The epidemiology and diagnosis of bluetongue with particular reference to Corsica

Abstract

Bluetongue (BT) and/or BT viruses (BTV) have been identified in the Mediterranean basin and the Balkans each year from 1998 to 2002 and in particular BTV serotype 2 in the French Island of Corsica (2000 and 2001). In response to these virus incursions, the French Veterinary Authorities carried out epidemiological studies that included virological, serological and entomological analysis, and two vaccination campaigns performed in the winter of 2000/2001 and the winter and spring of 2001 and 2002. Rapid and reliable serotype differentiation is essential at the start of an outbreak to allow an early selection of vaccine to control the spread of the virus. Thus, molecular tools, that complement conventional methods, have been developed for early detection of infection, determination of the serotype, and differentiation between natural infection and vaccination. Serological results showed that the first vaccination campaign during the winter of 2000/2001 did not provide full protection for all sheep and during the summer of 2001, 335 sheep flocks in Corsica were again infected by BTV 2 (7-fold more that in 2000). Entomological studies have demonstrated that the only proven vector of the disease, Culicoides imicola, was present in the island in 2000 and that it has successfully established itself in Corsica. The safety and immunogenicity of the commercial South African vaccine were studied. Fourteen sheep were vaccinated and then observed for clinical signs. Blood, sera, spleen and lymph nodes were collected and analyzed, and the results confirmed the safety and potency of using this vaccine to protect sheep from clinical disease. As a result, an intensive vaccination campaign was performed during winter and spring 2001/2002. No cases of BT had been observed by the end of summer 2002, indicating that the vaccination campaign has been successful in protecting sheep from infection.