Scientists fear that bird flu could spread from mammals to humans for the first time, marking a new stage in the evolution of the deadly virus.
New analysis concludes there is “strong evidence” that a Texas farmworker who tested positive for the H5N1 virus I caught it from sick dairy cows.
Although other people have been infected with the virus in recent years – some of whom have died – they all contracted it from birds.
There is growing concern about the inability of US authorities to contain the spread of the virus.
So far, 36 herds across nine states have tested positive. But analyzes of the milk suggest the virus has spread much more widely.
The longer it spreads uncontrolled in a domestic mammal, the greater the chance it will adapt to a new species and be transmitted to humans in close contact.
According to the New England Journal of Medicine report, the unidentified man’s symptoms were mild. He developed ocular conjunctivitis, but had no fever or difficulty breathing. His lungs were also clear.
He and the people he lived with were given antiviral medications as a precaution. No one else got sick.
The team, which included researchers from the Centers for Disease Control, said: “Given that the infected human was a dairy farm worker with exposure to sick, presumably infected cows in Texas and with no reported exposure to other mammals or birds, we believe that the genetic origin and epidemiological data constitute strong evidence of human infection following exposure to cows likely infected with the virus.
Some infected mammals
The highly pathogenic strain of H5N1 has spread worldwide through wild birds.
Initially, it was mainly poultry that became infected, and millions were culled to prevent further spread.
But some mammals have been infected, including small numbers of foxes, seals and dolphins in the UK.
The virus is also suspected to have spread between farmed mink and within seal colonies.
But the surprise was when it appeared in the United States in dairy cows, which were suffering from a sharp reduction in their milk production.
The virus has been spreading for months
Evidence suggests the virus has been spreading undetected since the start of the year. Some cows are asymptomatic.
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Scientists believe the man could have been infected either by an airborne virus in the milking parlor and landing in his eyes, or by a virus on his hands or gloves and transferred to his eyes.
Although the farm worker had only a mild infection, the H5N1 virus can be serious, even fatal, for humans.
According to the World Health Organization, 888 people were infected worldwide between 2003 and the end of March this year, with 463 deaths.
Safe Beef and Dairy
US authorities have detected viral fragments – but no active virus – in pasteurized milk. They say dairy and beef are safe.
The UK, a risk assessment by government scientists concluded that the threat of a similar outbreak in dairy herds is very low.
They say the animals are raised in different conditions and there is little chance of bovine flu being transmitted by wild birds across the Atlantic.
Sky news