How has the bird flu been able to spread so rapidly to over a hundred Minnesota poultry farms and kill nearly nine million chickens and turkeys?
The answer could be in the air.
A preliminary U.S. Department of Agriculture (USDA) report on what's causing the widespread transmission of H5N2 indicates there are "likely several ways" the virus could be traveling, but perhaps the most troubling possibility is that it can become airborne and ride the wind from one farm to another, according to a news release.
Testing conducted at outbreak sites confirmed there was "viable virus" present in the air both inside and immediately outside stricken farms, up to 1,000 meters away (though it is less potent from a longer distance).
"The results obtained to date indicate that (H5N2) can be aerosolized from infected flocks and remain airborne," the report says.
Investigators found evidence that a certain "cluster" of farms was infected by identical viruses, suggesting "possible transmission among those farms."
Additionally, environmental analyses suggested a relationship between sustained high winds (at least 25 miles per hour for two or more days) and an increase in the number of affected poultry operations.
While the investigation does support earlier theories that wild birds may be responsible for introducing the virus to commercial flocks, the detection of H5N2 in the air and the wind pattern data may shed some light on how it is seemingly spreading among different flocks.
At the latest count, just over 9 million birds have been affected by bird flu in Minnesota, on 108 farms across 23 counties, according to the Minnesota Board of Animal Health.
Farm security not up to scratch
A summary of the report states that while an explanation of H5N2's transmission is hard to pin down, a "likely cause" is the failure of some poultry operations to take effective biosecurity measures.
Investigators observed "sharing of equipment between an infected and noninfected farm," employees moving between farms, a lack of cleaning and disinfecting of vehicles that also move between farms, and "reports of rodents or small wild birds inside poultry houses."
Still, officials point out that "there is not substantial or significant enough evidence to point to a specific pathway or pathways for the current spread of the virus."
The Animal and Plant Health Inspection Service, the USDA agency that conducted the investigation, says it will provide regular updates to the report as testing continues.
H5N2 has killed some 49 million birds nationwide, NBC News reports.