Introduction to CWD;
Chronic Wasting Disease (CWD) is a fatal neuro-degenerative, transmissible spongiform encephalopathy (TSE) of the family Cervidae (Hamir, et.al., 2006). The family Cervidae includes mule deer, Odocolileus hemionus, white-tailed deer, Odocolileus virginianus, Rocky Mountain elk, Cervus elaphus nelsoni, and moose, Alces alces shirasi, among others (Sigurdon & Aguzzi, 2007). CWD is a prion disease, meaning it is a protein caused infection, that occurs naturally in the deer family (Song & Lawson, 2009). This protein is suspected to be an abnormal isoform (PrPSc) of the naturally occurring host prion protein (PrPC) (Blanchong, et. Al., 2009). Bovine spongiform encephalopathy (BSE), mad cow disease, is a similar prion effecting cattle as CWD affects Cervidae. Although, scientists are not sure of transmission route it is suspected that CWD is transmissible and infectious through direct contact with infected individuals or through environmental contamination (Song & Lawson, 2009). Tests have been performed showing susceptibility of altered mice to oral transmission, mimicking the suspected route of entry, and the incubation appears slower but lasts longer with oral infection (Trifilo, et.al., 2007). The approximate time from the initial infection to death is three years.
History of CWD;
The origin of CWD has yet to be determined (Sigurdson & Aguzzi, 2007). The infection was first noted in 1967 at a captive mule deer research facility. In 1978 pathologists recognized the TSE type brain lesions, also that CWD presented as a prion disease by the neuronal perikaryonic vacuoles, the accumulation of aggregated prion protein and prion infectivity in the brain. In the late 1970s and early 1980s the infection was seen in collections form Wyoming and Canada. Wild elk and deer on the eastern slopes of the Rocky Mountains presented with the disease in 1981. The disease patterned out from the mountains through the river valleys in Colorado and Wyoming. CWD was first noted in farmed elk from Canada in 1996. Ranched elk have found to be infected in several states and recently in South Korea.
Spread of CWD;
Estimates put the population of cervids in North America well over 30 million. The spread of CWD is suspected to be mainly from the transport of captive cervids and subsequent contact with local wild heard (Sigurdson & Aguzzi, 2007). In 2000 it was believed that the epidemic was contained within a 40,000 km2 of northern Colorado and southern Wyoming with a few isolated cases in Canada. However; recently cases have developed in twelve other states spreading east to New York and West Virginia as well as two Canadian provinces. The dispersal pattern of CWD is atypical with concentrated hot spots instead of spread contiguously. Due to the large expanse of cervid range in North America disease control is exceptionally difficult. Poor understanding of the routes of entry for CWD exacerbates the difficulties of...