Adaptation and transmission of a duck-origin avian influenza virus in poultry species.

A duck-origin avian influenza virus (AIV) was used to study viral adaptation and transmission patterns in chickens (Gallus gallus domesticus) and Pekin ducks (Anas platyrhynchos domesticus). Inoculated birds were housed with naïve birds of the same species and all birds were monitored for infection. The inoculating duck virus was transmitted effectively by contact in both species. Viruses recovered from infected birds showed mutations as early as 1 or 3 days after inoculation in chickens and ducks, respectively. Amino acid substitutions in hemagglutinin (HA) or deletions in neuraminidase (NA) stalk regions were identified in chicken isolates, but only substitutions in HA were identified in duck isolates. HA substitution-containing viruses replicated more efficiently than those with NA stalk deletions. NA deletion mutants were not recovered from contact chickens, suggesting inefficient transmission. Amino acid substitutions in HA proteins appeared in pairs in chickens, but were independent in ducks, indicating adaptation in chickens. In addition, our findings showed that a duck-origin virus can rapidly adapt to chickens, suggesting that the emergence of new epidemic AIV can be rapid.