The bird flu that's devastated some Midwestern farms likely spread by several means — on machinery and workers, by rodents and possibly even on the wind, the U.S. Department of Agriculture said in a new report released Monday.
The agency's Animal and Plant Health Inspection Service scientists studied genetic properties of virus samples on more than 80 turkey and chicken farms. The scientists determined that wild birds introduced the virus onto farm but that lapses in biosecurity on farms and environmental factors likely contributed to the spread of the disease.
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 then, 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.
The scientists also found that air samples collected outside of infected poultry houses contain virus particles, indicating the virus could be transmitted by air. 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 report said.
The government is conducting additional analyses to better characterize environmental factors that may contribute to virus spread.
The agency said it will continue to share what it learns with state officials and the industry and it is organizing a meeting in Iowa next month to focus on biosecurity.