The first outbreak of a rare bird flu in poultry has been detected on a duck farm in California, the World Organisation for Animal Health (WOAH) said on Monday.
Authorities said the discovery of H5N9 bird flu in poultry came alongside the detection of the more common H5N1 strain on the same farm in Merced county, California, and that almost 119,000 birds on the farm had been killed since early December.
“This is the first confirmed case of HPAI H5N9 in poultry in the United States,” the US Department of Agriculture said in the report to the WOAH.
“The USDA animal and plant health inspection service (APHIS), in conjunction with state animal health and wildlife officials, are conducting comprehensive epidemiological investigations and enhanced surveillance in response to the HPAI related events,” it added.
Highly pathogenic bird flu (HPAI), commonly called bird flu, is of rising concern to epidemiologists. The US National Library of Medicine lists H5N9 as a subtype avian influenza virus.
“Whether this novel H5N9 virus will cause human infections from its avian host and become a pandemic subtype is not known yet,” it warns on its website. “It is therefore imperative to assess the risk of emergence of this novel reassortant virus with potential transmissibility to public health.”
Bird flu has spread around the globe in recent years, leading to the culling of hundreds of millions of poultry. It also spread to dozens of mammal species, including dairy cows in the US, and killed a person in Louisiana earlier this year.
H5N1 avian flu in spreading in US cattle herds and poultry stocks, with the US Department of Agriculture reporting that more than 13,000,000 birds were affected in the last 30 days across all 50 states by the flu. H5N1 bird flu has infected or killed 136m birds since the outbreak began in 2022.
That has led to rising prices for eggs. The US Bureau of Labor statistics says that in September 2023, the average price for a dozen Grade A eggs was just over $2. Now more than a year later, the data shows that price has more than doubled to $4.16 in December 2024.
An avian flu outbreak at a duck farm on New York’s Long Island was reported last week with federal officials ordering the destruction of the operation’s entire 100,000 flock. The farm had been in operation since the 1640s.
Bird flu outbreaks are also increasing within dairy herds, with more than 900 herds infected across the US and 67 people infected. The increases do not yet suggest that a human pandemic is inevitable, but authorities are concerned about bird flu in domestic cats.
According to a study published last year in the academic journal Emerging Microbes and Infections, cat H5N1 genomes had unique mutations that could suggest “potential virus adaptation”. It found cats could “serve as mixing vessels for reassortment of avian and mammalian influenza viruses” as well as act as a “bridge” to infect other species.
The US Centers for Disease Control (CDC) says that “while the current public health risk is low, CDC is watching the situation carefully and working with states to monitor people with animal exposures”.