Wastewater monitoring reveals potential spread of avian flu among dairy cattle in the US

A study by researchers at Emory University, Stanford University, and Verily Life Sciences suggests that spikes in influenza A virus detected in wastewater samples from 59 sewer systems across the US may be indicative of the spread of H5N1 avian flu currently infecting dairy cattle. The US Department of Agriculture has reported over 30 herds infected with the virus, but there are concerns about its true extent and whether it can be effectively tracked in animals. Recent tests on milk purchased from grocery stores found fragments of the viral genome in five out of every ten samples tested; however, further testing revealed that these were not infectious. During a government news conference last week, officials admitted difficulties getting dairy farmers to allow them to test for infection. The researchers developed a new method to distinguish H5 influenza from other circulating A-strain flu viruses and applied it in wastewater treatment plants near areas where cattle had tested positive but not directly on farms. They found that as levels of the marker for all types of influenza virus began rising, so too did markers specific to the highly pathogenic H5N1 strain; concentrations were nearly as high as those seen with overall A-strain viruses. The stored samples used in this study came from two treatment plants sites near Amarillo and a third site in Dallas County between February 4th and April 16th, where wastewater processing permits allowed for the disposal of animal byproducts including dumped milk from dairies; these may explain why concentrations were so high. The researchers stress that no H5N1 outbreaks have been reported among sewersheds they tested but think it’s possible this is due to permitted dumping practices rather than actual infection in cattle, which would suggest a far more widespread outbreak than currently known if true. However, the study authors also acknowledge limitations of their findings and stress that without further investigation into potential sources within these areas, the origin cannot be confirmed; multiple lines of evidence do point towards animal origins though. The researchers’ testing method is sensitive enough to detect even small amounts of H5 genetic material but are unable to determine whether viruses would infect people or not as they did not attempt virus culture in their tests.