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Nsimalen, a village in Southern Cameroon, has been deforested over a surface of 370 hectares for the construction of the new Yaounde international airport (Cameroon). Mosquitoes night catches on human bait were performed over a year in two hamlets of this village, one adjoining the airport and the other situated 3 kilometers off the deforested area. The aim of the survey was to observe malaria vectors and transmission around the airport and to record malaria epidemiological changes resulting from deforestation. The findings showed that the main malaria vector was Anopheles moucheti (95% of the vector population). Anopheles gambiae was also present but in very small quantities. The increased density of the latter near the airport combined with the low parity rates, indicated that deforestation favoured the breeding of this species. Malaria transmission was estimated at 106 and 68 infective bites per man per year in hamlets close to and far away from the airport zone respectively. An. gambiae accounted for 13% of the transmission in the hamlet adjoining the airport and 0% three kilometers off the airport.

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.

The classical method to estimate the malaria transmission in an endemic area is based on the number and infectivity of human landing mosquitoes. To compare this method with CDC Miniature Light Trap a study was carried out in a forested area of South Cameroon. Light-trap and servant were placed in six different houses of the same village from 08 p.m. to 06 a.m. In average the human landing caught 29.9 anopheline females per night, while light-trap 52.4. The ratio of light-trap on human landing was 1.75 for Anopheles genus. This ratio varied with the species: 1.88 for An. nili and 0.54 for An. gambiae s.s. Light-trap showed disadvantages, especially the lack of steadiness and the fact that only 49.6% (n = 238) of potential vectors of malaria were in good standing for dissection of salivary glands. The authors concluded that human landing remained the most efficient method of catching for the estimation of human malaria transmission in the forested area of Africa. Nevertheless, the lower cost of light-trap is an important advantage.

The feasibility of using impregnated bednets in a malaria control strategy has been evaluated in a rural area of Cameroon. The benefit is well perceived by the population in terms of protection against nuisance but not in terms of prevention of the disease. The correct use of bednets is, however, unsatisfactory. The material should be adapted to the various sleeping accommodations, and efforts for education and information directed towards the potential users should be intensified.

Two methods of urinary chloroquine assay were tested in pregnant women in the town of Banfora (Burkina Faso): the method with bromothymol blue (Bergqvist) and the method with methyl-orange (Haskins and Mount or HMM II). Urinary assay of chloroquine was performed with both methods in 45 women chosen at random whether or not under chemoprophylactic treatment (21 taking a weekly prophylaxis of 300 mg of chloroquine, and 24 controls). The HMM II method proved to be more sensitive (100%) and more specific (91.7%) than the Bergqvist method (80.9% and 83.3% respectively); it was also more reliable with regard to positive (91.3% versus 80.9%) and negative (100% versus 91.3%) predictive values. Moreover, the quantitative appreciation of the levels of chloroquine excretion proved to be superior with the HMM II method. Finally, this method is faster to perform, easier to use and cheaper, making it the method of choice for field assay of chloroquine in urine.

A Knowledge, Attitude, Practice survey was carried out in July 1988 in Douala city, by cluster sampling and household visits. 98% of these households declared being disturbed by mosquitoes (bites, diseases, noise); 91% of families are using a vector control method; the main methods are: bed-nets (48%), insecticide sprays (39.5%) and mosquito coils (36.7%). The average cumulated expense by households for vector control (116.6 ECU/year) and care for diseases attributed to mosquitoes (147.4 ECU/year) was evaluated at the equivalent of about 3 months of "minimum monthly wages". More than 90% of people interviewed would accept buying and using an insecticide impregnated bed-net provided that the price of such a product be lower than the current habitual price for ordinary bed-nets. The distribution of the impregnation technique must be made at the level of impregnation centres, which should start impregnating the existing bed-nets and take care of informing the public.

From April 1988 to March 1989, 903 randomly chosen children were examined in the Maternal and Child Health Department of the Central Hospital of Yaounde (Cameroon) to determine the importance of malaria in general morbidity, the relation between clinical symptoms and parasite densities and to have some idea of the population's self-medication behaviour. We adopted the criteria formerly worked out in West Africa, i.e. a fever (t degree higher than 37.9 degrees C) without any obvious febrile disease and a parasitaemia higher than 10,000 red blood cells parasitized by Plasmodium falciparum/mm3. In the sample under investigation, the average plasmodic index was 32.5%, mainly P. falciparum (98% of all infections), while 120 children had a parasitaemia higher than the critical level of 10,000 par./mm3 (i.e. 13.3% of the whole sample and 40.1% of Plasmodium carriers. 559 of the 903 children were actually febrile and among them 94 had a so-called malaria crisis (i.e. 16.8% of fevers and 10.4% of all consultations). It was confirmed that not one single clinical symptom is pathognomic for malaria crisis but fever, splenomegaly and anaemia seemed to occur more frequently among sick children. It also appeared that the proportion of children with fever increased as their parasitaemia exceeded the critical threshold of 10,000 par./mm3, while splenomegaly tends to drop with very high parasitaemia. Faced with fever as a clinical symptom, self-medication is a common behaviour (65% of people interviewed admitted such practice); it is mainly based upon chloroquine tablet ingestion but at a subcurative dosage. Such self-medication could induce an underestimation of malaria morbidity from clinical statistics and, on the other hand, a growing drug pressure, which could play a role in the current spread of P. falciparum chloroquine resistant strains in Central Africa and elsewhere in sub-saharan regions.

Mass production of P. falciparum sporozoites requires an intensive production of mosquitoes and an experimental infection of this vector. A gambiae is the main vector of P. falciparum, and P. ovale in Burkina. In the first part we study 3 factors interfering with breeding and experimental infection of this anopheline species. They are: insectarium temperature, pattern and rhythm of blood feeding. In the second part, we study "parasite", "host" and "mosquito" parameters which interfere with the yield of experimental infections. The increase of temperature promotes growth of parasite, but it also enhances bacterial and mycosal pollution; and so, it reduces survival of mosquitoes. Natural feeding on rabbit gives a better laying and a larger blood meal than experimental feeding through an artificial membrane. Meanwhile, it requires a rabbit rearing. We finally adopted the following compromise: the two first blood meals are taken on rabbit, the next are taken on membrane covered devices. It is necessary to give non-parous females two consecutive blood meals that allow the first gonotrophic cycle. The optimal time is on the 3-4 day after emergence. For the mosquitoes reserved for experimental infections, it is necessary to infect them very soon to have more surviving females at the end of the sporogonic cycle. These mosquitoes receive their first and single blood meal an day 2 and can be infected on day 5. There is a positive correlation between the intensity of egg production and the mosquito mortality. Although blood meals are important for parasite development, we prefer to give only one blood meal on day 6 after infection to promote the vector survival rather than maturity of the parasite. This study has allowed to standardize breeding conditions and to obtain regularly 10,000 mosquitoes per day. The infection rate depends on parasite factors. P. falciparum gametocytes may be infectious to mosquitoes at densities as low as 5/mm3 of blood. Maximum infectiousness is reached between 50 to 450/mm3. At higher densities, infectiousness of gametocytes seems to decrease. In natural conditions, sex-ratio and maturity of gametocytes do not appear to interfer with infectiousness. The infection rate also depends on host parameters. They are yet unknown. We saw a specific phagocytosis of sexual stages in mosquito midgut, after infection with a high density gametocyte carrier, without any infected mosquito. On the other hanb, infectiousness of gametocytes seems to decrease with age of the gametocyte carrier. The role of immunity inmodulating the infectivity of gametocytes cannot be excluded. Finally, the infection rate depends on mosquito factors.(ABSTRACT TRUNCATED AT 400 WORDS)