Nature Study suggests the virus can spread through the respiratory system but infected milk is probably driving the outbreak in the US.
Cows can get infected with the highly pathogenic avian influenza H5N1 by breathing in virus-laden aerosols, according to a preprint1 posted on bioRxiv. But scientists say this mode of transmission is probably not driving the current outbreak among cattle in the United States.
H5N1 was first identified in cattle in Texas in March 2024. Since then, the virus has been detected in 157 herds and 4 people in contact with cattle across 13 US states. Studies have suggested that the main transmission route in cows is through infected milk, which is contaminating milking equipment.
Before the outbreak, researchers didn’t know that influenza A viruses, such as H5N1, could spread in cows. Scientists have raised concerns that should H5N1 spread effectively in cows through the respiratory system, it would be harder to control and the risk of it spreading to humans would increase, given the close contact that cows have with people.
To better understand infections in cows, several teams conducted challenge studies in which they experimentally infected animals with H5N1. The first results from one of these studies were posted on 13 July and have not been peer reviewed.