Peste des petits ruminants: Changing Livestock Management Practices to Reduce Transmission

Contrary to popular belief, the risk of transmission of the peste des petits ruminants virus does not increase with herd size, but rather with the use of certain livestock management practices. A new study identifies these practices in the hope of improving strategies for eradicating the virus. Peste des petits ruminants (PPR) threatens nearly 80% of the world’s sheep and goats. First reported in 1942 in Côte d’Ivoire, this highly infectious and often fatal disease is gradually spreading across the globe through close contact between animals. Infected animals engage in shedding of the virus through tears, nasal secretions, sputum, and feces. The disease spreads primarily through inhalation of fine droplets released into the air by coughing and sneezing. There is an urgent need to better understand the transmission of the virus in order to identify high-risk behaviors, which can inform the allocation of resources for managing the virus and guide global strategies and campaigns for its eradication. Thus, a new study , led by researchers at Penn State, examined livestock management practices such as the introduction of new animals into a herd and the use of seasonal grazing. In previous work, the researchers noted that the risk of peste des petits ruminants (PPR) virus transmission was higher among herds in pastoral villages—which rely almost exclusively on livestock for their livelihood—compared to herds in agropastoral villages, which rely on a mix of livestock and agriculture. However, the factors underlying these differences were unclear. Pastoral villages generally have larger herds. Intuitively, the researchers therefore hypothesized that herd size must influence the disease’s transmission rate. They were wrong, however. The infection rate might have increased with herd size, since an animal in a larger herd has the potential to interact closely with more individuals—a density-dependent transmission model—but this was not the case. Instead, the formation of social bonds and groups—independent of the overall herd size—appeared to be the more significant factor. Thus, an increased risk of transmission could clearly be attributed to farming practices such as the use of seasonal grazing areas, where numerous herds from different farmers come together, the introduction of new animals, or the separation of herd members. With evidence that these practices are associated with higher infection rates, researchers aim to improve or modify them to mitigate the risk. Measures, such as quarantine procedures surrounding the introduction of new animals or the return from grazing, could be implemented. It will be possible to focus veterinary care and preventive measures on when and where the risk is highest. The researchers hope that their ongoing work will help clarify the ecological mechanisms underlying PPRV transmission.