Spatial and seasonal distribution of Culicoides imicola in Iberia in relation to the transmission of African horse sickness virus

Abstract

Collections of biting midges were made over 24 months from sixty sites spread across Iberia. Information on the distribution of the vector of African horse sickness virus, Culicoides imicola, from these 3119 samples showed that this species was annually present across south-western Spain as far as 3 degrees 53'W and throughout most of Portugal, up to 41 degrees 5'N. C. imicola was found in all areas where African horse sickness epizootics had occurred in 1987-90 and also in areas outside the epizootic zones. Seasonal patterns of capture success of C. imicola, from seventeen frequently sampled sites where the vector was present, usually showed a late summer-early autumn peak. At the sites furthest south there was a discrete peak, mostly in September or October, before and after which the numbers captured increased or decreased steadily. At higher latitudes peak abundances occurred as early as May or as late as November, population build up was less uniform and numbers often declined rapidly after the peak was reached. Both the distribution and seasonal abundance patterns closely matched transmission patterns of African horse sickness virus, which rose during late summer and caused most cases during the autumn months.

Culicoides Biting Midges: Their Role as Arbovirus Vectors

“…As a direct result of the yearround presence of the vector, these regions are potential enzootic zones for AHS. Rawlings et al (152) have suggested that the northward expansion of C. imicola may be continuing in the Iberian peninsula aided by global climate change. If this is indeed the case, with a projected temperature increase during the early part of the twenty-first century in the order of 1 to 3.5Њ C and bearing in mind that a 1Њ C rise in temperature corresponds to 90 km of latitude and 150 m of altitude, this could extend the distribution of C. imicola and hence the risk of disease, into central Europe.…”

Host preferences and circadian rhythm of Culicoides (Diptera: Ceratopogonidae), vectors of African horse sickness and bluetongue viruses in Senegal

“…In southern Africa, Culicoides imicola Kieffer and Culicoides bolitinos Meiswinkel are proven vectors of African horse sickness virus (AHSV) (Venter et al, 1999;Venter et al, 2000;Meiswinkel & Paweska, 2003) and of bluetongue virus (BTV) (Rawlings et al, 1997;Venter et al, 2000;Mellor & Hamblin, 2004). Little is known about the biology and ecology of Culicoides species in West Africa, in particular those involved in the transmission of AHS and BT, which impedes the development of efficient vector control methods.…”

Bluetongue in Europe: past, present and future

“…BTV activity in Europe prior to 2001 was apparently restricted to the known range of C. imicola (Mellor & Pitzolis 1979;Jennings 1983;Mellor et al 1984;Boorman et al 1985;Mellor et al 1985;Boorman 1986;Rawlings et al 1997;Ortega et al 1998). The spread of BTV-9 as far north as Kosovo where C. imicola is absent was therefore a milestone in the epidemiology of BT in Europe, as it represented the first incontrovertible confirmation that field transmission by local northern Palaearctic vector species of Culicoides was possible on a large scale outside the distribution of C. imicola.…”