How can bats carry so many deadly viruses without becoming infected? A fascinating hypothesis emerges

March 18th, 2015

Bats may have evolved immunity to the many deadly viruses they carry because they have one power no other mammal has – flight, researchers hypothesize in a fascinating new paper in the current issue of Emerging Infectious Diseases.

It has been widely observed that bats are sources of high viral diversity and zoonotic viruses. “Although apparently not pathogenic in their reservoir hosts, some viruses from bats severely affect other mammals, including humans,” the authors note. Examples include severe acute respiratory syndrome coronaviruses, Ebola and Marburg viruses, and Nipah and Hendra viruses.

“We hypothesize that flight, a factor common to all bats but to no other mammals, provides an intensive selective force for coexistence with viral parasites through a daily cycle that elevates metabolism and body temperature analogous to the febrile response in other mammals,” the authors conclude. “On an evolutionary scale, this host–virus interaction might have resulted in the large diversity of zoonotic viruses in bats, possibly through bat viruses adapting to be more tolerant of the fever response and less virulent to their natural hosts.”

The increased metabolism and higher body temperatures of bats during flight might serve as an evolutionary adjuvant to their immune systems, “providing a powerful selective force against virulence and promoting the diversity of viruses that infect bat populations,” they theorize. “Perhaps counter-intuitively, this would enable bats to tolerate a greater diversity of viruses that have a high potential for virulence when transmitted to other mammals. The hypothesis also might help explain why co-evolved bat viruses cause high pathogenicity when they spill over into other mammals because the bat-derived viruses might survive well under both febrile and cooler conditions.”