Antibodies to influenza viruses (including the human A2-Asian-57 strain) in sera from Australian shearwaters (Puffinus pacificus).

Sera were collected from 320 shearwaters (Puffinus pacificus chlororhynchus) nesting on two islands off the east coast of northern Australia in December 1969. About 10% of these sera specifically inhibited the neuraminidase of the 1957 strain of human influenza (A2/Asian/57), some to high titre.The neuraminidase of A2/Hong Kong/68, which has shown considerable drift in man since 1957, was inhibited to a lesser extent by the shearwater sera while the neuraminidase of influenza A0 (Bel strain) was not inhibited at all. The sera showed no evidence of short-lived antibody to the internal antigen of influenza type A, suggesting that the birds had been infected a considerable time previously with an influenza virus possessing neuraminidase identical to that of the virus causing the human 1957 Asian pandemic. On the other hand, about 10% of the sera from one of the islands was found to be positive in immunodiffusion tests with influenza type A soluble internal antigen (ribonucleoprotein), suggesting that another, much more recent, epidemic of avian influenza had occurred on this island only. The surface antigens of the virus responsible for this epidemic have not so far been identified.Observations suggest that avian influenza may be common in wild birds and the finding of antibody to an antigen of human influenza virus in shearwaters is consistent with the idea that human influenza pandemics may originate from avian or animal reservoirs.