Bat virome
The bat virome is the group of viruses associated with bats. Bats host a diverse array of viruses, including all seven types described by the Baltimore classification system: (I) double-stranded DNA viruses; (II) single-stranded DNA viruses; (III) double-stranded RNA viruses; (IV) positive-sense single-stranded RNA viruses; (V) negative-sense single-stranded RNA viruses; (VI) positive-sense single-stranded RNA viruses that replicate through a DNA intermediate; and (VII) double-stranded DNA viruses that replicate through a single-stranded RNA intermediate. The greatest share of bat-associated viruses identified as of 2020 are of type IV, in the family Coronaviridae.
Bats harbor several viruses that are zoonotic, or capable of infecting humans, and some bat-borne viruses are considered important emerging viruses.[1][2] These zoonotic viruses include the rabies virus, SARS-CoV, MERS-CoV, Marburg virus, Nipah virus, and Hendra virus. While research clearly indicates that SARS-CoV-2 originated in bats,[3] it is unknown how it was transmitted to humans, or if an intermediate host was involved. It has been speculated that bats may have a role in the ecology of the Ebola virus, though this is unconfirmed. While transmission of rabies from bats to humans usually occurs via biting, most other zoonotic bat viruses are transmitted by direct contact with infected bat fluids like urine, guano, or saliva, or through contact with an infected, non-bat intermediate host. There is no firm evidence that butchering or consuming bat meat can lead to viral transmission, though this has been speculated.
Despite the abundance of viruses associated with bats, they rarely become ill from viral infections, and rabies is the only viral illness known to kill bats. Much research has been conducted on bat virology, particularly bat immune response. Bats' immune systems differ from other mammals in their lack of several inflammasomes, which activate the body's inflammatory response, as well as a dampened stimulator of interferon genes (STING) response, which helps control host response to pathogens. Preliminary evidence indicates bats are thus more tolerant of infection than other mammals. While much research has centered on bats as a source of zoonotic disease, reviews have found mixed results on whether bats harbor more zoonotic viruses than other groups. A 2015 review found that bats do not harbor more zoonotic viruses than primates or rodents, though the three groups harbored more than other mammal orders.[4] In contrast, a 2020 review found that bats do not have more zoonotic viruses than any other bird or mammal group when viral diversity is measured relative to host diversity, as bats are the second-most diverse order of mammals.[5]