Density and dispersal of the loaiasis vector Chrysops dimidiata in southern Cameroon.

By mark-release-recapture experiments, we assessed the density of loaisis vectors, Chrysops dimidiata Wulp plus some Chrysops silacea Austen (Diptera: Tabanidae) and estimated their range of flight in the secondary forest of southern Cameroon. In 1993, the release point was at the centre of the study area and recapture points were at 1,100 m radius. In 1994, releases were on the periphery of the study area and recapture sites were 400-8,000 m from the release points. Results were concordant and showed Chrysops female densities of 785-3,682 flies/ km2. The theoretical flight range was < 6,000 m, with a maximum distance of 4,500 m observed. These results are considered promising for the use of vector control methods against loaiasis.

Impact of repeated large scale ivermectin treatments on the transmission of Loa loa.

We have studied the impact of large-scale treatment with ivermectin on the transmission of loiasis in a forest village in south Cameroon where loiasis was highly endemic, with a prevalence of 30%. After one year of parasitological and entomological surveillance without treatment, all consenting residents aged > 5 years received ivermectin 200 micrograms/kg every 3 months. For ethical reasons, treatment was interrupted after 2 years, but parasitological and entomological surveillance continued for 18 months after the end of treatment. The prevalence of loiasis was reduced to < 10% and the mean microfilaraemia decreased by 90% in 2 years. The prevalence and average intensity of infection remained stable during the 18 months after treatment ended. Two vector species were identified, Chrysops dimidiata (representing about 90% of the fly population) and C. silacea. The infection rate (all stages) in Chrysops decreased by 75% and the infective rate (percentage of Chrysops harbouring third-stage larvae of Loa loa in the head) decreased by 85% in C. dimidiata and became zero in C. silacea. After the end of treatment, the infection and infective rates increased gradually. Large-scale treatment seemed an efficient method for the control of L. loa transmission provided high drug coverage was achieved. Nevertheless, because of the high risk of adverse effects when using the current microfilaricidal drugs, such a strategy remains unacceptable.

[Anopheles species and the transmission of malaria in the forest/savannah transition zone in central Cameroon]. / La faune anophélienne et la transmission du paludisme dans une zone de transition forêt/savane au centre du Cameroun.

A longitudinal study on malaria vectors and transmission was carried out in a forest-savannah transitional area in Cameroon. Indoor all night mosquito collections on human bait were performed during one year in two villages: Nditam and Ngoume. Nditam was located in a secondary forest block surrounded by savannah, while Ngoume was situated in an ancient forest block. The results showed that at Nditam, only one anopheline species was collected, that was Anopheles gambiae s.l.. The average daily biting rate was 2.4 bites per man per night. The sporozoitic index of An. gambiae was 9.4%. The entomological inoculation rate was therefore estimated at 0.225 infective bite per man per night that is to say 82 infective bites per man per year. Malaria transmission was low during the year, but an important increase was observed in September, when the rainfall was at its peak. At Ngoume, no Anopheles mosquito was collected. Therefore, malaria transmission was not observed in that village.

[Study of the distribution of human filariasis in West Province of Cameroon]. / Contribution à l'étude de la répartition des filarioses humaines dans la Province de l'Ouest du Cameroun.

A clinical and parasitological survey of onchocerciasis and loiasis has been carried out in 38 communities in the West Province of Cameroon prior to the implementation of a mass ivermectin treatment. The highest endemicity levels of onchocerciasis were recorded in the villages located at an altitude below 1400 m, and whose inhabitants go down to the valleys for agricultural activities. Conversely, low endemicity levels were recorded in the most populated part of the study area, which is located at an altitude above 1400 m; in the latter communities, the residents cultivate the high ground not far from their houses and are thus less exposed to transmission of onchocerciasis. Despite relatively low microfilarial loads, the prevalences of nodules were fairly high; this demonstrates that in some epidemiological situations the latter indicator gives an erroneous indication of the intensity of infection in the population. The prevalence of loiasis is very low in most of the villages of the study area.

[A rural epidemic of Igbo Ora virus (with interhuman transmission) in the Ivory Coast 1984-1985]. / Epidémie rurale a virus "Igbo Ora" (avec transmission inter-humaine) en Cote-d'Ivoire en 1984-1985.

The first outbreak caused by Igbo Ora virus is described. Virus circulation has been demonstrated up on thirty-three sick persons in Yamoussoukro area (Ivory Coast).