Scientists are warning of apossible new transmission route for chronic wasting disease in North America, as bats move closer to areas where the disease is prevalent among deer and elk.
Scientists say the risk is still hypothetical, as there is no evidence yet of the disease spreading to bats, cattle, or humans.
Chronic wasting disease (CWD) is a fatal neurological disease that affects deer, elk, and other members of the same family. It is caused by abnormal proteins known as prions, which gradually damage the brain, leading to loss of balance, confusion, and behavioral changes, ultimately resulting in death.
The disease has been recorded in 37 US states and is also spreading in parts of Canada, while the possibility of it reaching Mexico is raising concerns among experts. Peter Larsen, an associate professor at the University of Minnesota, predicts that by 2030 the disease will have spread to all contiguous US states, Canadian provinces, and Mexico
In contrast, vampire bats are moving north as temperatures rise. These bats live in Central and South America and feed on animal blood, making their presence near diseased deer a cause for concern.
The scenario that scientists fear involves a bat feeding on an infected deer and then transmitting the prions it was exposed to to another animal during a subsequent blood meal. If these proteins were able to adapt to a new species, cattle could develop a prion disease similar to mad cow disease.
However, this possibility has not been proven. There is no evidence that vampire bats can carry and transmit chronic wasting disease prions, nor have any cases of the disease been recorded among livestock as a result of this route.
Larsen believes Mexico warrants special attention because it lies between areas where chronic wasting disease is prevalent and the known habitat of vampire bats. Research into the disease in Mexico remains limited, and the transfer of deer from Texas ranches linked to facilities where the disease has been detected has raised concerns that it may have spread there undetected.
Larsen told the Center for Infectious Disease Research and Policy (CIDRAP): "If I had to guess, I would say there is a 70% chance that there are vampire bats feeding on animals with chronic wasting disease in Mexico."
Larsen believes that infected deer may become more susceptible to bats as the disease progresses, as they lose the ability to move normally and tend to stay in one place, especially on fenced farms.
Concerns about cross-species transmission are based on known precedents for prion diseases. In the mad cow disease crisis in Britain, people contracted the variant Creutzfeldt-Jakob disease after eating contaminated beef, and 178 people died as a result of the outbreak, mostly in the United Kingdom.
There is also an unconfirmed hypothesis that chronic wasting disease may have originated from mule deer exposure to scrapie, a prion disease that affects sheep and goats. This hypothesis does not prove that the disease was transmitted in the same way, but it does illustrate that scientists are investigating the possibility of prion diseases crossing species barriers.
But other experts believe the likelihood of chronic wasting disease (CWD) being transmitted from bats to cattle is extremely low. Martin Zalusky, a former veterinarian for the state of Montana, said that cattle are already exposed to environments that may be contaminated with excrement and carcasses of infected deer, though there is no evidence that they have contracted the disease.
Wyoming State Veterinarian Haley Hassell said there is no evidence of mad cow disease in the state, and chronic wasting disease is not currently a concern for cattle.
To date, no human cases of prion disease have been reported as a result of consuming meat from venison infected with chronic wasting disease. However, Larsen is calling for increased surveillance of the disease in Mexico and funding for research that tracks its spread among animals and in the environment.
