Rift Valley fever virus remains infectious in milk stored in a wide range of temperatures

Authors: DAWES, BRIAN - Stanford University; De La Mota-Peynad, Alina; REZENDE, IZABELA - Stanford University; BUYUKCANGAZ, ESRA - Stanford University; Harvey, Amanda; GERKIN, KELI - University Of Liverpool; WINTER, CHRISTABEL - Kenya Medical Research Institute; BAYRAU, BETEL - Stanford University; Mitzel, Dana; WAGGONER, JESSE - Emory University, School Of Medicine; PINSKY, BENJAMIN - Stanford University School Of Medicine; Wilson, William; LABEAUD, A. - Stanford University

Submitted to: Journal of Infectious Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2025
Publication Date: 2/10/2025
Citation: Dawes, B.E., De La Mota-Peynad, A.M., Rezende, I.M., Buyukcangaz, E.K., Harvey, A.M., Gerkin, K.N., Winter, C., Bayrau, B., Mitzel, D.N., Waggoner, J.J., Pinsky, B.A., Wilson, W.C., Labeaud, A.D. 2025. Rift Valley fever virus remains infectious in milk stored in a wide range of temperatures. Journal of Infectious Diseases. Article jiaf060. https://doi.org/10.1093/infdis/jiaf060.
DOI: https://doi.org/10.1093/infdis/jiaf060

Interpretive Summary: Rift Valley fever virus (RVFV) is an insect-transmitted virus that is widely distributed across Africa and the Arabian Peninsula, which causes devastating epidemics affecting humans as well as ruminant livestock. Humans are exposed to the virus via mosquitos or direct contact with infected animals. Among these direct risks are milking and drinking milk. This study the risk of RVFV in cow and goat milk using an infectious vaccine strain RVFV-MP12. The study demonstrated that RVFV remains stable for up to five days in refrigerated milk and up to two days in milk stored in warm ambient conditions. The study also demonstrated that commonly performed pasteurization techniques and boiling of milk fully inactivates RVFV in milk. These results demonstrate that virus contaminated milk throughout the milk supply chain could represent a widespread public health risk, and some of this risk is mitigatable via pasteurization. We also propose use of RVFV detection in milk as a non-invasive source of RVFV surveillance.

Technical Abstract: Rift Valley fever virus (RVFV) is a zoonotic arbovirus widely distributed across Africa and the Arabian Peninsula, which causes devastating epidemics affecting humans as well as ruminant livestock. The epidemiology of RVFV is difficult to disentangle, as the virus is spread to humans via mosquitos or direct contact with infected animals. Among these direct risks are milking and drinking milk which has been firmly established as a risk factor for RVFV exposure. However, no studies to date have addressed the potential infectious nature of contaminated milk products. Here, we spiked cow and goat milk with infectious RVFV-MP12 and measured RNA and infectious viral titers over time in a variety of temperature conditions. We demonstrate that RVFV remains stable for up to five days in refrigerated milk and up to two days in milk stored in warm ambient conditions. Additionally, we show that RVFV RNA remained detectable in milk regardless of condition for up to five days. Lastly, we confirmed that commonly performed pasteurization techniques and boiling of milk fully inactivates RVFV in milk. These results demonstrate that virus contaminated milk is theoretically infectious throughout the milk supply chain could represent a widespread public health risk, and some of this risk is mitigatable via pasteurization. We also propose use of RVFV RNA detection in milk as a non-invasive source of RVFV surveillance.