Sero-prevalence and sero-monitoring of Peste des petits ruminants (PPR) disease in small ruminants in Oromia Region, Ethiopia

Global PPR (goat plague) eradication efforts are ongoing, mainly through vaccination programs. The disease causes substantial economic losses in sheep and goats because of its high morbidity and mortality. Integrated assessment of epidemiological status and immune responses in vaccinated animals is essential for effective control and eradication. This study consisted of two components conducted in the Oromia Region, Ethiopia. First, a cross-sectional study was conducted from January 2024 to November 2024 in three districts (Goba, Sinana, and Dinsho) of the Bale Zone to assess the seroprevalence of PPR infection in non-vaccinated area and to evaluate the immune response status (sero-monitoring) in vaccinated area, along with associated risk factors. Second, a retrospective study was conducted using data obtained from the Oromia Agriculture Office to describe the extent of PPR disease outbreaks, the distribution of PPR cases, and vaccination activities in sheep and goats across the Oromia Region from 2016 to 2022. Zone and districts were selected purposively based on predefined criteria, while kebeles , villages, and farms were sampled using random sampling. Finally, Goats and sheep were sampled using random sampling after stratifying by species. Blood samples were collected from 420 non-vaccinated and 246 vaccinated sheep and goats, and 75 household owners were interviewed to assess potential risk factors. Retrospective data on PPR disease in the Oromia Region were also reviewed. Antibodies against PPR in vaccinated and non-vaccinated animals were detected using a competitive enzyme-linked immunosorbent assay at the Asella Regional Veterinary Laboratory and the Sebeta Animal Health Institute. The overall true seroprevalence in non-vaccinated animals was 15.6% (95% CI: 12.1%,19.8%) [12.3% (95% CI: 8.8%,16.7%) in sheep and 27.8% (95% CI: 17.5%,33.1%) in goats], whereas the true antibody seroprevalence in vaccinated animals was 80.3% (95% CI: 74.1%,85.8%) [79.9% (95% CI: 66.9%,93.3%) in sheep and 82.0% (95% CI: 72.8%,86.2%) in goats]. Logistic regression showed that goats were significantly more likely to be infected (AOR = 2.93; 95% CI: 1.6,5.5; P = 0.001). Species, sex, age, and herd size were significant risk factors among non-vaccinated animals ( p < 0.05), whereas only age was associated with antibody development in vaccinated animals. The interview results showed that all respondents (100%) indicated that their animals had the chance to contact other herds at watering points and/or during seasonal grazing, and 32% reported that their flocks had opportunities to encounter wildlife. In Oromia Region, a total of 347 active surveillance activities were conducted from 2017 to 2022, and 131 PPR outbreaks were confirmed, representing an overall outbreak confirmation rate of 37.8% (131/347). A total of 2,266 PPR-positive cases were identified through active surveillance, and 1,859,263 individuals at risk were vaccinated. In the region, a total of 20,840,010 small ruminants were vaccinated from 2017 to 2022, resulting in an overall vaccine coverage of 19.1%. These findings indicate ongoing PPRV circulation in the study area, underscoring the need to expand vaccination campaigns, assess vaccine efficacy and diagnostic tests, and strengthen surveillance to achieve PPR eradication.