H5N1 Influenza Continues To Circulate and Change

Highly pathogenic variants of H5N1 influenza virus that moved from Asia to India, Europe, and Africa have continued to evolve in Southeast China, giving rise to novel variants and raising concerns that these viruses will spread elsewhere and become endemic in wild birds throughout the world. More than half of the 250 persons infected so far with H5N1 died, and efforts to control the spread of this virus led to culling of more than 200 million domestic birds in Asia. The H5N1 viruses are overturning several concepts about how influenza viruses behave, including ideas about what species of birds safely transmit them and which bird species the viruses can sicken and kill; several species of cat can be infected with and transmit H5N1. Once a particular influenza virus becomes widespread among bird species within a region, control measures that depend on culling of flocks need to be augmented with vaccine use.