For farmers in Latin America, vampire bats live up to their "dark" reputation. Their bites weaken cows and cause infections. Worst of all, the rabies virus they sometimes carry kills livestock and occasionally infects humans. Now, scientists have developed an innovative way to vaccinate bats — using their unique penchant for mutual grooming.
Image source: TONIE ROCKE/U.S. GEOLOGICAL SURVEY
In a study recently published on the preprint platform biorXiv, researchers showed that when they applied a thick, gel-like oral vaccine to the fur of some members of common vampire bat colonies, mutual licking behavior helped the vaccine spread rapidly through the population. "The idea they've come up with is innovative — I don't know of any other way to vaccinate bats, let alone with an oral vaccine," said Luis Escobar, a disease ecologist at Virginia Tech in the U.S.
In Latin America, vampire bats cause an average of 450 rabies cases in cattle each year, costing farmers about $50 million. They can also transmit the deadly virus to pigs and horses, and occasionally to humans. Small-scale farmers are particularly hard hit.
To combat this threat, people have resorted to killing vampire bats by setting fires in their cave or tree roosts, often mistakenly killing ecologically beneficial bat species that feed on fruit and insects, said Gerald Carter, a bat researcher at Princeton University in the U.S.
A toxic gel was once considered a promising solution. It was hoped that applying the toxic gel to a few vampire bats would lead to the elimination of entire colonies as they licked each other. But this method was not particularly effective and could even backfire. The toxic gel usually killed only a portion of the population, and surviving members might spread rabies further when they dispersed to new habitats.
Vaccinating bats would be a more humane approach, but it is not easy. "We can't go around injecting vaccines into wild animals," said Tonie Rocke, an epidemiologist at the U.S. Geological Survey's National Wildlife Health Center and corresponding author of the paper. "If we tried that, we wouldn't get very far."
So her team borrowed the idea of the toxic gel. They mixed an experimental oral vaccine, which has been shown to prevent bats from transmitting the rabies virus, with a thick carboxymethyl cellulose gel — a thickener also used in human food. They also added a fluorescent compound to the gel to help track its distribution in bat colonies.
They tested the strategy in a small town in Jalisco, Mexico, where a colony of about 117 common vampire bats roosted in an abandoned house. One night in October 2024, they captured the bats with nets, applied the vaccine gel to the fur on the backs of 24 of them, and released them.
Three and seven days later, researchers captured a total of 48 bats, collected hair samples, and tested them for fluorescence. The strategy seemed to work — the team reported that 88% of the colony was vaccinated. Adult male bats had almost no gel on them, indicating that social grooming is more common among adult females and young bats.
Researchers say the need to vaccinate bats against rabies may become more urgent as growing livestock populations in many countries have led to an increase in bat numbers. In addition, climate change is helping vampire bats migrate northward; they have been found just 50 kilometers from the southern U.S. border.
This strategy could also be used for other bat species that carry rabies and help protect bats from another deadly fungal disease — white-nose syndrome. Rocke and colleagues have successfully tested a candidate vaccine for this disease in little brown bats.
Both Carter and Escobar are excited about the vaccine's potential but say it should be tested in larger-scale trials, and additional research is needed to demonstrate the impact of vaccination on bat populations.