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.

Chrysops silacea and C.dimidiata seasonality and loiasis prevalence in the Chaillu mountains, Congo.

Seasonal activity of the loiasis vectors Chrysops dimidiata Wulp and Chrysops silacea Austen (Diptera: Tabanidae) was studied during 1987-89 in villages and surrounding forest of the Chaillu Mountains, Congo. Chrysops were captured mainly in the hot rainy season (November-May) and densities of both species were higher in the forest than in villages. C.silacea predominated at all sites and C.dimidiata was rarely found in villages. In the rain forest, between 07.00 and 18.00 hours, 12 times more C.silacea and 3 times more C.dimidiata were collected with hand-nets (range 15-81 per man-day) than were caught in landing/biting collections on human bait. Chrysops man-biting rates were higher in villages closer to the forest, but variations in loiasis prevalence among villagers (microfilaraemia rates 16-37%) were not proportional to the intensity of contact between people and vectors in the villages, indicating that the majority of loiasis transmission probably occurs when people go into the forest.

Clinical manifestations of loiasis in an endemic area in the Congo.

The functional symptomatology of loiasis was studied in 101 Congolese subjects living in a village in a highly endemic area. 27.7% of them were carriers of Loa loa microfilariae. 5.9% were infected with Mansonella perstans. No subjects were found to have dermal microfilariae. In anamnesis, 51.5% of them reported episodes of Calabar swellings, 69.3% history of eyeworm and 10.9% episodes of subcutaneous migration of worms during the last 12 months. Pruritus and secondary dermal lesions were frequently demonstrated in 64.4% and 56.4% of the individuals respectively. Asymptomatic amicrofilaraemic subjects only accounted for 11.9% of the adult population. The study of the life-time risk of eyeworm, also conducted in the Pygmy and Bantu populations of another village, was shown to be useful in epidemiological evaluations.

Seroprevalence des infections a VIH1 a Djoumouna; Congo

Une etude destinee a localiser une zone de forte endemicite pour l'infection a VIH et pour le paludisme en vue des etudes sur les interactions VIH parasitoses a ete menee a Djoumouna; village situe a 25 Km de la sortie de Brazzaville. Les suspects serologiques en ELISA (1 pour cent) ont ete confirmes en Western Blot. Seuls 0;5 pour cent des individus examines avaient des anticorps anti-VIH1. Les raisons pouvant expliquer cette faible prevalencesont discutees