A human case of swine influenza virus infection in Europe--implications for human health and research.

Swine are susceptible to the same influenza A virus subtypes as humans--H1N1, H3N2 and H1N2--and the histories of influenza in pigs and people are closely linked. Many swine influenza viruses are a result of reassortment and their genes are composed of human and avian and/or swine virus genes. Indeed, it is known that both human and avian influenza viruses occasionally transmit to pigs, and that pigs can serve as "mixing vessels" for these viruses, meaning that viruses can exchange genetic material and lead to the production of a new "hybrid" virus. This has led to the thinking that perhaps pandemic viruses could emerge following reassortment in pigs. However, since nobody has observed the start of a pandemic, there remains no direct evidence to make this more than a theory.