinary Diagnostic Investigation Publication Type: Peer Reviewed Journal Publication Acceptance Date: May 5, 2008 Publication Date: N/A

Interpretive Summary: Chronic wasting disease is a fatal disease of deer and elk. Clinical signs, including weight loss, frequent urination, excessive thirst, and changes in behavior and gait, have been reported in mule deer and elk with this disorder. Clinical signs in captive white tailed deer are less well understood. In a previous study, a captive facility housed 200 deer, of which half were positive for the disease with no clinical signs reported. In this study, we examined 78 white tailed deer from a captive facility with a history of chronic wasting disease and no animals with clinical signs. Examination of the brain and lymph nodes demonstrated that the abnormal prion protein, a marker for disease, was observed in 60 of the deer. Biopsy of the rectal mucosa, a test that can be performed on live deer, detected 83% of the infected animals. The prion genetics of the deer was strongly linked to the rate of infection and to disease progression. The results demonstrate that clinical signs are a poor indicator of the disease in captive white tailed deer and that routine testing of live deer and comprehensive necropsy surveillance may be needed to identify infected herds. Technical Abstract: Chronic wasting disease CWD is a transmissible spongiform encephalopathy or prion disease of deer and elk in North America. All diseases in this family are characterized by long preclinical incubation periods following by a relatively short clinical course. Endpoint disease is characterized by extensive deposits of aggregates of the abnormal prion protein in the central nervous system,. In deer, the abnormal prion proteins accumulate in some peripheral lymphoid tissues early in disease and are therefore suitable for antemortem and preclinical postmortem diagnostics and for determining disease progression in infected deer. In this study, a herd of deer with previous CWD diagnoses was depopulated. No clinical suspects were identified at that time. Examination of the brain and nodes demonstrated that 79% of the deer were infected. Of the deer with abnormal prion in the peripheral lymphoid system, the retropharyngeal lymph node was the most reliable diagnostic tissue. Biopsy of the rectal mucosal tissue, a site readily sampled in the restrained or chemically immobilized deer, provided an accurate diagnosis in 83% of the infected deer. The retina in the eye of the deer was positive only in late stage cases. This study demonstrated that clinical signs are a poor indicator of disease, supports the use of the retropharyngeal lymph node as the most appropriate postmortem sample, and supports a further evaluation of the rectal mucosal tissue biopsy as an antemortem test on a herd basis.


Vol. 9, No. 5 May 2003


Chronic Wasting Disease in Free-Ranging Wisconsin White-Tailed Deer Damien O. Joly,* Christine A. Ribic,* Julie A. Langenberg,† Kerry Beheler,† Carl A. Batha,† Brian J. Dhuey,‡ Robert E. Rolley,‡ Gerald Bartelt,‡ Timothy R. Van Deelen,§; and Michael D. Samuel*¶ *United States Geological Survey-Wisconsin Cooperative Wildlife Research Unit, University of Wisconsin-Madison, Madison, Wisconsin, USA; †Wisconsin Department of Natural Resources, Madison, Wisconsin, USA; ‡Wisconsin Department of Natural Resources, Monona, Wisconsin, USA; §Wisconsin Department of Natural Resources, Rhinelander, Wisconsin, USA; and ¶United States Geological Survey–National Wildlife Health Center, Madison, Wisconsin, USA

Suggested citation for this article: Joly DO, Ribic CA, Langenberg JA, Beheler K, Batha CA, Dhuey BJ, et al. Chronic wasting disease in free-ranging Wisconsin white-tailed deer. Emerg Infect Dis [serial online] 2003 May [date cited]. Available from: URL:


Three White-tailed Deer shot within 5 km during the 2001 hunting season in Wisconsin tested positive for chronic wasting disease, a prion disease of cervids. Subsequent sampling within 18 km showed a 3% prevalence (n=476). This discovery represents an important range extension for chronic wasting disease into the eastern United States.

Chronic wasting disease (CWD) is degenerative and usually considered to be fatal in White-tailed Deer (Odocoileus virginianus), Mule Deer (O. hemionus), and Elk (Cervus elaphus) associated with the presence of transmissible protease-resistant prion proteins (PrPcwd) (1,2). Although the transmission route of PrPcwd is unknown, it may be transmitted in deer and elk by direct contact or indirectly from the environment (1,2). In experiments, clinical signs have appeared as early as 15 months after exposure (1) and include weight loss, anorexia, repetitive behaviors, hyperesthesia, and intractability. Signs progress to severe emaciation, extreme behavioral changes, excessive salivation, tremors, and mild ataxia (1,2). CWD was first recognized in captive Mule Deer in Colorado (3) and subsequently described in the free-ranging cervid populations of Colorado and Wyoming (1); prevalence in these disease-endemic areas varies spatially and among the three sympatric cervid species (4). Before its discovery in Wisconsin, CWD was detected in captive cervid farms in Colorado, Nebraska, South Dakota, Oklahoma, Kansas, Montana (USA), as well as Alberta, Saskatchewan (Canada), and South Korea (1). Apart from the contiguous areas of Colorado, Wyoming, and Nebraska, CWD had previously only been detected in two free-ranging Mule Deer from Saskatchewan, one Mule Deer from South Dakota, and in a number of Mule Deer from the western slopes region of Colorado (1). Previously, no cases of CWD were reported east of the Mississippi; however, subsequent to our research, CWD-positive cervids were found in Minnesota (captive Elk), Wisconsin (captive White-tailed Deer and Elk), and Illinois (free-ranging White-tailed Deer). Further, west of the Mississippi, the following CWD-positive animals have been found: Mule Deer in New Mexico and Utah; free-ranging Mule and White-tailed Deer in Saskatchewan, Canada; and captive Elk and White-tailed Deer in Alberta, Canada.

The Study In autumn of 1999 and 2000, the Wisconsin Department of Natural Resources (WDNR) submitted to the National Veterinary Services Laboratories (NVSL) (Ames, Iowa) brain material (obex) from 657 hunter-killed White-tailed Deer registered at hunter check stations across the state. None came from the study area we describe. Samples were tested for CWD prion by immunohistochemistry (IHC) (5). Prion was not detected in any samples. However, 3 of 445 White-tailed Deer shot in autumn of 2001 were positive for CWD. These deer were males, 2.5 years of age, and were shot within 5 km in south-central Wisconsin. WDNR subsequently conducted a sampling program to assess the distribution and prevalence of CWD in the vicinity of these three positive deer. We report the results of this sampling program.

Samples were collected from 500 adult (>1 year of age) White-tailed Deer within an approximate 18-km radius, and all samples were tested for CWD. Deer were submitted by hunters who were issued scientific collection permits, collected at roadside after vehicular collison, or collected by WDNR or U.S. Department of Agriculture sharpshooters. Data from collected deer included the geographic location based on the Wisconsin Public Land Survey System (township-range-section), sex, and age (estimated by using tooth eruption and tooth wear patterns [6]). Location of kill was indicated on a map by hunters during interviews by DNR staff. Samples of brain stem (obex) and retropharyngeal lymphatic tissue were fixed in 10% buffered formalin and submitted to NVSL for testing using IHC. We considered a deer to be CWD positive if either obex or retropharyngeal samples were IHC positive (1).

We used the spatial scan statistic provided by Kulldorff and Nagarwalla (7) (program SaTScan available from: URL: to assess the presence and location of CWD clusters within the surveillance area. Location data were collected to the survey unit “section” (approximately 2.6 km2). We pooled locations into 4X4 section quadrats for analysis to compensate for sections from which no deer were collected. In a separate analysis, sex and age were assessed as predictors of CWD status by using logistic regression (function glm in program R v. 1.5.0; available from: URL: (8). Model selection uncertainty was incorporated into the odds ratio (OR) estimates by using model averaging (9).

Results and Discussion

From March 2 to April 9, 2002, samples were collected from 505 deer; however, 29 deer were not included in the analysis because of sample autolysis, inappropriate tissue submission, or lack of availability of appropriate tissues (e.g., deer with no intact cranium or those shot in the head). Of the remaining 476 deer (87 males, 386 females, and 3 for which sex was not recorded), 15 (3.2%; 95% confidence limit [CI] 1.7% to 5.1%) were IHC positive, 11 in both obex and retropharyngeal lymph node samples and 4 from lymph nodes only. We inferred that deer that were only lymph node positive were in the earlier states of infection (1). Estimated prevalence varied spatially within the surveillance area. A cluster of higher than expected prevalence was detected in the north-central region of the sampling area (prevalence 9.4%; 95% CI 5.0% to 16.0%; p=0.003; n=127) (Figure).

Prevalence did not vary by sex (males: 3.4%, 95% CI 0.1% to 9.7%, n=87; females: 3.1%, 95% CI 1.6% to 5.3%, n=386; male vs. female OR 1.1, 95% CI 0.56 to 2.19), a pattern consistent with Mule Deer sampled in Colorado and Wyoming (4). Increasing prevalence with age was suggested, although we could not distinguish whether the OR differed from 1 (OR 1.13, 95% CI 0.93 to 1.39). We had a small sample (n=32) of older animals (>5 years of age), which weakened our ability to detect an increase in prevalence with age statistically. Miller et al. (4) found that CWD prevalence increased with age in male Mule Deer and then abruptly declined in older age classes. We did not have a sufficient sample size to evaluate a sex difference in prevalence by age.

The known range of CWD was extended by its detection in Wisconsin, which is the first report of the disease east of the Mississippi River. Although we do not know how the free-ranging deer population of Wisconsin became affected by CWD, the most commonly suggested hypothesis is that CWD in Wisconsin may have emerged through importing of an affected cervid. The current enzootic of CWD in free-ranging deer and elk is paralleled by an enzootic in the captive cervid industry, and the relationship between CWD-affected elk farms and recent (2000–2002) diagnoses of CWD in free-ranging deer in Nebraska, South Dakota, and Saskatchewan remains under investigation (1). Elk were imported to Wisconsin from CWD-affected herds in Colorado during the 1990s, and recently (September and October 2002) captive White-tailed Deer were found to be positive on two separate farms in central and southern Wisconsin (10). Furthermore, during epidemiologic investigations of these positive farms, WDNR discovered that deer had escaped in March 2002 from one of these farms, one of which was later shot and found to be CWD positive (9). We stress that these positive captive deer are likely not the source of CWD in this free-ranging White-tailed Deer outbreak because of the captive deer’s distance from the area where the CWD-positive free-ranging deer are (approximately 130 km). No direct evidence exists that CWD came to Wisconsin by the captive cervid industry. However, further investigation on possible links between CWD cases in captive and free-ranging cervids in Wisconsin is ongoing.

Conclusions The state of Wisconsin is undertaking an integrated research, surveillance, and management program to determine the distribution of CWD in the Wisconsin free-ranging deer population and eventually eliminating the disease from the known affected area of south-central Wisconsin (10,11). As of March 2003, a total of 39,636 deer had been sampled statewide for CWD as part of this surveillance and management program (data are available from: URL: Computer simulation of CWD dynamics in western cervid populations (12) indicated that CWD could severely reduce deer numbers. Disease transmission may occur at a greater rate and consequently have a larger impact on the population in the eastern United States, where White-tailed Deer densities are typically an order of magnitude larger than western deer and elk populations (e.g., deer densities in the CWD-affected area are estimated to be currently >20 deer per km2) (WDNR, unpub. data). Deer and deer-related activities, such as hunting, wildlife viewing, and other social factors, are an important component of the Wisconsin culture and economy (approximately $1 billion/year) (13), prompting an aggressive research and management strategy to combat CWD in Wisconsin’s free-ranging deer population.



Wednesday, September 03, 2008 Accelerated High Fidelity Prion Amplification Within and Across Prion Species Barriers



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