The UK government’s Human Animal Infections and Risk Surveillance (HAIRS) group has said the risk posed to people in contact with bird flu-infected animals is at most “very low”.

The group’s risk statement follows news of a case of avian influenza (bird flu) in a person in the state of Michigan in the United States.

The case was confirmed last week in a worker on a dairy farm where bird flu had been identified in the cows.

The individual was being monitored because of their exposure to the infected cattle.

The HAIRS group said recent detections of bird flu in dairy cattle in the United States are likely result of one or more incursions of the H5N1 strain of bird flu, clade genotype B3.13.

This is a reassortant (genetically changed) virus from Eurasian/North American origins and has only been detected in the United States, with the first wild bird cases being reported in November 2023.

The HAIRS group risk statement confirms the zoonotic risk that this genotype poses to people in contact with infected animals is very low, and highlights evidence gaps and recommendations for mitigating the risk of zoonotic transmission.

However, the group said that it is a “rapidly emerging situation” and there remain several evidence gaps.

Therefore, a full assessment is not possible at this stage and the statement will be reviewed as the evidence becomes available, the group said.

Bird flu in US dairy farms

HAIRS said it is unknown exactly how or when the virus was introduced into the implicated dairy farms in the United States, or how long the virus has been circulating undetected.

“There are several possible routes of introduction including contact with wild bird cases, infected mammals or from undetected infected poultry,” the group said.

“No mortality in the affected dairy herds directly attributed to infection has been reported, with infected dairy cattle recovering within approximately 2 weeks of clinical onset.

“The United States Department of Agriculture (USDA) have stated that cow-to-cow transmission is believed to be occurring through mechanical transmission (for example, contact with poorly disinfected milking equipment) and farm-to-farm transmission through the movement of animals, shared equipment or people.”