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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.

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)

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.

Five schools were chosen in different districts of Brazzaville where the intensity of malaria transmission, determined in a previous study, is representative of the very varied conditions observed in this town in relation to urbanization. The parasitological and serological results found in schoolchildren are analysed according to the level of transmission to which they are exposed, and compared with the results of a longitudinal survey carried out in the rural area of the Brazzaville region. In the urban area malaria prevalences in schoolchildren aged from 5 to 9 years and from 10 to 14 years vary considerably according to the districts. They are, respectively, 78.9% and 84% in Massina, 58.8% and 71.7% in Talangai, 32.3% and 46.9% in Bacongo and 5.6% and 12.6% in Moungali. In Poto-Poto, no positive thick films were found in a representative sample of 62 schoolchildren aged 6 and 7 years who have always lived in this district, and the malaria prevalence is only 6.9% in schoolchildren aged 14 and 15. In the rural area, the malaria prevalence is 76.4% in schoolchildren aged 5 to 9 and 82% in those aged from 10 to 14. According to standard immunofluorescent technique, 63% of children aged 6 and 7 years living since birth in the central part of the Poto-Poto and Moungali districts have no detectable antibodies. In the rural area, all children over 4 years of age are seropositive. These results show that the decrease in vectorial density which accompanies urbanization has considerable parasitological repercussions.(ABSTRACT TRUNCATED AT 250 WORDS)

The lack of serum haptoglobin in Africans has been investigated in the Congo, Central Africa, where HpO prevalence is about 30%. This study shows that it is possible to suppress ahaptoglobinaemia within a few weeks by antimalarial chemoprophylaxis, that it does not occur in protected individuals, that ahaptoglobinaemia reappears at its original incidence levels after interruption of chemoprophylaxis, and that some individuals are more susceptible in relation to Hp2 gene. Malaria is the only significant cause of ahaptoglobinaemia in subjects both with and without detectable parasitaemia. The possible mechanisms involved are discussed.

Malaria is holoendemic in rural areas in the Brazzaville region: according to the villages, the crude parasite rate in schoolchildren varies from 81% to 94%. Prevalence of classes 3 to 5 parasite densities is high until the age of 15 (41%-63%) and appears to reflect the entomological inoculation rate. Parasite rates and densities in young children are lower than expected. This is probably due to the widespread use of antimalarials by this age-group.

A retrospective study of 1,003 children permits us to identify precisely rates and causes of mortality in children under 5 years old in a rural holoendemic malaria area of the People's Republic of the Congo. The mortality rates are distinctly lower than those generally observed in tropical Africa. Infant mortality (0-1 year) was found to be 71%, mortality 13%, early neonatal mortality (0-7 days) 41% and mortality between 1-5 years, 49%. Main causes of mortality are those related to pregnancy (prematurity, obstetrical pathology) and with infectious diseases particularly measles. On the other hand, no death seems to be attributable directly to malaria in this study.

For a growing number of citizens, the upheavals caused by rapid urban development completely transform malaria epidemiology in tropical Africa. This paper is the first of a series on this phenomenon in Brazzaville, capital of the Congo Republic, where a third of the country's population is already concentrated. After describing the main human and physical geographical aspects of the town, the most significant results of the previous studies of this town and the surrounding rural area are reviewed. They show the existence, until the beginning of the 1950s of a stable, holoendemic situation characterized by a malaria prevalence approaching 90% in children in both urban and rural areas. Since then the intensive development of anti-malaria campaigns in urban areas over about ten years led temporarily to a considerable decrease in the level of endemicity, while in rural areas it remained unchanged. In the 1960s, the vector control and systematic chemoprophylactic measures gradually stopped, permitting the study of a new malaria dynamic related only to the evolving particularities of a changing urban ecosystem.

A study of the relations between plasma haptoglobin levels and malaria endemicity was carried out on selected specimens collected in 1980-1985 during studies on malaria transmission in various populations of the Brazzaville region of the Republic of the Congo. The prevalence of ahaptoglobinemia in school-children is 2.2% in Moungali and 2.9% in Poto-Poto, two districts of Brazzaville where malaria transmission intensity is less than one infective mosquito bite per person per year and malaria prevalence in schoolchildren is less than 10%. In contrast, ahaptoglobinemia prevalence is 48% in schoolchildren from the village of Djoumouna, where malaria transmission intensity reaches 1,000 infective bites per person per year and malaria prevalence in schoolchildren is 94%. Intermediate values, between 11.1% and 23.4% are observed in schoolchildren from Talangaï, Massina, and Linzolo, districts or villages where malaria transmission intensity is between 20 and 250 infective bites per person per year and malaria prevalence in schoolchildren is between 66% and 81%. These findings indicate that ahaptoglobinemia prevalence is correlated with the level of malaria endemicity and provide additional support for the hypothesis that malaria is the main cause of ahaptoglobinemaia in African populations. The haptoglobin system may be of considerable interest in the investigation of the mechanisms of anemia in malaria.

In highly malaria-endemic areas, thick smears are usually positive regardless of the clinical context. Therefore the simple positivity or negativity of the thick smear is not an adequate criterion for distinguishing malaria from other causes of fever. In order to define simple parasitological and clinical criteria for diagnosing clinical malaria with a small risk of error, a study was undertaken in a rural area in the Congo where malaria transmission is intense and perennial. Results of the systematic determination of the parasite density of 1562 samples from persons of all ages considered representative of the population of the studied area are compared to those from 327 febrile patients, 204 patients detected during medical consultations held in the villages and 123 febrile schoolchildren detected during surveys for fever. The analysis of the clinical data and the parasitological results clearly demonstrates the importance of the parasite density determination for the diagnosis of clinical malaria. Clinical Plasmodium falciparum malaria is unlikely to occur in children under 15 years if the parasite/leucocyte ratio is less than 1.5. On the contrary this diagnosis is very probable if the parasite/leucocyte ratio is higher than 2. Clinical criteria were too non-specific to serve as useful diagnostic criteria.

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.

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.