Serosurveillance and Postvaccination Seromonitoring of Peste Des Petits Ruminants in Small Ruminants in Central Gondar Zone, Northwest Ethiopia

Abstract

Peste des petits ruminants (PPR) is a highly contagious transboundary viral disease of small ruminants caused by the PPR virus (PPRV). Despite Ethiopia’s goal of eradicating PPR by 2027 through a risk-based vaccination strategy, the disease remains endemic, with 554 outbreaks reported nationwide. This cross-sectional study was conducted in the North Gondar Zone, Ethiopia, between June 2024 and February 2025 to evaluate antibody responses in vaccinated small ruminants and estimate PPRV seroprevalence in unvaccinated flocks. A multistage cluster sampling design was used to select the study sites, while individual animals were selected using a haphazard sampling approach to approximate random sampling. A total of 600 serum samples were collected, including 300 from vaccinated and 300 from unvaccinated small ruminants; samples from vaccinated animals were obtained ~28 days postvaccination. All samples were tested for anti-PPRV antibodies using competitive enzyme-linked immunosorbent assay (c-ELISA). Overall individual-level seropositivity in the vaccinated population was 75%, comprising 75.73% in sheep and 72.1% in goats, serving as a proxy measure of flock immunity. In unvaccinated animals, PPRV seroprevalence was 14.33% (95% confidence interval [CI]: 10.6%–18.82%). Multivariable logistic regression identified age and flock size as the main risk factors influencing seropositivity. Adult animals were 2.89 times as likely to be seropositive as young animals (95% CI: 1.17–7.15; p = 0.022), and animals in medium-sized flocks were more likely to test positive than those in small flocks (AOR = 2.26; 95% CI: 1.11–4.63; p = 0.026). No significant differences were observed across districts, species, sex, production systems, newly introduced animals, or animal movement (p  > 0.05). The observed seropositivity was slightly below the commonly used 80% population immunity target associated with reducing transmission under the PPR eradication framework. The detection of PPRV antibodies in unvaccinated animals indicates previous exposure to PPRV and highlights the need for strengthened surveillance to assess whether active virus circulation persists in the area. To achieve effective control and eventual eradication of PPR, intensified vaccination programs combined with active surveillance are needed. Furthermore, refining vaccination strategies in alignment with global and national eradication plans is essential to establish PPR-free zones in these districts.