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Deer populations in the United States are affected with a spreading case of chronic wasting disease, a contagious neurological disease. While cases of CWD only affect members of the deer family, health experts are concerned about the possibility of transmission to humans.
The chronic wasting disease is a transmissible spongiform encephalopathy caused by prions that infect the members of the deer family, such as mule deer, elk, moose, and reindeer. Prions are infectious agents made of pure misfolded proteins that cause neurodegenerative disorders in both humans and animals. According to the Centers for Disease Control and Prevention, prions are transmissible and can induce abnormal folding of prion proteins, normal specific cellular proteins, abundant in the brain. The abnormal folding of the proteins leads to neurological symptoms, brain damage, and eventually death.
As of January 2018, at least 22 states including those in the Midwest, Southwest, and some areas on the East Coast of the US have reported cases of CWD. In areas where the disease has established, the infection rate is likely to exceed 10 percent or 1 in 10 deer. Infection rate in local areas is 25 percent or 4 in 10 deer, while some captive deer may have an infection rate of at least 79 percent of 4 in 5 deer. Overall, the CWD occurrence remains low at the national level.
Deer affected by CWD exhibit signs and symptoms of brain damage, such as movement difficulties, weight loss, behavioral changes, decreased interactions with other animals, tremors, and repetitive walking patterns. These symptoms are the reason why the disease has been referred to as the “zombie deer disease.” Symptoms usually manifest after the incubation period of one year.
Deer are not the only animals known with a prion disease. Cows have the bovine spongiform encephalopathy or which is more commonly known as mad cow disease, and this can be fatal. Mad cow disease infects cattle but has been known to be transmissible to humans through consumption of contaminated meat. Determining mad cow disease can be difficult because of the long incubation period from two and a half to five years. Symptoms of mad cow disease include gait abnormalities, behavioral changes, tremors, hyper-responsiveness to specific stimuli, ataxia or involuntary movement of the hind limb, and frenzy. As of February 2015, there were 24 confirmed cases of mad cow disease in North America – 20 in the US and 4 in Canada.
While there are no reports of CWD spreading in human communities, scientists expressed worry that the disease may infect humans soon, as evident with the mad cow disease. In a study by the prion researcher Dr. Stefanie Czub, macaque monkeys have been found to be susceptible to the zombie deer disease. The research team was able to infect the primates that could indicate possible transmission to humans. Since 1996, there have been 231 confirmed cases of vCJD in 12 countries including Italy, Taiwan, Japan, Saudi Arabia, and Ireland.
An example of a prion disease transmissible to humans is the Variant Creutzfeldt–Jakob disease or vCJD, caused by mad cow disease. It is a neurological disease characterized by behavioral changes, psychiatric problems, and painful sensations. The disease is rapid and fatal with a life expectancy of about 13 months. Symptoms of vCJD include:
- Changes in personality
- Anxiety and depression
- Loss of memory
- Thinking impairment
- Sudden, jerky movements
- Difficulty in speaking and swallowing
Late-stage vCJD causes health complications such as respiratory failure, a secondary bacterial infection like pneumonia, and heart failure. Diagnosis of the disease is based on criteria of clinical symptoms, such medical history, personal background, a neurological exam, and screening tests. Additional screening tests used by doctors for vCJD diagnosis are electroencephalogram to determine abnormal brain pattern, magnetic resonance imaging to check gray or white matter in the brain, and lumbar puncture to analyze the presence of a particular protein associated with vCJD.
There is no cure or effective treatment for Variant Creutzfeldt–Jakob disease. Doctors can only provide supportive treatments to alleviate pain and make the patient’s life as comfortable as possible. For this reason, health experts recommend the following when encountering an elk or a moose:
- Avoid any of the deer family that behaves like zombies. Zombie-like characteristics include acting dead or acting abnormally.
- Avoid consuming or handling their meat to prevent transmission of the prions to you.
- Never touch poop and urine from any member of the deer family.
- For deer meat handlers, always wear protective gears when handling and properly dispose of them when necessary. Do not put any equipment or tools away without cleaning them properly.
- For deer meat eaters, do not consume the brain, spinal cord, eyes, spleen, tonsils or lymph nodes of deer.
Any sightings of strange-behaving or suddenly dead members of the deer family should be reported to the local health or wildlife department.
[메디컬리포트=Ralph Chen 기자]