Chronic Wasting Disease

Chronic Wasting Disease and its Effects on Humans

Wildlife diseases take new meaning as hunting season begins. Some of these diseases are zoonotic. Conditions like tularemia, Lyme, toxoplasmosis, E. coli infections, and trichinellosis are long-standing, substantial concerns for those that hunt in the United States.

Chronic Wasting Disease

Within the last few years, chronic wasting disease (CWD) has started to cause concern among wildlife professionals and hunters. This fatal neurologic condition affects captive and wild populations of whitetail deer, elk, moose, and many other cervid species. The number of animals affected, as well as the affected geographical area has been significantly increasing. There are now 30 states in the United States that have tested deer and returned a positive CWD result. There have also been over 200 captive deer facilities that have returned positive tests.

CWD is a transmissible spongiform encephalopathy associated with the misfolding of the cellular prion protein PrPC. It is the only prion disease in wildlife and voraciously spreads among the corvid species. There is a substantial mystery around the disease, as its origin, mechanisms of transmission, and prevalence are not entirely understood. Like other prion diseases, CWD cannot be treated, but some things can be done to delay the onset of prion disease.

Symptoms That Indicate CWD

The misfolded proteins characteristic of this disease accumulate in the central nervous system and result in symptoms like:

  • Impaired coordination
  • Weight loss and emaciation
  • Muscle wasting
  • Frequent urination
  • Hypersalivation
  • Listlessness

Death is also common — deer affected with CWD were 4.5 times more likely to perish each year than non-infected deer. As a result, the wild corvid populations will likely decline significantly in an area affected by CWD.

Zoonotic Transmission Potential

Though there have been no documented cases of CWD transmitting to humans, there is uncertainty around the possibility. The incubation period of prion diseases like CWD can be up to ten years or more. This means that an infected person would have been exposed between 2006 to 2010 when there were very few cases of CWD. The similarities between chronic wasting disease and existing zoonotic diseases, like bovine spongiform encephalopathy, have been a driving factor behind the concern with its spread to humans.

The CDC recommends not eating CWD-infected meat because current studies have suggested primates can contract it from consuming tainted meat. Contrarily, studies with different non-human primates have conflicting results, showing no biochemical, clinical, or pathological evidence of CWD transmission.

Another factor for concern is the presence of CWD prions in the soil and environment, so other animals could potentially spread the disease. Several studies that examined environmental contamination found a transmission route to various animal species, including sheep, cattle, goats, raccoons, and ferrets. The spread to other species raises concerns about an increase in virulence and zoonotic potential of newly generated prion strains from the new host animals.

Method of Detection

The best way to prevent CWD spread is through disease detection before an animal has time to spread the prions in its environment. There are no current field-testing methods. One current detection method for chronic wasting disease begins with testing a postmortem sample with an enzyme-linked immunosorbent assay (ELISA kit). ELISA’s relatively low sensitivity necessitates the sample to be taken from a deceased animal. The tissue sample is most commonly taken from the medial retropharyngeal lymph nodes, but brain tissue can also be examined for a diagnosis.

Key Points

Chronic wasting disease is a neurological condition affecting deer species in over half of the states in the US. Though there have been zero documented cases of zoonotic transmission from deer to humans, multiple studies suggest it could jump the species barrier. Other studies must be done to find a more conclusive answer to the transmission question; however, the CDC has taken a conservative approach and recommended that humans not consume meat from infected animals.

Laboratory ELISA testing paves a way for greater understanding of CWD. As skilled scientists and epidemiologists continue to study this disease, more answers will be gleaned so that the effects of CWD can be minimized.

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Christophe Rude

Christophe Rude

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