Key points about chronic wasting disease (CWD) PA veterinarians should know

Posted: December 7, 2012

A fact sheet with answers to the top questions about CWD and updated information about two positive cases found this fall in Pennsylvania. CWD is a chronic degenerative neurological disease affecting the central nervous system of cervids.

By Dave Wolfgang, Penn State Extension Veterinarian

Background

Chronic wasting disease or CWD is a chronic, degenerative neurological disease affecting the central nervous system of cervids. CWD was first diagnosed as a prion disease in 1978 in Colorado. The first mule deer with signs compatible with CWD were recorded in 1967.

CWD belongs to a family of diseases known as transmissible spongiform encephalopathies (TSE's). Chronic wasting disease, scrapie, transmissible mink encephalopathy, and variant Cruetzfeldt- Jakob disease (vCJD) are all members of the TSE family.

To date, there has never been a human disease case associated with CWD.

CWD is not a contagious disease that spreads naturally between animals.

The infectious agent is introduced when CWD is ingested from an environmental reservoir or vertically transferred to offspring. CWD affects the four major antlered species in the US: Whitetail deer, mule deer, elk, and moose.

The prion is most concentrated in the brain and large nerve trunks. However, affected animals can shed the prion in saliva, blood, and to a lesser extend in other bodily fluids such as urine and feces. It is believed that saliva and ingestion of the prion is the major route for the disease to spread between susceptible animals. There is no treatment and infected cervids die.

The incubation period typically ranges from 1 to 3 years. CWD-affected animals gradually lose weight, muscle mass, strength and coordination. Following the onset of clinical signs, the infected animal's condition deteriorates until it dies or is destroyed. Deer as young as 8-12 months can shed the prion, but the highest prevalence for identifying infected animals by age is 3-5 years.

The prion is extremely resistant to degradation and is not destroyed by common disinfectants or cooking. The prion has been found to bind to certain minerals in soil and may remain infective in some circumstances for decades. Some clays are especially good at holding the prion and may actually increase the infectivity of the prion. This is one reason to strongly advocate against providing salt blocks, protein blocks, or other nutrient/feeding strategies that congregate deer or cause them to lick/chew at ground. Feeding plots and well maintained forest land that promote browsing are considered much safer.

Recent Cases in PA and Neighboring States

In the last few months 2 positive cases associated with one deer farm in PA have been identified as infected with CWD. The other animals on that farm were tested and found to be negative for CWD.

In PA, the PA Game Commission (PGC) controls the wild deer population and the PA Department of Agriculture (PDA) controls the deer population behind fences.

PDA has had a surveillance program for many years which encourages deer farmers to submit to the diagnostic laboratory a brain sample from each animal that died on the farm. A positive result invokes an immediate premise quarantine. Tracebacks and traceforwards are instituted to identify all potentially infected cohorts.

PGC has instituted a Deer Management Area (DMA) around the site in Adams County and the DMA extends into York County. It is hoped that all deer harvested in the DMA area were or will be tested.

High risk materials in the DMA were collected and were/will be decontaminated via alkaline digestion.

In 2005 CWD was diagnosed in NY State. That outbreak was associated with one site and following a control and elimination period, surveillance and monitoring over the past few years has revealed zero new cases.

In 2005 WV identified several cases of CWD in free ranging deer. Hampshire County is just south of Bedford Co., PA. That outbreak is ongoing.

In 2010 VA and in 2011 MD each indentified a free ranging deer with CWD. In both of those cases the deer identified was found close to the WV outbreak area.

Consumer Safety Issues

There has never been a case of human disease associated with the consumption of venison.

CDC policy recommendation is: do not consume meat from known positive animals

If there is some concern about the deer harvested, the carcass should be de-boned and only muscle cuts of meat used. There is no known food safety reason not to consume venison if prepared properly.

The brain, spinal cord and spleen are higher risk tissues if prions are suspected. These portions of the carcass should be discarded in a licensed landfill or incinerated or decontaminated by alkaline digestion.

In PA hunters or interested citizens can submit samples for CWD testing to the PA Animal Diagnostic Lab System at a cost for service fee. It is important that the samples are collected properly. Please contact the laboratory directly for instructions prior to submitting samples- 717-787-8808 pvl@pa.gov or via the PDA website.