An epidemiological research program on arboviruses has been in progress in Madagascar since I976. Extensive serological surveys have demonstrated an active viral circulation, mainly of the flavivirus group, in the human population. Numerous viral strains were isolated from mosquitoes. These strains included two new viral species, several cosmopolitan viruses, such as Sindbis and West Nile, and several African viruses, especially Rift Valley fever virus, which was isolated from mosquitoes caught in a rain forest area.
During 1985, 3,216 ticks were collected from cattle in the slaughterhouse in Antananarivo, the capital of Madagascar. Monospeciflc pools of unfed ticks were constituted and inoculated i.c. into suckling mice for virus isolation attempts. Five viral strains were isolated from 5 out of I35 pools of Boophilus microplus, while an 113 pooIs of Amblyomma variegatum remain negative. The strains were identifIed as Congo-Crimean haemorrhagic fever (Congo-CHF) virus by complement fixation and neutralization tests. All but 2 (MgAr951 , MgAr955) were reisolated. Prior to isolation of these strains, the Congo-CHF virus had not been introduced into our laboratory. The main characteristics of the 5 strains are given in table I ; they are typical of classical Congo-CHF viruses.
These strains represent the first isolation of Congo-CHF virus in Madagascar, and also the fIrst virus isolation from ticks in this country.
The tick B. micropus is not known to be a good vector. Nevertheless, it has been demonstrated to be a vector of Babesia bovis and Borrelia theileri in Madagascar. Moreover, although it is generally considered as a one- host tick , B. microplus has been found in Madagascar on several different hosts : cattle, sheep, goats, horses, dogs and also on humans. Although B. microplus may not play the same vectorial role as Hyalomma, which is not present in Madagascar, in the transmission of Congo-CHF virus, it may play an important epidemiological role in maintaining the virus over along period.
Since the Congo-CHF antigen was not included in the previously mentioned serologic surveys, and in light of the high pathogenicity of this virus which has recently been isolated from human cases in several African countries , there is a need for clinical, serological and epidemiological surveillance of the viral activity in the human population, especially in cattle-breeding areas.