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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.

In order to describe malaria transmission in a future antigamete vaccine trial area, a longitudinal entomological study was conducted, together with parasitological and immunological surveys, from June 1997 to May 1998 in two nearby villages in a tropical rain forest area 100 km east of Yaoundé. Koundou is located along the main road in an open and degraded environment combining cultivated lands and forests; Ebolakounou is located 5 km from the road in forest surroundings. Indoor mosquito night catches no human volunteers were performed twice a month, in ten houses. We determined the entomological infection rate as 176 infected bites per human per year in Koundou (47.7% for An. moucheti, 47.3% for An. gambiae and 5% for An. funestus) and only 17.7 infected bites/human/year in Ebolakounou, with An. gambiae only. Transmission appears to be ten times higher in the village situated in a degraded environment than in the village situated in the rainforest.

In 26 villages (1987 population 12,302), hyperendemic for savanna onchocerciasis in North Cameroon, ivermectin was distributed annually between 1987/89 and 1995. Each year until 1992, ophthalmologic examinations were performed before treatment. A final examination was made in 1995. The effects of ivermectin on ocular onchocerciasis were assessed by following (a) the ophthalmologic indices in three cohorts of males recruited before treatment in 1987, 1988 and 1989, who were treated and examined annually, and (b) the indices recorded yearly in the cross-section of males aged 15-19 years. The indices in 1995 from patients who had received up to eight doses were compared with those calculated before treatment in individuals of similar age. In the cohorts, the prevalences of microfilariae in the anterior chamber (MFAC) and of punctate keratitis (PK) recorded in 1995 were markedly reduced; there was a non-significant decrease in sclerosing keratitis (SK), and a significant worsening in the fundus indices in the cohorts. The cross-sectional analysis showed significant decreases in the prevalences of MFAC, PK and SK, and a significant increase in the mean visual acuity; there was no significant change in any fundus index. The findings suggest that repeated ivermectin treatment does not prevent the appearance of initial retinal lesions or the worsening of existing retinal lesions.

Pyrimethamine, in combination with sulfadoxine, is currently one of the major alternative drugs used for the treatment of chloroquine-resistant Plasmodium falciparum malaria infections in Africa. The mechanism of pyrimethamine resistance has been strongly associated with a single, key point mutation in the dihydrofolate reductase-thymidylate synthase gene, resulting in the substitution of the wild-type allele Ser-108 by either Asn-108 or Thr-108. The pyrimethamine-resistant phenotype and/or genotype were determined in 273 Cameroonian clinical isolates obtained in Yaounde by in vitro assays and polymerase chain reaction-restriction fragment length polymorphism over a 5-year period. The in vitro assays showed that 42% (18 of 43) and 63% (69 of 110) of the isolates obtained in 1994-1995 and 1997-1998, respectively, were resistant to pyrimethamine (50% inhibitory concentration [IC50] > 100 nM). The polymerase chain reaction showed that 43% (55 of 127) and 59% (50 of 85) of the isolates in 1994-1995 and 1997-1998, respectively, had the mutant Asn-108 allele. The pyrimethamine-resistant genotype (Asn-108) corresponded with the pyrimethamine-resistant phenotype (IC50 > or = 100 nM) in a large majority (> 95%) of the isolates. The results of our study suggest an increasing prevalence of pyrimethamine resistance in Yaounde. Our study further suggests that pyrimethamine resistance can be monitored by a technique that can be adopted by malaria research centers in Africa.

A study on blood incoagulability due to snake bites was carried out in the Soudanian savanna of North Cameroon, in a provincial hospital receiving patients with severe envenoming coming from areas within 250 km of the hospital. Clinical and biological examinations were conducted on 57 voluntary patients to determine the aetiology of blood incoagulability. The aetiology of this syndrome is complex and seems to depend on the variability of venom components and/or the time between bite and hospital admission inducing a diversity of biological signs. Furthermore, the presence of bleeding and the 30 minute whole blood clotting test performed in dry tube were tested in view to propose simple diagnosis and monitoring indicators. It appeared that the combination of the two indicators allowed an early diagnosis of blood incoagulability and a valid monitoring test particularly well adapted to peripheral African health centres. The recommended treatment is intravenous immunotherapy using F(ab')2, renewed in case of persistence of bleedings or a whole blood clotting test higher than 30 minutes. However, the interval between immunotherapy administration renewals remains to be defined.

The usefulness of an isotopic in vitro assay in the field was evaluated by comparing its results with the therapeutic response determined by the simplified WHO in vivo test in symptomatic Cameroonian patients treated with chloroquine. Of the 117 enrolled patients, 102 (87%) completed the 14-day follow-up, and 95 isolates obtained from these patients (46 children, 49 adults) yielded an interpretable in vitro test. A total of 57 of 95 patients (60%; 28 children and 29 adults) had an adequate clinical response with negative smears (n = 46) or with an asymptomatic parasitaemia (n = 11) on day 7 and/or day 14. The geometric mean 50% inhibitory concentration of the isolates obtained from these patients was 63.3 nmol/l. Late and early treatment failure was observed in 29 (30.5%) and 9 (9.5%) patients, respectively. The geometric mean 50% inhibitory concentrations of the corresponding isolates were 173 nmol/l and 302 nmol/l. Among the patients responding with late and early treatment failure, five isolates and one isolate, respectively, yielded a discordant result (in vivo resistance and in vitro sensitivity). The sensitivity, specificity, and predictive value of the in vitro test to detect chloroquine-sensitive cases was 67%, 84% and 86%, respectively. There was moderate concordance between the in vitro and in vivo tests (kappa value = 0.48). The in vitro assay agrees relatively well with the therapeutic response and excludes several host factors that influence the results of the in vivo test. However, in view of some discordant results, the in vitro test cannot substitute for in vivo data on therapeutic efficacy. The only reliable definition of "resistance" in malaria parasites is based on clinical and parasitological response in symptomatic patients, and the in vivo test provides the standard method to determine drug sensitivity or resistance as well as to guide national drug policies.

Since 1969, 63 cases of airport malaria have been reported in Western Europe, 24 of which occurred in France. Most were due to Plasmodium falciparum. In 1994, 7 cases occurred in and around Roissy Charles de Gaulle airport (CDG), showing 4 types of contamination: among employees working on airstrips or opening containers, among residents living near the airport, among people living at some distance from the airport after a secondary transport of vectors, and by vectors transported in luggage. In-flight or stop-over infection is not considered as airport malaria. The infective anophelines originated from airports where malaria transmission occurs, mostly in subsaharan Africa. A tentative list is given taking into account aerial traffic with France. Surveys in the airports of Dakar (Senegal), Cotonou (Benin), Abidjan (Cote d'Ivoire) and Yaoundé (Cameroun) found potential vectors in all of these from July to September. After 1994, the Contrôle Sanitaire aux Frontières (CSF) in charge at CDG concentrated its efforts on the flights at risk, as well as information and sensitization of airline companies, which resulted in 73% and 87% of the flights at risk being properly disinsected in 1995 and 1996. Despite pyrethroid resistance in Anopheles gambiae s.s. in West Africa, the efficacy of aircraft spraying with permethrin aerosols is still acceptable. However, surveillance of resistance should be improved and search for nonpyrethroid insecticides suitable for aircraft strongly encouraged.

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.

The prevalence of various species and subgroups of trypanosomes in infected flies from three sleeping sickness foci in Cameroon was determined by the use of polymerase chain reaction (PCR). The predominant tsetse species found were Glossina palpalis palpalis. Microscopical examination of 943 non-teneral tsetse flies revealed an average infection rate of 10.4%. A total of 90 flies were analyzed for trypanosome identification with primer sets specific for Trypanosoma (Trypanozoon) brucei s.l., T. (Duttonella) vitax, T. (Nannomonas) simiae, and forest type T. (Nannomonas) congolense. PCR succeeded in identifying 52 of the 90 infected flies. Other primers were also tested on microscope positive/PCR-negative infections, and trypanosome subgroups were detected (Kilifi type and savannah type T. congolense). PCR amplification allowed identification of immature infections and revealed mixed-infections. The PCR technique failed to identify 42.2% (38/90) of the parasitologically positive flies and the reasons for this failure are discussed.

There is accumulating evidence for the involvement of genetic factors in the human response to malaria infection, mostly based on results obtained in studies of severe clinical malaria. The role of major gene(s) controlling blood parasitemia levels in human malaria has also been detected by means of segregation analysis. To confirm and to localize such gene(s), we performed a sib-pair linkage analysis investigating the role of five candidate chromosomal regions: 6p21 (HLA-tumor necrosis factor region), 2q13-q21 (genes coding for interleukin-1 alpha and beta), 14q11 (locus coding for the alpha chain of T cell antigen receptor), 7q35 (gene cluster for the beta subunit of T cell receptor), and 5q31-q33, which includes several candidate genes and was recently linked to a locus controlling infection levels by Schistosoma mansoni, denoted as SM1. The analysis was carried out on nine families from a southern Cameroon village, and the phenotype under study was blood infection levels with Plasmodium falciparum. No linkage was found with any of the four markers outside the 5q31-q33 region. A trend in favor of linkage was observed in the distal part of the 5q31-q33 region, especially with the marker D5S636 (P < 0.05 using the Monte Carlo P value), which was the marker that provided the highest evidence for linkage with SM1. These results suggest that a locus influencing P. falciparum levels in malaria could be located in the same genetic region as that containing SM1, indicating that the 5q31-q33 region may be critical in the control of different parasite infections.

There is now accumulating evidence for the involvement of genetic factors in the control of immune response against malaria. These arguments come from numerous animal models, from population studies showing associations of red blood cell genetic defects as well as HLA antigens with severe malaria, and from familial studies including a recent segregation analysis, which led to detection of a major gene effect predisposing to high infection levels. The heterogeneity and complexity of this genetic control is one of the main findings of these previous studies, and probably a major cause of the difficulty in developing an effective malaria vaccine. A segregation analysis of blood infection levels is performed here in 44 pedigrees living in the tropical rain forest of southern Cameroon and exposed to high vectorial transmission intensity. The results confirm the existence of complex genetic factors controlling blood infection levels in human malaria but are not consistent with the parent-offspring transmission of a single Mendelian gene. This study also shows the dramatic effect of age on infection levels and its interaction with a putative major gene suggesting that genetic related differences are much more important in children than in adults. Further genetic studies focused on children may help to identify the nature of the genetic factors involved in the expression of human malaria, by means of linkage analyses using both familial information and genetic markers.

Resistance to antifolate antimalarial drugs (cycloguanil, a biologically active metabolite of proguanil, and pyrimethamine) is associated with a Ser- to Asn-108 point mutation in the dihydrofolate reductase-thymidylate synthase gene of Plasmodium falciparum. The frequency of this mutation was studied in 127 clinical isolates obtained in Yaounde, Cameroon using a simple and rapid molecular technique based on the polymerase chain reaction and restriction fragment length polymorphism. Of the 127 isolates, pure wild-type Ser-108 codon, pure mutant-type Asn-108 codon, and mixed codons were observed in 66, 55, and six parasites, respectively. The proportion of antifolate-resistant, pure mutant-type codon, with respect to pure wild-type or mixed alleles, was 43% (55 of 127). The results of the molecular assay were compared with those of semimicro isotopic in vitro assay in 34 isolates. All 17 pure Ser-108 isolates and two isolates with mixed alleles were sensitive to both pyrimethamine (50% inhibitory concentration [IC50] < 100 nM) and cycloguanil (IC50 < 50 nM). Fourteen of 15 isolates with the mutant-type Asn-108 codon were resistant to pyrimethamine and cycloguanil. One isolate with Asn-108 showed a slightly elevated pyrimethamine IC50 (78 nM), which was within the sensitive range. This study provides further evidence that antifolate-resistant P. falciparum isolates are already present in Yaounde, Cameroon.

Simultaneously with a control of breeding sites primarily for Culex quinquefasciatus and secondarily for anophelines with Bacillus sphaericus in the town of Maroua (120,000 inhabitants) in North Cameroon, a survey of anopheline populations and of transmission rates of malaria was performed. Monthly night catches in 8 districts of the town emphasized the relation between the biting rate by Anopheles in the districts and two main factors. One factor was the distance of a district from the breeding sites, i.e., natural flooded areas along the periphery of the town or artificial breeding sites (ditches, puddles) filled with rain water during the rainy season and with water from the water network throughout the year. The second factor was the density of the habitation that reduced dispersal of female mosquitoes from the breeding sites and the risk for inhabitants to be injected because of scattered bites. The treatment with B. sphaericus was followed by a delay (2 months) in the beginning of the transmission period and a decrease in the incidence of malaria cases studied in a health facility of the town. It thus seems to be possible to reduce malaria transmission by applying B. sphaericus to the breeding sites, but this requires a good knowledge of the location and dynamics of breeding sites and an improved formulation of the pesticide.

Sulfadoxine-pyrimethamine is one of the alternative antimalarial drugs used to treat chloroquine-resistant Plasmodium falciparum malaria. The molecular target of sulfadoxine, an analog of p-aminobenzoic acid that inhibits the folate biosynthetic pathway, is dihydropteroate synthase (DHPS). The nucleotide sequence of the DHPS gene was determined in 32 clinical isolates obtained in Yaounde, Cameroon, and compared with the sequence of reference clones and Cambodian strains of P. falciparum. Of the 32 Cameroonian isolates, 31 displayed one of the sulfadoxine-sensitive mutation patterns: Ala-436/Ala-437/Ala-581/Ala-613 (n = 20), Ser-436/Gly-437/Ala-581/Ala-613 (n = 6), Ser-436/Ala-437/Ala-581/Ala-613 (n = 4), and Ala-436/Gly-437/Ala-581/Ala-613 (n = 1). One isolate had a sulfadoxine-resistant profile characterized by a double mutation: Phe-436/Ala-437/Ala-581/Ser-613. Although the majority of the isolates had a sulfadoxine-sensitive genetic profile, further studies are needed to correlate the mutation patterns and in vitro and in vivo sulfadoxine sensitivity.

Two strategies were tested to control Culex quinquefasciatus with Bacillus sphaericus in Maroua (population 130,000), Cameroon. The treatment of all potential breeding sites (27,000) with B. sphaericus during the dry season caused up to a 90% reduction in the adult biting rate. Because of the short persistence of B. sphaericus and the occurrence of new breeding sites, unacceptable levels of adult biting rates were reached again in 5 months. In the second strategy, two treatments per year of the most productive breeding sites (10,000) stopped the biting rate increase during the rainy season. The results were only partially successful because of variations in B. sphaericus toxicity. The first treatment required 1,200 man-days of work vs. 200 for the simplified treatments. The density of breeding sites depends on the rainfall and the presence of a tap-water network. A sustained control program of Cx. quinquefasciatus will depend upon the dynamics of the principal breeding sites and an improved formulation of B. sphaericus.

Using stringent Western blot (WB) criteria, human T cell lymphotropic virus (HTLV) type I seroprevalence among 3783 persons from representative rural populations of Cameroon averaged 1.1% and was higher in females (1.5%) and in Pygmies (2.0%), increasing with age. Furthermore, an HTLV-I Gag-indeterminate WB profile (HGIP), exhibiting strong reactivities to p19, p26, p28, p32, p36, and pr 53 but lacking both p24 and env reactivity, was observed in 1.6% of the same populations. The prevalence of the HGIP was similar between males and females, did not increase with age, and appeared to cluster in tropical forests of southern Cameroon, especially among Pygmies (reaching 4%). These contrasting epidemiologic features, together with the lack of detection by polymerase chain reaction of HTLV-I sequences in the peripheral blood mononuclear cells of the persons with HGIP, strongly suggest that such a WB profile does not appear to reflect an HTLV-I-related viral infection but possibly an environmental (viral or parasitic) factor endemic in tropical rain forest areas.

In order to get an accurate measure of malaria transmission by mean of human bait attraction, three methods of catches for human-bail mosquitoes were compared in a Cameroonian village of high anopheline density. These three methods were 1) the classical human landing catches where the man was in the same time bait and catcher, 2) the single-nets which acted as a trap and 3) the double-nets where the outer net acted as a trap and the inner avoided mosquito bites. The anopheline densities per man with human landings were 1.6 time higher than those obtained with single-nets, these later being 4.7 times higher than those obtained with double-nets. In the three methods, the results were similar for the anophelines species catched and for their respective proportions. The samples of Anopheles nili and An. gambiae had comparative parity rates and sporozoitic indexes. From these results, in order to estimate the malaria transmission it can be envisaged to change the standard human-bait catch for the human-baited single bed-net catch; on the contrary the double-net have to be discarded because of their poor results.

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 study aimed at determining individual factors associated with participation in community treatment with ivermectin was conducted in a village hyperendemic for onchocerciasis in northern Cameroon. The respective influences of sex, age, place of residence, distance between the compound and the dosing point, compound size, and participation in treatment by authoritative individuals in the compound was evaluated using univariate and multivariate analysis. Participation in treatment was closely associated with the attitude of the compound heads. Participation of compound heads in treatment increased as the household size increased, and as the distance to the distribution point diminished. This may be explained by the fact that getting information on health programmes is easier in large households whose members are involved in various social activities, and in compounds located near the village centre. Staff involved in health education should take this issue into account, and try to ensure circulation of information particularly to those living in small or remote compounds.

Mass treatments with ivermectin have been undertaken each year since 1987 in an area hyperendemic for onchocerciasis in northern Cameroon. The impact of these successive treatments on the incidence of infection in humans was evaluated by comparing the prevalence of skin microfilariae (PMF) and the mean microfilarial skin densities (MFD) observed in 1987 and 1992 in 5-7-year-old children who had never taken the drug but who were members of the treated communities. In 1992, the PMF and the MFD in children in this age group who never received ivermectin were reduced by 55% and 77%, respectively, in comparison with the values observed in 1987, before the first treatment round. These results reflect a pronounced reduction in the intensity of the transmission of Onchocerca volvulus in the treatment zone. The influence of the ivermectin treatment coverage in the human population, as well as the vectorial capacity and the dispersal of the vector blackflies, on the transmission of onchocerciasis is discussed.

A female fourth stage larva of Meningonema, probably of M. peruzzii Orihel et Esslinger, 1973, was recovered in Cameroon, from the cerebrospinal fluid of a patient harbouring Loa loa, but without any neurological signs. This observation is the first human case of Meningonema (Filarioidea Splendidofilariinae) which usually parasitizes the central nervous system of African Cercopithecinae. However, as indicated by Orihel and Esslinger, it seems probable that the perstans-like microfilariae described in cases of cerebral filariasis in Zimbabwe belonged to the same species.

In ongoing studies on experimental transmission of Plasmodium falciparum in the city of Yaounde gametocyte carriers are daily being identified among dispensary patients with malaria-like complaints. This species comprises 93% of all parasitemias and because of the selection criteria most patients have it as a recent infection. 17% of all P. falciparum-positives carry detectable gametocytes with little difference between youngsters and adults. Blood of adult carriers is taken and infection of Anopheles gambiae mosquitoes is attempted by membrane feeding; the establishment of infection is judged by the presence of oocysts.

An entomological study was carried out during 1990 in the town of Edea in the south of Cameroon to study anthropophilic mosquitoes with special reference to malaria transmission. Man-biting mosquitoes were caught regularly during one night each month in two different districts: Bilalang which is a well planned suburb with 160 houses on a hill-top, provided with a piped water supply; and Pongo which is a densely urbanised suburb in a valley. From 188 man-nights 1030 mosquitoes were collected, comprising 700 Culex quinquefasciatus (68%), 262 Anopheles gambiae (25%) and others species (7%) belonging to the genus Anopheles, Mansonia, Culex and Aedes. The estimated annual biting rates of mosquitoes were 811 bites per man in Bilalang and 2,866 in Pongo. The estimated yearly malaria inoculation rates were 3.8 and 30.2 infective bites per man in Bilalang and Pongo, respectively. In different parts of Pongo district much variation existed; extreme values of the estimated yearly inoculation rate were zero and 86.3 in two houses 200 m apart, located on the top of a hill and in the bottom of a valley, respectively. This study is one of the first conducted on malaria transmission in a moderate sized African town; it shows that the mosquito populations are typically urban and differ greatly from rural ones.

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.

Culex quinquefasciatus, which is sometimes the vector of Bancroft's filariasis, is a harmful mosquito, the immature stages of which live in collections of waste water resulting from human activity. Larval control, the most appropriate method, is at present carried out with chemical insecticides. But the toxicity of these compounds, together with phenomena of resistance, and the cost of substitute insecticides have turned research towards products of biological origin, and one of the most promising is a liquid concentrate of Bacillus sphaericus strain 2362. This was applied experimentally over an area of 200 hectares in a large city in the south of Cameroon, characterized by a short dry season during which mosquito density is at its highest. Spraying was carried out every three months for a year in a concentration of 10 g/m2 and its efficacy evaluated at the level of adult mosquitos through an indirect system of capture on human baits. The results of this study show, in essence, a reduction by 52.7% in the number of females captured in the overall study area treated, and that the impact of treatment is greater during the period of high mosquito density (55.1%) than in the low density period (40.7%). After analysis of the full set of results, the authors conclude that the pattern of rainfall, the conditions in which the insecticide is applied and reinvasions of mosquitos from untreated areas were the principal factors limiting the efficacy of this control campaign.(ABSTRACT TRUNCATED AT 250 WORDS)

The high number of blackfly bites in a moist forest area of Cameroon, around the Sanaga river, was causing considerable nuisance and had led to a local ground-based larval control campaign. We have reviewed the 25 years of almost uninterrupted weekly larvicide applications in this area and emphasized the problems related to application difficulties, environmental pollution and blackfly resistance to the insecticides. Although the number of larvicidal compounds readily available is now limited, the future of blackfly control at this site does not seem to pose real technical difficulties because of its economic importance (hydroelectric dam) and the progress made in the fields of resistance management, search for new insecticide molecules and development of new control methods.

In villages near Sanaga river, in the forest zone of south Cameroon, Anopheles nili Theobald is the main species of mosquito regularly found biting man inside houses. Its densities are related to the flow level of the river. It is also the main malaria vector in terms of intensity and seasonal duration of transmission. The yearly malaria inoculation rate due to An. nili alone is 104 infective bites/man, varying between 3 infective bites/man in October and 20 in March. Anopheles gambiae Giles is a less important vector in the area but reached its peak in the dry season, when the Sanaga river is at its lowest level. These observations underline the influence of local ecology on malaria transmission and the need for entomological studies in each situation.

In most of the large scale vector control programs, the larviciding operations are not fully successful, resulting in a surviving vector population due to the use of sublethal doses. This problem leads the authors to study the effect of such doses upon the future of the residual population in order to know if it represents an epidemiologically dangerous population. One insect growth regulator was selected to study this phenomenon using Onchocerca volvulus as the parasite and Simulium damnosum s.l. as the vector. The experiment was conducted under field conditions by treating a river of a savanna area in north Cameroon where onchocerciasis remains endemic. The sublethal doses yielding 20% in adult blackflies from treated larvae was determined and the effects on physiological and vectorial capacities were assessed. The authors also carried out observations on the peritrophic membrane formation and the passage of microfilariae into the hemocele. The observation of flies fed on Onchocerca after larval treatment showed that this insecticide had a light effect on female longevity but did not induce any modifications in the life cycle of the parasite. An unusual high proportion of infected females, observed by the authors, is probably due to an anomaly in the phenomenon of limitation. However, the histological analysis showed to the evidence that no apparent difference between treated and untreated blackflies was observed although the process of blood meal digestion seemed slightly altered in treated flies.

A one year entomological survey was carried out to precise the malaria vectors and the malaria transmission in Yaounde, the Cameroon capital (800,000 inhabitants). The study was done in two districts not yet fully urbanized: Nkol Bikok and Nkol Bisson. The latter is located at the periphery and has a pool. Anopheles gambiae was the only human malaria vector. Its agressivity for man depended on the urbanization of the district. Annual man biting rate was 284 in Nkol Bikok and 1,813 in Nkol Bisson. The densities were maximum in May-June and in October-November, corresponding to the end of the short and long rainy seasons. The presence of A. gambiae was permanent except in August-September in Nkol Bikok. In Nkol Bisson the density was higher in the houses near the pool. The yearly inoculation rate (h) was 14 in Nkol Bikok and 30 in Nkol Bisson. The vectorial transmission was observed in may in Nkol Bikok and during four months (June, August, January, February) in Nkol Bisson. These entomological data showed clearly that malaria transmission actually occurred in Yaounde and that the probability to receive at least one infected anopheline bite per year was very near to 1 for inhabitants unprotected against mosquito bites.

Due to current spreading of chemoresistant strains of Plasmodium falciparum malaria control must incorporate vector control programmes. Due to well known constraints house sprayings cannot be performed as before. Personal protection can be developed and a large scale use of insecticide treated bed-nets appeared to be very useful to reduce man-vector contact in Asia, South America and West and East Africa. No trial has been done in forest Central Africa where transmission is permanent. We performed such a trial in the southern part of Cameroon (using deltamethrin, at 25 mg/m2) and obtained similar data to those observed in The Gambia, Burkina Faso and Tanzania with a noteworthy reduction of both transmission and high parasitaemia of P. falciparum (respectively 78% and 75%) meaning a drop of malaria morbidity.

A mass chemotherapy campaign to treat onchocerciasis with ivermectin was carried out in northern Cameroon, in the North Vina valley, a savanna area that is part of the extended Vina-Pendé-Longone focus. More than 20,000 people aged five years and over were treated at least once and more than 30,000 treatments were distributed. One to four treatments were given at intervals of six months or one year. Clinical and parasitological examinations of representative samples of the treated population and full ophthalmological examinations of males aged 15 to 35 years were carried out before each treatment to assess the efficacy of the different protocols of treatment. Secondary effects were recorded daily during the week after administration of ivermectin in the whole population treated. The evolution of arterial blood pressure was monitored over seven days in about 300 adults living in the hyperendemic region. The impact of mass treatment on natural transmission of the disease was evaluated by daily capture and dissection of blackflies during the month before and the two months after treatment. All levels of onchocerciasis endemicity were represented in the study area (maximum community microfilarial load (CMFL), 300 microfilariae per biopsy). Six months and one year after the first treatment, loads were down by more than 90% and more than 60% respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Chadian refugees, most of whom are free from onchocerciasis, settled recently in a camp in a savanna area of the northern Cameroon where the prevalence is about 80% and the blindness rate is 4% of the adult population. In view of the risks of onchocerciasis facing the immigrants, the authors carried out an entomological survey in this region aimed at determining the modes of transmission and assessing the possibilities for the control of this disease. After a three-month survey in the study area, it appears clearly that 1) transmission takes place only during the rainy season, 2) the main vectors are the two savanna species, Simulium damnosum s.s. and Simulium sirbanum, 3) the larval breeding sites are not located on the principal river, the Faro, but on its small seasonal tributaries, 4) the local populations still free from onchocerciasis and the Chadian refugees who farm close to these tributaries run the risk of getting serious ocular lesions in the long run which could lead to blindness. The conclusions of this survey prompted the authors to envisage an onchocerciasis control campaign in this area against the larval stages of the vectors.

In view of the risks of onchocerciasis facing Chadian refugees who have settled in a camp in a savanna hyperendemic area of northern Cameroon, the authors concluded that a vector control directed against the black fly larvae located on small seasonal tributaries of the main water course of this area should be carried out during the four to five months of the rainy season, i.e., during the whole period of transmission of this disease. The operations were undertaken during two consecutive rainy seasons. The first year consisted in developing ground-based control techniques and evaluating the larvicidal efficacy at the larval level. The second year was, particularly, devoted to the study of the impact of the vector control on the biting rate and on the transmission of onchocerciasis. Every week, three of the tributaries close to the camp were treated with an Emulsifiable Concentrate of temephos. Throughout the rainy season, the larvicide eliminated almost all the pre-adult black fly stages on these water courses. At the point in a high onchocercal endemicity area, it also reduced the biting rate by 60% and the Annual Transmission Potential by 72%, i.e., to values corresponding to the lower meso-endemicity threshold. Since these results were obtained at a very unfavourable point from the standpoint of black fly density and onchocerciasis transmission, the authors consider that vector control carried out under these conditions protects the local populations and the Chadian refugees effectively from black fly bites and a risk of severe onchocerciasis.