From birds to animals on land, sea: what’s driving deadly strain of H5N1?

EARLIER THIS week, the United States Department of Agriculture confirmed that a form of avian influenza that has devastated wild bird populations around the world has been found, for the first time, in dairy cattle in Texas and Kansas.

Last week, officials in Minnesota announced that the highly pathogenic H5N1 strain had been found in goats, the first detection of the virus in a domestic ruminant.

Since 2020, avian flu has killed tens of thousands of seals and sea lions in a vast area from the coast of northeast United States to Chile. The infection has also infiltrated mainland Antarctica for the time.

In February this year, the Cambodian health ministry said a 9-year-old boy infected with the virus had died, and several others were sick.

What is this new type of bird flu infection, and how bad is it?

Bird/ avian flu is an infectious viral illness seen mainly among poultry and some wild birds. Not all strains of the virus are dangerous — many of them have circulated for long among at least 100 bird species such as wild waterfowl without causing them much harm.

From time to time, the virus jumps from wild birds to poultry farms. While replicating in cramped warehouses of farmed birds, it evolves into a highly pathogenic form that causes a bigger wave of illness and death than usual.

The currently circ ula tingh5n 1 is one such highly pathogenic type, which is thought to have descended from a virus that devastated farm bird population sin china from 1996 on ward. The new H5N1 type first emerged in Europe in 2020, and spread rapidly to Africa and Asia. By late 2021, it had reached North America, and it appeared in South America in the fall of 2022. In February 2024, the virus raced through mainland Antarctica.

As of December 2023, this H5N1 strain had been reported in more than 80 countries, resulted in the culling of millions of chickens and turkeys at commercial poultry farms, and struck numerous species of wild birds such as gulls and terns, killing them by the thousands.

In January, Dr Chris Walzer of the Wildlife Conservation Society said the ongoing bird flu outbreak was the worst globally and in US history, with hundreds of millions of birds dead since 1996.

Which animal species have been infected?

Besides farm birds and wild birds, some of which are already on the verge of extinction, the H5N1 virus has been reported in animals including foxes, pumas, skunks, and black and brown bears in North America, and farmed minks in Spain and Finland. Small mammal species that are often kept in filthy, overcrowded enclosures with ample opportunities for viral reassortment, are considered especially vulnerable.

But it is marine mammals that are the worst affected. More than 20,000 sea lions and a handful of dolphins have died in Chile and Peru after being infected with H5N1. Deaths of seals have been reported on both US coasts, and in Argentina.

“Sampling efforts suggest that more than 95 per cent of the Southern elephant seal pups born along 300 km of the Patagonia coastline died at the end of 2023. It’s the first report of massive elephant seal mortality in the area from any cause in the last half-century. The sight of elephant seals found dead or dying along the breeding beaches can only be described as apocalyptic,” Dr Walzer said in a statement.

Humans are theoretically also at risk, but they rarely contract bird flu. Most cases of human infection involve people who have come in contact with a large number of sick birds at poultry farms. The Cambodia case represents an exception.

What’s behind the large-scale spread of the virus?

The precise factors behind the outbreaks remain unknown. Some scientists suggest that climate change could be a reason.

Studies have shown that rising global temperatures impact the behaviour of birds in ways that hasten the spread of the flu. Birds are often forced to move into new territories, and mix with species that they usually don’t interact with, which possibly boosts the chances of the virus spreading farther.

Higher sea surface temperatures may also have a role to play. Warmer water near northern Chile has led to a fall in the forage fish population, and that has made sea lions weaker and more susceptible to disease, Liesbeth van der Meer, director of the environmental group Oceana in Chile, told The Associated Press.