Insecticide resistance in the Anopheles gambiae complex in Benin: a nationwide survey.

Benin has embraced World Health Organization-recommended preventive strategies to control malaria. Its National Malaria Control Programme is implementing and/or coordinating various actions and conducting evaluation trials of mosquito control strategies. Mosquito control is based on the use of insecticide-treated nets and indoor residual spraying, but the efficacy of these strategies to control malaria vectors is endangered by insecticide resistance. Here, we present the results of a nationwide survey on the status of insecticide susceptibility and resistance in Anopheles gambiae s.l. (Diptera: Culicidae) carried out in Benin in 2006-2007 (i.e. before extensive vector control was undertaken). Overall, our study showed that the S molecular form of An. gambiae s.s. predominates and is widely distributed across the country, whereas the frequency of the M form shows a strong decline with increasing latitude. Susceptibility to DDT, permethrin, carbosulfan and chlorpyrifos-methyl was assessed; individual mosquitoes were identified for species and molecular forms, and genotyped for the kdr and ace-1 loci. Full susceptibility to chlorpyrifos-methyl was recorded and very few samples displayed resistance to carbosulfan. High resistance levels to permethrin were detected in most samples and almost all samples displayed resistance to DDT. The kdr-Leu-Phe mutation was present in all localities and in both molecular forms of An. gambiae s.s. Furthermore, the ace-1(R) mutation was predominant in the S form, but absent from the M form. By contrast, no target modification was observed in Anopheles arabiensis. Resistance in the An. gambiae S molecular form in this study seemed to be associated with agricultural practices. Our study showed important geographic variations which must be taken into account in the vector control strategies that will be applied in different regions of Benin. It also emphasizes the need to regularly monitor insecticide resistance across the country and to adapt measures to manage resistance.

[Will climate and demography have a major impact on malaria in sub-Saharan Africa in the next 20 years?]. / Le climat et la démographie peuvent-ils avoir un impact important sur le paludisme en afrique subsaharienne dans les 20 prochaines années?

The purpose of this review of the literature is to present factors possibly affecting the spread of malaria in sub-Saharan Africa over the next 20 years. Malaria is a vector-borne disease that depends on environmental and human constraints. The main environmental limitations involve susceptibility of the vector (mosquitoes of the Anopheles genus) and parasite (Plasmodium falciparum) to climate. Malaria is a stable, endemic disease over most of the African continent. Climatic change can only affect a few regions on the fringes of stable zones (e.g. altitude areas or Sahel) where malaria is an unstable, epidemic disease. Higher temperatures could induce a decrease of malaria transmission in regions of the Sahel or an increase in the highlands. The extent of these overall trends will depend on the unpredictable occurrence of major meteorological phenomenon as well as on human activities affecting the environment that could lead to dramatic but limited outbreaks in some locations. The most influential human factors could be runaway demographic growth and urban development. Estimations based on modeling studies indicate that urbanization will lead to a 53.5% drop in exposure to malaria by 2030. However this reduction could be less than expected because of adaptation of Anopheles gambiae and An. arabiensis, the main vectors of malaria in sub-Saharan Africa, to the urban environment as well as increasing vector resistance to insecticides. Another unforeseeable factor that could induce unexpected malaria epidemics is mass migration due to war or famine. Finally immunosuppressive illnesses (e.g. HIV and malnutrition) could alter individual susceptibility to malaria. Social constraints also include human activities that modify land use. In this regard land use (e.g. forest clearance and irrigation) is known to influence the burden of malaria that is itself dependent on local determinants of transmission. Overall the most important social constraint for the population will be access to malarial prevention and implementation action to control this scourge.

Chlorfenapyr: a pyrrole insecticide for the control of pyrethroid or DDT resistant Anopheles gambiae (Diptera: Culicidae) mosquitoes.

Owing to the development and spread of pyrethroid resistance in Anopheles gambiae in Africa there is an urgent need to develop alternative insecticides to supplement the pyrethroids. Chlorfenapyr is a pyrrole insecticide first commercialized for the control of agricultural pests and termites. Performance against An. gambiae bearing kdr (pyrethroid and DDT resistance) or Ace-1(R) insensitive acetylcholinesterase (organophosphate and carbamate resistance) mechanisms was studied using a variety of adult bioassay tests including a simulated-experimental hut system (tunnel tests) that allows uninhibited mosquito behaviour/insecticide interactions. Strains resistant to pyrethroids and organophosphates showed no cross resistance to chlorfenapyr. In cone bioassays on treated netting the mortality of adult mosquitoes showed an unexpected curvilinear response, with highest mortality occurring at intermediate dosages. Adults expressed irritability to chlorfenapyr at higher dosages, which might explain the dosage-mortality trend. Toxic activity of chlorfenapyr was slow compared to conventional neurotoxic insecticides and additional mortality occurred between 24h and 72 h. In tunnel tests, the dosage-mortality trend showed a more typical sigmoid response and most mortality occurred during the first 24h. Mosquito penetration through the holed, treated netting showed only limited inhibition and blood-feeding was not inhibited. Mortality rates in the kdr strain exposed to chlorfenapyr treated netting in tunnel tests were much higher than with permethrin treated netting over the same 100-500 mg/m(2) dosage range. Chlorfenapyr has potential for malaria control in treated-net or residual spraying applications in areas where mosquitoes are pyrethroid resistant. For treated-net applications chlorfenapyr might be combined with pyrethroid as a mixture to provide personal protection as well as to give control of resistant mosquitoes.

Multiple insecticide resistance mechanisms in Anopheles gambiae and Culex quinquefasciatus from Benin, West Africa.

Because free-insecticide treated net distribution is planned in Benin (West Africa) during the next few years, we investigated the type, frequency and distribution of insecticide resistance mechanisms in Anopheles gambiae and Culex quinquefasciatus mosquitoes in four localities selected on the basis of contrasting agricultural practices, use of insecticides and environment. Bioassays with WHO diagnostic test kits were carried out using pyrethroid, carbamate, organophosphate and organochlorine insecticides. An. gambiae mosquitoes were identified to species and to M or S molecular forms using PCR techniques. Molecular and biochemical assays were carried out to identify kdr and Ace.1 mutations in individual mosquitoes and to detect any increase in the activity of enzymes typically involved in insecticide metabolism (oxidase, esterase and glutathion-S-transférases). WHO diagnostic tests showed high frequency of resistance in An. gambiae and Cx. quinquefasciatus to permethrin and DDT in three areas. This was consistent with the presence of target site insensitivity due to kdr mutation and to increased metabolism through enzymatic activity. Kdr was expressed in both M and S forms. However, less than 1% of An. gambiae or Cx. quiqnuefasciatus showed the presence of the Ace.1(R) mutation. Carbamate/OP resistance was present at higher frequency in Culex than in An. gambiae. Dieldrin resistance was present in both species at all four localities. A higher frequency of pyrethroid-resistance was found in An. gambiae mosquitoes collected in urban areas compared to those collected in rice growing areas. The expansion of vegetable growing within urban areas probably contributed to selection pressure on mosquitoes. The detection of multiple resistance mechanisms in both An. gambiae and Cx. quinquefasciatus in Benin may represent a threat for the efficacy of ITNs and other forms of vector control such as indoor residual spraying in the future.

Preliminary field testing of a long-lasting insecticide-treated hammock against Anopheles gambiae and Mansonia spp. (Diptera: Culicidae) in West Africa.

The efficacy of an experimental long-lasting insecticide-treated hammock (LLIH) with a long-lasting treated net used as a blanket and made of the same fabric (polyethylene) was tested in a concrete block experimental hut, against the malaria vector Anopheles gambiae s.l. and the arbovirus vectors and nuisance mosquitoes Mansonia africana (Theobald) and Mansonia uniformis (Theobald). The LLIH was treated with the pyrethroid insecticide permethrin. It was evaluated concurrently with ignited mosquito coils over 20 successive weeks. In total, 2,227 mosquitoes (130 An. gambiae and 2,097 Mansonia spp.) corresponding to 27.8 mosquitoes per trap-night were collected in the untreated hut (control). The repellent effect of both coils and LLIH significantly reduced the number of mosquitoes entering the huts (35- 60%). There was no significant difference between LLIH and mosquito coils in blood-feeding inhibition (93-97%) or in mortality (88-98%). The LLIH is more cost-effective and user-friendly than mosquito coils, which need to be replaced nightly to protect people sleeping indoors from mosquito bites. The effects of LLIH on exophagic vectors also need to be investigated because most people that sleep in hammocks are outdoors.

Characterization of insensitive acetylcholinesterase (ace-1R) in Anopheles gambiae (Diptera: Culicidae): resistance levels and dominance.

Characterization of insecticide resistance provides data on the evolutionary processes involved in the adaptation of insects to environmental changes. Studying the dominance status and resistance level represents a great interest, in terms of understanding resistance evolution in the field to eventually adapt vector control. Resistance and dominance levels conferred by the G119S mutation of acetylcholinesterase (ace-1R) of the mosquito Anopheles gambiae s.s. (Diptera: Culicidae) were studied for various insecticides belonging to different classes, using strains sharing the same genetic background. Our survey shows that the homozygote resistant strain AcerKis displayed a very high resistance level to various carbamates (range 3,000- to 5,000-fold) compared with that of various organophosphates (range 12- to 30-fold). Furthermore, the dominance status varied between semi-recessivity with fenitrothion and chlorpyrifos methyl insecticides to semidominance with temephos, carbosulfan, and propoxur. These results indicate that this resistance mechanism could spread rapidly in the field and then compromise the use of organophosphate and carbamate compounds in public health. This study underlines the necessity to monitor the ace-1R mutation in natural populations before planning and implementing malaria control programs based on the use of these insecticides.

Species Identification and Resistance Status of Anopheles gambiae s.l. (Diptera: Culicidae) Mosquitoes in Guinea.

Insecticide resistance is one of the primary threats to the recent gains in malaria control. This is especially true in Guinea, where long-lasting insecticidal nets are currently the primary vector control intervention. To better inform the national malaria control program on the current status of insecticide resistance in Guinea, resistance bioassays were conducted, using Anopheles gambiae s.l. Giles, in three sites. Molecular analyses were also done on An. gambiae s.l. to determine the species and find whether the target-site mutations kdr and Ace1R were present. Susceptibility tests revealed resistance to DDT and pyrethroids, although mosquitoes were susceptible to deltamethrin in two of the three sites tested. Mosquitoes were susceptible to bendiocarb, except in Kissidougou, Guinea. The kdr-west mutation was widespread and the frequency was 60% or more in all sites. However, the Ace1R mutation was present in low levels. Insecticide susceptibility should continue to be monitored in Guinea to ensure insecticide-based vector control methods remain effective.

[Pyrethroid and DDT resistance of Anopheles gambiae s.s. (Diptera: Culicidae) in five agricultural ecosystems from Côte-d'Ivoire]. / Situation de la résistance d'anopheles gambiae s.s. (Diptera : Culicidae) aux pyréthrinoïdes et au DDT dans cinq ecosystèmes agricoles de Côte-d'Ivoire.

The promotion of pyrethroid impregnated bednets among the populations is a major activity of the National Malaria Vector Control Programs in African tropical countries. However pyrethroid resistance in Anopheles gambiae, a major malaria vector, has been observed in several parts of Côte-d'Ivoire since 1993. As insecticides used in agriculture against pests are frequently considered as important factors responsible for resistance in malaria vectors, we have evaluated insecticide resistance of An. gambiae populations taking into account the main crops cultivated in Côte-d'Ivoire. Five areas were selected according to the use of insecticide either in agriculture or for domestic purposes: a urban area where vegetables and rice are main crops, a rural rice growing area, a rural area of coffee/cocoa production, a rural area of fruit farming and a rural area without any use of agricultural insecticide. Susceptibility tests were carried out using WHO diagnostic test kits. About 6500 females of An. gambiae were exposed to insecticide impregnated papers (permethrin 1%, deltamethrin 0.05%, DDT 4%) for one hour. Results confirmed that both mortality rates and knockdown time analysis were important to study the resistance data. By using mortality rates, populations of An. gambiae were found to be resistant to pyrethroids and DDT in four of the five areas. Resistance was the highest in urban area, lower in fruit and coffee/cocoa areas and at low level in rice growing area. An. gambiae from area without agricultural treatment was found susceptible to pyrethroids but slightly resistant to DDT A significant increase of knockdown time was observed in all areas with the 3 insecticides. These results agreed with previous studies showing that kdr mutation was the main resistance mechanism to pyrethroids in An. gambiae populations in Côte-d'Ivoire. They also agreed with knockdown time which is an early indicator of resistance development for the population in area without agricultural treatment. In this population the frequency of homozygous resistant individuals was probably too low to have a significant decrease of mortality rates to pyrethroids.

[Influence of social perceptions and practices on the use of bednets in the malaria control programme in Ivory Coast (West Africa)]. / Representations sociales et pratiques liées à l'utilisation des moustiquaires dans la lutte contre le paludisme en Côte d'Ivoire (Afrique de l'Ouest).

The National Malaria Programme in Ivory Coast has encountered difficulty in winning public acceptance of insecticide-treated bednets. We speculate that resistance to the use of bednets could be rooted in social perceptions, beliefs and practices in the communities. The purpose of this study was to identify sociocultural and environmental factors that could be used to support promotion strategies and acceptance of impregnated bednets in Ivory Coast. Survey findings confirmed that bednets were not in widespread use among the population (25%). The most widely used methods were burning mosquito coils (50%) and indoor spraying (31%). Use of impregnated bednets was low (6%). Most survey respondents (73%) indicated initial appreciation for the effectiveness of bednets in protecting against mosquitoes as a nuisance. However only 9% of respondents thought that impregnated bednets provided protection against malaria although they did not necessarily use them. Design was a determinant factor for the use, and even acceptance, of bednets. The population want rectangular, permanently impregnated bednets large enough to accommodate at least 2 persons. Cost was a major obstacle to wider use by the population. According to our data the best price for the population would be between 2000 and 2500 FCFA as compared to the current price of 3500 FCFA in Ivory Coast.

[Use of agricultural insecticides in Benin]. / Utilisation des insecticides agricoles au Bénin.

The use of insecticides in households and in agriculture has been incriminated in the emergence of insecticide resistance in insect vectors. For farming staff, the emergence of vector resistance is due to indoors spray of insecticides using aerosols and other low quality products in rural and urban settings against mosquitoes. On the other hand, public health specialists believe that the phenomenon of resistance could be due to massive use of insecticides in agriculture for field pests control. In Turkey, the implication of agricultural use of pesticides in the selection of vector resistance is clearly established. This study was framed to identify potential practices favouring the emergence of insecticide resistance in the Republic of Benin. Interviews and focus group discussions were organized with cotton, rice and vegetables farmers. The final aim of these surveys was to point out practices likely to favour the emergence of resistance. The research is conducted in 3 cotton fields, 2 rice fields and 2 vegetable plantations. After filling and signing concerned forms, farmers are subjected to quantitative and qualitative questionnaires to generate data on: insecticides being used, the various doses applied for pests eradication, the frequency of treatments, the cost of treatments (cost/hectare/year) the origin of insecticides, the place of purchase, safety precautions and related health hazards. The results of this study have shown that the use of insecticides in agriculture is a clear fact. During treatments, insecticide residues get in contact with mosquito breeding sites where they diffuse into water and exercise a selection pressure on larvae. This partially explains the high levels of resistance recorded in with strains of Anopheles gambiae collected in agricultural settings under insecticides pressure. Pyrethroids and more specifically deltamethrin and cyfluthrin are the insecticides mainly used in studied localities. Bedrooms of farmers are used as storage place for half-used and un-used insecticides containers. For a proper management of insecticides, cotton and vegetable plantations farmers receive assistance from the ministry of rural development. Because of the importance of cotton production in the Republic of Benin, trainings on management of insecticides in agricultural settings are frequently organised by the ministry of rural development and are opened to farmers and their family members (husbands, wives, children and relatives...). In the long run, the whole family learns and becomes very versant with the use of insecticides, spraying frequencies, spraying devices and spraying techniques.

Malaria transmission in the lagoon area of Cotonou, Benin.

A study of the prevalence and intensity of malaria transmission in the lagunar area of Benin was carried out by means of repeated cross-sectional surveys of the child population. Six areas were selected: two urban areas of Cotonou, three lagunar villages and one savanna village. Slide positive rates and prevalence of antibodies to P. falciparum sporozoites were examined in June-July 1989 (long rainy season), October-November 1989 (short rainy season) and March-April 1990 (short dry season). Parasite rates in children 2 to 9 year-old showed holoendemic malaria, in the savanna village (89.4-94.2%) and hyperendemic malaria in the lagunar zone (60.7-83.5%). Levels of P. falciparum antisporozoite antibodies were higher in the sample from the periurban sector of Ladji compared with the nearby traditional lagunar villages and lowest in children living in the central urban sector. Cotonou had higher levels of malaria transmission compared with other West African cities.

[Coastal urban malaria in Cotonou (Republic of Benin). Entomological study]. / Le paludisme urbain cotier à Cotonou (République du Bénin). Etude entomologique.

A one year entomological was carried out the survey in the coastal town of Cotonou to study the urban transmission of malaria. Three representative areas of Cotonou were chosen. The method adopted concerned night catches on human bait and dissection of A. gambiae s.l. The density of the vector (A. gambiae s.l.) fluctuated with the level of urbanization of the areas the annual aggressivity rates reached 1179 in the town center, 3666 in an the outskirts and 3363 in intermediate areas. Mean sporozoitic index was 1.7% and corresponding annual inoculation rate 46. In center of the town, transmission is seasonal and short, with a very high level. Sporozoitic index is 12% and the corresponding inoculation rate is 1.02. Outside of the town, transmission is seasonal and long: lasting 8 months. Transmission is imperceptible in the middle of the dry season and at the beginning of the long rain season. Malaria transmission into urban areas is generally low but in coastal like zones Cotonou, the intensity may be higher.

[Morbidity and severity of malaria attacks in carriers of sickle-cell trait]. / Etude de la morbidité palustre et de la gravité des accès pernicieux chez les porteurs du trait drépanocytaire.

The authors made a survey in a permanent high Plasmodium falciparum transmission area to compare frequency and severity of malaria attacks in children belonging to different haemoglobin types before 15 years; 291 young out-patients of the local infirmary and 467 outpatients of the hospital were examined. Diagnosis of malaria was inferred from clinical and parasitological criteria and subsequent evolution of the disease. Pathogenic threshold of parasitaemia was similar in all haemoglobin type groups of children and was about 3,000 parasite-infected red cells per mm3. Malaria was diagnosed more often among HbAA patients, than among other patients. Mortality rate in AA haemoglobin children was higher than 3% whereas in sickle cell trait carriers no death could be certainly attributed to malaria. The S gene rate was significantly weaker (p < 0.05) in subjects attacked by Malaria (5%) than in all other groups of children. In the endemic malaria areas the susceptibility of S gene carriers appears to be lesser than in AA haemoglobin children and could explain the paradoxically lower rate of mortality in this group.

[Plasmodium falciparum or P. malariae parasitemia in carriers of sickle cell trait in various Benin biotypes]. / Parasitémies à Plasmodium falciparum ou P. malariae chez les porteurs du trait drépanocytaire dans différents biotopes du Bénin.

The prevalence of malaria and the frequency of gene S were surveyed in two different regions of Benin, savana and coastal lacustrine regions. In both regions, prevalence of malaria was not significantly different between Hb AA people and Hb AS people. Gene S prevalence was not modified by age, excepted for Hb SS which was not found in people upper than 25 years. In holoendemic area, i.e. lacustrine region, means of P. falciparum parasitaemia were significantly lower in Hb AS children than in Hb AA children. Sickle cell trait did not reduce the prevalence of malaria but seemed to decrease the level of parasitaemia.

[Infectivity of Anopheles melas vis-a-vis Plasmodium falciparum in the coastal lagoon area of Benin]. / Infectivité d'Anopheles melas vis-à-vis du Plasmodium falciparum dans le milieu côtier lagunaire du Bénin.

In this article An. melas infestation rate for P. falciparum is compared to the rate of An. gambiae in the coastal and lagoon area of Benin where the two species are sympatric. We studied the variation of An. gambiae complex infestation rate in three zones where the two species occur in different proportions. This infestation rate is higher in areas where An. gambiae is prevalent. In a second experiment we separated An. melas and An. gambiae according to cytogenetic and biometrical analysis. Then we established the infestation rate of each species by microscope examination of salivary glands and presence of P. falciparun C.S. antigens by ELISA method. In areas where An. melas is the most abundant species (80-90%), the sporozoitic index and antigen C.S. + P. falciparum rate are significantly lower. These results are confirmed by the infestation rates observed for each species. In conclusion, An. melas infestation rate is significantly lower than the An. gambiae one. An. gambiae is the best malaria vector in Africa. In spite of an environment such as Ganvie where animals are rare, which increases anthropophilic and endophilic tendencies of An. melas, antigens CS P. falciparum rate of An. gambiae (3.5%) are significantly higher than An. melas (1.9%).

[Resistance of malaria vectors to pyrethrins used for impregnating mosquito nets in Benin, West Africa]. / Résistance des vecteurs du paludisme vis-à-vis des pyréthrinoïdes utilisés pour l'imprégnation des moustiquaires au Bénin, Afrique de l'Ouest.

Impregnated bednets can be considered a major tool for reducing Anopheles bites, malaria morbidity and overall mortality. The resistance of Anopheles gambiae to pyrethroids used to impregnate bednets and curtains has already been noted in the urban area of Cotonou in Benin (18, 21). In this study, we wished to find out if the resistance observed in Cotonou is localized only in this town or is already extensive throughout Benin. In this case, such resistance would be a handicap to the promotion of impregnated bednets in Benin. The study was carried out in 15 localities throughout the different ecological zones of Benin. The study has also taken into account environmental factors favouring the emergence of resistance. We did susceptibility tests with WHO test kits for adult mosquitoes using impregnated papers. The papers were impregnated with permethrin 0.25%, deltamethrin 0.025% and lambdacyhalothrin 0.1%. We also tested DDT 4% to find out if there was a cross resistance between DDT and the pyrethroids. Two mosquito species were tested: An. gambiae and An melas. In northern Benin, where farmers use insecticides against cotton pests, vectors are susceptible to deltamethrin and lambdacyhalothrin and resistant to permethrin. In the south, An. gambiae is resistant to deltamethrin and permethrin. This resistance is high in the urban zone of Cotonou, in the coastal and lagoon areas and at Kraké, a frontier viliage with Nigeria. The resistance observed in southern Benin is confirmed by the lengthening of the knock-down time of mosquitoes which were exposed for 1 hour to insecticide in impregnated WHO test tubes, and by a reduction of permethrin and deltamethrin remanence effect.

[The transplacental transport of Plasmodium falciparum in non-febrile parturient women in a holoendemic region]. / Note sur le passage transplacentaire de Plasmodium falciparum chez des parturientes non fébriles en région holoendémique.

Plasmodium falciparum parasitaemia measure, placenta print on microscope slide, immunofluorescence titration of Plasmodium antibodies and electrophoresis of haemoglobin were performed in 53 mothers and their child who did not shown any clinical signs of malaria. 51% from the mothers presented a patent parasitaemia associated with a high density of schizonts on uterine villi surface. Parasite density in children's blood was low and there was no correlation between mother's parasitaemia or placental schizogonia and newborn children's parasitaemia. We observed a higher prevalence of malaria attack, although the difference was not significant, in sickle cell women than in women whose haemoglobin was normal. In sickle cell women schizogonia occurred in placenta as in women whose haemoglobin was normal.

[Development of chemoresistance of Plasmodium falciparum to chloroquine and mefloquine in Benin between 1980 and 1989]. / Evolution de la chimiosensibilité de Plasmodium falciparum à la chloroquine et à la méfloquine au Bénin entre 1980 et 1989.

Resistance of P. falciparum to chloroquine has been notified in 1986 in non-immune visitors. Authors organized surveys of in vivo and in vitro tests to follow evolution of the phenomena. The increase in number of P. falciparum strains resistant to chloroquine was sudden in 1986 but stopped to rise from this date, and even seemed to decrease gently. The geographical distribution of the resistance, restricted to the region of Cotonou, could be explained by illegitimate chloroquine distribution. But authors propose further investigations on relations between chloroquine resistant strains and the 3 anopheles species involved in malaria transmission in Benin. Resistance to mefloquine is rare in Cotonou region, but higher in rural zone.

[Malaria and pregnancy: attitude of health care personnel during prenatal care in Cotonou, Benin]. / Paludisme et grossesse: attitude du personnel de santé lors des consultations prénatales á Cotonou, Bénin.

The purpose of this study was to evaluate the state of knowledge and use of drug in pregnant women diagnosed with malaria at the first prenatal examination. Survey data were conducted of physicians and paramedical staff working the public and private sector in Cotonou, Benin from November 1996 to January 1997. A questionnaire including items on the type of antimalarials used, therapeutic regimens and compliance with the treatment posology and duration guidelines as defined by the WHO and recommended by the National Program against Malaria. A study of informational supports allowed validation of responses obtained during the interview on the day of survey. A random two-degree, stratified sample of 208 prescribers including 109 physicians, 51 midwives, and 48 nurses was interviewed. Data analysis showed that chemoprophylaxis was prescribed by all midwives, 87.5 p. 100 of nurses, and 8.2 p. 100 of physicians. Midwives prescribed this strategy in all pregnant women. For 5.5 p. 100 of physicians and 6.3 p. 100 of nurses, primigravid women were considered as a target group. Chloroquine was the most widely used antimalarial. It was sometimes used in association with proguanil. Of the other drugs used for prevention, quinine was prescribed by 2.4 p. 100 of nurses and 1.1 p. 100 of physicians. The therapeutic regimes and posologies used by the health care workers were not in compliance with the policies of the National Program for Control of Malaria. The findings warrant the creation of an organization to promote consultation and communication between health care authorities and workers.

[The value of malaria antibody level determination in non-immune subjects in a holoendemic area]. / Intérêt du dosage des anticorps palustres chez les sujets non immuns en zone holoendémique.

The use of indirect immunofluorescence in non-immune people under heavy risk of chloroquine resistant Plasmodium falciparum malaria has a fair interest for diagnosis because of atypical clinic features and poor parasite density in thin smears. Indirect immunofluorescence has been used in Cotonou where chloroquine resistant strains of Plasmodium falciparum was described since 1986. This lead to detect numerous cases of malaria with negative thin smear. Under epidemiological considerations, non-autochthonous people's antibody acquiring curve related to residence time in endemic area is parallel to the autochthonous children's antibody acquiring curve. However, average of antibody titer is strongly lesser in non-autochthonous population even after living more than 12 years in holoendemic area. This can reveal a lesser capacity to acquire immunity in non-autochthonous people due to a lesser exposure or to prophylaxis. This has to be pointed out when prophylactic strategies are proposed to those who live endemic areas. Authors propose to look back upon past obsolete prophylactic methods as repellents, insecticides, mosquito nets, air conditioned, etc.