Effectiveness of Pasteurization for the Inactivation of H5N1 Influenza Virus in Raw Whole Milk

Highly pathogenic avian influenza (HPAI) clade 2.3.4.4b H5Nx viruses continue to cause episodic incursions and have been detected in more than 12 taxonomic orders encompassing more than 80 avian species, land and marine mammals, including recent detections in dairy cattle. The HPAI H5N1 spillover to these important livestock species creates a new interface for human exposure and raises food safety concerns. Presence of H5N1 genetic material in one out of five retail pasteurized milk samples in the USA has prompted the evaluation of pasteurization processes for the inactivation of influenza viruses. Our study examined whether pasteurization could effectively inactivate HPAI H5N1 inoculated raw whole milk samples. We heated 1 mL of non-homogenized cow’s milk samples to attain an internal temperature of 63°C or 72°C and spiked with 6.3 log EID ₅₀ of clade 2.3.4.4b H5N1 virus. Complete inactivation was achieved after incubation of the H5N1 spiked raw milk at 63°C for 30 minutes. In addition, complete viral inactivation was observed in seven out of eight replicates of raw milk samples treated at 72°C for 15 seconds. In one replicate, a 4.56 log reduction was achieved, which is about 1 log higher than the average viral quantities detected in bulk tanks in affected areas. Therefore, we conclude that pasteurization of milk is an effective strategy for mitigation of risk of human exposure to milk contaminated with H5N1 virus.