Study confirms bird flu is transmitted efficiently and sustainably among mammals

A recent study conducted by Cornell University and published in Nature confirmed that the H5N1 virus, responsible for one variant of bird flu, managed to enter farms through dairy cows and from there moved on to other animal species, including domestic cats and raccoons.

News of the presence of bird flu in American livestock spread quickly throughout April. Preliminary tests by the U.S. Department of Agriculture and the Food and Drug Administration (FDA) found traces of the virus in both cattle and raw milk.

A new report confirms that the H5N1 virus, belonging to the 2.3.4.4b (highly pathogenic) clade, has infected dairy cattle herds in several US states. Affected mammals showed clinical signs such as loss of appetite, changes in fecal consistency, difficulty breathing, and decreased milk production. In addition, complete viral genome sequences were detected in dairy cows, birds, domestic cats, and wildlife circulating on farms, including raccoons.

“The efficient and sustained transmission of the virus from mammal to mammal is unprecedented. “This is worrying because it may force the virus to adapt, improving its ability to infect and transmit to other species, including humans,” the researchers warned.

An unprecedented surge

In recent years, America has faced an unprecedented wave of bird flu. Since 2021, the disease has been appearing in poultry farms at an alarming rate. But what has epidemiologists wary is the growing transmission of the virus to mammals. To date, infections have been recorded in sea lions, foxes, mice, ferrets, dogs, cats, cows, and even polar bears.

The evidence of the virus spreading among cows, as well as its recirculation among farm animals, shows that avian influenza has adapted to transmit efficiently in an unconventional population. It also highlights the virus’s remarkable ability to cross species barriers.

In parallel with the report published in NatureThe Food and Agriculture Organization of the United Nations (FAO) has called for an urgent and unified response to combat bird flu.

“The recent increase in avian influenza outbreaks is deeply worrying (…) Since late 2023, we have seen an increase in human cases and the spread of the virus to new animal species. The emergence of new strains of A/H5N1, which are more easily transmitted, increases the threat of a pandemic. Immediate and coordinated preventive measures are essential,” said Kachen Wongsatapornchai, Regional Director of FAO’s Emergency Centre for Transboundary Animal Diseases.

While authorities in some countries are developing strategies to detect and contain bird flu on poultry farms, others have already ordered vaccines against the virus. Europe will have access to almost 600,000 doses, mainly for livestock farmers and veterinarians. The vaccine is the only preventive against zoonotic bird flu approved by the European Union.

While there are cases of bird flu in humans, experts say there is no reason to believe the virus has mutated and can be transmitted from person to person through the air. All the cases so far have been among workers working near poultry farms.