Bird flu virus found in one-fifth of US milk samples, testing shows

Remnants of the bird flu virus have been detected in roughly one in five commercial milk samples tested by US health officials.

Since last month, the H5N1 strain has been identified in 33 dairy herds across eight US states, with experts racing to locate the origins of the current outbreak.

The Food and Drug Administration (FDA) first announced on Tuesday that genetic traces of the virus had been found in pasteurised milk. Now, early results from a sampling study suggest bird flu could be widespread in America’s milk supplies.

In a statement, the FDA said around one-fifth of retail samples tested for H5N1 and that a greater proportion of positive results originated from milk in areas with infected herds.

The study was “nationally representative,” the agency added.

The PCR tests used to analyse the samples can detect both live and dead virus fragments, but cannot distinguish between the two.

“Additional testing is required to determine whether intact pathogen is still present and if it remains infectious, which would help inform a determination of whether there is any risk of illness associated with consuming the product,” the FDA said.

However, the FDA continues to believe that America’s commercial milk supply is safe and authorities have reaffirmed that the risk to humans remains low.

Only one person, a dairy worker from Texas, one of the affected states, has been infected. The individual developed conjunctivitis, or ‘pink eye’, after close contact with a cattle herd.

There have been no reports of human-to-human transmission.

Mandatory testing of dairy cows moving across state borders was implemented by the US Department of Agriculture (USDA) on Wednesday, in a bid to contain the virus and understand the extent of the outbreak.

Texas, Kansas, Michigan and Ohio are among the eight affected states, according to USDA.

A separate survey of commercial milk products has also been conducted by scientists at Ohio State University.

The research collected 150 samples from around the Midwest, representing dairy processing plants in 10 different states, including some where herds have tested positive for H5N1. Genetic testing found viral fragments in 58 samples, the US health website Stat reported.

The presence of H5N1 in cattle has raised concerns among scientists. The virus’ apparent ability to spread between cows is significant because it provides more opportunities for it to evolve to better infect other mammals, potentially including humans.

Since 2020, the virus has killed tens of millions of birds worldwide, along with thousands of mammals, including sea lions, elephant seals and even one polar bear.

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