Disease Information (12) (Provided by Prion Molecular Biology Lab, Foreign Animal Diseases Division) ( 07/05/11 ) | |||||
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Part | Charger | leeyh | date | 07/05/11 | |
Chronic Wasting Disease
1. Definition / Geographical distribution
Chronic wasting disease(CWD) is a transmissible spongiform encephalopathy (TSE) that occurs in native North American deer and elk. The deer species that have been affected are mule deer, black-tailed deer and white-tailed deer. CWD was first observed in elk and deer in the 1960s in research facilities in the USA. CWD has been found endemically in wild mule deer and elk in north eastern Colorado and south eastern Wyoming and it has been estimated that CWD has been occurring in this area for greater than 30 years. Its origin is unknown.
The disease was long thought to be limited in the wild to a relatively small endemic area in northeastern Colorado, southeastern Wyoming, and southwestern Nebraska, but it has recently been found new areas of Colorado and Nebraska, as well as in wild deer in New Mexico, South Dakota, Wiskonsin, and Saskatchewan.
2. Host range/Transmission
CWD has been found in white tail deer, elk, mule deer and black tail deer. Clinically diseased animals could be infectious to other animals for a period of up to 18 months prior to their death. The means of transmission of CWD is unknown but spread of CWD is believed to occur primarily by animal to animal contact. The spread can also occur when a susceptible animal is exposed to the agent present in its environment. This later situation exists on promises with herds infected with CWD for an extended period of time.
Experimental and circumstantial evidence suggests infected deer and elk probably laterally transmit the disease through animal to animal contact and/or contamination of feed or water sources with saliva, urine, feces and possibly placental material. The exact mode of CWD transmission in nature, however, remains unknown. There is no field evidence to show that CWD has been naturally transmitted to other species besides cervids. At present, the risk of transmission of CWD to other animal species or to humans is unknown.
3. Clinical signs/Incubation period
The maximum incubation period is 36 months, with an average incubation of 22 months. The diagnosis of CWD should be considered in cervids over 16 months of age having a compatible contact history, and displaying any of the following signs: excess salivation, unusual behaviour (including decreased interactions with other animals, listlessness, depression, aggressive or violent behaviour), neurological signs (including paralysis, difficulty in swallowing, head pressing, ataxia, polydipsia / polyuria, proprioception deficiencies, or recumbency), weight loss, retention of winter hair coat, and pneumonia. Signs usually last for weeks or months before the animal dies; however, some animals may not show clinical signs except for acute pneumonia, or fatal injury.
4. Diagnosis
The diagnosis of CWD is based on microscopic examination of brain tissues. Both histopathologic examination and immunohistochemistry (IHC) are used in routine diagnosis of clinical cases. Western blots and negative stain electron microscopy have also been used to confirm diagnoses. There are no validated live animal tests for diagnosis.
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