University of Michigan scientists and their colleagues used glowing fluorescent gel to test the potential effectiveness of vaccines to control rabies and other diseases in wild bats. The study, originally published in the journal Nature Ecology & Evolution by the universities of Michigan and Glasgow, found that a low-effort vaccination program could substantially reduce rabies transmission in wild vampire bats, thus reducing the risk of lethal infections in humans and livestock. The gel was applied to wild vampire bats at three colonies in Peru, where it simulated the spread of an orotopical (orally or topically) rabies vaccine through the use of a fluorescent tracer dye called rhodamine B, a dye typically used to test water flow. Spread between bats during grooming, these vaccines have been shown to protect multiple bats against rabies for every individual vaccinated in the laboratory, but their levels of spreading in wild bats was unknown until now. After grooming, the gel is ingested by the bats, leading to fluorescence in the hair follicles. The scientists collected these hair samples and monitored them under fluorescent microscopic analysis. The results demonstrated that orotopical rabies vaccines would protect 2.6 bats for every bat that receives the vaccine, compared to a single bat protected by conventional vaccines. Fluorescent gel is applied to the mouth of a vampire bat in a rural area near Lima, Peru, to test the potential effectiveness of a “spreadable” rabies vaccine. The bright red gel causes bat hair follicles to fluoresce under the microscope, so that researchers can track the spread of the biomarker through the bat population. Photo by Kevin Bakker, University of Michigan. “We provide the first evidence that vaccinating bats could lead to meaningful reductions in human and livestock rabies,” said the study’s lead author, Kevin Bakker. Through mathematical models, Bakker and his team were able to show not only that observed levels of the vaccine transfer would reduce probability, size, and duration of outbreaks, but that the vaccine could control the disease more effectively than the current method of spreading a lethal, orotopical gel. “Our mathematical models reveal that bats would have to be effectively eliminated to reduce rabies more efficiently than vaccines,” Bakker said, noting that 40 years of culling the bats has been ineffective in Latin America. “Our field studies imply that this level of culling effort is not practically attainable in real-world campaigns.”