Sero-epidemiology and molecular detection of Bluetongue virus in Indian ruminants.

Bluetongue (BT) is a non­contagious arthropod­borne viral disease of domestic and wild ruminants. It is endemic to India and clinical outbreaks of disease have been reported mainly in sheep, although BT is often asymptomatic in other ruminant species. In the present serological survey, a total of 576 serum samples, comprising of 416 cattle and 160 sheep, covering different agro­climatic zones of Rajasthan, Uttar Pradesh, and Karnataka states, were screened for the presence of Bluetongue virus (BTV) specific antibodies using competitive enzyme­linked immunosorbent assay (c­ELISA). Overall 73.08% (304/416) of the cattle and 53.30% (87/160) of the sheep serum samples were positive for BTV antibodies. The prevalence of BTV antibodies in cattle in different agro­climatic zones ranged between 60­80% in Rajasthan and 66­70% in Uttar Pradesh. During the study, a nested polymerase chain reaction (PCR) based on the BTV NS1 gene (genome segment 5) was optimized for detection of BTV's nucleic acid from a cell adapted strain of BTV­23, and field derived clinical blood samples. In the present study, 19/70 of cattle and 9/30 of sheep blood samples tested positive for BTV RNA by the nested PCR, which amplified specific products of 274 bp and 101 bp sizes, respectively. From this study, it can be concluded that cattle showed higher percentage of sero­positivity in comparison to sheep. The improved sero­surveillance system for BTV in endemic areas will be of great help to understand the epidemiology of BTV and to formulate effective control and preventive strategies.