title: African horse sickness: transmission and epidemiology.
abstract: African horse sickness (AHS) virus causes a non-contagious, infectious, arthropod-borne disease of equines and occasionally of dogs. The virus is widely distributed across sub-Saharan African where it is transmitted between susceptible vertebrate hosts by the vectors. These are usually considered to be species of Culicoides biting midges but mosquitoes and/or ticks may also be involved to a greater or lesser extent. Periodically the virus makes excursions beyond its sub-Saharan enzootic zones but until recently does not appear to have been able to maintain itself outside these areas for more than 2-3 consecutive years at most. This is probably due to a number of factors including the apparent absence of a long term vertebrate reservoir, the prevalence and seasonal incidence of the vectors and the efficiency of control measures (vaccination and vector abatement). The recent AHS epizootics in Iberia and N Africa spanning as they do, 5 or more yr, seem to have established a new pattern in AHS virus persistence. This is probably linked to the continuous presence of adult C imicola in the area. Culicoides imicola is basically an Afro-Asiatic insect and prefers warm climates. Therefore its continuous adult presence in parts of Iberia and N Africa may be due to some recent moderations of the climate in these areas.
authors.affiliation: Institute for Animal Health, Pirbright Laboratory, Woking, Surrey, UK.
authors.forename: P S
authors.initials: PS
authors.lastname: Mellor
mesh_terms: D000352:Africa, Northern / Q000453:epidemiology; D000355:African Horse Sickness / Q000453:epidemiology / Q000635:transmission*; D000356:African Horse Sickness Virus / Q000502:physiology*; D000818:Animals; D001096:Arachnid Vectors / Q000382:microbiology; D002519:Ceratopogonidae / Q000382:microbiology*; D009033:Culicidae / Q000382:microbiology; D006736:Horses; D007303:Insect Vectors / Q000382:microbiology*; D011174:Portugal / Q000453:epidemiology; D013030:Spain / Q000453:epidemiology; D013987:Ticks / Q000382:microbiology