Bats Join the List of Mammals Susceptible to Bird Flu, Raising Concerns

In a concerning development for wildlife health and potential human risks, scientists have discovered that vampire bats in Peru have been exposed to H5N1, the highly pathogenic avian influenza virus responsible for bird flu. This finding adds bats to the growing list of mammals susceptible to the virus, creating new worries about its potential evolution and spread.

Researchers from the University of Glasgow reported in November that more than a dozen vampire bats in Peru were found carrying H5N1 antibodies, indicating they had been infected with the virus but survived. Vincent Munster, a virus ecologist at Rocky Mountain Laboratories who wasn’t involved in the study, described the finding as “very worrisome.” Each time the virus jumps to a new mammalian host, it gains opportunities to mutate and evolve, potentially bringing it closer to spreading efficiently among humans. Even more concerning, preliminary findings from Bangladesh suggest that flying foxes—large fruit-eating bats with foxlike faces—may have died from bird flu, indicating the virus could affect multiple bat species.

The significance of bats becoming infected with H5N1 cannot be overstated. Bats already serve as reservoir hosts for several pathogens that pose serious risks to humans, including coronaviruses, Ebola, and Nipah virus. If multiple bat species prove susceptible to H5N1, their large colonies could become reservoirs for the virus, according to Gregory Gray, an infectious diseases epidemiologist at the University of Texas Medical Branch. This scenario could transform bats into vectors for bird flu transmission to other animals and potentially humans. The vampire bat findings emerged from research led by wildlife veterinarian I-Ting Tu, who began studying viruses in these bats in Peru just as bird flu swept across South America’s coast in 2022-2023, killing at least 560,000 seabirds and 10,000 sea lions in Peru alone.

Tu’s research journey was challenging and emotionally difficult. After securing permits and organizing logistics, her team collected samples from hundreds of vampire bats across three regions of Peru: coastal areas where bats feed exclusively on marine animals, Andean regions where they feed on livestock and occasionally humans, and mixed-diet sites where bats consume both marine and land-based prey. Tu described the fieldwork as a trail of “blood and tears,” suffering multiple bites while handling the vampire bats for the first time. The research involved invasive procedures, including anesthetizing the animals and inserting tubes into their stomachs to analyze their blood meals, which some bats didn’t survive—an outcome that left Tu wracked with guilt.

Despite these difficulties, the research yielded crucial findings. While no H5N1 genetic material was found in the bats—likely because they had already cleared the virus before sampling—14 bats that had exclusively fed on marine animals during the outbreak carried antibodies against H5N1. Study co-author Susana Cárdenas-Alayza, a conservation biologist at Cayetano Heredia University in Lima, wasn’t surprised by this discovery. During the 2022-2023 outbreak, the coastal environment was heavily contaminated with the virus, with sick animals everywhere—sea lions coughing and pups climbing over their dead parents in what she described as an “apocalyptic” scene. Vampire bats, which can walk and jump on land, likely became infected while feeding on infected marine animals, targeting areas like eyeballs and anuses where viruses are often shed.

The implications of these findings are particularly concerning at mixed-diet sites, where vampire bats that feed on infected marine animals might subsequently pass H5N1 to livestock or humans. Daniel Streicker, a disease ecologist at the University of Glasgow and study co-author, emphasized the need to address key questions about how efficiently H5N1 can replicate in bats, transmit among them, and spread to other species. The team discovered that H5N1 can attach to various tissues in vampire bats—including lungs, kidneys, and liver—and infect cells from those tissues in laboratory settings. However, transmission among bats appears limited, as only those that foraged on marine animals carried antibodies, suggesting the virus may not yet be optimized for bat-to-bat spread.

As marine animals along the Latin American coast continue to experience bird flu outbreaks, scientists warn that repeated jumps of H5N1 from sea life to vampire bats could create new pathways for the virus to establish itself in novel hosts and acquire new traits. This evolution could potentially make the virus more deadly or contagious. Researchers are also investigating what other avian influenza viruses bats may harbor, noting that in 2017, a virus related to H9N2 (another concerning bird flu virus) was discovered in flying foxes in Egypt. The scientific community emphasizes the urgent need to strengthen surveillance systems to monitor potential virus crossover into domestic animals, particularly given the frequent interactions between bats and livestock. As Gray suggests, this interface between wildlife and domesticated animals is where we should “keep a pulse on” to protect both animal and human health from emerging infectious disease threats.