Simulating the Transmission of Rift Valley Fever Virus via Raw Milk Consumption in Inter-Epidemic Periods

Rift Valley fever virus (RVFV) is a zoonotic, vector-borne disease affecting livestock and humans. The consumption of raw unpasteurized milk has been epidemiologically linked to RVFV exposure in humans and recognized as a potentially important non-vector route for RVFV transmission. This study aims to investigate the potential of RVFV transmission to humans through the consumption of infected raw milk. For this purpose, we conducted agent-based stochastic simulations to assess the potential for RVFV transmission through ingestion of contaminated raw milk. We created synthetic populations of cows, humans, and mosquitoes representing local farm dynamics in Kisumu, Kenya. A total of 1000 farms were simulated with binomial and Poisson distributions utilized to generate cow and human populations, respectively. Given our prior field data, we varied the probability of consuming raw milk from 1% to 80%. We also varied the probability of infectious raw milk causing RVFV infection at 10% and 40%. Results indicate that when the probability of infectious raw milk causing an infection is set at 10%, the cumulative incidence of RVFV infections in humans through raw milk consumption varies between 0.4 and 13% during the inter-epidemic periods. When the probability of infectious raw milk causing an infection is set at 40%, the percentage of cumulative milk infections ranges from 3.7 to 28%. Findings highlight the great potential for RVFV infection and spread through infectious milk consumption and the need for further evaluation of milk as a potential pathway of RVFV transmission to humans. Raw milk consumption in RVFV endemic settings remains an ongoing public health threat.