Transmission indices of Loa loa in the Chaillu Mountains, Congo.

A longitudinal entomological survey of the vectors of loiasis was conducted in the Missama area (Lekoumou region) in the Congo from September 1987 to August 1989. The principal catching site was a palm grove surrounded by forest 3 km from the village. Landing/biting densities of Chrysops were measured by standardized fly catches lasting 11 hr carried out twice a month. Vector landing densities were also assessed in the Bantu and Pygmy villages and in the fields. Populations of Chrysops from the palm grove were examined 6 times a month for infection with the infective stage of Loa loa. Chrysops silacea was the predominate vector except at the beginning of the rainy season, when C. dimidiata was the prevailing species. Chrysops were caught throughout rainy season, from October to June. The host-seeking activity of C. silacea was greatest in the middle of this season (February), but occurred sooner (October) for C. dimidiata. The following variables associated with transmission were calculated from our observations in the palm grove (the first figure corresponds to the first year of the study and the figure in parentheses corresponds to the second year). It was calculated that 2.658 (2.185) C. silacea and 1.412 (1.182) C. dimidiata could bite a person in the palm grove per year, including an average of 14.4 (12.7) infective C. silacea and 9.8 (7.2) infective C. dimidiata. The percentage of all dissected flies with third stage larvae in the head and the mean number of larvae in the head/infective fly were 0.57% and 10.1 +/- 6.8 for C. silacea and 0.66% and 11.2 +/- 6.5 for C. dimidiata, respectively. The estimated annual transmission potentials were 171.1 (102.9) for C. silacea and 116.1 (73.8) for C. dimidiata. In the palm grove, transmission was ensured by 2 effective vectors during the rainy season (October to May). Although the annual biting rate for both species was twice as low in the village as in the forest, our data suggest that effective transmission occurs there also.

Chrysops silacea and C. dimidiata: fly densities and infection rates with Loa loa in the Chaillu mountains, Congo Republic.

The densities, infection rates with Loa loa, and parous rates of Chrysops silacea and C. dimidiata were studied in various ecological zones throughout the Chaillu mountains in the People's Republic of the Congo. In the rainy season, C. dimidiata was the major vector in the forest, whereas C. silacea was predominant in the cleared forest zones. Fly densities were higher in the forest (natural forest or palmgrove) than in the villages. Parous and infection rates varied according to the ecological zone. The infection rate of parous females was related to the microfilarial rate in the human population, indicating that the Chrysops populations were extremely stable in the rainy season.

Epidemiology of Mansonella perstans filariasis in the forest region of south Congo.

A study of Mansonella perstans filariasis conducted in the Chaillu mountains, Southern Congo, showed that 108 of 134 Pygmies (80.6%) and 79 of 302 Bantus (26.2%) presented with microfilaraemia. The mean microfilarial densities were also significantly higher in the Pygmies (1213 ml-1 of blood) than in the Bantus (136 ml-1). Ninety eight per cent of the Culicoides taken which had bitten man in the daytime were C. grahamii, and 0.8% of these were infected with filarial larvae. Two other species of Culicoides (C. kumbaensis and C. rutshuruensis) might also play a role in the transmission of M. perstans.

[Ceratopogonidae (Diptera) of the Congolese Mayombe. II. Contribution to the study of a Culicoides community]. / Les Ceratopogonidae (Diptera) du mayombe congolais. II--Contribution à l'étude d'un peuplement de Culicoides.

Owing to adapted methods of sampling and regular captures carried out during one year, the study of a Culicoides community could be realized in the Mayombe mountain in Congo. Nineteen species were recorded. Quantity and frequency of each of them have been computed. For the principal species feeding habits, phototaxis, sex-ratio, seasonal fluctuations are analysed. Influence of climatic parameters is discussed.

[Ceratopogonidae (Diptera) of the Congolese Mayombe. I. Daily pattern of the biting activity of female Culicoides grahamii Austen, 1909]. / Les Ceratopogonidae (Diptera) du Mayombe congolais. I--Rythme d'activité journalier des femelles de Culicoides grahamii Austen, 1909.

Owing to appropriate sampling methods, the study of the daily pattern of biting of female "Culicoides grahamii Austen, 1909" was achieved in the Congolese Mayombe. It was discovered that this pattern was rhythmical in close connection with the sunrise and sunset. Many climatic parameters were simultaneously studied (temperature, hygrometry, brightness). This starting factor of this rhythmical pattern seems to be a brightness which agrees to a total shortwave radiation on the ground, equal or inferior to 25 cal x m-2 x h-1. It seems that the temperature does not play any role.