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Emergence of bluetongue in France 2000-2004: Lessons for surveillance

Gerbier G., Cetre-Sossah C., Biteau-Coroller F., Zientara S., Roger F.. 2006. In : ISVEE. Proceedings of the 11th Symposium of the International Society of Veterinary Epidemiology and Economics, Cairns, Australia. Cairns : ISVEE, 3 p.. (ISVEE Proceedings, 1177-360X, 11). International Symposium on Veterinary Epidemiology and Economics. 11, 2006-08-06/2006-08-11, Cairns (Australie).

Bluetongue (BT) is a vector-borne disease transmitted by biting midges. Since 1999, several BT outbreaks of serotypes 2, 4 and 16 have been recorded in the Western Mediterranean region. In response, France implemented entomological and serological surveillance, in addition to clinical surveillance, in Corsica island (infected area) and on the French Mediterranean coast (area at risk). In 2000, Culicoides imicola, the main vector of BT was discovered in Corsica. Entomological surveillance started in 2002 on 12 sites in Corsica and on 19 sites on the mainland. Settlement of C. imicola was documented in Corsica during 3 consecutive years. On the mainland, some erratic specimens were trapped in 2003 and by 2004 a settled population was discovered. This is the Northernmost population of proved BT vector found in Europe. Serological surveillance was used to evaluate herd immunity and detect new serotypes. In Corsica, 91% of adult sheep were Elisa positive in 2002. To detect circulation of BT virus, slaughtered calves were systematically blood sampled and sentinel goats were sampled periodically to find any seroconversion. As a result, viral circulation of BT serotype 4 was detected as early as May 2003, while clinical signs were only declared in August 2003. On the mainland, no BT positives have been detected to date. The 3-year surveillance has shown a) the gradual expansion of BT vectors to the North, and b) the silent spread of the virus before clinical signs are expressed. Ongoing adaptation of surveillance is then necessary to design and implement appropriate control measures.

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