March 24, 2025

New bird flu strikes poultry farm in Mississippi, US

A new strain of a highly pathogenic bird flu known as H7N9 has surfaced at a poultry farm in Mississippi where chickens are raised for breeding.

The strain found in Noxubee County was confirmed on March 12 and all of the roughly 46,000 birds either died or were euthanised after the infection spread, according to the US Department of Agriculture's (USDA) Animal Plant Health Inspection Service and Mississippi's Board of Animal Health. None of the birds entered the food supply.

Authorities didn't say how the birds were infected, although federal wildlife agents had been identifying low-pathogenic versions of the H7N9 virus for several years in wild birds. It is possible that the strain found in the chickens is circulating in wild birds, but most researchers think it may have acquired its deadly attributes once it got into the Noxubee chicken operation.

Richard Webby, an infectious disease expert at St. Jude Children's Research Hospital in Memphis, Tennessee, said most bird flu outbreaks follow that pattern: a low-pathogenic version is introduced to commercial poultry, and it becomes highly pathogenic once inside.

The introduction of H5N1 — the bird flu virus that's been infecting dairy cows, commercial poultry, pet cats, wild animals, and wild birds since March 2024 — into poultry and livestock populations was a notable exception to this trend: it was already circulating among wild birds and animals as a highly pathogenic virus.

John Korslund, a veterinarian and former USDA researcher, agreed with Webby and noted that the operation housed breeder broilers: chickens that are grown and maintained for breeding purposes, not for their meat.

This is significant as breeders live for months, if not years.

If a low-pathogenic virus "happens to get into a broiler meat flock, the birds don't get sick and they go on to slaughter," he said. But when a breeder flock picks up that virus, "the virus can replicate for weeks ... this may well be what happened in Mississippi."

- Los Angeles Times