Infectiousness of raw (unpasteurised) milk from influenza H5N1-infected cows beyond the USA

Pasteurisation has been proven to inactivate the influenza H5N1 virus, rendering pasteurised cow milk safe for consumers. In the USA, almost all (99%) of the commercial milk supply produced on dairy farms complies with the Grade A Milk Safety Program and the Pasteurized Milk Ordinance, which include measures for ensuring dairy product safety.1

 

No infectious H5N1 virus has been detected in retail pasteurised dairy milk products; however, approximately 20% of retail milk samples contain traces of H5N1 genetic materials.1 The US Food and Drug Administration showed that all 297 samples from its first retail sample survey and all 167 samples from its second retail sample survey tested negative for live H5N1 virus.1

 

Researchers from the US Department of Agriculture and the US Food and Drug Administration found that raw milk samples from four affected states in the USA contained a highly pathogenic avian influenza (HPAI) virus, with 39 (24·6%) of 158 quantitative real-time RT-PCR-positive bulk milk tank samples containing the infectious virus.2 HPAI H5N1 viruses show a strong tropism for the mammary glands of lactating cows, wherein the epithelial cells that secrete milk display a high expression of sialic acid receptors with an α2,3 and α2,6 galactose linkage, yielding milk containing high infectious viral RNA loads.3