Two British poultry workers have tested positive for bird flu, health officials have announced, bringing the total number of human infections recorded in the UK to three.
Both individuals recently worked on an infected poultry farm in England, with one case likely to have breathed in contaminated material, the UK Health Security Agency (UKHSA) said.
Neither of the workers displayed symptoms of the disease and both are now testing negative, the agency said.
There are also no signs that the bird flu H5N1 virus jumped to other people, though close contacts of the individuals have been approached by UKHSA, officials said.
Both cases were picked up by a UKHSA programme that tests all workers on infected farms in England.
“Current evidence suggests that the avian influenza viruses we’re seeing circulating in birds around the world do not spread easily to people,” said UKHSA chief medical adviser Professor Susan Hopkins.
“However, we know already that the virus can spread to people following close contact with infected birds and this is why, through screening programmes like this one, we are monitoring people who have been exposed to learn more about this risk.
“Globally there is no evidence of spread of this strain from person to person, but we know that viruses evolve all the time and we remain vigilant for any evidence of changing risk to the population.”
UK officials have only detected the H5N1 strain of bird flu once before in humans.
In January last year, health officials announced that a duck keeper called Alan Gosling had acquired the infection from close, regular contact with a large number of infected birds, which he had kept in and around his home over a long period of time. Gosling also recovered fully.
The virus, which has killed hundreds of thousands of birds over the past year in an unprecedented global outbreak, can be deadly in humans. Estimates suggest that it can kill up to 50 per cent of the people it infects.
UKHSA scientists said one of the two poultry workers who test postive likely breathed in viral material from the farm.
“For the second individual it is more difficult to determine which is the case,” the UKHSA added.
As part of the government’s asymptomatic surveillance programme, poultry workers are asked to take swabs of their nose and throat for up to 10 days following exposure to infected birds.
Some workers may also be asked to have finger-prick blood tests to see if UKHSA can detect antibodies against avian influenza.
The UKHSA did not specify when or where in England the two poultry workers had tested positive. It said the level of risk to human health from bird flu remains very low, but warned that it “remains critical that people avoid touching sick or dead birds”.
Although the H5N1 virus does not yet appear to have adapted to spread efficiently between humans, there is evidence it can spread between other mammals including ferrets, mink and even sea lions.
Experts worry that the global spread of the virus and its progress into mammals increases the risk of an adaptation that will allow it to take off in humans.