A patient in the US has become the first person to be hospitalised with bird flu despite having no known contact with animals, sparking an urgent investigation to understand how the person contract the infection.
The US Centre for Disease Control and Prevention confirmed a human case of avian influenza A in the state of Missouri on Friday.
Experts have suggested that the patient may have consumed milk infected with H5N1, which is circulating among cattle.
Bird flu, which is also known as avian influenza, is a highly contagious viral disease affecting the respiratory and digestive system of many species of birds. In rare cases, it can affect humans.
So far there is evidence of wild bird-to-cow, cow-to-cow, cow-to-poultry, and one case of cow-to-human transmission.
The case in Missouri is the first time that a patient has become sick without exposure to infected animals, raising fears that the virus may have been acquired through human-to-human transmission.
However, the CDC has said that the risk to the general public remains low and contact tracing has found no additional cases.
The patient had underlying medical conditions and was treated with influenza antiviral medications. They were subsequently discharged and have recovered.
It is the 14th human case of H5 reported in the US during 2024. All other cases were reported in people working on farms who had interacted with sick cattle.
While outbreaks of H5 have been reported in commercial and backyard poultry flocks in 2024, outbreaks in cattle have not been reported in Missouri.
Dr Benjamin Anderson, assistant professor in the Department of Environmental and Global Health at the University of Florida, said the discovery of the case was "very concerning".
"We don’t know if the individual had indirect exposure to people or products from agricultural settings," he told Fox News Digital.
"We also do not yet know the sequence of the virus to determine if it is related to the strains circulating in dairy cattle or not."
He added that officials would need to pay "very close attention" to the case.
Thomas Peacock, an influenza virologist at the Pirbright Institute, told Stat News: “The obvious question I would ask is: Have you ruled out that they’re not someone who’s got a big tub of raw milk in their fridge? Because that just seems like such an obvious route for a cryptic infection.”
Bird flu infections generally happen when the virus makes direct contact with the eyes, nose or mouth.
The virus can also be inhaled through droplets, small aerosol particles or dust.
Some strains of bird flu can cause symptoms similar to severe human flu, such as a fever, cough, tiredness and muscle aches.
Severe infections can cause pneumonia and acute respiratory distress syndrome.
