Peste des petits ruminants virus (PPRV) causes a contagious disease of high morbidity and mortality in global sheep and goat populations and has spread to more than 70 countries in Asia, the Middle East, and Africa. PPRV threatens 80% of the global small ruminant population of nearly 2 billion animals and the livelihoods of over 330 million farmers who rely directly on small ruminants. PPRV, a Morbillivirus like rinderpest virus and human measles virus, is spread by direct contact with infected hosts, aerosols, or fomites. Following the eradication of rinderpest, PPRV has also been shown to elicit seroconversion in cattle. Using a large serosurvey form northern Tanzania, we investigated PPRV age-seroprevalence and household survey data to determine significant risk factors and specific management practices for increased PPRV seroprevalence and to identify the age cohort(s) responsible for PPRV transmission among sheep, goats, and cattle. We used generalized linear mixed models within a catalytic framework to calculate the force of infection (FOI), the per capita infection rate of susceptible hosts, and reproductive number estimates. Serum samples and household surveys were collected in 9 agropastoral (AP) and 11 pastoral (P) villages in the Arusha, Kilimanjaro, and Manyara regions of northern Tanzania during 2016.
Results/Conclusions
PPRV seroconversion is widespread among sheep, goats, and cattle. The overall observed seroprevalence was 21.1% and differed with management practice (AP: 5.8%, P: 30.7%). Seroprevalence increased across age groups, with the oldest age groups reporting 53.6%, 46.8% and 11.6% in sheep, goats, and cattle, respectively. Seroconversion varied significantly by sex, species, and management system. We calculated the age-specific FOI using a catalytic model framework and determined the age group with the highest FOI was aged 2-3 years for sheep and goats and 3.5-4.5 years for cattle. Pastoral management systems had higher FOI and a wider range of ages with a higher FOI than agropastoral systems. In agropastoral systems, the highest FOI was seen in ages 2-3 years (sheep and goats) and 3.5-4.5 years (cattle). In pastoral systems, the highest FOI was in ages 2-3 years (sheep), 3-5 years (goats), and 3.5-4.5 years (cattle). We also explored confinement and grazing practices, seasonal camp and market attendance, herd size, and demographics for their impact on seroprevalence. Insights from future studies on specific management practices will lead to improved control strategies through feasible changes in non-vaccination practices, geographical areas and host species to target, and discovery of additional ecological mechanisms driving PPRV seroconversion.