Low-level endemic circulation of porcine reproductive and respiratory syndrome virus in slaughtered pigs from Meghalaya, Northeast India: A cross-sectional seroepidemiological study

Background and Aim: Porcine reproductive and respiratory syndrome (PRRS) is a major transboundary viral disease of pigs, causing substantial economic losses worldwide. Repeated outbreaks and molecular evidence from Northeastern states indicate endemic virus circulation. Meghalaya, where pig production is dominated by smallholder and backyard systems with limited biosecurity, remains poorly characterized from a seroepidemiological perspective. This study aimed to estimate the apparent and true seroprevalence of PRRS virus in slaughtered pigs from Meghalaya and to evaluate selected animal-level risk factors. Materials and Methods: A cross-sectional serosurvey was conducted between August 2023 and July 2024 at an organized slaughterhouse in Shillong, Meghalaya. A total of 413 serum samples were collected from apparently healthy pigs originating from four districts: Ri Bhoi, East Khasi Hills, Eastern West Khasi Hills, and West Jaintia Hills. Sera were screened for virus-specific immunoglobulin G antibodies using the HerdChek® PRRS X3 Antibody Test based on the enzyme-linked immunosorbent assay. Apparent seroprevalence and corresponding 95% confidence intervals (CIs) were calculated using the Agresti–Coull method, while true prevalence was estimated using the Rogan–Gladen estimator. Univariate analysis was performed to assess associations between seropositivity and age, sex, breed, and district of origin using chi-square or Fisher’s exact tests, with odds ratios and 95% CIs used to quantify associations. Results: Out of 413 serum samples tested, 21 were seropositive, resulting in an apparent seroprevalence of 5.08% (95% CI: 3.31–7.69). The estimated true prevalence was 3.94% (95% CI: 2.98–6.60). District-wise seroprevalence ranged from 1.23% to 8.85%, with the highest proportion of seropositive animals observed in East Khasi Hills. No statistically significant associations were detected between seropositivity and age, sex, or breed (p > 0.05). Conclusion: The detection of antibodies in slaughtered pigs confirms low-level endemic circulation of the virus in Meghalaya. Although the observed prevalence was moderate, the findings indicate a latent risk of future outbreaks under prevailing low biosecurity production systems. Sustained surveillance, strengthened biosecurity measures, and integration of serological monitoring into regional disease control programs are essential to safeguard pig health, rural livelihoods, and food security in Northeast India. Keywords: backyard pig farming, enzyme-linked immunosorbent assay, Meghalaya, Northeast India, porcine reproductive and respiratory syndrome virus, seroepidemiology, slaughterhouse surveillance, swine health.