Spanish flu: Encyclopedia II - Spanish flu - Mutation theory

Spanish flu - Mutation theory

One prevailing theory hypothesizes that two primary mechanisms in genetics -- genetic drift and antigenic shift -- were involved in the creation of the virus strain found at Fort Riley in Kansas. The fort bred its own swine and poultry for local consumption. As is the case with the avian flu in Asian countries, poultry in the United States characteristically contract a certain strain of influenza. Swine also characteristically contract a specific strain of influenza; however, the two strains (one infecting avian species, the other infecting swine) can usually cross-infect the opposite species. Occasionally, when the viruses cross infect from one species to another, one influenza strain can incorporate the other strain's properties and change drastically (so called "shift"). On the other hand, genetic drift is the random incorporation of mutations into the genome. The new influenza can have the potential to kill half or more of the poultry and/or swine population, but what really concerns epidemiologists is genetic "shift", which is also theorized to have occurred at the fort. The strain that was jumping from swine to poultry or vice-versa jumped to humans (the genetic "shift") allowing the influenza that was confined to swine and poultry to become a human pathogen. At the same time, the new strain was highly infectious and deadly because humanity had never experienced such a strain of influenza.

Recently, scientists (see below) have reconstructed the virus, and the evidence gained from that reconstruction suggests that the virus jumped directly from birds to humans, without traveling through the swine. This does not eliminate the idea that the pandemic started with a Fort Riley cook, however; indeed, he could have been preparing chicken when he contracted the virus.

Adapted from the Wikipedia article "Mutation theory", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki