[Dengue, arbovirus and migrations in the Indian Ocean]

An arbovirus requires a competent haematophagous arthropod for transmission from one vertebrate to another susceptible host. Air transportations allow quick transfers from place to place and the diffusion of potential vectors or infectious hosts. The merchandise transportation by containers allowed the diffusion of Ae. albopictus from Asia through Africa and America. Emerging arbovirusis may occur in zones where they do not exist. Dengue which originally was located in southeastern Asia, is the most important arbovirusis in the world. The occurrence of dengue haemorrhagic fever (DHF) in Asia and America, mostly in urban areas, increased the global concern about dengue. Likewise, cases of DHF are not reported in Africa and in the Indian Ocean southwestern islands. The principal vector of dengue, Aedes aegypti, was present during the dengue 1 outbreak in Comoros, in 1993. In the other islands, only few specimens of Ae. aegypti are observed, and described mostly as none anthropophilic forms. The role of Ae. albopictus as vector of dengue was suspected and reported during outbreaks in Seychelles and Réunion island in 1977-1978. Yellow fever, present in Africa mostly in restricted areas, is absent in Asia. Japanese encephalitis considered as an emerging disease in India could expand through the islands. Rift valley fever, with periodic epizootics in domestic ungulates in Africa, was described as a new disease in Madagascar in 1990-1991. Crimean-Congo haemorrhagic fever is also present in Madagascar. Humans can be infected by vector bite or by handling infectious animal products. The distribution of other viruses (West Nile, Sindbis, Wesselsbron or Chikungunya) is discussed.