The influence of raw milk exposures on Rift Valley fever virus transmission

Abstract

Rift Valley fever virus (RVFV) is a zoonotic phlebovirus that can be transmitted to humans or livestock by mosquitoes or through direct contact with contaminated bodily fluids and tissues. Exposure to bodily fluids and tissues varies by types of behaviors engaged for occupational tasks, homestead responsibilities, or use in dietary or therapeutic capacities. While previous studies have included milk exposures in their analyses, their primary focus on livestock exposures has been on animal handling, breeding, and slaughter. We analyzed data from multiple field surveys in Kenya with the aim of associating RVFV infection to raw milk exposures from common animal species. Of those with evidence of prior RVFV infection by serology (n = 267), 77.2% engaged in milking livestock compared to 32.0% for 3,956 co-local seronegative individuals (p < 0.001), and 86.5% of seropositive individuals consumed raw milk compared to 33.4% seronegative individuals (p < 0.001). Individuals who milked and also consumed raw milk had greater odds of RVFV exposure than individuals whose only contact to raw milk was through milking. Increased risks were associated with exposure to milk sourced from cows (p < 0.001), sheep (p < 0.001), and goats (p < 0.001), but not camels (p = 0.98 for consuming, p = 0.21 for milking). Our data suggest that exposure to raw milk may contribute to a significant number of cases of RVFV, especially during outbreaks and in endemic areas, and that some animal species may be associated with a higher risk for RVFV exposure. Livestock trade is regulated to limit RVFV spread from endemic areas, yet further interventions designed to fully understand the risk of RVFV exposure from raw milk are imperative.

Unique Outbreak of Rift Valley Fever in Sudan, 2019

“…RVFV periodically emerges to cause epizootics among livestock and epidemics in persons living nearby ( 2 ). It is mainly transmitted by the bite of infected mosquitoes or by direct contact with infected animals and their products ( 3 ). In addition, RVFV transmission is maintained vertically among both humans and vector mosquito populations ( 4 , 5 ).…”

Archaeology and contemporary emerging zoonosis: A framework for predicting future Rift Valley fever virus outbreaks

“…RVF is an ideal candidate for a longitudinal modelling study. Its emergence coincided with British Imperialism in this region of Eastern Africa and sits at the nexus of food production, human–animal relationships (Cook et al, ; Grossi‐Soyster, Lee, King, & LaBeaud, ), local cultural agency, and European hegemony. Colonial interventions were characterized by massive landscape modifications, wide‐spread demographic transitions, and new practices governing animal husbandry and trading, all driven by major political and infrastructural upheaval.…”

“…Colonial interventions were characterized by massive landscape modifications, wide‐spread demographic transitions, and new practices governing animal husbandry and trading, all driven by major political and infrastructural upheaval. RVF has been well studied from a contemporary epidemiological perspective (Cook et al, ; Grossi‐Soyster et al, , ; LaBeaud et al, ; LaBeaud, Ochiai, Peters, Muchiri, & King, ); thus, new research is easily situated within an established framework.…”

“…Research shows that the diversification of professions associated with animal husbandry and slaughter has implications for understanding disease transmission. Humans are exposed via animal husbandry, slaughter and butchery, and ingesting diseased meat, milk, and blood (Mohamed et al ; Cook et al, ; Grossi‐Soyster et al, ). Ethnoarchaeological research provides important evidence of human behaviour, in particular, as it relates to changing slaughtering practices over time.…”

Increased Susceptibility of Cattle to Intranasal RVFV Infection

“…In addition to health risks, the loss of fetuses and newborn livestock to RVFV infections can have a severe socioeconomic impact on farmers (19). Together this data suggests that vaccinating livestock against RVFV may be highly beneficial not only in protecting livestock but also to the people who are in direct contact with them (20,21). Since the risk of human infections increases as the seropositivity increases in animal populations (22), surveillance systems in countries where RVFV circulates are extremely important.…”