Influenza viruses found in bats, known as “bat flu,” are distinct strains of influenza A viruses identified within bat populations. Their discovery expanded the understanding of influenza virus ecology, highlighting bats as a new animal species capable of harboring these viruses. Researchers continue to study these unique strains to understand their characteristics and implications.
The Unique Nature of Bat Influenza
Bat influenza viruses possess distinct biological characteristics. Genetic analyses show these bat-origin viruses are phylogenetically divergent from influenza viruses found in avian and mammalian hosts. The first two complete bat flu genomes, H17N10 and H18N11, were discovered in New World yellow-shouldered fruit bats (Guatemala, 2009-2010) and flat-faced fruit bats (Peru, 2010). These discoveries challenged previous assumptions about influenza A virus host range.
A key difference is how these bat flu viruses enter host cells. Unlike most influenza viruses that use sialic acid receptors for attachment and entry, the hemagglutinin (HA) proteins of H17N10 and H18N11 do not bind to these conventional receptors. Instead, H17N10 and H18N11 utilize Major Histocompatibility Complex class II (MHC-II) molecules as their entry mechanism. This distinct cellular entry pathway explains their unique behavior and limited ability to infect cells typically susceptible to other flu viruses.
Transmission to Other Species
A central question regarding bat influenza is its ability to infect humans or other animal species. To date, no documented cases of natural human infection linked to bat influenza viruses exist. This limited transmission stems from their unique cellular entry mechanism.
Laboratory studies show that pure bat influenza viruses, such as H17N10 and H18N11, replicate poorly in human and other mammalian cell lines. While some research suggests bat flu viruses can enter human cells via MHC-II receptors, they would require significant genetic changes to infect and spread efficiently among people. Studies in animal models like ferrets and mice have also shown only limited replication for these bat-derived viruses.
Assessing the Pandemic Potential
While direct natural transmission to humans has not been observed, scientists monitor bat influenza viruses due to the theoretical risk of viral reassortment. This process involves two different influenza viruses co-infecting a single host cell and swapping genetic segments, potentially creating a new hybrid virus. The internal genes of bat influenza viruses are considered compatible with human influenza viruses, meaning they could theoretically exchange genetic information.
If an animal, such as a pig, were simultaneously infected with both a bat influenza virus and a human or avian influenza virus, it could serve as a “mixing vessel” for reassortment. This genetic exchange could potentially lead to the emergence of a novel virus capable of infecting humans and spreading efficiently. Although experimental conditions have shown reassortment between H17N10 and H18N11 viruses, compatibility for reassortment with conventional influenza A or B viruses appears limited in laboratory settings. This theoretical pathway of genetic reassortment, rather than direct transmission, is the primary reason for ongoing scientific surveillance of bat influenza viruses.