Scrapie in goats is just one of several prion diseases. They have no cure and can bring down an entire goat or sheep operation with one diagnosis. But what are prion diseases and why won’t antibiotics help?
What Are Prions?
Prions are stable above 1,000 degrees Fahrenheit, resistant to formaldehyde, and exist within the soil for decades. Proven zoonotic, prion diseases pass between mammals and humans. Prions cause scrapie in goats and sheep, mad cow disease, and chronic wasting disease in the deer family. Within humans, prion diseases classify depending on cause and effect: Fatal Familial Insomnia and Creutzfeldt-Jakob disease, variant and sporadic CJD, and kuru. And they’re always fatal.
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Prions are proteins that exist naturally within our DNA; in humans, they reside on chromosome 20. Healthy prions cause no problems. But when one becomes misshapen and meets a healthy prion, that prion also mutates. This causes a chain reaction, which damages tissue, primarily in the brain. Astrocytes consume the dead tissue and tiny holes appear, which gives prion diseases the scientific name “transmissible spongiform encephalopathies” (TSE). And when enough holes develop, functions controlled by that area of the brain become impaired. The body degrades until the affected person or animal dies.
Prions enter the body several ways: inherited genetically, through consumption, or through blood transfusion or open cuts in the skin. Sometimes they twist sporadically. The rate of development is dependent on how many prions enter the body: a single or inherited case can take 60 years to develop in humans but the mad cow disease epidemic presented teenagers succumbing to symptoms after essentially “living off” tainted hamburgers. Livestock diagnosed with TSEs are usually no younger than 18 months.
What Can Get Prion Diseases?
Scrapie, in goats and sheep, has been documented since 1732 and has long been believed intransmissible to humans. Animals contract it through milk consumption, contact with placental tissues, or through cuts in the skin. The agent sheds in feces and resides in the soil, which means a healthy sheep may consume the agent by eating grass grown on contaminated land. As the sheep and goat disease progresses, they smack their lips, have an altered gait, and feel an itching sensation, which makes them scratch against fences until patches of skin or wool scrape off. Eventually, animals collapse into convulsions then die.
Chronic wasting disease, in members of the deer family, was first recognized in Colorado in 1978. It has since spread to 23 other U.S. states and two Canadian provinces. In 2016, it was discovered on an elk farm in Korea and several wild reindeer herds in Norway, the first-ever instances of CWD overseas. Claims it cannot pass beyond the deer family were squashed in 2015, when researchers in Texas grew wheat grass in soil contaminated with CWD, then fed it to hamsters. The hamsters succumbed to CWD, which proved it was both zoonotic and could be transmitted by plants. Though most experts will hold that CWD cannot pass to humans, they warn hunters not to consume brain or spinal tissue. “There is no proof of transmission from wild animals and plants to humans,” says professor of neurology Claudio Soto, Ph.D. “But it’s a possibility that needs to be explored and people need to be aware of it. Prions have a long incubation period.” In 1997-1998, three young adults in the U.S. developed sporadic Creutzfeldt-Jakob disease (CJD) and all had consumed venison, though researchers did not find a causal link to CWD.
Bovine spongiform encephalopathy (BSE), also called mad cow disease, began when British agriculture introduced the practice of processing meat and bone meal into feed as supplementary protein for beef cattle. BSE, though it sometimes presents sporadically in the U.S., has not become an epidemic because the U.S. produces enough cottonseed and soybeans to supplement protein in feed. British cattle began developing symptoms similar to scrapie in goats and sheep, but industry officials advised farmers to keep pushing meat into the food system. As more BSE-tainted meat processed back into the cattle feed, more cattle succumbed. Bureaucrats panicked about the loss of revenue and insisted the meat remain on the market for humans, believing any pathogens would be killed if cooked. Between 460,000-482,000 BSE-infected cattle entered the food system before the government instituted controls on high-risk offal in 1989.
Human prion diseases include Fatal Familial Insomnia (FFI), an inherited ailment marked by the inability to sleep in addition to the common prion symptoms of myoclonus (jerky movements), memory loss, and personality changes. Creutzfeldt-Jakob disease (CJD) causes similar symptoms but 86 percent is sporadic (no known cause), eight percent genetic, and five percent iatrogenic, meaning it’s caused by medical treatments such as transplants or blood transfusions. Human TSEs are literally one in a million and take so long to develop that patients usually die from other causes before TSE symptoms can present. MRI imaging is the only sure way to diagnose a TSE in a living patient, and diagnoses usually happen about one year before death.
It wasn’t known how prions transmit, or even what they were, until the 1960s when several scientists studied kuru, the “cannibalism disease” in Papua New Guinea. They theorize that one person either ate a sheep with scrapie or developed twisted prions sporadically, then that person died and their relatives practiced funerary cannibalism: eating the deceased as a way to honor them. Brains and spinal cords contain the most prions, and those parts were given to women and children. When white missionaries arrived in Papua New Guinea, they discovered children as young as 10 dying of kuru.
Two decades after the “prion” got its official name, British citizens came down with similar symptoms. Researchers eventually traced it back to BSE-tainted beef. To date, 177 Britains have died of variant CJD, the name for mad cow disease in humans, and 52 elsewhere, mostly in Western Europe. It’s said one in 2,000 Britains carry the prions, which is why people who have resided in Great Britain during certain years cannot donate blood in the U.S.
Should We Worry?
There is no cure for prion diseases and they are always fatal.
Though prion research is new, scientists and livestock/food officials have made strides. The mad cow epidemic proves those prions can be zoonotic, which puts attention back to scrapie in goats and sheep, challenging the claims that it cannot pass to humans.
The USDA in the United States instituted the National Scrapie Eradication Program, which urges sheep and goat producers to educate themselves, report scrapie symptoms, and to submit brain matter for testing. The USDA will also recall beef from suppliers that have slaughtered “downer cows,” animals already showing some type of ailment. The European Union banned the export of British beef from March 1996 to May 2006. High-risk materials, such as brains and trigeminal ganglia, are appropriately disposed of within U.S. and U.K. slaughterhouses, and there is now a ban on feeding meat and bone meal to cattle.
Recent research isolated alleles (genetic material) that can lend resistance to scrapie. In 2009, scientists discovered a mutation among the Fore, the Papua New Guinea tribe with the highest kuru occurrences, which stops misfolded prions within the brain. Alleles S146 and K222 help resist scrapie in goats, and UC-Davis Veterinary Genetics Laboratory offers testing to private goat owners to see if they have this trait in their herds, so they can encourage it by breeding within dairies and meat goat farming operations.
Though our chances of contracting prion diseases are still remarkably lower than about any other foodborne illness, it is a terrifying concern that they cannot be treated. Education is our biggest tool among scientists, food authorities, and the farmers producing the meat. Avoiding mad cow disease, and scrapie in goats has come a long way and continues to show hope.
“Grass Plants Can Transport Infectious Prions” – May 16, 2015, University of Texas Health Science Center at Houston https://phys.org/news/2015-05-grass-infectious-prions.html
Chronic Wasting Disease Alliance http://www.cwd-info.org
“Genetic Mutation Blocks Prion Disease” by Boer Deng https://www.nature.com/news/genetic-mutation-blocks-prion-disease-1.17725
The Family that Couldn’t Sleep: A Medical Mystery by D.T. Max
“Breeding Scrapie Resistant Goats: A New DNA Test to Enhance Goat Health and Your Business” by Stephen N. White Ph.D. and David A. Schneider DVM, Ph.D., DACVIM(LAIM)
“Variant Crutzfeldt-Jakob Disease (vCJD)” – Centers for Disease Control and Prevention https://www.cdc.gov/prions/vcjd/risk-travelers.html
Originally published in the July/August 2018 issue of Goat Journal and regularly vetted for accuracy.