Curent epidemiological aspects of human african tripanosomiasis in former historic sectors in Mali.

Summary The goal of this study is to describe current epidemiological aspects of human African trypanosomiasis in former historic sectors known for this disease in Mali. We began a study from April to May if 2002 in the districts of Kolondieba, Kenieba, Kati and Kolokani. In the course of study we looked for blood and serum antitrypanosoma antibodies and Trypanosoma brucei gambiense by card agglutination and the mini-column technique, respectively, in 2080 subjects collected during the study period. Than we installed traps along waterways in search of the vector. The seroprevalence from blood samples of the human African trypanasomiasis in the study areas was 5.9%. 5.16% of positive blood samples also corresponded to positive serum samples No trypanosoma were isolated by mini-column test. The tsetse flies were captured from the human subjects' villages. According to these results, we can say that the African human trypanosomiasis no longer poses a public health problem in Mali. However, all contributing environmental and vectorial factors are presently primed for a resurgence of an African trypansomiasis epidemic in the studied area.

Drastic reduction of populations of Simulium sirbanum (Diptera: Simuliidae) in central Sierra Leone after 5 years of larviciding operations by the Onchocerciasis Control Programme.

The major vectors of the blinding form of human onchocerciasis in West Africa are two blackfly species, Simulium sirbanum and Simulium damnosum s.s. (Diptera: Simuliidae), identified at the adult stage as the 'savanna group' of the Simulium damnosum complex. In 1988, in the central part of Sierra Leone, the average daily biting rate (females/man/day) by savanna blackflies (mostly S. sirbanum) during the peak of the dry season (April-May) was 59.9, making up 69.1% of total captures on average. There was evidence of a strong long-range immigration of adult females of S. sirbanum through eastern Guinea in the dry season, with a reverse movement towards Guinea in the rainy season. Therefore, in 1989, the World Health Organization's Onchocerciasis Control Programme (OCP) extended its vector control operations from central West Africa to rivers of central and northern Sierra Leone, and to rivers of eastern Guinea. Four years of efficient larviciding drastically reduced adult populations of S. sirbanum in Sierra Leone. In the peak of the dry seasons of 1993 and 1994, the average biting rate by savanna blackflies in central Sierra Leone had dropped to 1.0, making up only 4.3% of total captures on average. Yearly biting rates by S. sirbanum in central Sierra Leone were therefore reduced to 2% of their pre-intervention levels. Based on larval samples, the S. sirbanum has been replaced by two forest species, S. leonense in the south and S. squamosum in the north. Since 1992, it has been possible to calculate accurate transmission rates for blinding onchocerciasis, based on DNA-probe identifications. From 1993, the risk of transmission has not only been reduced by vector control but also by mass distribution of ivermectin to rural communities. In terms of control strategy, the authors conclude that larviciding operations could be alleviated in central Sierra Leone without increasing the risk of blinding onchocerciasis transmission, as long as the migration of S. sirbanum through eastern Guinea and northern Sierra Leone is prevented.

[ Onchocerciasis control program in West Africa: socioeconomic development and risk of recrudescence of transmission. 1. Experimental study of the transmission of Onchocerca volvulus strains from Southwestern Sierra Leone by Simulium sirbanum]. / Le programme de lutte contre l'onchocercose en Afrique de l'ouest: développement socio-économique et risque de recrudescence de la transmission. 1. Etude éxperimentale de la transmission des souches d'Onchocerca volvulus du sud-ouest de la Sierra Leone par Simulium sirbanum.

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.

[Onchocerciasis control program in West Africa: socioeconomic development and risk of recrudescence of transmission. 2. Experimental study of the transmission of Onchocerca volvulus strains from Southwestern Sierra Leone by Simulium yahense and Simulium squamosum]. / Le programme de lutte contre l'onchocercose en Afrique de l'ouest: développement socio-économique et risque de recrudescence de la transmission. 2. Etude éxpérimentale de la transmission des souches d'Onchocerca volvulus du sud-ouest de la Sierra Leone par Simulium yahense et Simulium squamosum.

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.