3 JUL 202511:40 PM ET by Richard Pallardy

For farmers in Latin America, vampire bats live up to their dark reputation. Their bites weaken cows and open the way for infections. Worst of all, the rabies they sometimes carry can kill livestock and, occasionally, people as well. Now scientists have developed an innovative way to vaccinate the bats against the virusÄby making use of their extraordinary fondness of mutual grooming.

In a study published as a biorXiv preprint on 12 June, researchers showed that after they applied an oral vaccine in the form of a thick gel to the fur of some members of a colony of common vampire bats (Desmodus rotundus), mutual licking helped spread the vaccine rapidly through the population. "The idea that they are proposing is innovativeÄI don't know of any other effort to vaccinate bats, let alone vaccinate bats orally," says Luis Escobar, a
disease ecologist at Virginia Tech who was not involved in the study.

Vampire bats cause an average of 450 rabies outbreaks annually in cattle in Central and South America, costing farmers an estimated $50 million, and they can spread the fatal virus to pigs and horses as well. Small farmers are especially hard hit. "A low-income family that only has one cow is going to
be more impacted if a cow dies, compared to a rancher," Escobar says.

To ward off the threat, people have culled vampire bats by setting fire to caves or tree hollows where they live, often killing ecologically beneficial fruit- and insect-eating bat species in the process, says Gerald Carter, a bat researcher at Princeton University who was not involved in the new study.

Poisonous gels called vampiricides once seemed a promising solution. Common vampire bats are highly social animals that routinely groom each other, and the hope was that applying a toxic gel to a few bats would wipe out the rest of the colony after they licked it off each other's fur. But the approach doesn't
work particularly wellÄand it may even backfire. Vampiricides often kill off only part of a colony, and surviving members can spread rabies further when they disperse to new roosts.

Vaccinating bats would be a more gentle approachÄbut it isn't easy. "We
can't be going around and injecting wild animals with vaccines," says the paper's corresponding author, Tonie Rocke, an epidemiologist with the U.S. Geological Service National Wildlife Health Center. "We wouldn't get very far if we tried to do that."

So instead her team built on the vampiricide approach. They took an oral vaccine experimentally shown to prevent bats from shedding the rabies virusÄwhich would make them harmless to cattleÄand mixed it with a carboxymethyl cellulose gel, a thickening agent also used in human food products. They also added a fluorescent compound to the gel to help them track its distribution across the colony.

Then they tested the strategy in Casimiro Castillo, a township in Mexico's Jalisco State where a common vampire bat colony with an estimated 117 members was roosting in an abandoned ranch house. One night in October 2024, they caught the bats using nets and applied the vaccine gel to the fur on the backs of 24 of the animals. Then they released them again.

The researchers again captured a total of 48 bats three and seven days later and took hair samples from them, which they examined for fluorescenceÄassumed to be a sign that another bat had licked and ingested the vaccine. The trick appeared to work; 88% of the bats in the colony were vaccinated, the team reports. Adult male bats were the least likely to have the gel on their fur, suggesting that social grooming is more prevalent among adult female and juvenile bats.

The need for a rabies vaccine for bats is likely to become more urgent, the authors say, because growing livestock populations in many countries are causing bat populations to increase as well. Moreover, climate change is helping the vampire bats move northward; they have already been found just 50 kilometers from the United States' southern border.

Both Carter and Escobar are enthusiastic about vaccination's potential, although they say it should be tested in larger trials. Studies are also needed to show vaccination's impact on bat populations. The vaccine prevents the animals from shedding virus, but it's not clear if it benefits them; if it does, it could cause populations to grow even more.

The researchers say the strategy could also be used in other bat species that carry rabies, including in the United States, where 90% of rabies deaths are a result of human-bat contact. It could also help protect bats themselves from a very different threat: white nose syndrome, a fatal fungal disorder that has devastated North American bats the past two decades. Rocke and her colleagues have had some success testing a candidate vaccine against the fungus in little brown bats (Myotis lucifugus). Perhaps in the future such vaccines could be spread through grooming as well, she says.

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