Health
PUBLIC health experts still don’t know how a bird flu virus has been spreading for months among dairy cows in the US – although early evidence points to contaminated milking equipment.
Since late March, 52 dairy herds across nine US states have tested positive for H5N1, a bird flu virus that has killed millions of birds and thousands of mammals worldwide. Genetic analysis of samples from infected cattle suggests the outbreak began when cows on a Texas farm contracted the virus from wild birds. It then spread to other herds as infected cows moved between farms. But how the virus jumps from cow to cow is unclear.
“This is a critical question that is still under investigation,” said Andrew Pekosz at Johns Hopkins University in Maryland during a press briefing on 15 May. “There are most likely two ways the virus is spreading,” he said.
The first is respiratory transmission. Infected cows may be expelling the virus in small droplets of mucous or saliva that other cows then inhale or ingest when sharing food and water, says Seema Lakdawala at Emory University in Atlanta, Georgia.
However, infected cows show mild to no respiratory symptoms, and their nasal swabs contain low concentrations of the virus, suggesting another mode of transmission.
“I think it’s the milking equipment,” says Lakdawala. Raw milk from sick cows contains high concentrations of H5N1 and can thus transmit the virus. Several cats contracted bird flu after drinking unpasteurised milk, for instance. This is why it is crucial that humans avoid raw milk products.
Although adult cows don’t drink raw milk, they do share milking equipment. Dairy workers normally wash a cow’s udder before hooking it up to the milker and again after removing it. But not all dairies disinfect the milking
