Vampire bats have invaded the United States, and scientists fear they could spread deadly zombie deer disease to humans.

In 2022, Peter Larsen wakes up in the Guyana rainforest with a strange sensation in his leg. A University of Minnesota researcher sleeping in an outdoor house turned on his headlamp and found a vampire bat (the very animal he traveled to South America to study) sucking his blood.

This encounter was both interesting and alarming. What if he got sick, Dr. Larsen wondered. After all, bats are natural reservoirs of several serious viruses and pathogens, including rabies, Ebola, Marburg disease, and coronaviruses like SARS, largely due to their unique immune systems.

This disturbing episode led Dr. Larsen to consider the unique pathogens these highly social mammals may bring with them or acquire as they adapt to a changing world. Rising temperatures are causing the common vampire bat (desmodus round) is gradually expanding its range northward from Latin America. Meanwhile, chronic wasting disease (CWD), a deadly and incurable neurological disease affecting North American deer, is spreading south.

For wildlife epidemiologists, these converging trajectories set the stage for new threats. CWD is caused by infectious misfolded proteins called prions that circulate freely in the blood of sick deer. Vampire bats live by feeding on the blood of large mammals, which puts them in direct conflict with pathogens.

If these bats started feeding on infected deer, could they ingest those prions and act as airborne reservoirs, transmitting the disease’s damaged proteins to new populations of wildlife, livestock, or humans?

Nature of the threat

CWD belongs to the family of transmissible spongiform encephalopathies, which includes “mad cow disease” in cattle and scrapie in sheep.

Unlike viruses and bacteria, this disease is not caused by live microorganisms. It is caused by prions. Prions are normal proteins that have been misfolded into a broken shape. Once inside a host’s body, prions force other healthy proteins to misfold in a cascade of reactions, slowly deteriorating the nervous system and leaving the brain riddled with microscopic holes.

CWD is known to infect deer, elk, and elk with devastating consequences. After an incubation period of 16 to 36 months, animals suffer from weakness, excessive thirst, and severe cognitive impairment. They have blank stares, wide postures, and have lost their natural fear of humans, giving the condition the nickname “zombie deer disease.”

Neuropathic deer are ideal targets for vampire bats. These fist-sized mammals survive solely on blood and typically seek out large, easily accessible prey in the dark.^{. They use their razor-sharp teeth to create a painless wound and secrete an anticoagulant to trap the pooled blood.}

Studies have detected infectious prions circulating freely in the blood of CWD-positive animals throughout the disease’s long incubation period. The authors note that a 20-milliliter blood meal taken from an infected deer can contain a large number of infectious doses.

The highly prosocial nature of bats can amplify disease. If the bats cannot find food, the roosting mates regurgitate their blood meal and share it with hungry bats. They also groom each other communally. From an epidemiological perspective, this behavior could effectively spread prion-infected bloodmeal to other bats, spreading exposure throughout a colony of up to several thousand individuals.

nightmare scenario

The geographic overlap between these two species is no longer a distant concern. Prediction models say climate change could push vampire bats into Texas, New Mexico, and Arizona within the next few decades.

To make matters worse, the disease may already be driving bats to the border. A new paper says a Texas ranch unknowingly exported hundreds of live white-tailed deer to Mexico from 2021 to 2025. Officials later confirmed that these Texas facilities housed CWD-positive animals.

Prions persist in the soil for years, and the disease’s long incubation period gives the pathogen ample opportunity to establish itself in new environments. Dr. Larsen, co-director of the Minnesota Prion Research and Outreach Center, suspects that duplication is already occurring.

“If I had to guess, I’d say there’s a 70% chance that vampire bats are already feeding on it. [CWD-] We had positive animals in Mexico,” Dr. Larsen said.

The central fear is that the bat’s body could transform the prion in dangerous ways. When a prion passes through the gastrointestinal tract of a new species, its molecular structure changes, potentially changing the animals it can infect.

“Prions don’t actually mutate like viruses or bacteria that change their genomes,” says Brent Race, DVM, a scientist at the National Institutes of Health’s Rocky Mountain Laboratory. “If bats are susceptible to CWD, the prions produced may fold differently than typical CWD, increasing their ability to infect other species, including humans and livestock. Of course, this is highly speculative.”

A call for vigilance and surveillance

Before sounding the alarm, some experts urge caution. Dr. Rodrigo Morales of the University of Texas at Houston School of Medicine said the new research is important, but the lack of a definitive animal model means the threat remains hypothetical.

“This is still a hypothesis because there are no clear or frequent interactions between infected animals. [deer] “Unfortunately, there are no models yet to suggest this is likely to occur,” Dr. Morales said. Therefore, interpretation must be considered carefully. ”

He pointed out that bats’ specialized digestive tracts could naturally destroy prions. “If you catch an infected animal and take a sample of its blood, it may be detected, but that doesn’t mean the amount of prions present in the blood is sufficient to transmit the disease,” he added.

Still, the potential economic and public health implications are too great to ignore. The study’s authors call for a thorough assessment of ecological risks and cross-border monitoring. Testing large animals is difficult, but monitoring at-risk populations is essential.

This study mammal journal.