Impact of Co-Infections on Peste Des Petits Ruminants Vaccine Efficacy: Insights from an Outbreak in Sheep and Goats in Andhra Pradesh, India

Abstract

Aim: To study the interaction between Peste des Petits Ruminants virus (PPRV), gastrointestinal helminthic infestation, and secondary bacterial infections in PPR vaccinated sheep and goats. Place and Duration of study: Manimeswaram village, Krishna District, Andhra Pradesh, India during February 2023. Methodology: 20 lambs aged 4-6 months died in a flock of 250 animals with symptoms of pyrexia, diarrhea, and anorexia. RT-PCR targeting the N gene of PPRV confirmed viral presence in samples from six clinically affected animals and necropsy tissue from one. A multifactorial analysis was conducted on samples from two flocks: the affected flock, exhibiting illness and mortality, and a control flock that appeared healthy. Results: PPR antibodies were detected in most animals from both flocks, indicating adequate vaccine response. PPRV was detected in both the affected and control flocks; however, gastrointestinal helminths and secondary bacterial infections were observed only in the affected flock. Clinical illness was observed only in animals positive for both PPR virus and gastrointestinal helminths infections, while animals free of parasitic infestation remained asymptomatic. Statistical analysis showed a significant negative correlation (r = -0.479) between parasitic infestation and animal health, whereas the correlation between PPR virus presence and animal health was not significant. A stronger negative correlation (r = -0.624) was observed between co-infection with parasites and PPR virus and animal health. These findings suggest PPR virus alone had a limited direct impact on health and mortality, whereas co-infection with parasites significantly worsened outcomes. Mortality was highest in 4 to 8 month old lambs, likely due to delayed vaccination. Conclusion: The findings of the study emphasize the importance of effective anthelmintic treatment prior to PPR vaccination and highlight the necessity of vaccinating lambs soon after maternal immunity declines to enhance disease control.