Public health experts around the world are sounding the alarm as cases of a virulent strain of avian influenza called H5N1 rise in mammals. Bird flu has infected humans in the past, mostly people who work directly with diseased poultry, but there has never been widespread human-to-human transmission of the virus. If there were, it could be a catastrophe: The original H5N1 mutation had a 50 to 60 percent mortality rate in humans.

The latest outbreak of H5N1, which began in the U.S. in late 2021, has resulted in the culling of 58 million birds thus far and led to a marked increase in the cost of eggs and poultry at the supermarket. It’s America’s second major surge of H5N1 since the strain was first detected in southern China in the late 1990s — the first significant U.S. wave kicked off in 2014 and was contained mainly to the Midwest.

Since 2021, H5N1 has been found in at least 47 states. It’s circulating among wild birds, cropping up in wild mammals, and, crucially, bouncing between mink. That last development is what really has experts alarmed. More broadly, the H5N1 outbreak fits a pattern scientists have been ringing alarm bells about for years now: Climate change is throwing ecosystems out of whack and spurring the spread of disease, putting wildlife and human health at risk.

The past few years have seen an uptick in the size and pace of bird flu outbreaks. The virus has moved outside the bounds of its typical seasons, which coincide with birds’ spring and fall migrations. In the past year, H5N1 has been detected in the summer months in Italy, when high temperatures should have extinguished it, and in the depths of winter in Canada, when migrating birds are few and far between. The factors influencing these outbreaks are still largely unknown. The virus may be hanging out in the environment for longer or spreading with greater frequency and ease between birds.

Vaillancourt suspects one overarching explanation. “How come this virus is popping up in the middle of summer in the Mediterranean Sea or when it’s minus 20 or 30 in a commercial farm in Canada?” he asked. “There’s close to 80 countries in the world with this problem, we’ve never seen that before. That’s why we’re seriously looking at climate change.”

Read the full article about bird flu by Zoya Teirstein at Grist.