CSU Veterinary Diagnostic Laboratories Lablines Vol 2 #2
CHRONIC
WASTING DISEASE IN NORTHEASTERN COLORADO
Terry
Spraker
Chronic Wasting Disease (CWD) is a specific transmissible spongiform
encephalopathy affecting free-ranging and captive mule
deer, white-tailed deer, and elk. This disease was first observed by
biologists with the Colorado Division of Wildlife in captive
mule deer in the late 1960s and was diagnosed as a spongiform encephalopathy
in captive deer and elk in 1978. In 1981, a
free-ranging elk from Rocky Mountain National Park was found with CWD and
the first free-ranging mule deer with CWD was found
northwest of Fort Collins in 1984. Presently, CWD is found in free-ranging
deer and elk in northeastern Colorado and southeastern
Wyoming, and in captive deer and elk at wild animal facilities at Fort
Collins, Colorado, and at Sybille, Wyoming. Recently, several
elk were positively diagnosed with CWD in a game farm in South Dakota.
CWD
is a neurological disease characterized by a spongiform degeneration of the
brain, primarily affecting the thalamus and brain
stem. Clinical signs of CWD are excessive salivation, emaciation or wasting,
behavior changes, and weakness. At necropsy, few
changes besides emaciation, ulcers, and secondary pneumonia are seen. CWD is
believed to be caused by an altered prion protein.
This prion protein is antigenically similar to the prion protein thought to
be the cause of scrapie in domestic sheep and goats.
Over the last several years, the Colorado Division of Wildlife has collected
deer and elk heads from hunted and road-killed animals
throughout Colorado to delineate the regional distribution of CWD in
cervids. We remove the brains from these heads and examine
them both histologically and immunohistochemically to determine
Elk with chronic wasting disease.
(Photo removed - JW)
if
they are affected by CWD. To date, we have examined approximately 3,500
cervids. The prevalence of CWD in deer is highest
(approximately 5%) in a relatively small area bounded by the Wyoming border,
Fort Collins, Rocky Mountain National Park, and
Estes Park. The prevalence of CWD in elk in the same area is less than 1%.
CWD has been diagnosed in deer east of Fort Collins,
but the number of animals found positive in this area is extremely low.
CWD
has been known to occur around the Fort Collins area for over 30 years and
during this time there have been no cases of a
spongiform encephalopathy in cattle here, or anywhere else in the United
States. The few cases of scrapie in domestic sheep from the
Fort Collins area were from sheep recently brought into the state or were
from scrapie- infected flocks and were not associated with
deer or elk. Scrapie has not been linked to any disease in humans, however,
bovine spongiform encephalopathy (mad cow disease)
has been linked to new variant Creutzfeldt-Jacob disease in humans in Great
Britain.
The
only method to diagnose CWD is to examine several specific areas of the
brain histologically and immunohistochemically. The
immunohistochemical stain was developed for diagnosis of scrapie but also
stains the prion protein in deer and elk brains and is
used for confirmation of diagnosis for all cases of CWD.
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