[Influence of mosquito nets impregnated with deltamethrin on the aggressivity cycle of Anopheles gambiae in Djoumouna, Congo]. / Influence des moustiquaires imprégnées de deltaméthrine sur le cycle d'agressivité d'Anopheles gambiae à Djoumouna, Congo.

Several studies recently done in Africa south of the Sahara have clearly demonstrated that pyrethroid impregnated bednets should actually reduce malaria inoculation rate due to Anopheles gambiae and therefore high Plasmodium falciparum parasitaemia and malaria morbidity, even mortality. Nevertheless some concerns were recently raised on an eventual shift in the usual behavior of this species induced by the presence inside the house of bednets treated with pyrethroid insecticide known to have a deterrent or excito-repellent effect, and which could therefore lead to a biting behavior earlier than usual. The current limited study, done in Djoumouna, a place well known for the very high density of An. gambiae, has shown that the temporary presence inside a house of a bednet impregnated with deltamethrin (12.5 or 25 ma a.i./m2) has not induced any shift in the biting cycle of this species, but it actually reduced by some 50% its biting rate noticed on human beings. It is worth underlining that all sporozoite infected specimens were actually caught after midnight. This biting behavior of An. gambiae could explain why impregnated bednets are so efficient in reducing man-vector contact and malaria transmission.

Etude de la specificite du card agglutination test for trypanosomiasis dans le diagnostic de masse de la trypanosomiase humaine africaine a trypanosoma brucei gambiense au Congo

Ce travail qui a consiste en un depistage de masse de la trypanosomiase humaine africaine dans un village connu comme indemne de cette pathologie; a ete realise dans le cadre plus vaste de la mise en place d'une strategie de la maladie du sommeil mieux adaptee aux differentes conditions epidemiologiques locales. Les resultats ont confirme l'excellente specificite du card agglutination test for trypanosomiasis (CATT) ainsi que l'interet de la recherche des discordants CATT sang et CATT serum + dans le depistage de la maladie

Assessment of the incidence and prevalence of clinical malaria in semi-immune children exposed to intense and perennial transmission.

In order to determine the incidence and prevalence of clinical malaria in children exposed since birth to intense and perennial transmission, two successive longitudinal surveys, a weekly survey over four months and a daily survey over 10 days, were carried out in 1983-1984 among 182 children aged 5-13 years in Linzolo, Republic of the Congo, a village where malaria is holoendemic. By age group, prevalence of clinical malaria was found to be between 3.2% and 2.4% at ages 5-6 years, between 2.5% and 1.8% at ages 7-8 years, between 1.6% and 1.1% at ages 9-10 years, and between 0.5% and 0.3% at ages 11-13 years. For these four age groups, respectively, the annual incidence of clinical malaria was estimated during the first survey as 3.0, 2.1, 1.8, and 1.2 attacks, and during the second survey as 5.2, 2.7, 2.0, and 0.8 attacks. No difference was observed in the incidence of malarial attacks between children who use bed-nets and those who do not use them. Also investigated were the customs of the inhabitants of the village in the presence of febrile syndromes in the children, and the importance of antimalarial drug consumption in these cases. It was observed that almost all of these syndromes were rapidly treated with antimalarials, and that in half of the cases these drugs were administered by the parents themselves.

[Malaria in a forest-savannah mosaic zone of Central Africa, Brazzaville region. I. Results of entomological studies]. / Etudes sur le paludisme dans une zone de mosaïque forêt-savane d'Afrique Centrale, la région de Brazzaville. I. Résultats des enquêtes entomologiques.

Anopheles gambiae is the main malaria vector in rural areas in the Brazzaville region; the other vectors collected in this area (A. funestus, A. moucheti, A. nili) are much rarer and have little epidemiological importance. Malaria transmission is intense and perennial; according to the villages, the level of exposure of the population varies from about 200 to 1,000 infective bites per person per year.

Malaria and urbanization in central Africa: the example of Brazzaville. Part II: Results of entomological surveys and epidemiological analysis.

92 night-bite collections on human bait (550 man-nights) and 234 collections of the house-resting fauna were carried out from October 1982 to May 1984 in Brazzaville. A total of 19,531 Culicidae were captured, of which 1,893 were Anopheles, almost exclusively A. gambiae. An average sporozoite rate of 3.41% was found from dissection of 1,291 A. gambiae: one female A. moucheti was also found to be infected. Considerable differences in the intensity of transmission of malaria were observed in the different districts of the town. Whereas the inhabitants of Brazzaville received on average 22.5 infective bites per person per year, in reality this number varies according to the district, from over 100 infective bites per person per year, to less than one infective bite per person every three years. With the help of classical quantitative epidemiological models, the authors analyse here the over-all results, as well as those of two areas of the town, the first area characterized by a high anopheline density, and the second by the rarity of anopheles.

Malaria and urbanization in central Africa: the example of Brazzaville. Part III: Relationships between urbanization and the intensity of malaria transmission.

The authors present a map of malaria transmission intensity in Brazzaville from which they analyse the impact of urbanization on anopheline density and transmission of malaria. Whereas at first each new human settlement promotes the introduction or the proliferation of A. gambiae, the major vector of malaria in Central Africa, urban growth later proves to be unfavourable to this vector. Apart from the canalization of surface water and improvement in sanitation, it is the increase in population density which seems, by its direct or indirect consequences in urban areas, to determine the decrease in malaria transmission intensity. By favouring the absorption of the last remaining open spaces and by the accompanying domestic pollution, urbanization tends to eliminate an increasing number of A. gambiae breeding places; by limiting the dispersion of anopheles from breeding sites, it tends to focus malaria transmission and by thinning out the subsisting anopheline population among a denser human population, it tends to reduce the degree of exposure of each person.

Malaria and urbanization in central Africa: the example of Brazzaville. Part V: Pernicious attacks and mortality.

The current incidence of pernicious attacks and of mortality due to malaria were studied in Brazzaville. The results of this study, which concerned all the medical units of the town, were analysed in terms of previous studies on the epidemiology of malaria transmission in the various districts of the town. It was estimated that the annual incidence of pernicious attacks in children in Brazzaville is 1.15 per thousand between 0 and 4 years, 0.25 per thousand between 5 and 9 years and 0.05 per thousand between 10 and 14 years. The annual mortality due to malaria was estimated at 0.43 per thousand between 0 and 4 years and 0.08 per thousand between 5 and 9 years. These values are about 30 times lower than those expected from the results of previous studies of the mortality due to malaria in intertropical Africa. Whereas considerable differences in intensity of malaria transmission exist in the different districts of Brazzaville, the incidence of pernicious attacks and the resulting mortality are remarkably unvarying whatever the level of transmission. In particular, similar results were observed for the sector Mfilou-Ngamaba-Ngangouoni, where malaria is holoendemic with over 100 infective bites per person per year and a parasite rate of 80.95% in schoolchildren, and the central sector of Poto-Poto-Ouenze-Moungali, where malaria is hypoendemic with less than one infective bite per person every three years and a parasite rate of less than 4% in schoolchildren. These results are discussed in terms of previous observations in urban and surrounding rural areas.(ABSTRACT TRUNCATED AT 250 WORDS)

[Plasmodium falciparum and drepanocytic gene in Popular Republic of Congo. I. Prevalence of malaria and drepanocytic trait among school children in Brazzaville area (author's transl)]. / Le paludisme à Plasmodium falciparum et le gène de la drépanocytose en République Populaire du Congo. I. -- Prevalence du paludisme et du trait drepanocytaire, en milieu scolaire dans la région Brazzavilloise.

From 1978 to 1979, 5 surveys, among schoolchildren, were carried out during the rainy season in the neighbourhood of Brazzaville (R.P. Congo): 3 in PK 45 village (northern part of the capital), 2 in Djoumouna village (southern part), and 1 in "Talangai" (a suburb of the capital). 868 exams (plasmodic and splenic index fitted with hemoglobin composition [Hb AA or Hb AS]) were done. It appeared that 19,6% of schoolchildren examined were heterozygous sicklers (AS). This percentage confirmed the previous results from other authors in different countries of Central Africa. On the other hand, in spite of an intense transmission, both plasmodic and splenic index were, on the average, relatively low (24,5 and 24,8% respectively). Plasmodium falciparum was largely predominant (95,3% of infections) but P. ovale and P. malariae were also found (1,9% for each species). From our study no obvious "protecting effect" can be attributed to sickle cell trait because plasmodic index of children AA and AS were similar (23,8 and 27,6% respectively). A slight decrease of splenic index was noticed in AS in regard to AA (19,4 and 26.1% respectively). It is difficult to consider this no significative regression as a definitive proof of a premunition stronger in AS than in AA. Effectively some splenic infarctus are well known to be a regular physiopathological process occurring in homozygous SS but often in heterozygous AS too. In such highly endemic and stable malaria area the problem of a suitable antimalaria strategy remains to be solved.