Mad Cow, Chronic Wasting and Other Prion Diseases

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Mad Cow, Chronic Wasting & Other Prion Diseases | W. Jean Dodds, DVM

Prion diseases are quite rare and relatively unknown, yet always deadly. This group of diseases has the potential to jump between species via routes such as ingestion or from a blood transfusion. Scientists believe prion diseases could spread between animals through body fluids like feces, saliva, or urine, either through direct or indirect contact through environmental contamination of soil, food or water. As of right now, naturally occurring prion diseases from aerosols  have not been identified, but these diseases can be transmitted efficiently if they are airborne. In this instance, prion diseases could be used as biological warfare just like rabbit fever and the plague.

Bear in mind that efforts thus far have contained the spread of prion diseases and that aggressive research is underway to keep ahead of them. In this article, we will look at some of the significant research that was recently completed or is ongoing.

Background of Prion Diseases

“Prion Diseases” derived the name from the prion proteins that are present in abundance in the brain and nervous system. The scientific name for this group of neurodegenerative diseases is transmissible spongiform encephalopathies (TSE).

Prions are believed to be the causative agents of these diseases. When pathogenic agents enter the body, they have the ability to cause abnormal folding of specific prion proteins. TSEs are known for long incubation periods, spongiform changes associated with neuronal loss, and their failure to induce an inflammatory response.

Well known prion diseases are Mad Cow Disease, Chronic Wasting Disease (CWD), and Variant Creutzfeldt-Jakob Disease (vCJD). Prion diseases are further categorized by the route of infection: inherited, sporadic or acquired.

2005 Study: Risk of oral infection with bovine spongiform encephalopathy agent in primates.

Possibly the best known prion disease is Mad Cow (bovine spongiform encephalopathy – BSE). It is believed that BSE originated in the 1970s from feeding cattle meat-and-bone meal that contained BSE-infected products from a spontaneously occurring case of BSE or from scrapie-infected sheep products starting. [Scrapie is a prion disease that infects sheep and has been documented since the mid 18th Century.] The outbreak was exacerbated and spread throughout the United Kingdom by feeding prion-infected, bovine meat-and-bone meal to young calves.

Humans who ate infected meat developed vCJD. On a side note, there is no evidence at this time that a human could develop vCJD from consuming muscle meat (ground beef, roast or steaks) or drinking cow milk, unless the beef meat contained brains or nerve tissue.

Cats can develop feline spongiform encephalopathy (FSE) and the cause is the same agent that is responsible for BSE in cattle.

Since the major outbreak of the 1990’s, the good news is that many governments have instituted public health control measures such as specific feeding  bans. For instance, certain high-risk cow parts like brains and spinal cords are not allowed to be used to make any animal feed, including pet food.

Regarding this significant study, the researchers used macaque monkeys, which are genetically close to humans, so are often used to gauge the potential for infection.

According to the 2005 study authors, “We gave two macaques a 5 g oral dose of brain homogenate from a BSE-infected cow. One macaque developed vCJD-like neurological disease 60 months after exposure, whereas the other remained free of disease at 76 months.”

2011 Study: Grass Plants Bind, Retain, Uptake, and Transport Infectious Prions

This study of prion retention in the environment had fascinating results:

  • Plants can bind prions contained in brain extracts from diverse prion-infected animals, including CWD-affected cervids.
  • Prions – attached to leaves and roots from wheat grass plants – remain capable of seeding prion replication in vitro.
  • Prions naturally excreted in urine and feces from sick hamsters or cervids were able to contaminate plant tissue. These results suggest that the majority of excreted prions are efficiently captured by plants’ leaves and roots.
  • Leaves can be contaminated by spraying them with a prion-containing extract, and prions remained detectable in living plants for as long as the study was performed (several weeks).
  • Prion contaminated plants transmit prion disease to animals upon ingestion, producing a 100% infection rate and incubation periods not substantially longer than direct oral administration of sick brain homogenates.
  • Plants were able to take up prions from contaminated soil and transport them to aerial parts of the plant.

2011 Study: The nature of the infectious agents: PrP models of resistant species to prion diseases (dog, rabbit and horses)

Currently, dogs, rabbits and horses are immune to prion diseases. For the longest time, however, nobody could explain why. In 2011, a researcher in Australia simulated how these proteins change shape as their temperature and pH changes. The conclusion was that the immune proteins from these species are more stable than the others because of a salt bridge that connects two of their parts.

Ongoing Study: First evidence of intracranial and per-oral transmission of Chronic Wasting Disease into Cynomolgus macaques: a work in progress

Nowadays, you may be hearing more about Chronic Wasting Disease (CWD), which afflicts some elk, deer and moose (cervids) in at least 22 US states. Thus far, there are no known cases of the disease jumping species to humans or cows. However, this ongoing study reported that Macaque monkeys were fed muscle tissue or brain tissue from infected CWD elk and deer. Other test subjects were given brain tissue from asymptomatic deer. In both instances, CWD was able to infect the monkeys.

Hemopet reached out to the research team to ask whether the muscle meat was naturally infected with CWD or if the team added it to the meat. This is the correspondence:

Hemopet: We are wondering if the infected muscle tissue fed to the Macaque monkeys was naturally occurring or if the research team infected the muscle with CWD.

Dr. Czub: The infected muscle tissue was from free-ranging WTD and MD, all hunter kills were from the US and from a WTD farm depopulation in Canada. So, no experimental infection, all was “natural”.

Out of an abundance of highly warranted caution, the Centers for Disease Control & Prevention (CDC) vehemently recommends that hunters in affected areas have venison tested before consumption.

Conclusion

You probably noted that throughout the article we stated the knowledge that we have now. We have to should remember that we know relatively little about prions and their associated diseases. Furthermore, TSEs can jump between species and they possibly can mutate.

W. Jean Dodds, DVM
Hemopet / NutriScan
11561 Salinaz Avenue
Garden Grove, CA 92843

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