This post was originally published at Mind the Science Gap on Nov. 29, 2012.
In early October a deer tested positive for Chronic Wasting Disease for the first time in Pennsylvania. The positive result, which was found in a farm herd, resulted in the quarantine of all the deer on the property. Earlier this month, a deer escaped the quarantine and was running free in Pennsylvania. Two days ago that deer was shot and killed to prevent further disease transmission. That doe is still undergoing testing to determine if she was infected. As a result of all of these events unfolding, Pennsylvania has swiftly put plans into action. Chronic Wasting Disease (CWD) is nearly impossible to eradicate once it establishes itself in a population, and in order to save PA’s deer herds, they needed to act fast.
Chronic Wasting Disease is endemic (established in wild populations) in Colorado and Wyoming. It has also been reported in wild herds in Illinois, Kansas, Maryland, Minnesota, Missouri, Nebraska, New Mexico, New York, North Dakota, South Dakota, Texas, Utah, Virginia, West Virginia, and Wisconsin. CWD has been found in captive herds in other states, such as Iowa. States with no confirmed cases often have CWD task forces and policies to prevent introduction of the pathogen. For example, Washington recently began requiring hunters returning from CWD-endemic areas to undergo testing and processing to remove infectious material.
CWD is a type of transmissible spongiform encephalopathy (TSE), a group of disease that includes Bovine Spongiform Encephalopathy (Mad Cow), Scrapie (a disease commonly found in sheep), Creutzfeldt-Jacob disease (a neurodegenerative disease in humans), and Fatal familial insomnia (a disease where protein misfolding results in insomnia which progresses to delusions and eventually death). TSEs are all caused by a pathogenic organism known as a prion. Prions are rather unique in that they are not a virus or bacteria, but a protein with an abnormal structure. These prions can be infectious and transmissible (like CWD and Mad Cow) or inherited (like the fatal insomnia).
The precise transmission method is unknown. It is possibly transmitted either through direct contact or through prion – contaminated feed and water. The latter is the most disturbing in terms of controlling the disease. The prion is environmentally stable, meaning that it can infect other animals after being in the soil for years.
CWD in Deer
Visible signs in deer (and related animals) include:
- Ataxia (lack of coordination)
- Low body condition (animal would appear underweight or unusually skinny)
- Walking in circles or repetitive patterns
- Standing with a wide stance (legs far apart)
- Small head tremors
- Somnolence (drowsiness)
- Carrying the head low to the ground
- Excessive drinking, urination, salivation, and drooling
- Wet hair around the chin and neck (caused by the salivation/drooling)
There is no treatment or vaccine. Once acquired, the disease is fatal.
Can Humans Get Sick From Infected Deer?
So far, no disease in humans has been definitively linked to eating meat from a CWD infected animal. However, the CDC recommends that people not eat any meat from an infected animal or an animal which looked ill.
Mad cow disease (which is in the same group as CWD) can be transmitted from food animals to humans, so researchers are continuing to conduct research to determine if CWD is a danger to humans. Study results are mixed. A 2004 study (Belay et.al.) noted that human prion proteins (which are naturally occurring in healthy people) could be damaged by a CWD prion, showing a possible avenue for disease transmission. The article also notes that cases of neurodegenerative diseases have been found in people who have eaten venison, but these cases were either ultimately caused by another prion disease or were not prion related. Ultimately, the authors pointed out that these studies were not conclusive and more research was necessary. A 2010 article (Holman et.al.) noted that while CWD is endemic in the western states, this region had one of the lowest rates of human prion disease.
Take home message – there is no conclusive evidence that CWD causes disease in humans, however scientists are being cautious and continuing to carry out research.
What’s being done?
Check points are being run in Pennsylvania counties where the positive deer had lived (Adams County and York County). The check points take a sample of spinal material and lymph nodes to test for CWD. In instances where the hunter is not planning to mount the deer’s head as a trophy, the entire head is cut off and bagged for sampling. Butchers are also submitting samples to the state. Hunters should get the result of these tests within about six weeks.
Neighboring states are also taking action. Virginia has banned the transport of whole carcasses and certain parts of deer taken in PA into the state. The meat must be butchered, deboned, and wrapped before transport from PA to VA, and spinal cord, heads, and antlers with tissue attached may not be brought into the state. CWD has been found in wild populations in Virginia, but this was in one county in the northern part of the state. By taking these precautions the state is protecting deer herds in the remaining vast majority of the state.
What can hunters do?
Attend any information sessions that may be held in your area. The CDC ran an information session recently in Central PA in order to educate hunters about what was happening, and address any concerns they may have. Consult state wildlife officials to see if testing is recommended.
Penn State veterinarian and PA CWD Task Force Member Dr. David Wolfgang has proposed that salt licks should be banned to prevent potential transmission. Not only do deer congregate around salt licks and exchange fluids (the human equivalent would be sharing a lollipop with your family, closest friends, and anyone else in the neighborhood who happened to wander by), but the salts that leech into the ground cause the deer to continue to bite at the ground for years after the lick is gone. Removing salt licks would remove a situation where one infected deer could infect every deer in the area.
In the field, hunters should take the following precautions:
- Don’t take deer that appear sick, thin, or uncoordinated (see symptoms above)
- Wear gloves while field dressing deer
- Avoid handling the brain, spinal cord, eyes, spleen, and lymph nodes
- Bone-out the meat, or have a butcher do it for you
As always, if you have eaten venison and you are feeling ill, consult your physician. Hope everyone has a safe, happy, successful hunting season!