Transmission of CWD Among Cervids
The routes by which CWD can be transmitted are still under investigation. The CWD prion is shed through bodily fluids of infected animals (e.g. saliva, urine and feces) and can bind to soils and other materials. The major routes of transmission are likely through ingestion or inhalation of the prion from live or dead infected animals and through contact with contaminated materials, including contaminated soils.
The CWD prion is very hardy and is shed for months to years in bodily fluids well before the animal appears to be ill. It can remain infectious in the environment for at least two years and probably much longer.
The natural movement of wild cervid populations infected with CWD will spread the disease along the habitats they frequent, such as river valleys.
Risk to Other Animals
To date, there is no direct evidence, including studies conducted in known affected areas such as Wyoming and Colorado, that domestic pets and traditional livestock have become infected with CWD. This includes dogs, cats and cattle. Other animals have been infected with CWD in research studies. Further studies are required to better understand and assess the risk. Due to these unknown risks, carcasses of cervids positive for CWD should be properly disposed of through approved methods of disposal and not left accessible to other animals.
Changes Seen in Cervids with CWD
Cervids appear healthy for the first year or two of infection, but behavioural changes occur as the abnormal prion accumulates in the nervous system. Studies indicate that infected animals are more susceptible to being killed by vehicles, predators and hunters. In the final stages of the disease, animals show loss of body weight; increased drinking, salivation and urination; separation from the herd and neurological signs such as tremors, wide-based stance, drowsiness and paralysis. Affected animals are also more susceptible to pneumonia. Once clinical signs are evident, death occurs within weeks to months.
Testing Live Animals for CWD
There is currently no reliable, cost-effective, welfare-friendly live animal test. Research is ongoing to identify better live animal tests.
In dead animals, testing requires the sampling of one or more of these tissues: lymph nodes in the throat area, tonsils and brain.
There is no treatment available for animals affected by CWD, nor is there a vaccine to prevent this disease.
The Possible Pre-existence of CWD
The studies that have been conducted in Colorado and Wyoming indicate this disease first became established in the 1960s and is a relatively new disease of cervids. Epidemiological evidence in other areas also suggests CWD is a newly introduced disease to those regions.
Other sources of information include: