Tree shrew as a new animal model to study the pathogenesis of avian influenza (H9N2) virus infection

Outbreaks of avian influenza virus continue to pose threats to human health. Animal models such as the mouse, ferret, and macaque are used to understand the pathogenesis of avian influenza virus infection in humans. We previously reported that the tree shrew (Tupaia belangeri, family Tupaiidae), which is regarded as a "low-level primate", has α2,3- and α2,6-linked sialic acid receptor distributions similar to those of humans and is potentially a useful mammalian model for studying mild human influenza (H1N1) virus infection. In this study, we used the tree shrew experimental model to investigate the pathogenesis of avian influenza A (H9N2) virus infection and the effect of the E627K mutation in the PB2 gene, an adaptation to mammalian hosts. Evidence of disease, virus titers in the upper and lower respiratory tract, histopathology and induction of proinflammatory cytokines are described. We also established ex vivo culture models of tree shrew respiratory tissues to study the tropism and replication of the H9N2 virus. Our results demonstrated that the tree shrew is a viable new in vivo experimental model for avian influenza research that provides results comparable to those observed in ferrets. The disease spectrum and pathogenesis in tree shrews correlate well with what is observed in humans.