The Distribution of Vectors of Arboviruses of Livestock in Northern Australia

Summary

Arboviruses such as bluetongue viruses, akabane and ephemeral fever cause or threaten various production losses and export trade impediments to cattle and sheep-based industries. The distribution of these viruses is determined largely by the distribution of the insect species which transmit them. Biting midges of the genus Culicoides include species implicated to various degrees of certainty as vectors of these arboviruses. Culicodes species because of their small size are considered highly suited to wind-assisted dispersal over long distances and this is thought to have introduced vectors such as C. brevitarsis and C. wadai into northern Australia from SE Asia. Further introductions are a constant possibility. C. wadai is thought to have been introduced as recently as the early 1970's. Many species in SE Asia are not yet present in Australia including known vectors such as C. imicola and closely related species such as C. nudipalpis and C. orientalis.

The vector status of most SE Asian species is unknown but the intense arbovirus activity prevalent in SE Asia suggests a number of species may be acting as vectors. The distribution and abundance of vector species in Australia is not static but changes due to climatic variation and as a result of long term expansion in some recently introduced species such as C. wadai. When last surveyed in the mid 1980's, C. wadai was expanding its distribution. Consequently areas currently considered vector free are threatened by the possibilities of long-term permanent expansions of new or recently introduced species and also short-term temporary invasions of existing vectors during and following periods of favourable climatic conditions.