Recent influenza A (H1N1) infections of pigs and turkeys in northern Europe.

The most recent introduction of an avian influenza A virus without reassortment into mammals occurred in 1979 when H1N1 strains could be isolated from diseased pigs in northern Europe. This newly introduced avian virus formed a stable lineage in pigs and, in the meantime, spread all over Europe. In 1991 highly pathogenic H1N1 strains closely related to a contemporary swine virus were isolated from turkeys of a breeding farm near Bremen, Germany. Outbreaks in several farms in Germany, France, and the Netherlands indicate that the "avian-like" swine viruses can easily be reintroduced into an avian population causing severe economical losses.