Avian influenza viruses in humans: lessons from past outbreaks.

BACKGROUND: Human infections with avian influenza viruses (AIV) represent a persistent public health threat. The principal risk factor governing human infection with AIV is from direct contact with infected poultry and is primarily observed in Asia and Egypt where live-bird markets are common. AREAS OF AGREEMENT: Changing patterns of virus transmission and a lack of obvious disease manifestations in avian species hampers early detection and efficient control of potentially zoonotic AIV. AREAS OF CONTROVERSY: Despite extensive studies on biological and environmental risk factors, the exact conditions required for cross-species transmission from avian species to humans remain largely unknown. GROWING POINTS: The development of a universal ('across-subtype') influenza vaccine and effective antiviral therapeutics are a priority. AREAS TIMELY FOR DEVELOPING RESEARCH: Sustained virus surveillance and collection of ecological and physiological parameters from birds in different environments is required to better understand influenza virus ecology and identify risk factors for human infection.