Unusual influenza A viruses in bats

Abstract

Influenza A viruses infect a remarkably diverse number of hosts. Two completely new influenza A virus subtypes were recently discovered in bats, dramatically expanding the host range of the virus. These bat viruses are extremely divergent from all other known strains and likely have unique replication cycles. Phylogenetic analysis indicates long-term, isolated evolution in bats. This is supported by a high seroprevalence in sampled bat populations. As bats represent ~20% of all classified mammals, these findings suggests the presence of a massive cryptic reservoir of poorly characterized influenza A viruses. Here, we review the exciting progress made on understanding these newly discovered viruses, and discuss their zoonotic potential.

Figure 1

Altered receptor-binding sites in H17 and H18 HA. A binding cavity defined by the 130-loop, the 220-loop and the 190-helix is occupied by sialic acid in 2009 H1 HA [56]. Polymorphisms surrounding the binding cavity and the absence of conserved binding-site residues dramatically flatten the binding pocket in structures of H17 and H18. H17 and H18 fail to bind canonical sialic acid receptors (see text for details).

Figure 2

Comparison of the NA active site. Surface representations of the active sites for N1 (2HU4) and N2 (2QWK) in the presence of the neuraminidase inhibitor oseltamivir [59,60]. The substrate binding pocket is framed by the 150- and 430-loops. The bat influenza virus N10 active site (4FVK) is shown with oseltamivir from the N1 and N2 structures superimposed. The substrate binding pocket is dramatically opened relative to N1 and N2. A predicted clash between N10 and the modeled oseltamivir is denoted with a red circle.