Chronic wasting disease (CWD) was first described in captive deer more
than 35 years ago near Fort Collins, CO. Since 1998, CWD has spread
to wild and domestic animal populations in several states and provinces.
It belongs to the family of diseases known as transmissible spongiform
encephalopathies (TSEs), so called because these diseases cause microscopic
holes in brain tissue giving it a sponge-like appearance. TSEs include
diseases such as scrapie in sheep, bovine spongiform encephalopathy
(BSE) in cattle (aka Mad Cow Disease), chronic wasting disease in cervids
and Creutzfeldt-Jakob disease in humans. These diseases affect the central
nervous system and result in lesions in the brain. The causative infectious
agents are modified, rogue proteins called prions.
CWD infects elk, white-tailed deer, and mule deer, but is not known
to naturally infect other species of wildlife (including predators and
scavengers), livestock, or humans. There is no treatment for CWD and
it is typically fatal. The mode of transmission of CWD is not well understood.
Transmission from infected animals to uninfected animals via nose to
nose contact, saliva, urine and feces are considered the likely routes.
Transmission may also occur through environmental contamination. Clinical
signs of the disease are not unique and are similar to those for other
conditions, such as malnutrition. Infected cervids may not show clinical
signs of CWD for several years. Currently, diagnosis of CWD requires
testing by immunohistochemical staining (IHC) or ELISA (enzyme-linked
immunosorbent assay) of a specific portion of the brain and spinal cord.
Also, a tonsil biopsy technique for live mule deer and white-tailed
deer, but not elk, has been developed.