First human case of bird flu due to exposure to ill dairy cows recorded in the US

The infection in a human, which is only the second in US history of a person infected with bird flu, is believed to be linked with the recent outbreak of avian influenza A(H5N1) in dairy cows.

The current outbreak of highly pathogenic avian influenza (HPAI) began in 2022, with H5N1 being the primary strain. Until recently, it had never been detected in ruminants.

But in late March, the USDA reported that cows sickened by a ‘mystery disease’ that made them produce thick, colostrum-like milk and lowered their appetite, was in fact avian flu. The detections are thought to be linked to wild waterfowl, but federal agencies are investigating multiple scenarios.  

Until recently, experts believed cows to be ‘dead-end hosts’, meaning that infected cows were unlikely to further transmit the virus to other cows or to humans. However, people with close or prolonged unprotected exposures to infected animals or environments are thought to be at greater risk of infection.

The Centers for Disease Control and Prevention said the person presumed to be infected with the A(H5N1) strain ‘had exposure to dairy cattle in Texas’ and their only symptom was eye redness consistent with conjunctivitis. They are being treated with an antiviral flu drug and are recovering but have been told to isolate.

“This infection does not change the H5N1 bird flu human health risk assessment for the US general public, which CDC considers to be low,” the organization said.

Cow-to-cow transmission ‘cannot be ruled out’

Over the weekend, the USDA also confirmed a case of HPAI in a Michigan dairy that had recently received cows from Texas. The strain of the virus found in Michigan was ‘very similar’ to the strain confirmed in Texas and Kansas and means that cow to cow transmission ‘cannot be ruled out’.