Worobey said the timing is provocative because of the correlation of that sudden shift in the flu virus' evolution with historical events in the late nineteenth century.
"In the 1870s, an immense horse flu outbreak swept across North America," Worobey said, "City by city and town by town, horses got sick and perhaps five percent of them died. Half of Boston burned down during the outbreak, because there were no horses to pull the pump wagons. Out here in the West, the U.S. Cavalry was fighting the Apaches on foot because all the horses were sick. This happened at a time when horsepower was actual horse power. The horse flu outbreak pulled the rug out from under the economy."
According to Worobey, the newly generated evolutionary trees show a global replacement of the genes in the avian flu virus coinciding closely with the horse flu outbreak, which the analyses also reveal to be the closest relative to the avian virus.
"Interestingly, a previous research paper analyzing old newspaper records reported that in the days following the horse flu outbreak, there were repeated outbreaks described at the time as influenza killing chickens and other domestic birds," Worobey said. "That's another unexpected link in the history, and the there is a possibility that the two might be connected, given what we see in our trees."
He added that the evolutionary results didn't allow for a definitive determination of whether the virus jumped from horses to birds or vice versa, but a close relationship between the two virus species is clearly there.
With regard to humans, the research sheds light on a longstanding mystery. Ever since the influenza pandemic of 1918, it has not been possible to narrow down even to a hemisphere the geogr
|Contact: Daniel Stolte|
University of Arizona