3 min
Batty pathogens: Why do bats spread so many diseases?
Let’s face it — bats get a bad rap. Their links to disease outbreaks and their spooky association with vampires influence their notoriety. In reality, bats are truly remarkable. Bats support our agricultural industries as vital members of food webs. And, contrary to their portrayal in popular Halloween blockbusters, they are gentle and tidy creatures that groom themselves like cats. So why is it that when we hear of disease outbreaks, it always seems to be bats? According to University of Florida Emerging Pathogens Institute member Jim Wellehan, D.V.M., what sets bats apart isn’t black magic at all. But rather, it’s their long history of co-existing with viruses, the unique tradeoffs of flight and, perhaps most of all, a history of adapting to new pathogens. “(Infectious disease) has been the biggest factor in all of evolution,” said Wellehan, who is also a professor at the UF College of Veterinary Medicine. “People are always looking for an excuse (as to) why bats are magic, and the truth is bats have just been exposed to a lot of stuff and selected for those genes accordingly.” While humans are the most populous mammals on Earth, bats are a massive group of animals. Behind rodents, they represent the second-largest group of mammalian biodiversity, accounting for a whopping 20% of all mammal species. With over 1,400 species, it’s no surprise that pathogen diversity in bats is just as extensive and complex. Jim Wellehan's research focuses on comparative infectious disease, pathogen evolution, molecular diagnostics and pathogen discovery. View his profile here Bats, as we know them, have been on Earth for over 50 million years. This extensive period has given pathogens plenty of time to evolve alongside the winged mammals. Bats carry viruses like Ebola, Hendra virus, Nipah virus and SARS-CoV-2, which causes COVID-19. One factor that is important in this viral diversity is flight. Flight provides bats with many evolutionary advantages, such as predator evasion, access to new food sources and the ability to exploit diverse habitats. Flight also dramatically increases the chance of rapid pathogen transmission, as they can travel long distances and past many geographic barriers. Many species are highly social, which increases transmission rates as they live in close proximity and groom one another. “When I first learned about Darwin and evolution, ‘survival of the fittest,’ I assumed, meant ‘smartest and fastest and strongest,’ but if you look at our genomes, turns out that's wrong,” said Wellehan. “The genes that are selected for are mostly immune-related. The most important thing is to have enough genetic diversity in your population so that someone has immunity genes that are effective against the next pathogen that doesn't even exist yet. With their increased mixing and contact rates, bats have done this more often than most animals.” Generally, pathogens are most likely to cause disease when they first infect a new host species, as the susceptible animals have not yet developed the necessary defenses. Pathogens, along with their hosts, have no choice but to evolve to survive. With such a wide variety of species, it is not surprising that bats also carry a large proportion of mammal-associated viruses. This is not to say that bats are immune to all pathogens. As the most rapidly evolving factor in life, infectious disease is an incredibly dynamic part of medicine. Bats can get sick from lyssaviruses, including rabies. Additionally, white nose disease, a fungal infection that targets hibernating bats, has been a growing concern in the United States for the past decade. Though bat pathogens are a significant concern, habitat disturbance plays a larger role in bat population pathogen emergence, ultimately affecting humans as the dominoes fall. “Pathogen transmission to humans and conservation efforts go hand in hand,” Wellehan said. “When populations get under stress, that's when ecological balances get shifted, and zoonotic jumps occur. ... It turns out that if we think of ourselves as something separate from nature, it doesn't work so well.” So, while bats may embody the spirit of Halloween, their “magic” lies in evolution and resilience, shaped by millions of years of flying in the face of viruses, not spooky legends. Looking to know more? We can help. Jim Wellehan is available to speak with reporters about bats simply click on his icon now to arrange an interview today.
