Biologists are raising concerns about a potential pathway for a fatal, incurable neurological disease, similar to mad cow disease, to reach humans in the United States. The proposed scenario involves vampire bats, which are expanding their range northward, interacting with deer infected with chronic wasting disease (CWD).
Researchers theorize that if a vampire bat feeds on a CWD-infected deer, it could ingest prions – misfolded proteins that cause neurological damage. Subsequent bat feeding, potentially on cattle, could then expose livestock to these prions. Repeated exposure, they warn, might allow a strain of the disease to cross the species barrier and develop into a condition in cattle resembling mad cow disease. Humans could then be at risk of infection through the consumption of contaminated beef, leading to a fatal neurological illness.
"I don’t know why more people aren’t paying attention to this, because it gets scary really fast," said Peter Larsen, an associate professor at the University of Minnesota.
Disease Spread and Potential Transmission
CWD, a contagious neurological illness, is spreading through deer populations and has been detected in 37 U.S. states. Forecasts suggest it could spread across all lower 48 states, every Canadian province, and Mexico by 2030. While vampire bats have not yet established populations in the U.S., warming temperatures are facilitating their northward expansion from Central and South America through Mexico.
Surveillance in Mexico is limited, but concerns have been raised that CWD may already be circulating there, potentially bringing infected deer and vampire bats into contact. Larsen estimates a 70 percent probability that vampire bats are already feeding on CWD-positive animals in Mexico. A single blood meal from an infected deer, even one not showing symptoms, could contain infectious doses of CWD prions.
Infected deer can become disoriented, making them easier targets for bats, especially on fenced ranches. A bat could theoretically encounter a CWD strain capable of causing prion disease and shed infectious prions through saliva or droppings, potentially exposing cattle and other species. Scientists note that prion diseases have crossed species barriers before, citing the emergence of variant Creutzfeldt-Jakob disease in humans after consuming contaminated beef during the mad cow crisis of the 1980s and 1990s, which resulted in 178 deaths, primarily in the UK.
Larsen believes the species barrier is "porous" and that it is likely only a matter of time before CWD causes prion disease in other species, including humans. He advocates for increased surveillance in Mexico and greater federal funding to track the disease's movement.
Expert Reservations
Other animal health experts caution that Larsen's proposed transmission chain is highly speculative. Martin Zaluski, former Montana state veterinarian, stated that prion diseases typically remain confined to individual species and described the likelihood of bats transmitting CWD to cattle as "extremely slim." He pointed out that cattle already graze on land potentially contaminated by deer through urine, feces, and carcasses, yet no disease has been documented in livestock from such exposure.
Wyoming State Veterinarian Hallie Hasel confirmed there is no evidence of mad cow disease in the state and that CWD infecting cattle is not a current concern. Furthermore, there has never been a documented case of a person contracting a prion disease from eating CWD-infected venison. Despite this, Larsen recommends having any deer meat tested for CWD before consumption.