Detection of Bluetongue Virus Antibody in Small Ruminants in Gujarat State, India

Abstract

Bluetongue (BT) is an economically significant, non-contagious, arthropod-borne viral disease of domestic and wild ruminants, transmitted primarily by Culicoides midges. The disease is endemic in tropical and subtropical regions, including large parts of India, and poses serious challenges to livestock productivity due to high morbidity, mortality, reproductive losses and trade restrictions. The present study investigated the seroprevalence of bluetongue virus (BTV) antibodies in small ruminants across different regions and districts of Gujarat using two serological assays: the indirect enzyme-linked immunosorbent assay (i-ELISA) and the agar gel immunodiffusion (AGID) test. A total of 1140 serum samples from sheep and goats were collected from 13 districts representing five major agro-climatic regions of the state. Overall seroprevalence was 30.26% by i-ELISA and 21.05% by AGID, with i-ELISA consistently detecting a higher number of positive samples. Regional seroprevalence varied, with the highest rates recorded in Saurashtra and South Gujarat and the lowest in North Gujarat. District-wise prevalence ranged from 20.93% to 38.89% (i-ELISA) and 13.95% to 34.78% (AGID). Breed- and age-wise analyses revealed higher seropositivity in indigenous breeds and in animals above three years, suggesting cumulative exposure to circulating BTV. Goats exhibited seroprevalence rates of 31.44% (i-ELISA) and 22.13% (AGID), with substantial regional and breed variation. Animals with a previous history of abortion showed higher seropositivity, reinforcing the association between BTV infection and reproductive losses. Comparison of the two diagnostic tests indicated that i-ELISA was more sensitive, identifying 105 additional positive samples not detected by AGID; AGID exhibited 69.57% sensitivity and 100% specificity relative to i-ELISA. The study confirms widespread exposure of small ruminants to BTV in Gujarat and highlights the superiority of i-ELISA for surveillance. These findings underscore the need for continuous monitoring and strengthened vector control strategies to mitigate the impact of bluetongue on livestock health and productivity.