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From: TSS (
Subject: Re: CWD in S. Colorado - oh, the mystery of it!
Date: February 4, 2005 at 9:54 am PST

In Reply to: CWD in S. Colorado - oh, the mystery of it! posted by nina bossert on February 4, 2005 at 7:50 am:

Chronic Wasting Disease and Potential Transmission to Humans

Ermias D. Belay,*Comments Ryan A. Maddox,* Elizabeth S. Williams,† Michael W. Miller,‡ Pierluigi Gambetti,§ and Lawrence B. Schonberger*
*Centers for Disease Control and Prevention, Atlanta, Georgia, USA; †University of Wyoming, Laramie, Wyoming, USA; ‡Colorado Division of Wildlife, Fort Collins, Colorado, USA; and §Case Western Reserve University, Cleveland, Ohio, USA

Suggested citation for this article: Belay ED, Maddox RA, Williams ES, Miller MW, Gambetti P, Schonberger LB. Chronic wasting disease and potential transmission to humans. Emerg Infect Dis [serial on the Internet]. 2004 Jun [date cited]. Available from:

Chronic wasting disease (CWD) of deer and elk is endemic in a tri-corner area of Colorado, Wyoming, and Nebraska, and new foci of CWD have been detected in other parts of the United States. Although detection in some areas may be related to increased surveillance, introduction of CWD due to translocation or natural migration of animals may account for some new foci of infection. Increasing spread of CWD has raised concerns about the potential for increasing human exposure to the CWD agent. The foodborne transmission of bovine spongiform encephalopathy to humans indicates that the species barrier may not completely protect humans from animal prion diseases. Conversion of human prion protein by CWD-associated prions has been demonstrated in an in vitro cell-free experiment, but limited investigations have not identified strong evidence for CWD transmission to humans. More epidemiologic and laboratory studies are needed to monitor the possibility of such transmissions.


Risk for Transmission to Humans
Epidemiologic Studies

The increasing detection of CWD in a wider geographic area and the presumed foodborne transmission of BSE to humans, resulting in cases of vCJD, have raised concerns about the possible zoonotic transmission of CWD (32). In the late 1990s, such concerns were heightened by the occurrence of CJD among three patients 30 years of age who were deer hunters or ate deer and elk meat harvested by family members (Table 2). However, epidemiologic and laboratory investigations of these case-patients indicated no strong evidence for a causal link between CWD and their CJD illness (33). None of the patients were reported to have hunted deer or eaten deer meat harvested in the CWD-endemic areas of Colorado and Wyoming. Such a history in unusually young CJD patients, if present, would have supported a causal link with CWD. Moreover, the testing of brain tissues from >1,000 deer and elk harvested from areas where the patients hunted or their venison originated did not show any evidence of CWD (33). In addition, the lack of homogeneity in the clinicopathologic manifestation and codon 129 of the prion protein gene among the three patients suggested that their illnesses could not be explained by exposure to the same prion strain. In vCJD, homogeneity of the genotype at codon 129 and the clinical and pathologic phenotype were attributed to the patients' exposure to the same prion strain, the agent of BSE.

In 2001, the case of a 25-year-old man who reportedly died of a prion disease after an illness lasting ≈22 months was investigated (Table 2). Although this man had hunted deer only rarely, his grandfather hunted deer and elk throughout much of the 1980s and 1990s and regularly shared the venison with the case-patient's family. The grandfather primarily hunted in southeastern Wyoming, around the known CWD-endemic area. The case-patient's illness began with a seizure and progressed to fatigue, poor concentration, and depression. Memory loss, ataxia, speech abnormalities, combative behavior, and recurrent seizures also developed. Histopathologic, immunohistochemical, and Western blot testing of brain autopsy samples confirmed a prion disease diagnosis. Analysis of the prion protein gene indicated a P102L mutation coupled with valine at the polymorphic codon 129 in the mutant allele, confirming a diagnosis of Gerstmann-Sträussler-Scheinker syndrome (GSS). This case-patient was unusually young even for a person with a GSS P102L mutation. It remains unknown whether the possible exposure of the case-patient to CWD-infected venison potentially contributed to the early onset of his prion disease.

In 2001, two additional CJD patients 26 and 28 years of age were reported from a single state (Table 2) (34). The patients grew up in adjacent counties and had illness onset within several months of each other. As a result of this fact and their unusually young age, a possible environmental source of infection, including exposure to CWD-infected venison, was considered. One of the patients died after an illness lasting 5–6 months that was characterized by progressive aphasia, memory loss, social withdrawal, vision disturbances, and seizure activity leading to status epilepticus and induced coma. Histopathologic, immunohistochemical, and Western blot testing of brain biopsy and autopsy samples confirmed a CJD diagnosis. The patient's disease phenotype corresponded to the MM2 sporadic CJD subtype reported by Parchi et al. (35). This patient did not hunt, and family members provided no history of regularly eating venison. The patient may have occasionally eaten venison originating from the Upper Peninsula of Michigan while away from home during his college years. However, ongoing surveillance has not detected CWD in Michigan deer (36).

The second patient died from an illness lasting <16 months. The patient's illness began with behavioral changes, including unusual outbursts of anger and depression. Confusion, memory loss, gait disturbances, incontinence, headaches, and photophobia also developed. Western blot analysis of frozen brain biopsy tissue confirmed a prion disease diagnosis. Immunohistochemical analysis of brain tissue obtained after the patient's death showed prion deposition consistent with GSS. A prion protein gene analysis could not be performed because appropriate samples were lacking. However, prion protein gene analysis of a blood sample from one of the patient's parents indicated a GSS P102L mutation. The patient did not hunt but may have eaten venison from Michigan once when he was 1–2 years old. The GSS diagnosis greatly reduced the likelihood that the two patients reported from adjacent counties had disease with a common origin.

Recently, rare neurologic disorders resulting in the deaths of three men who participated in "wild game feasts" in a cabin owned by one of the decedents created concern about the possible relationship of their illnesses with CWD (Table 2) (37). Two of the patients reportedly died of CJD, and the third died from Pick's disease. More than 50 persons were identified as possibly participating in these feasts; the three patients were the only participants reported to have died of a degenerative neurologic disorder. Reanalysis of autopsy brain tissues from the three patients at the National Prion Disease Pathology Surveillance Center indicated that two of them had no evidence of a prion disease by immunohistochemical analysis. CJD was confirmed in the third patient, who had clinicopathologic, codon 129, and prion characteristics similar to the most common sporadic CJD subtype (MM1/MV1) (35). This patient participated in the feasts only once, perhaps in the mid-1980s. In addition, the investigation found no evidence that the deer and elk meat served during the feasts originated from the known CWD-endemic areas of Colorado and Wyoming.

In 2003, CJD in two deer and elk hunters (54 and 66 years of age) was reported (38). The report implied that the patients had striking neuropathologic similarities and that their illness may represent a new entity in the spectrum of prion diseases. A third patient (63 years of age), who was also purported to have been a big game hunter, was subsequently reported from the same area. However, none of the three patients were reported to have eaten venison from the CWD-endemic areas of the western United States. The 66-year-old patient hunted most of his life in Washington State. Although information about the 54-year-old patient was limited, there was no evidence that he hunted in CWD-endemic areas. The third patient was not a hunter but ate venison harvested from Pennsylvania and Washington. The neuropathologic changes, Western blot profile, and genotype at codon 129 of the three patients each fit the MM1, VV1, or VV2 sporadic CJD subtype, indicating absence of phenotypic similarity among the cases or atypical neuropathologic features (35).

To date, only two nonfamilial CJD cases with a positive history of exposure to venison obtained from the known CWD-endemic areas have been reported. One of the patients was a 61-year-old woman who grew up in an area where this disease is known to be endemic, and she ate venison harvested locally. She died in 2000, and analysis of autopsy brain specimens confirmed that the patient's CJD phenotype fit the MM1 subtype, with no atypical neuropathologic features. The second patient was a 66-year-old man who was reported to have eaten venison from two deer harvested in a CWD-endemic area. Both deer tested negative for CWD, and the patient's illness was consistent with the MM1 CJD phenotype.

Despite the decades-long endemicity of CWD in Colorado and Wyoming, the incidence of CJD and the age distribution of CJD case-patients in these two states are similar to those seen in other parts of the United States. From 1979 to 2000, 67 CJD cases from Colorado and 7 from Wyoming were reported to the national multiple cause-of-death database. The average annual age-adjusted CJD death rate was 1.2 per million persons in Colorado and 0.8 in Wyoming. The proportion of CJD patients who died before age 55 in Colorado (13.4%) was similar to that of the national (10.2%). The only CJD case-patient <30 years of age in Colorado had iatrogenic CJD linked to receipt of human growth hormone injections. CJD was not reported in persons <55 years of age in Wyoming during the 22-year surveillance period.


The lack of evidence of a link between CWD transmission and unusual cases of CJD, despite several epidemiologic investigations, and the absence of an increase in CJD incidence in Colorado and Wyoming suggest that the risk, if any, of transmission of CWD to humans is low. Although the in vitro studies indicating inefficient conversion of human prion protein by CWD-associated prions raise the possibility of low-level transmission of CWD to humans, no human cases of prion disease with strong evidence of a link with CWD have been identified. However, the transmission of BSE to humans and the resulting vCJD indicate that, provided sufficient exposure, the species barrier may not completely protect humans from animal prion diseases. Because CWD has occurred in a limited geographic area for decades, an adequate number of people may not have been exposed to the CWD agent to result in a clinically recognizable human disease. The level and frequency of human exposure to the CWD agent may increase with the spread of CWD in the United States. Because the number of studies seeking evidence for CWD transmission to humans is limited, more epidemiologic and laboratory studies should be conducted to monitor the possibility of such transmissions. Studies involving transgenic mice expressing human and cervid prion protein are in progress to further assess the potential for the CWD agent to cause human disease. Epidemiologic studies have also been initiated to identify human cases of prion disease among persons with an increased risk for exposure to potentially CWD-infected deer or elk meat (47). If such cases are identified, laboratory data showing similarities of the etiologic agent to that of the CWD agent would strengthen the conclusion for a causal link. Surveillance for human prion diseases, particularly in areas where CWD has been detected, remains important to effectively monitor the possible transmission of CWD to humans. Because of the long incubation period associated with prion diseases, convincing negative results from epidemiologic and experimental laboratory studies would likely require years of follow-up. In the meantime, to minimize the risk for exposure to the CWD agent, hunters should consult with their state wildlife agencies to identify areas where CWD occurs and continue to follow advice provided by public health and wildlife agencies. Hunters should avoid eating meat from deer and elk that look sick or test positive for CWD. They should wear gloves when field-dressing carcasses, bone-out the meat from the animal, and minimize handling of brain and spinal cord tissues. As a precaution, hunters should avoid eating deer and elk tissues known to harbor the CWD agent (e.g., brain, spinal cord, eyes, spleen, tonsils, lymph nodes) from areas where CWD has been identified.

SEAC Statement
18th January 2005
Position statement - Chronic wasting disease in UK deer


1. The Food Standards Agency asked SEAC to consider the possible public and animal health implications of chronic wasting disease (CWD), in particular the level of risk posed to consumers of meat from infected animals. The committee also considered the possibility that BSE may be present in UK deer.


2. CWD has emerged as an endemic transmissible spongiform encephalopathy (TSE) in certain captive and free-ranging species of cervid (deer) in some areas of North America. The disease is characterised by weight loss and behavioural changes in infected animals, usually over a period of weeks or months leading to death. CWD has not been found in the UK or elsewhere in Europe. No definitive or suspected cases of transmission of CWD to humans have been reported.

3. SEAC considered a review of the published, and some unpublished, research on CWD, together with surveillance data on TSEs in European cervids and information on UK cervid populations (1).


4. The origins of CWD are unknown. On the basis of epidemiological data, it is highly improbable that CWD originated from the recycling of mammalian protein in processed feed. It has been suggested that CWD may have arisen from transmission and adaptation of scrapie from sheep to cervids, as a result of a spontaneous change of endogenous prion protein (PrP) to an abnormal disease-associated form, or from an unknown source.

5. Data supporting any of these possible origins of CWD are either absent or equivocal. Although CWD could have originated from scrapie, the differing properties of the two prion diseases in strain typing bioassays, whilst limited, do not support this hypothesis. Evidence for multiple strains of CWD is equivocal. It seems most likely that CWD arose from a spontaneous change of endogenous PrP resulting in a disease-associated and laterally-transmissible form of PrP, although direct data to support this hypothesis are lacking.

Host range

6. The known natural hosts for CWD are mule deer (Odocoileus hemionus hemionus), black-tailed deer (Odocoileus hemionus columbianus), white-tailed deer (Odocoileus virginianus) and Rocky Mountain elk (Cervus elaphus nelsoni). The prevalence and geographical distribution of CWD in these species appears to be increasing in North America in a manner which is unlikely to be due simply to increased surveillance.

7. There are no direct data relating to the transmissibility of CWD to UK cervid species. However, comparison of a limited number of PrP codons indicates some homology in the endogenous PrP gene of European and North American cervid species. Thus, the possibility that UK cervids may be susceptible to CWD cannot be excluded, in particular red deer (Cervus elaphus elaphus) which are closely related to elk.

8. There is no evidence to suggest that CWD is present in UK cervids. However, because surveillance in the UK is very limited, a low level prevalence of CWD cannot be ruled out. The committee endorsed the opinion of the European Food Safety Authority on CWD surveillance in the European Union (2004) .

9. Transmission studies using parenteral routes of administration to cattle, sheep and a single goat, together with data from in vitro PrP conversion experiments, suggest that a significant barrier to CWD transmission to these species may exist. No transmission has been evident so far in an on-going oral transmission study in cattle after six years. Furthermore, no signs of infection have been observed from monitoring of cattle co-habiting areas with infected cervids, or in cattle, sheep or goats in close contact with infected cervids in research facilities. Thus, although the data are limited, there is currently no evidence to suggest that CWD can be transmitted naturally to cows, sheep or goats, and it is likely that there is a strong species barrier to such transmission.

Routes of transmission

10. Epidemiological data indicate that lateral transmission between infected and susceptible cervids occurring naturally is sufficiently effective to maintain epidemics in both captive and free-living populations. There is good evidence from studies of cervids inhabiting paddocks previously inhabited by infected animals or contaminated with infected carcases, that CWD can be transmitted laterally between animals via the environment. The precise mechanism of transmission is unclear. It is possible that the infectious agent is shed in the saliva, faeces or urine or as a result of decomposition of infected carcases and transferred to other cervids grazing the contaminated areas. It is also possible that some maternal transmission occurs.

11. There have also been suggestions that the lateral transmission of CWD may be influenced by environmental factors.


12. Information on the pathogenesis of CWD is limited. The data show that, following oral challenge, PrPCWD is first detected in the oral and gut-associated lymphoid tissues before spreading more widely within the lymphoid system and then to the brain. Involvement of the retropharyngeal lymph nodes or tonsils in the pathogenesis may not occur in some elk. At the microscopic level, the nature and distribution of the tissue lesions are similar to those found for scrapie. The available data suggest the pathogenesis of CWD is similar to scrapie.

BSE in UK deer

13. Both captive and free-ranging cervids in the UK may have been exposed to contaminated feed prior to the reinforced mammalian meat and bone meal ban instituted in 1996. A study to look at the potential susceptibility of red deer to BSE has shown no signs of transmission of the disease by the oral route, but it is at a very preliminary stage. Although a theoretical possibility exists, there is no evidence from the very limited surveillance data to suggest that BSE is present in the UK cervid population.

Human health implications

14. Epidemiological data on possible CWD infection of humans are very limited. The possibility that clinical symptoms of CWD in humans differ from those of Creutzfeldt-Jakob Disease (CJD) cannot be excluded. There is no significant difference between the prevalence of CJD in CWD endemic areas and other areas of the world. However, because CJD surveillance in the USA is relatively recent, not all CJD cases may have been identified. Additionally, detection of a small increase in prevalence of such a rare disease is very difficult. Investigation of six cases of prion disease in young people (< 30 years of age) in the USA found no definite causal link with consumption of venison from known CWD endemic areas. The disease characteristics in these cases were indistinguishable from sporadic CJD or Gerstmann-Sträussler-Scheinker syndrome. Likewise, in a study of three hunters (> 54 years of age) diagnosed with sporadic CJD, no link with consumption of venison from CWD endemic areas was found. No causal link was found in an investigation of three men with neurological illnesses who were known to partake in “wild game feasts”. Only one of these subjects was found to have a prion disease and this was also indistinguishable from sporadic CJD.

15. Preliminary results from transmission experiments in transgenic mice expressing human PrP suggest the presence of a significant species barrier to transmission of CWD to humans. However, these findings must be interpreted with caution as they may not accurately predict the human situation. Data from in vitro experiments on conversion of human PrP by disease-associated forms of PrP, including PrPCWD, are equivocal.

16. The committee concluded there is no evidence of transmission of CWD to humans from consumption of venison, and that there may be significant barriers to transmission. Nevertheless, as the data are extremely limited a risk cannot be ruled out should CWD enter UK herds.


17. There is no evidence that CWD (or BSE) is present in the UK cervid population. However, because only limited surveillance is conducted in the cervid population, a low level prevalence of CWD cannot be ruled out. It is recommended that further surveillance of TSEs in UK cervids is conducted.

18. There is no evidence of transmission of CWD to humans from consumption of meat from infected cervids. Although epidemiological and experimental data on potential transmission of CWD are extremely limited, they suggest that there may be a significant species barrier. It would be helpful if further studies were available assessing the potential species barrier for transmission to humans.

19. Although limited, there is no evidence CWD can be transmitted to cattle, sheep or goats by natural means.

20. In summary, it appears that CWD currently poses relatively little risk to human health, or to the health of cattle, sheep or goats in the UK. Nevertheless, as a risk cannot be excluded a watching brief should be maintained.

January 2005


Chronic Wasting Disease in UK deer

Alan Harvey (FSA).Wildlife Information Network.


Annex 1 (pdf)

Annex 2 (pdf):

Annex 3 (incl. appendices) (pdf)

Annex 4 (pdf)

Annex 5 (pdf):

ALL of these false reassurances we have heard time and time again, and ALL have been proven wrong.

AS with the BSE TO HUMANS AND BSE to GOAT. IT was always it never happend under natural conditions, just in the lab, so not to worry. NOW WE HAVE TO WORRY;


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