Why do bats spread so many diseases?

Q: Why do bats spread so many diseases?

 Let us start with positive things. In reality, bats are truly remarkable.

Bats support our agricultural industries as vital members of food webs.

 Bats are beneficial for their role in natural pest control, pollination, and seed dispersal, which helps ecosystems and agriculture thrive. They are also valuable for human health and science, as some species eat mosquitoes and can be a source of compounds used in medicine, and their guano is a potent fertilizer.

 Bats consume massive quantities of insects, including crop pests and mosquitoes that can carry diseases like West Nile virus. Studies estimate that their pest control saves the  agricultural industry billions of dollars annually. 

Many species are vital pollinators for a wide variety of plants, such as bananas, avocados, peaches, cloves, and agave (a key ingredient in tequila). 

Fruit-eating bats play a crucial role in seed dispersal, helping to regenerate forests after disturbances. Some fruit bats can be responsible for up to 95% of the seed dispersal in certain rainforest areas. 

Scientists have discovered compounds in vampire bat saliva that are being studied for potential use as a medicine for stroke patients. Researchers are studying bats' unique resistance to DNA damage and diseases like malaria to find ways to improve human health. 

Bat droppings, or guano, are a highly valuable and rich natural fertilizer, which is used in gardening. 

We have many more benefits from bats. 

But their links to disease outbreaks and their spooky association with vampires influence their notoriety. 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? People associate them to black magic too!

What sets bats apart isn't black magic at all. But rather, it's their long history of coexisting with viruses, the unique trade-offs 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. 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 more than 1,400 species, it's no surprise that pathogen diversity in bats is just as extensive and complex.

Bats, as we know them, have been on Earth for more than 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 people hear about Darwin, evolution and  'survival of the fittest,' , they usually think about smartest, fastest and strongest. But if you look at our genomes, turns out that's wrong. 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  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. 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.

The secret is in evolution and resilience, shaped by millions of years of flying in the face of viruses.

Source: https://news.ufl.edu/2025/10/bat-pathogens/