Chiropteran influenza viruses: flu from bats or a relic from the past?

•Novel influenza A-like viruses were detected in bats.•Bat influenza viruses are divergent from influenza B, C and influenza D viruses.•Bat influenza viruses represent a distinct IAV lineage that circulates in bats.•Lack of canonical functions in bat HA and NA likely poses a strict species barrier.•A common ancient ancestor might be the origin of classical and bat IAV.

The identification of influenza A-like genomic sequences in bats suggests the existence of distinct lineages of chiropteran influenza viruses in South and Central America. These viruses share similarities with conventional influenza A viruses but lack the canonical receptor-binding property and neuraminidase function. The inability to isolate infectious bat influenza viruses impeded further studies, however, reverse genetic analysis provided new insights into the molecular biology of these viruses. In this review, we highlight the recent developments in the field of the newly discovered bat-derived influenza A-like viruses. We also discuss whether bats are a neglected natural reservoir of influenza viruses, the risk associated with bat influenza viruses for humans and whether these viruses originate from the pool of avian IAV or vice versa.