Some of these human and avian influenza viruses might become adapted to pigs and then begin circulating in pig populations. The co-circulation of avian, human, and pig viruses in pigs is of significant concern because of the potential for a genetic exchange, or "reassortment" of material between these viruses. Such an occurrence has the potential to produce a new pandemic influenza strain.
Last week, a researcher at China's Harbin Veterinary Research Institute announced that pigs from farms in parts of China had been infected with the H5N1 strain of avian influenza.
Because the findings remain preliminary and are not necessarily indicative for widespread infection among pigs, assessing the consequences of this information for public health is difficult. Providing a detailed risk assessment of the current situation requires an understanding of the main factors influencing the potential for the emergence of a pandemic influenza strain: the prevalence of H5N1 and human H3N2 virus in pigs in
The role of pigs in genetic reassortment is not fully understood. While there has been no known natural occurrence of reassortment of influenza viruses in pigs that resulted in a new pandemic strain, the probability of this occurrence is not negligible.
The chances for genetic reassortment depends upon both the duration of H5N1 circulation in pigs as well as the simultaneous presence of human and pig influenza A viruses (such as H3N2 or H1N1). As long as human and avian influenza viruses are co-circulating -- whether in humans or in pigs -- the possibility of an exchange of genetic material exists.
To better understand the implications of the findings in
Source: World Health Organization