They found the virus on air particles outside barns housing
infected flocks, prompting their belief the virus can be carried by winds.
But the main transmission between poultry barns is people and
equipment, they say.
More than
49 million birds died or were euthanized this spring in 15 states as the virus
spread from the Pacific Northwest into Midwest farms, making it the worst
outbreak the U.S. has experienced.
Hard hit
were turkey farms in Minnesota, the nation's leading turkey grower, and chicken
farms in Iowa, the leading egg producer.
The USDA
says its staff found that infected and non-infected farms shared equipment,
employees moved between them, and vehicles weren't disinfected when moving
between farms.
It also
heard reports of rodents or small wild birds inside the poultry houses.
"We
are compiling these observations and will present our findings in a subsequent
update of this report.
“Until
then, USDA is collaborating with affected industries and states to implement
more stringent biosecurity procedures while continuing to work on identifying
and mitigating other possible disease pathways in poultry farms
nationwide," the report said.
As for
wind, they report that preliminary analysis of wind data "shows a
relationship between sustained high winds and an increase in the number of
infected farms approximately five days later."
The disease
appears to have been eradicated from commercial flocks in Canada. There were
outbreaks in the Fraser Valley area around Christmas and three farms in Oxford
County, Ont., in April.
