[The effect of ivermectin on the longevity of Simulium damnosum]. / Etude de l'effet de l'ivermectine sur la longévité de Simulium damnosum.

Studies on various blood-sucking arthropods have shown an increased mortality after feeding on hosts previously treated with ivermectin. We investigated in Cameroon the survival of blackflies (Simulium damnosum s.s. and S. sirbanum) fed on patients who had been treated at a dose of 150 micrograms/kg 3-13 days before the blood meal. The mortality rates were not significantly reduced when compared with those of flies fed on untreated individuals.

[Control of onchocerciasis with ivermectin: results of a mass campaign in northern Cameroon]. / Lutte contre l'onchocercose par ivermectine: résultats d'une campagne de masse au Nord-Cameroun.

A mass chemotherapy campaign to treat onchocerciasis with ivermectin was carried out in northern Cameroon, in the North Vina valley, a savanna area that is part of the extended Vina-Pendé-Longone focus. More than 20,000 people aged five years and over were treated at least once and more than 30,000 treatments were distributed. One to four treatments were given at intervals of six months or one year. Clinical and parasitological examinations of representative samples of the treated population and full ophthalmological examinations of males aged 15 to 35 years were carried out before each treatment to assess the efficacy of the different protocols of treatment. Secondary effects were recorded daily during the week after administration of ivermectin in the whole population treated. The evolution of arterial blood pressure was monitored over seven days in about 300 adults living in the hyperendemic region. The impact of mass treatment on natural transmission of the disease was evaluated by daily capture and dissection of blackflies during the month before and the two months after treatment. All levels of onchocerciasis endemicity were represented in the study area (maximum community microfilarial load (CMFL), 300 microfilariae per biopsy). Six months and one year after the first treatment, loads were down by more than 90% and more than 60% respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

[Campaign against the vectors of onchocerciasis in the surroundings of a refugee camp located in a savanna zone of Cameroon]. / Lutte contre les vecteurs de l'onchocercose aux alentours d'un camp de réfugiés situé en zone de savane du Cameroun.

In view of the risks of onchocerciasis facing Chadian refugees who have settled in a camp in a savanna hyperendemic area of northern Cameroon, the authors concluded that a vector control directed against the black fly larvae located on small seasonal tributaries of the main water course of this area should be carried out during the four to five months of the rainy season, i.e., during the whole period of transmission of this disease. The operations were undertaken during two consecutive rainy seasons. The first year consisted in developing ground-based control techniques and evaluating the larvicidal efficacy at the larval level. The second year was, particularly, devoted to the study of the impact of the vector control on the biting rate and on the transmission of onchocerciasis. Every week, three of the tributaries close to the camp were treated with an Emulsifiable Concentrate of temephos. Throughout the rainy season, the larvicide eliminated almost all the pre-adult black fly stages on these water courses. At the point in a high onchocercal endemicity area, it also reduced the biting rate by 60% and the Annual Transmission Potential by 72%, i.e., to values corresponding to the lower meso-endemicity threshold. Since these results were obtained at a very unfavourable point from the standpoint of black fly density and onchocerciasis transmission, the authors consider that vector control carried out under these conditions protects the local populations and the Chadian refugees effectively from black fly bites and a risk of severe onchocerciasis.

[Study of the transmission of onchocerciasis in the surroundings of a refugee camp located in the savanna zone of Cameroon]. / Etude de la transmission de l'onchocercose aux alentours d'un camp de réfugiés situé en zone de savane du Cameroun.

Chadian refugees, most of whom are free from onchocerciasis, settled recently in a camp in a savanna area of the northern Cameroon where the prevalence is about 80% and the blindness rate is 4% of the adult population. In view of the risks of onchocerciasis facing the immigrants, the authors carried out an entomological survey in this region aimed at determining the modes of transmission and assessing the possibilities for the control of this disease. After a three-month survey in the study area, it appears clearly that 1) transmission takes place only during the rainy season, 2) the main vectors are the two savanna species, Simulium damnosum s.s. and Simulium sirbanum, 3) the larval breeding sites are not located on the principal river, the Faro, but on its small seasonal tributaries, 4) the local populations still free from onchocerciasis and the Chadian refugees who farm close to these tributaries run the risk of getting serious ocular lesions in the long run which could lead to blindness. The conclusions of this survey prompted the authors to envisage an onchocerciasis control campaign in this area against the larval stages of the vectors.

[Ivermectin and the reduction of the rate of infection of simuliids in a forest focus of human onchocerciasis]. / Ivermectine et modalités de la réduction de l'infection des simulies dans un foyer forestier d'onchocercose humaine.

Eight patients from a forest onchocercian area "Grandes rivières", in Ivory Coast, were treated with a single oral dose of ivermectin (12 mg). The density of dermic microfilariae was estimated at days 0, 7 and 180; the mean numbers of ingested microfilariae and of developing larvae in the vectors S. soubrense-S. sanctipauli, engorged on the treated patients were recorded. Comparisons were made with non treated patients, having a similar density of microfilariae than the 8 treated patients at day 7. Results confirm the reduction induced by ivermectin of the dermic microfilarial density and the resulting reduction of the infection of the simuliids. Furthermore 7 days after treatment, a new phenomenon is demonstrated: for a similar dermic microfilarial density, simuliids take up a number of microfilariae 100 times lower from treated than from untreated patients. To explain this phenomenon, it is suggested that ivermectin induces a change in the microfilarial distribution in the layers of the dermis. Six months after treatment, this low uptake of microfilariae by the vectors had disappeared, and the infection rate of the engorged similiids was much higher than at day 7 although the dermic microfilarial density was similar.