La faune anophelienne dans une agglomeration urbaine de Kinshasa (R.D.C) en 1994-1995

Les auteurs ont effectue des captures des moustiques adultes dans les collectivites peripheriques de la zone de Ndjili (Kinshasa). Les resultats demontrent l'existence d'une cohabitation entre les Culicides et les anophelines. Dans ce dernier groupe; A. gambiae s.l. represente 99;2 pour cent de la population anophelienne. Les collectivites marecageuses et maraicheres abritent plus de moustiques que les autres. Les femelles sont moins nombreuses que les males (31;8 pour cent) mais les sex-ratios les plus importants observes dans les collectivites montrent la dynamique des femelles d'anopheles

Impact of deltamethrin-impregnated bednets on biting rates of mosquitoes in Zaire.

In a rural area of Zaire, the whole population of a village was protected by deltamethrin-impregnated mosquitoes bednets. A similar village was observed as a control. Biting rates for mosquitoes were recorded in both villages. The principal man-biting species were Mansonia africana, Mansonia uniformis, and Aedes aegypti. In the village protected by the impregnated mosquito bednets, the number of Mansonia bites was reduced 96% indoors and at a lesser rate outdoors. Biting rates of Ae. aegypti dropped to 0 indoors, but the outdoor biting rate remained unchanged. It is concluded that the reduction in mosquito bites is not only caused by the repellent action of the deltamethrin but also by a reduction in mosquito numbers.

[Mosquito nets impregnated against malaria in Zaire]. / Moustiquaires imprégnées contre le paludisme au Zaïre.

On the Bateké plateau 60 km east of Kinshasa, Zaïre, where malaria is stable, three villages have been selected for a trial of malaria control using bednets impregnated with deltamethrin at 25 mg per square meter from February to November 1991. One village (3,000 inhabitants) has been provided 800 impregnated bednets and an other one (2,900 inhabitants) kept 800 non impregnated bednets. The third village (900 inhabitants) served as a control and has remained without nets. Anopheles gambiae was the main and nearly exclusive vector of malaria. Its biting density was reduced by 94% in the village protected by impregnated bednets and the inoculation rate dropped from 182 infective bites/man/year to 3.7 a decrease of 98%. The longevity of the vector expressed by its expectation of life decreased from 11.02 days to 3.64 days. In the village where inhabitants were protected by non impregnated nets, as well as in the control, the entomological indexes did not change. In the village protected with impregnated nets the malaria prevalence decreased by 50%, five months after the beginning of the experiment. The high parasitemia, above 10,000 and 20,000 parasites per mm3 decreased by 77% and 83% in the 0-7 year age group and by 67% and 65% in the 8-14 year group in the protected village. These high parasitemias are good markers of the clinical malaria risk. The experiment can be considered as very satisfactory on the point of view of public health.

[The culicidian fauna and its nuisance in Kinshasha (Zaire)]. / La faune culicidienne et sa nuisance à Kinshasa (Zaïre).

A public health study to inventory bloodsucking mosquitoes was conducted in Kinshasa and its regions. 20 culicidian species were represented by 7 Anopheles, 6 Culex, 5 Aedes and 2 Mansonia. In general, the number of bites/man/night (b/m/n) was in average 141.5 of Cx. quinquefasciatus, 60.1 of Cx. antennatus, 21.1 of M. africana, 16.3 of An. gambiae and 7.7 of M. uniformis. The nuisance is different from region to other. Culex quinquefasciatus is the most abundant and aggressive species in the urban area with an average of 400 b/m/n. In certain suburban zones, Culex antennatus is predominant, with aggression on the order of 176.5 b/m/n. The Anopheles gambiae complex is predominant in the semi-rural zone at the periphery of the city with 26.05 b/m/n. Other mosquitoes are equally implicated in their aggression and nuisance to man, in particular, Mansonia africana, Mansonia uniformis and Aedes aegypti. A geographical distribution map has been established for the preponderant species in Kinshasa.

Efficacy of Bacillus sphaericus against the malaria vector Anopheles gambiae and other mosquitoes in swamps and rice fields in Zaire.

The microbial control of Anopheles gambiae and other mosquitoes with a granular formulation of Bacillus sphaericus (Vectolex) was evaluated in rice fields and swamps, located around the suburban region of Kingabwa-village in Kinshasa, Zaíre. Ten treatment cycles with 15-day intervals were carried out with the same application rate, 10 kg/ha, during the dry season (May to September 1991). The treatments reduced larval populations of An. gambiae by 98% after 48 h, but repetitive applications were required every 15 days to maintain control. The persistence of B. sphaericus spores was more apparent in rice fields than in swamps. A significant reduction in nuisance biting by Culex quinquefasciatus and Mansonia uniformis was observed. For An. gambiae, a decrease of 13.6% in human biting was noted during the post-treatment period. The entomological inoculation rate was reduced from 0.238 to 0.143. The efficacy of B. sphaericus does not appear to offer outstanding potential for control of An. gambiae in rice fields and swamps and seems to be limited due to different factors tied to ecology and natural conditions in the fields.

[The Anopheles fauna and the transmission of human malaria in Kinshasa (Zaire)]. / La faune anophélienne et la transmission du paludisme humain a Kinshasa (Zaïre).

A longitudinal epidemiological study of malaria and its vectors was conducted in Kinshasa. 264 night-bite collections on human bait (1,056 man nights) and 384 collections of the house-resting fauna were carried out from April 1989 to October 1990. The anophelian fauna was identified and inventoried, 7 Anopheles species were found: Anopheles gambiae, An. funestus, An. paludis, An. hancocki, An. counstani, An. brunnipes, and An. nili. A single species, An. gambiae s. l. is responsible for the transmission of malaria, it represents 93.27% of the anopheline fauna. The average number of anophele bites man day was 16.28 bites/man/night, it varied between 1 b/m/n in urban area to 26.05 b/m/n in semi-rural area. The average of the sporozoite index for An. gambiae was 3.3%, but it varied from 0% in the urban area to 6.52% in the semi-rural area. The entomological inoculation rate (h) was 197 infective bites per year. This rate fluctuated from 1 infective bite each 128 nights in urban area to 1.7 infective night-bite in semi-rural area. Other epidemiological index were also determined: the level of daily survival rate (p = 8.75 days), the vectorial capacity of 17.97 and the Macdonald's stability 3.5 bites on man taken by a vector during its entire lifetime.

Field trials with Vectolex (Bacillus sphaericus) and Vectobac (Bacillus thuringiensis (H-14)) against Anopheles gambiae and Culex quinquefasciatus breeding in Zaire.

Under field conditions in Kinshasa, Zaire, an aqueous suspension of Bacillus thuringiensis (H-14), Vectobac (12-AS), lost most of its larvicidal activity at all concentrations after 48 h against Culex quinquefasciatus breeding in polluted gutter water and Anopheles gambiae breeding in clear water irrigation ponds. However, good control of Cx. quinquefasciatus was obtained using a granular formulation of B. sphaericus, Vectolex-G (ABG-6185), at concentrations of 10-30 kg/ha. High concentrations of Vectolex-G gave excellent control of An. gambiae breeding in irrigation ponds. The Vectobac-G was less active against An. gambiae than Vectolex-G, in spite of good dispersion of Vectobac-G particles.