While there is no record to date of sustained human-to-human bird flu transmission, the recent virus mutations show it may be inching closer to humans, according to health experts on 29 April.

The bird flu or avian influenza A (H5N1) virus outbreak in poultry farms is not a new occurrence. It has periodically been reported all around the world, including poultry farms in parts of India.

Migrating wild birds bring the virus to poultry farms. However, in recent years, this bird flu virus H5N1 has jumped to mammals.

In 2023, the H5N1 virus killed a record number of birds and also spread to otters, sea lions, foxes, dolphins, and seals, among others. More recently it also affected numerous cattle farms across the US. Health officials in the US found fragments of bird virus in pasteurised milk sold in stores, including in about 20 per cent of samples in initial testing across the country.

"This shows that the H5N1 bird flu virus has now adapted for circulating among mammals. It is now able to easily spread from mammal to mammal, rather than having to jump each time from bird to mammal. This shows the virus has made suitable adaptations already. And bird flu virus has moved one step closer to humans," said Co-chairman of the Indian Medical Association’s National COVID-19 Task Force.

Importantly, "there is no record to date of sustained human-to-human transmission. This can only occur if the virus makes more adaptations by mutating. The concern now is the virus has found a new host among cattle, which is always in contact with man," he added.

Can bird flu infect humans?

Bird flu -- a common phenomenon seen in India -- raised infection concerns among humans in Jharkhand’s Ranchi last week. Two doctors and six staff members of the Regional Poultry Farm in Hotwar were quarantined for two days. However, their throat swab samples sent for tests on April 27, were found to be negative.

According to data from the World Health Organisation, from 2003 to 2023, a total of 873 human cases of infection with influenza A (H5N1) and 458 deaths have been reported globally from 21 countries. However, to date, no sustained human-to-human transmission has been detected.

"Human infection due to avian influenza happens only with close contact with infected animals. Although the risk for human infection is rare, such occurrences come with a high mortality rate," said biologist Vinod Scaria.

The high mortality rate is because "humans have no prior immune memory for this particular type of influenza virus", said Dr Jayadevan.

The WHO believes that available epidemiological and virological evidence does not indicate that current bird flu viruses have acquired the ability to sustain transmission among humans. However, the recent episode of transmission to cattle, where it has reportedly affected one human, has raised fresh concerns.

Genomic analysis suggests that it has silently been spreading among the cattle for months - since December or January.

"Scientists are worried whether the virus will now make further adaptations where it can not only easily infect man, but also spread from man to man, in which case it could become a major catastrophic event. We hope it will not happen," Said doctor.

The WHO advises people in close contact with cattle and poultry to regularly wash hands and employ good food safety and food hygiene practices, pasteurise milk, as well as to get vaccinated against seasonal human flu, to reduce the risk that H5N1 could recombine with a human avian virus.

"Appropriate personal protection while handling infected birds/dead birds or excreta is very important and awareness of this among the public is important," said Scaria.