Replication of influenza A viruses of high and low pathogenicity for chickens at different sites in chickens and ducks following intranasal inoculation

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Abstract
Ten specific pathogen free light breed chickens and 10 commercial layer ducks were inoculated intranasally with one of five avian influenza A viruses which had been characterised as showing high or low pathogenicity for chickens. Recovery of the two viruses of low pathogenicity was restricted to the respiratory tract and gut of both species. Highly pathogenic viruses were recovered from all organs sampled. With two of the highly pathogenic viruses, A/duck/Ireland/113/83 (H5N8) and A/chicken/Vic‐toria/85 (H7N7), the sites of recovery in ducks were similar to those seen in chickens except that virus was absent from the brain, apart from low levels detected in brain samples taken on day 5 from ducks infected with A/duck/Ireland/113/83. The levels recovered from organs of ducks for these two viruses were also similar to those in chickens, except for lower levels in kidney and liver for ducks infected with A/chicken/Victoria/85, and a delayed peak of recovery of both viruses in ducks. The third.highly pathogenic virus, A/turkey/England/50–92/91 (H5N1), could not be recovered from any site in ducks. For all three highly pathogenic viruses mortality and morbidity were rapid and complete in chickens but absent in ducks.