First bird flu case with no known animal contact seen in US

The US authorities have reported the first-ever case of an H5 strain of avian influenza without a known occupational exposure to sick or infected animals in the country.

The precise variant of the virus is under investigation, but has not yet been confirmed, so it isn't clear if it is the same H5N1 strain that has caused a major outbreak in poultry and dairy cattle this year.

There have been 14 human cases of H5 flu in the US so far in 2024, mostly from exposure to animals or consumption of poorly cooked meat. The latest case involved an individual with underlying medical conditions who was hospitalised by the infection, but recovered after treatment with antiviral medicines, according to the Missouri Department of Health and Senior Services (DHSS).

The lack of known animal exposure is worrying, as the fear is that a bird flu strain may emerge that is more easily transmissible between humans and so become a potential pandemic threat.

H5N1 bird flu is also a particularly concerning pathogen as the mortality rate in the hundreds of cases where humans have been infected through contact with animals in the last 20 years is around 50%, according to the WHO. Still, there have been no reports of deaths among the US human cases this year and most have been relatively mild.

No ongoing transmission among close contacts or otherwise has been identified, according to the Centers for Disease Control and Prevention (CDC), which said its current assessment "is that the risk to the general public from H5N1 remains low [as] there has been no sign of unusual influenza activity in people, including in Missouri."

The Missouri case was detected through routine flu season surveillance, said the CDC, and is also the first time that an H5 strain has been picked up by the national surveillance system. The state hasn't had any reported cases of bird flu in cattle, but has seen signs of the disease in poultry and wild bird populations.

H5N1 has claimed the lives of around 280 million birds since October 2021, precipitating the biggest decline in wild bird populations in decades, as well as thousands of deaths among mammals like seals and sea lions that live in close proximity to sea birds.

In the past few years, a highly pathogenic strain of H5N1 has emerged that can jump between 50 animal species, raising the threat level, and the WHO has said the next pandemic is most likely to be caused by an influenza virus.

In June, a man in Mexico died in what the WHO said was the first lab-confirmed human infection with the H5N2 strain of bird flu, once again without any history of exposure to poultry or other animals.