Experts maintain the milk supply is safe. Their focus is on keeping the people who work with cows from getting sick.

The U.S. government announced new measures yesterday to slow the spread of the H5N1 influenza virus among cattle, following the revelation that milk sold commercially in 10 states contained fragments of the virus. An order issued by the U.S. Department of Agriculture (USDA) restricts the movement of dairy cattle between states and mandates the reporting of infected cows.

A senior official from the US Food and Drug Administration (FDA) said today that its nationwide survey of retail milk has found remnants of H5N1 avian flu viruses in one in five samples, with the highest concentrations in regions where outbreaks in dairy cattle have been reported.

Donald Prater, DVM, acting director of the FDA Center for Food Safety and Applied Nutrition (CFSAN), shared the new findings with state health officials who took part in a scientific symposium on H5N1 hosted by the Association of State and Territorial Health Officials (ASTHO). The results come in the wake of earlier findings this week from more limited FDA sampling, along with similar findings from a smaller set of samples tested by a lab that's part of the National Institute of Allergy and Infectious Diseases Centers of Excellence for Influenza Research and Response (CEIRR) Network.

The response has echoes of the early days of 2020, when the coronavirus began its deadly march around the world. Today, some officials and experts express frustration that more livestock herds aren’t being tested for avian flu, and that when tests and epidemiological studies are conducted, results aren’t shared fast enough or with enough detail. They fear that the delays could allow the pathogen to move unchecked — and potentially acquire the genetic machinery needed to spread swiftly among people. One dairy worker in Texas has already fallen ill amid the outbreak, the second U.S. case ever of this type of bird flu.

“So far there is only one confirmed human case. Rick Bright, an expert on the H5N1 virus who served on President Joe Biden's coronavirus advisory board, said, 'there's a fine line between one person and 10 people with H5N1. By the time we've detected 10, it's probably too late'.”

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A day after the Food and Drug Administration (FDA) announced that H5N1 avian flu fragments have been found in retail milk samples, the US Department of Agriculture (USDA) today announced that lactating dairy cows must be tested before interstate transport.

The movement of dairy cows, some of which aren't showing disease symptoms, from already affected states such as Texas has been a source of H5N1 spread to dairy herds in states such as Idaho and Michigan. Also, the identification of virus fragments in finished milk suggests that the virus may be more widespread in dairy cows than currently known.

“Thijs Kuiken, an avian influenza researcher at Erasmus Medical Center, says the “very sparse” information released by the U.S. government has international implications, too. State and federal animal health authorities have “abundant information … that [has] not been made public, but would be informative for health professionals and scientists” in the United States and abroad, he says, “to be able to better assess the outbreak and take measures, both for animal health and for human health.” He notes that even the new sequences released by USDA do not include locations of the samples or the date they were taken. The release appears to include data from only 39 cows.”

“The agency said it has been trying to see if it could grow virus from milk found to contain evidence of H5N1, which is the gold standard test to see if there is viable virus in a product. The lengthy statement the agency released does not explicitly say FDA laboratories were unable to find live virus in the milk samples, but it does state that its belief that commercial, pasteurized milk is safe to consume has not been altered by these findings.”

The genetic data point to a single spillover event that probably occurred in late 2023, Michael Worobey, an evolutionary virologist at the University of Arizona, told STAT on Tuesday.

A new strain of avian flu has been sweeping the globe since 2020, leaving thousands of dead seabirds in its wake. This past summer, it arrived at a colony of Caspian terns at Rat Island in the Salish Sea, with catastrophic results.

Highly pathogenic avian influenza (HPAI) viruses circulate in wild birds and can infect domestic poultry. H5NX 2.3.4.4b is a clade of HPAI responsible for major avian epidemics seen in Europe in the 2016–2017 and 2020–2021 seasons, with the 2021–2022 season being the largest so far in terms of geographic spread and number of detections in non-avian animals [1]. While in recent months poultry infections have declined, HPAI H5NX continues to circulate in wild birds, and HPAI H5N1 genotypes have infected several mammal species in Europe, the Americas, and Asia [2]. Indeed, HPAI H5N1 detected in red foxes in The Netherlands have been found to carry a PB2-E627K mutation that increases viral replication in mammalian cells [3]. Furthermore, HPAI H5N1 was identified to have a neurotropism in these foxes, causing infection in the brain.

South Africa’s poultry industry is under siege as it grapples with two distinct bird flu strains – H5N1 and H7N6.