Brain organoids’ findings indicate that deer prions have difficulty infecting human brains.
In the US, chronic wasting syndrome is becoming more common in deer, which has sparked worries that humans could contract the deadly neurological condition. However, a new study indicates that the illness may have a difficult time infecting people.
The misfolded brain protein known as a prion is the cause of chronic wasting disease, or CWD, rather than a virus or bacteria. A recent study demonstrating that CWD prions do not infect human brain tissue uses tiny, lab-grown organs called organoids, which validates earlier findings.
The study’s 180-day duration saw brain organoids subjected to large dosages of prions derived from mule deer, elk, and white-tailed deer remain clear of illness, according to research published in the June 2024 Emerging Infectious Diseases. Organoids exposed to human prions, on the other hand, which result in Creutzfeldt-Jakob disease, contracted the illness rapidly. The results imply that a significant species barrier keeps CWD from migrating from deer to people.
However, brain organoids may not have all the characteristics that would make them prone to infection and are not a perfect replica of the genuine thing. In addition, fresh strains of prions may emerge, some of which may aid deer prions in attaching themselves to human brain proteins that are beneficial.
A contagious illness
Chronic wasting disease has expanded significantly throughout North America since it was first identified in Colorado in 1967. Only Colorado and Wyoming have documented examples of wild deer and elk prior to 2000. As of right now, four Canadian provinces and thirty additional states have the disease. Animals kept in captivity are also affected; outbreaks are now occurring in some institutions, and infected populations have been eliminated in others.
It’s more likely that contaminated deer meat may end up on a plate if certain hunters aren’t inspecting their kills. (In the US, each state has its own hunting regulations and suggestions.) Furthermore, even cooked meat may still be dangerous since proteins are not harmed by heat in the same way that bacteria or viruses are.
Lessons learned from earlier instances
The 1980s and 1990s saw an outbreak of mad cow disease, another prion disease, which was brought on by people eating meat from infected cattle. This, according to Haigh, helped raise awareness of chronic wasting disease. Even though the deer disease was identified earlier than mad cow disease, at the time most people weren’t concerned about the danger to humans.
Previous studies have indicated that prions might find it difficult to transition across different species. Research with mice engineered to carry the human form of PrP has suggested that human transmission is a potential scenario, albeit a less likely one than with prions derived from cattle. However, research on macaques, a popular animal substitute for humans, suggests that it is uncommon for chronic wasting syndrome to spread from deer to people.
A case report that was presented at the annual conference of the American Academy of Neurology in Denver in April captured the attention of reporters. It detailed a neurological condition that killed two hunters. The people had previously eaten deer meat from a population where chronic wasting illness was prevalent. However, the U.S. Centres for Disease Control and Prevention and the report both state that Creutzfeldt-Jakob disease, a distinct prion illness that can occur sometimes, is most likely the cause of both deaths.
Barriers to infection
Although the mad cow prion afflicted hundreds of individuals beginning in 1994 (symptoms may not appear for ten or more years), McKenzie notes that the barrier to human transmission is quite high. As of 2022, there have only been 178 cases of Creutzfeldt-Jakob disease caused by contaminated meat in the United Kingdom, the epicentre of the outbreak, and 55 cases worldwide, despite the fact that millions of people are thought to have been exposed to sick animals during the outbreak in the 1980s and 90s.
Additionally, prions strains, which twist PrP proteins in various ways, may be relevant. Determining the variations in deer prions’ bending and curling behaviours may aid in identifying which may cling to human or animal PrP.
That being said, compared to regular PrP, prions are more difficult for scientists to characterise. It is more difficult to investigate the possibility that prion infections could spread from one species to another because of this ignorance.
For example, chronic wasting illness is caused by at least five separate prion strains, each of which affects a distinct range of cervid species. Although certain animals may be able to infect other species in the lab, CWD has only ever been discovered in cervids in the field. It is therefore feasible that new strains that are more dangerous to humans could evolve, even though the results in brain organoids imply that at least some of the current strains don’t pose a high hazard to people.