Current Status of Bluetongue Disease, Its Vector and Pathogenesis in India

Bluetongue (BT) is a Culicoides (Diptera: Ceratopogonidae) borne, infectious, noncontagious, economically important viral disease of sheep and other domestic and wild ruminants. Humans are not affected although some species of Culicoides feed on human blood also. The disease has the potential to spread rapidly, which can cause serious socio-economic consequences in view of mandatory trade barrier on the movement of animals, their germplasm, embryo and other animal products from BT endemic to BT free countries. The first outbreak of BT in sheep and goats in the country was recorded in 1964 in Maharashtra State. Since then, several outbreaks of BT have been reported in sheep in almost all states of the India. A serological survey has indicated the presence of bluetongue virus (BTV) antibodies in the Indian cattle, buffalos, goats, camels and some wild ruminants. However, clinical BT has not been observed in cattle or buffalo to date, whereas in goats, there are sporadic reports of occurrence of clinical BT either alone or as co-infection with peste des pestis ruminants. Although BTV has been isolated from Culicoides midges, the particular species responsible for transmission has not yet been identified. BTV is the prototypic member of the genus Orvivirus, family Reoviridae. BTV a non enveloped icosahedral virus consists of a ten segmented, double stranded RNA genome encapsidated in a double layered protein coat. Immunization programme is in progress in India and multivalent inactivated adjuvant vaccine containing BTV serotypes 1, 2, 10, 16 and 23 has been developed. Discovery of VLPs and CLPs has opened a new era of vaccination. The vector of BT is the Dipteran spp. Culicoides. About 60 spp. of Culicoides are reported from India. The early ecological study indicates that Culicoidesmonocoli Maheshwari may be the potential vector. The studies on BT in India are in primary stages, which may open several of vital fields for future investigation.