Highly pathogenic H5N1 influenza viruses have been isolated from a number of avian and mammalian species.
Despite intensive control measures the number of human and animal cases continues to increase.
A more complete understanding of susceptible species and of contributing environmental and molecular factors is crucial if we are to slow the rate of new cases.
H5N1 is currently endemic in domestic poultryin only a handful of countries with sporadic and unpredictable spread to other countries.
Close contact of terrestrial bird or mammalian species with infected poultry/waterfowl or their biological products is themajor route for interspecies transmission.