Influenza viruses: From birds to humans

Avian influenza viruses are the precursors of human influenza A viruses. They may be transmitted directly from avian reservoirs, or infect other mammalian species before subsequent transmission to their human host. So far, avian influenza viruses have caused sporadic - yet increasingly more frequently recognized - cases of infection in humans. They have to adapt to and circulate efficiently in human populations, before they may trigger a worldwide human influenza outbreak or pandemic. Cross-species transmission of avian influenza viruses from their reservoir hosts - wild waterbirds - to terrestrial poultry and to humans is based on different modes of transmission and results in distinctive pathogenetic manifestations, which are reviewed in this paper.

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