Epidemiological investigation of Peste des petits ruminants in selected regions of Tanzania

Thesis

Peste des petits ruminants (PPR), one of the most economically important disease of small ruminants has been earmarked for eradication following the successful global eradication of rinderpest. The disease is caused by peste des petits ruminants virus (PPRV). For eradication to be successful, the different PPR situations and contexts in each region and country must be well understood and reflected upon. In this study, the objective was to conduct an epidemiological assessment of the spread and persistency of PPR in selected areas of Tanzania with focus on distribution of antibodies to PPRV, PPRV genetic diversity and identification of practices by small stock farmers in response to this disease. The study was carried out using samples collected between 2013 to 2016. Sera samples were collected from clinically healthy sheep and goats for detection of antibodies to PPRV, together with blood, swabs and tissues for detection of the virus using molecular assays. A questionnaire was also administered in order to collect demographic characteristics, knowledge and practices relating to this disease from small ruminant farmers during sample collection. The overall true seroprevalences from samples collected in 2013 and 2015 was 27% (n = 3838) and for samples collected in 2016 was 30% (n = 328). Seroprevalences for samples collected in 2013, 2015 and 2016 show that the disease is continuing to spread in the country as seropositivity was observed in regions where previously no disease had been reported. Presence of the virus was found in samples collected in Morogoro and Arusha regions in 2016. Molecular characterization of the virus clustered them into two lineages, II and III. This confirmed presence of two lineages circulating in animals from the same herd, adding another dimension into the complexity of the disease in Tanzania. Other findings were confirmation of co-infections with Mycoplasma capricolum subspecies capripneumoniae, Pasteurella multocida and Capripoxvirus which cause similar clinical signs to PPR, complicating clinical diagnosis but emphasizing the importance of laboratory confirmation. Small ruminant farmers’ knowledge by regions on the disease occurrence was found to be high in Arusha region (northern Tanzania) and low in Morogoro region (eastern Tanzania), corresponding with the seroprevalences observed from samples collected in 2013, 2015 and 2016 in the said regions. Risk practices identified during outbreaks included trading of live animals, use of veterinary drugs and unattendance to sick animals. These risk practices could facilitate the spread of the disease in the country especially as the disease is transmitted through contact with infected animals. In conclusion, this study has revealed that PPR continues to spread within Tanzania as evidenced by antibodies to PPRV detected in areas that previously did not have the disease. Presence of two PPRV lineages shows the ability of lineages to co-circulate in an endemic area as well as in the presence of co-infections with other diseases in the local herd. Overall, there is poor knowledge by small ruminant farmers in the study areas that may be contributing to the spread of PPR. It is therefore recommended that annual vaccinations be carried out after well designed participatory surveillances are conducted to improve the herd immunity to levels that can contain the spread of PPR as a control measure. These vaccinations should take into consideration the geographical distribution of PPR in Tanzania so as to create buffer zones to stop further spread to areas with low or no disease, within and in neighboring countries. Genetic diversity of the virus strains circulating in the country should be further investigated by whole genome sequencing and how they compare to other strains. To prioritize on small ruminant farmer’s knowledge on the disease and emphasize how their participatory disease surveillance can help with the ultimate goal of eradicating PPR in Tanzania, regionally and globally.

Southern African Centre for Infectious Disease Surveillance, SACIDS, (grant WT087546MA from the Wellcome Trust) and Swedish Research Council (grants 348-2013-6402 and 348-2014-4293)