Inactivation of avian influenza virus in raw milk yogurt

Authors: Harrell, Telvin; Alvarez Narvaez, Sonsiray; Porto Fett, Anna; VINAYAMOHAN, POONAM - Orise Fellow; Luchansky, John; SHWANI, ABDULKARIM - Orise Fellow; Suarez, David

Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2025
Publication Date: 11/4/2025
Citation: Harrell, T.L., Alvarez Narvaez, S., Porto Fett, A.C., Vinayamohan, P., Luchansky, J.B., Shwani, A., Suarez, D.L. 2025. Inactivation of avian influenza virus in raw milk yogurt. Food Microbiology. Volume 135. https://doi.org/10.1016/j.fm.2025.104975.
DOI: https://doi.org/10.1016/j.fm.2025.104975

Interpretive Summary: In March of 2024 an unprecedented outbreak of highly pathogenic avian influenza occurred in dairy cows. The virus caused mastitis and made at least some of the cows sick. The virus was found in large amounts in the milk from infected cows. Avian influenza virus can also spread to humans, a zoonotic infection, and there was concern that the virus in the milk could infect people. Fortunately standard pasteurization of milk inactivated the virus and most milk and other dairy products are safe. However, there is an increasing trend for people to drink raw milk and consume raw milk origin dairy products. This study examined whether avian influenza virus would be inactivated during the making of yogurt from raw milk spiked with avian influenza virus. A combination of the incubation of milk at 42 C and the drop in pH in the yogurt effectively killed the virus. If raw milk yogurt was made properly, there seems to be little risk of human infection from avian influenza virus.

Technical Abstract: In March 2024, highly pathogenic avian influenza (HPAIV) H5N1 was first detected in U.S. dairy cattle and has since spread to herds across at least 17 states. Infected cows typically present with mastitis, decreased milk production, and poor milk quality with high viral loads in milk. While commercial pasteurization of milk effectively inactivates avian influenza virus (AIV), growing consumer interest in raw milk and derived products raises public health concerns due to the risk of zoonotic transmission. Standard yogurt production includes an initial heating step at 82°C for 30 min. to denature milk proteins which also inactivates AIV. However, some home yogurt recipes omit this initial heating step. This project determined whether AIV present in raw milk could remain viable through fermentation and persist in the final yogurt product. Raw milk (ca. pH 6.7) was spiked with AIV (ca. 7.5 log10 50% egg infectious doses (EID50) per mL and inoculated with a commercial starter culture to produce yogurt. The viability of the virus was determined before and after fermentation (ca. 7.3 h) at 42°C with resultant pH drop = 4.4. A significant (p < 0.05) reduction of viable AIV (= 4.1 log10 EID50) was observed in both the yogurt and the control samples of raw milk incubated at 42°C but without starter culture (ca. pH 6.63). Viral inactivation was likely due to the ca. 7.3 h incubation at a sublethal temperature and/or the resulting pH below 4.4. Thus, properly fermented yogurt has a negligible risk of transmitting AIV to humans.