Biologists are sounding the alarm over two growing threats on a potentially dangerous collision course with the US.

Researchers warned that vampire bats moving north could combine with chronic wasting disease (CWD), a fatal, contagious neurological illness spreading south through deer populations, potentially creating a pathway for a mad cow-like disease to reach humans.

Like mad cow disease, the incurable condition would be caused by abnormal proteins that destroy the brain, triggering behavioral changes, loss of coordination and eventually death.

The feared chain of transmission would begin when a vampire bat feeds on a deer infected with CWD and ingests the malformed proteins, known as prions, in its blood.

The bat could then expose cattle to those prions when it feeds again.

Researchers fear repeated exposure could eventually allow a strain of the disease to breach the species barrier and cause a fatal illness in cattle resembling mad cow disease.

Humans could then potentially become infected by eating contaminated beef, developing a deadly neurological condition.

Peter Larsen, an associate professor at the University of Minnesota, said: ‘I don’t know why more people aren’t paying attention to this, because it gets scary really fast.’

However, there is currently no evidence that vampire bats transmit CWD, that cattle have contracted the deer disease or that it has infected humans.

Vampire bats are nocturnal mammals native to Central and South America that survive exclusively on blood.

Although they have not established populations in the US, warming temperatures are allowing them to expand northward through Mexico and closer to states where CWD is already present.

The fatal deer disease has now been detected in 37 states, and Larsen said forecasts indicate it could circulate across all of the lower 48 states, every Canadian province and Mexico by 2030.

Surveillance in Mexico remains limited, but deer shipped there from Texas ranches were later linked to facilities found to be CWD-positive, raising concerns that the disease may already be circulating undetected south of the border.

That possibility means bats and infected deer may have already encountered each other.

‘If I had to guess, I would say it’s 70 percent possible that there are already vampire bats feeding on [CWD-] positive animals in Mexico,’ Larsen told CIDRAP.

A single blood meal taken from an infected deer, even one that is not yet showing symptoms, could contain several infectious doses of CWD prions, according to Larsen.

As the disease progresses, infected deer become disoriented and often remain in one location, making them easier targets for opportunistic vampire bats, particularly on fenced ranches where they cannot roam freely.

Larsen said a bat could theoretically encounter a CWD strain capable of causing prion disease in the animal. 

It might then shed infectious prions through its saliva or droppings, potentially exposing cattle and other species.

Scientists do not know whether that would happen, but prion diseases have crossed species barriers before. 

One leading, but unproven, hypothesis suggests CWD emerged after mule deer housed near sheep were repeatedly exposed to scrapie, another fatal prion disease.

The most notorious example occurred during the mad cow crisis of the 1980s and 1990s, when people developed a human prion illness known as variant Creutzfeldt-Jakob disease after eating contaminated beef. 

The outbreak killed 178 people, mostly in the UK.

‘I don’t think the species barrier is absolute. I think it’s porous,’ Larsen said. ‘I think it’s likely that CWD will cause prion disease in other species, including humans, and that it’s just a matter of time.’

Other animal-health experts stressed that Larsen’s proposed chain of transmission remains highly speculative.

Former Montana state veterinarian Martin Zaluski said prion diseases generally remain confined to individual species and described the likelihood of bats transmitting CWD to cattle as extremely slim.

Cattle already graze on land potentially contaminated by infected deer through their urine, feces and carcasses, yet there is no evidence that the exposure has caused disease in livestock, he noted.

Wyoming State Veterinarian Hallie Hasel also said there was no evidence of bovine spongiform encephalopathy, the formal name for mad cow disease, in the state and that CWD infecting cattle was not currently a concern.

There has never been a documented case of a person contracting a prion disease from eating CWD-infected venison. Nevertheless, Larsen said he would have any deer meat tested for CWD before consuming it.

He also called for greater surveillance in Mexico and increased federal funding to track how the disease is moving through animals and the environment.

‘I view this as an all-hands-on-deck alarm,’ Larsen said. ‘We need to mobilize now.’