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Bird Flu: Is a Pandemic Looming in Our Future?

Author(s): Deanne Erdmann, MS, Christopher Burnett, BA, and Nancy Moreno, PhD

Avian Influenzas: Change Mechanisms (part 2)

Occasionally, major changes occur in the genetic structure of the influenza virus that drastically affect the way it interacts with the immune system and causes disease. These changes, called antigenic “shifts,” result in new combinations of influenza A virus subtypes. One way that antigenic shifts can occur is if a common human strain of influenza A virus and an avian influenza virus both infect the same animal. Viruses, in general, easily swap genetic material. In the case of flu, such a reassortment could result in a new strain, different from both original strains. Pigs are susceptible to both bird and mammalian viruses, and thus serve as excellent “mixing vessels” for recombining genetic material from related viruses. Humans living near poultry and pigs have long been thought to be at risk for exposure to such new strains. Antigenic shift was responsible for the emergence of the Hong Kong flu in 1969. This flu was caused by H3N2, which arose when the human H2N2 subtype reassorted with genes from bird viruses that contained the H3 subtype.