Prediction of areas around the Mediterranean at risk of bluetongue by modelling the distribution of its vector using satellite imaging

Bluetongue is an infectious disease of ruminants caused by a virus transmit ted by biting midges, one species of which, Culicoides imicola, is the majo r vector in the Old World. Following an epizootic of African horse sickness , a related disease, in Iberia and Morocco between 1987 and 1991, C imicola was trapped for two years at 44 sites in the affected region and models we re developed for predicting the abundance of C imicola at these sites. Disc riminant analysis was applied to identify the best model of three levels of abundance from 40 Fourier-processed remotely sensed variables and a digita l elevation model. The best model correctly predicted the abundance level a t 41 of the 44 sites. The single most important variable was the phase of t he annual cycle of the normalised difference vegetation index. The model wa s used to predict the abundances of C imicola elsewhere around the Mediterr anean and predicted high levels of abundance in many areas recently affecte d by bluetongue, including the Balearics, Sardinia, Sicily, eastern Greece, western Turkey, Tunisia and northern Algeria. The model suggests that east ern Spain, the island of Ibiza, the provinces of Lazio and Puglia in Italy, the Peloponnese and parts of northern Algeria and Libya may be at risk of bluetongue in 2001.