'Strong evidence' bird flu virus has passed from mammals to humans for first time
Scientists have found ‘strong evidence’ that bird flu has spread from mammals to humans for the first time, sparking fears of a new global health crisis.
Hundreds of people have been infected with bird flu, also known as H5N1, since 2003. Until now, all of these cases had come from birds – but the current outbreak in the US has seen herds of dairy farm cows infected in nine different states.
New analysis has now concluded there is “strong evidence” a Texas farm worker who tested positive for the H5N1 virus caught it from sick dairy cattle. It makes up one of 36 herds in the US that have so far tested positive, contributing to growing concerns that American authorities are failing to contain the spread. Testing of milk has also suggested the virus has spread far beyond the reported nine states.
Bird flu has a greater likelihood of adapting to a new species, and subsequently infecting humans who have made close contact, if it spreads unchecked in a domesticated mammal for a long time.
The current outbreak in the US has seen herds of dairy farm cows infected in multiple states
The New England Journal of Medicine report found that the man, whose identity remains unknown, had only suffered mild symptoms. He is said to have developed conjunctivitis but did not have a fever or breathing difficulties. His lungs were also clear. The man, along with the people he lived with, were treated with antiviral drugs as a precaution, and nobody else became infected.
Scientists on the case, including researchers from the Centres for Disease Control, said: “Given the infected human was a dairy farm worker with reported exposure to sick, presumably infected cows in Texas and without reported exposure to other mammals or birds, we believe the genetic and epidemiological data are strong evidence of infection of the human following exposure to presumably virus-infected cows.”
The World Health Organisation reports that 888 people have been infected worldwide between 2003 and the end of March this year, with 463 deaths. The highly pathogenic strain of H5N1 has already seen some mammals infected, including small numbers of foxes, seals and dolphins in the UK.
It was originally thought that the virus spread between farmed mink and within sealion colonies, before it emerged in the US in dairy cows, who were suffering from a high reduction in milk production.
Around 888 people have been infected worldwide since 2003
Scientists believe the virus may have been spreading undetected since the start of the year, with some cows being asymptomatic. It is thought that the man became infected by an airborne virus in the milking parlour landing in his eyes, or by a virus being transferred from his hands to his eyes. While the farm worker only suffered mild symptoms, bird flu can be fatal in some humans.
US authorities say dairy products and beef are safe, and have detected viral fragments, but not active virus, in pasteurised milk.
In the UK, a risk assessment led by government scientists found the threat of a similar outbreak in dairy herds is very small, as animals are kept in different conditions and have little chance being infected by wild birds carrying the cow flu across the Atlantic.