The bird flu virus that has beset dairy farms since early last year may be spreading through the air in so-called milking parlors and through contaminated wastewater, as well as from milking equipment, scientists have found.

The Department of Agriculture has said that the virus spreads primarily from milking equipment or is carried by dairy workers and vehicles traveling between farms.

But in the new study, scientists found live virus in the air of milking facilities, suggesting that cows and farmworkers might have become infected by inhaling the pathogen. The virus may also spread by water used to clean cattle barns or contaminated with discarded milk.

The study was posted online last week and has not been peer reviewed for publication. But the results are consistent with those from other teams who found that contaminated milking equipment might not explain all cases of bird flu observed on farms.

In the new study, researchers also found infected cows with no visible symptoms, suggesting that bird flu may spread from cows that appear healthy.

Just as people can become infected with the seasonal flu virus by touching a sick person, from contaminated surfaces or by inhalation, “there is no one way” that bird flu spreads, said Seema Lakdawala, a virologist at Emory University who led the work.