Bird flu antibodies found in dairy workers in Michigan and Colorado
Blood tests have shown that about 7 per cent of workers on dairy farms that had H5N1 outbreaks had antibodies against the disease
By Grace Wade
7 November 2024
Farm workers exposed to infected dairy cattle have been found to carry bird flu antibodies
Helen King/Getty Images
There may be more bird flu cases in humans in the US than we previously thought. Health departments in two states took blood tests of workers on dairy farms known to have hosted infected cattle and found that about 7 per cent of them have antibodies for the disease. This included people who never experienced any flu symptoms.
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Since March, a bird flu virus known as H5N1 has been circulating in dairy cows across the US. So far, 446 cows in 15 US states have tested positive for the virus. Since April, 44 people in the US have tested positive for H5 – the influenza subtype that includes H5N1. All but one of these cases occurred in workers on H5N1-infected poultry or dairy farms.
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To better understand how many farm workers may have contracted the virus, the US Centers for Disease Control and Prevention (CDC) collaborated with state health departments in Colorado and Michigan to collect blood samples from 115 people working on dairy farms with H5N1-infected cattle. All of the samples were obtained between 15 and 19 days after cows on the farms had tested positive for the virus.
Nirav Shah at the CDC and his colleagues then removed seasonal influenza antibodies from the samples before testing them for the presence of H5N1 antibodies. They found H5N1 antibodies in eight of the samples, or about 7 per cent, suggesting that eight of the workers had been unknowingly infected with the virus. What’s more, four of the workers didn’t recall ever having symptoms.
“This is critical because, before this point, the recommendations for [H5N1] testing largely have focused on symptomatic workers,” says Meghan Davis at Johns Hopkins University in Maryland. “When workers don’t know that they are infected, they inadvertently may expose other people in their communities to the infection.”
