RESUMO
As part of the return of savanna migrants installed since a long time in forest regions, in the south of Sierra Leone, we carried out an experimental study about a cross-transmission between Simulium sirbanum from Missira (West-Mali) and the forest strain of Onchocerca volvulus in the south-west of Sierra Leone. This study will allow to know if there is a risk of onchocerciasis transmission recrudescence in relation to the reinstallation of these migrants in their native region. Because of the very high limitation to the forest strain of O. volvulus microfilariae output of the peritrophic membrane reduction with savanna black-flies and according to the very low mature parasite out put of S. sirbanum with this strain observed along this experimentation, the forest strain of O. volvulus from the south Sierra Leone appears maladjusted to S. sirbanum, the main vector of onchocerciasis in savanna regions. This observation implicates a very low intensity of transmission for this forest strain by savanna onchocerciasis vectors. The return of savanna migrants in their native region, installed in the south Sierra Leone since several decades, could not be, in a short time, an origin of onchocerciasis recrudescence in savanna regions of the Onchocerciasis Control Programme area cleaned by an effective vector control carried out since 1975 sustained now by a chemotherapeutic treatment reducing the human parasite reservoir. However, the preservation of this acquired necessitates an epidemiological supervision increased, because the interactions between the vector and the parasite for a long time could carry away a mutual adaptation and a sickness recrudescence.
Assuntos
Onchocerca volvulus , Oncocercose/prevenção & controle , Animais , Humanos , Oncocercose/parasitologia , Oncocercose/transmissão , Serra Leoa/epidemiologia , Simuliidae/parasitologia , Fatores SocioeconômicosRESUMO
The movements of human populations towards the mining wealth of the northern parts of Sierra Leone are favorable to a high contact rate between onchocerciasis patients coming from the south-western area of this country and the vector species Simulium yahense and Simulium squamosum which assume the essential of onchocerciasis transmission in the above-mentioned mining area. In fact, the Onchocerca volvulus strains concerned by this contact seem to be more pathogenic than those locally transmitted. In order to assess the danger it could represent for the Onchocerciasis Control Programme in West Africa, we carried out the experimental study of transmission which may result from this contact when more or less infected onchocerciasis patients are involved. The results indicated that this transmission by S. yahense may reach high proportions only when heavily infected onchocerciasis patients are implicated. We took also notice of the low capacity of S. squamosum to transmit the O. volvulus strains from the south-western Sierra Leone, irrespective of the microfilarial load of patients. Thus, in the most favorable conditions of a high parasite-vector contact of the study, involvement of S. yahense and onchocerciasis patients with high skin microfilarial loads is the only occurrence to which a high risk of intensive transmission may be related. The authors consider that the probability of such a risk occurring will be drastically reduced, due to the considerable decrease of skin microfilarial loads in human communities which regularly have the advantage of ivermectin (Mectizan) mass treatments.
