Spatial and Temporal Dynamics of Peste des Petits Ruminants Outbreaks and Their Clinical Impact in Small Ruminants in North Shewa Zone, Ethiopia: Implications for Eradication

Abstract

Peste des petits ruminants (PPRs) is an economically significant disease affecting small ruminants. Owing to its impact on livestock and rural livelihoods, Ethiopia joined the global PPR eradication program and implemented risk-based vaccination strategies in 2018. However, gaps remain in understanding the geographic distribution, seasonal trends, and impact of this disease. To address these gaps, a repeated cross-sectional study was conducted between September 2018 and August 2024 in the North Shewa Zone to confirm PPR outbreaks via rapid antigen detection methods, specifically the pen-side test and dipstick technique. In addition, a retrospective analysis was performed to assess the spatial and temporal distributions of outbreaks, along with associated morbidity, mortality, and case fatality rates. The results revealed 48 confirmed PPR outbreaks over 6 years, occurring in 15 out of 24 districts, with an average of 8 outbreaks annually and a 0.33 proportion of affected districts, indicating low and localized spread. A total of 192 clinical samples were collected from symptomatic sheep and goats, all of which tested positive for PPRV. In total, 6415 PPR cases were documented, with a morbidity rate of 0.72%, a mortality rate of 0.11% (951 deaths), and a case fatality rate of 14.82%. Kewet had the highest number of outbreaks (7), whereas Mojana-Wedera recorded the highest number of cases (2718). Seasonally, 60% of the outbreaks occurred during the long rainy season, leading to 4472 cases and a fatality rate of 16.79%. Yearly trends showed consistent patterns, with 2023 having the highest number of outbreaks (15) and 2021 having the fewest (5). The year 2024 had the highest number of cases (2706). Despite continued viral circulation, the low morbidity and mortality rates, relative to the high transmissibility and fatality rates of the PPR in naïve populations (infection rates of up to 100% and mortality rates of 10%-90%), reflect significant control progress. While PPR remains endemic in the North Shewa Zone, the reduced incidence and clinical impact indicate measurable advancements toward eradication. Nonetheless, recurrent outbreaks across seasons and districts necessitate sustained, adaptive interventions. The study recommends strengthening surveillance, enhancing postvaccination sero-monitoring, and optimizing vaccine allocation to accelerate eradication.