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Bird Flu Species Jumping
November 23, 2004
>>"Sometimes ... [flu viruses] change a little bit, which is called drift. But on other occasions they really change in a major way - that's called shift. Sometimes they jump species, which is what we are seeing now in Asia." The danger with jumping species is that people are infected with viruses for which they have no immunity.<<
Right now scientists are looking at drifts due to point mutations and shifts due to reassortment. However, the real mover in evolution and emergence is recombination, which takes drifts due to mutation and shifts due to reassortment, and then recombines them to make new genes.
Recombination between highly homologous genes cause more drifts. Recombination between less homologous genes causes shifts, but can also cause drifts if the newly acquired sequences represent a small portion of the gene. These drifts can happened repeatedly over a short time frame, as long as there is a high frequency of dual infections.
The current H5N1 outbreak is being fueled by a large number of dual infections which lead to both types of recombinant drifts. The recombinants in Vietnam and Thailand include drifts between avian and mammalian isolates, which leads to species jumping.