[Comparison of specific composition and mosquitoes population dynamics in two villages of the centre of Côte-d'Ivoire, with and without irrigated rice growing area]. / Comparaison de la composition spécifique et de la dynamique des populations de moustiques dans deux villages du centre de la Côte-d'Ivoire, avec et sans périmètre de riziculture irriguée.

Entomological surveys were undertaken between October 1994 and August 1995 and from April to August 1995 in the villages of Kafiné and Pékaha, respectively These villages are located in the centre of Côte-d'Ivoire in a humid savannah area in the prefecture of Niakaramandougou. Rice plots are located to about 500 meters from the first habitations of Kafiné. They also form an enclosure around the village causing a great culicidian nuisance. On the other hand in the village of Pékaha, situated at 8 km from the enclosure, one can find a non-developed low ground area with swamps according to the season which has caused the multiplication of anthropophilic Culicidae. Five genera of mosquito were caught in the two villages: Anopheles, Aedes, Culex, Mansonia and Uranotaenia. The genus Anopheles is by far the most predominant in Kafiné with 84.3% (n=17556). Mansonia, Culex and Aedes respectively constitute 12%, 3% and 0.01% of the total anthropophilic mosquitoes. In the contrary the genus Mansonia was the most predominant in Pékaha with 78.2% (n=6642). Anopheles, Aedes and Culex respectively represent 13.2%, 8.3% and 0.1% of the total number of mosquitoes caught during the surveys. If in the village of Kafiné, the culicidian nuisance is mainly due to anopheles mosquitoes (84.3%) and particularly to An. gambiae s.s. (70.6%), in the village of Pékaha, dwellers suffer more from Mansonia (78.2%) bites than those of Anopheles (13.2%).

Current distribution of a pyrethroid resistance gene (kdr) in Anopheles gambiae complex from west Africa and further evidence for reproductive isolation of the Mopti form.

In the field, the kdr mutation, involved in pyrethroid resistance, has been found widely distributed in the Savanna form of Anopheles gambiae s.s., but never in wild populations of the Mopti form or An. arabiensis, even in areas where both occur in sympatry with resistant Savanna populations. Under laboratory conditions, Mopti and Savanna forms were fully able to interbreed and the kdr mutation was transmissible from one form to the other. Both forms appeared to be exposed to pyrethroid selection pressure in the field. The absence of the kdr mutation in the Mopti form and the total lack of Mopti-Savanna heterozygotes in field populations provides further evidence of a pre-copulatory barrier to gene flow between these two forms. Molecular markers, including kdr, are powerful tools for studying population genetics and circulation of resistance genes, and should be used through an integrated approach for a better understanding of the speciation process.

Evaluation of a polymerase chain reaction assay for detection of pyrethroid insecticide resistance in the malaria vector species of the Anopheles gambiae complex.

A published polymerase chain reaction assay proved reliable for detecting nerve-insensitivity (kdr-type) resistant and susceptible alleles to the pyrethroid insecticide permethrin in the malaria vectors Anopheles gambiae s.s. and An. arabiensis and the nonvector species An. quadriannulatus. The assay detects pyrethroid susceptible and resistance alleles mediated by a mutation in region II of the para-type sodium channel gene, showing that resistance is conferred by pyrethroid target site insensitivity. Analysis of results of the assay suggests that more than 1 mechanism conferring pyrethroid resistance is operating in an An. gambiae s.s. strain from Côte d'Ivoire. The value of the assay as a tool for monitoring this mode of insecticide resistance in wild populations is discussed.

[Atypical activity rhythm in Aedes aegypti in a sub-sudanian savannah zone of Côte d'Ivoire]. / Rythme d'activité atypique chez Aedes aegypti en zone de savane sub-soudanienne de Côte d'Ivoire.

Ae. aegypti is vector of many arboviruses of medical and/or economical importance. It transmits the yellow fever, dengue and Chikungunya viruses. Small water collections constitute its potential breeding sites. Three different populations of Ae. aegypti are known in Africa: a selvatic population breeding in tree holes and rock holes, a population breeding in discarded containers in peri-domestic area and a third population which breeds in drinking water containers and various receptacles inside habitations. The biting activity of this vector is diurnal in East Africa, but it occurs usually at sun set in West Africa. An entomological survey was carried out in a village situated in Sudan savannah zone of Côte d'Ivoire to appreciate Aedini populations in dry season. Mosquito collections were organized from 4 p.m. to 6 a.m. The results showed an atypical biting activity rhythm in dry season, characterized by a permanent activity during the whole night up to 6 a.m., a pronounced tendency to endophagy and a peak biting aggressivity at midnight inside as well as outside houses. The epidemiological implications of such an atypical rhythm of biting activity are analysed. It is suggested to appreciate the extent of this phenomenon through some more investigations in the villages of the area and determine the induced stegomyian focus.

[Feeding preferences of malaria vectors in the city of Bouaké and in the surrounding villages of Côte d'Ivoire]. / Préférences trophiques des vecteurs du paludisme dans la ville de Bouaké et dans les villages environnants de Côte d'Ivoire.

A study of the bloodfeeding behaviour of An. gambiae and An. funestus was carried out in the city of Bouaké and surrounding villages. The results showed that 99.4% of An. gambiae in the city feed on human hosts. In villages, 98.8% of An. gambiae and all An. funestus feed on human hosts. In this area, the anthropophily of major malaria vectors is almost exclusive.

[ The aggressive cycle of Anopheles gambiae s.s. inside houses and malaria transmission in the Bouake region (Côte d'Ivoire). Value of using impregnated mosquito nets]. / Le cycle d'agressivité d'Anopheles gambiae s.s. à l'intérieur des maisons et la transmission du paludisme dans la région de Bouaké (Côte d'Ivoire). Intérêt de l'utilisation de la moustiquaire imprégnée.

The biting indoor cycle of Anopheles gambiae s.s. was studied in a rural zone near Bouaké from 6 pm to 6 am. The cycle was characterized by a peak between midnight and 1 am (n = 19,181). The parturity rate of biting females regularly increased from 6 pm until 3 am, then remained at a high level up to 6 am (n = 14,239). Infected bites were observed from 7 pm to 6 am with a maximum between 0 and 3 am, and 96.7% of them were obtained between 11 pm and 4 am (n = 219). It appears that malaria transmission occurs essentially at the moment when villagers are in bed. The correct use of impregnated bed nets may thus greatly reduce malaria transmission.

[The impact of rice fields on malaria transmission in the city of Bouaké, Côte d'Ivoire]. / Impact d'aménagements de rizières sur la transmission du paludisme dans la ville de Bouaké, Côte d'Ivoire.

This study evaluates the impact of rice fields in the city of Bouaké on anopheline fauna and malaria transmission. The Anopheles species represents between 11.4 to 39.2% of mosquitoes in the districts with rice fields and 5.2 to 47.8% in lowland districts with market-gardening. An. gambiae constitutes more than 98% of anopheline population in the city. In the lowland districts with market-gardening, biting rates of An. gambiae varied from 3650 to 6935 bites per man per year. Seasonal variations were correlated with rainfall. The mean annual parturity rate was 72% and the mean sporozoitic index 2%. Malaria transmission started at the beginning of the rainy season and attained its height during the second half of this season. Depending on the district, inhabitants were infected with 78 to 134 bites per year. The mean biting rate of An. gambiae in the districts with rice fields varied from 4745 to 22,630 bites per man per year. Seasonal variations were not correlated with rainfall, but with the growth of rice and the two annual cycles of rice cultivation. The parturity rates of the population of An. gambiae were low (46.2% to 57.2%), especially after rice transplantation. The mean infection rates were between 0.7 and 1.0%. The transmission period covered 7 to 11 months depending on the district with two annual peaks observed at the end of rice cultivation. Inhabitants were infected with 44 to 155 bites per year. Rice fields in Bouaké do not seem notably to have modified malaria transmission in the city.

[The epidemiology of malaria in the southwestern forests of the Ivory Coast (Tai region)]. / Epidémiologie du paludisme dans le sud-ouest forestier de la Côte d'Ivoire (région de Taï).

An epidemiological study on malaria was undertaken between July 1995 and July 1996 in two villages (Zaïpobly and Gahably) and their encampments (Kouassikro, Hamanikro and Konankro), in the south-western forest area of Côte d'Ivoire (region of Taï). The parasitological scheme comprised a total of 2023 tests performed on children aged from 0 to 14 years. The species found were Plasmodium falciparum, P. malariae and P. ovale with a proportion of 84%, 14% and 2% respectively. The global parasite prevalence of all Plasmodium species was 85% and malaria was holoendemic. The average parasitic density decreased progressively as the age increased, in contrast to the plasmodic index which did not vary. All the malarial indexes were similar in the villages and their encampments. Only overall fever prevalence was permanent and in all age groups it was higher in the encampments than in the villages. The entomological findings showed that transmission was permanent and intense throughout the year, with a recrudescence during the rainy season. Transmission was attributed to Anopheles gambiae s.l. in 85% of the cases whereas An. funestus played a secondary role. The average sporozoïtic index was 7.6% and varied between 1.1% and 16.7%. The entomological inoculation rate was of 400 infected bites per person-year for An. gambiae s.l. In such conditions of intense transmission, acquisition of premunition starts at a very early age. This assertion is verified by the average parasite density and the frequency of high parasitic densities which were at their maximum between 1 and 4 years of age and decreased thereafter as the age increased. The paludometric and entomologic indexes obtained are the most elevated ever to have been observed in Côte d'Ivoire, as a result of considerable ecological changes linked to the deterioration of the forest environment over the past 30 years. This deterioration has probably been caused by demographic pressure resulting from internal and foreign immigration to the Taï region and more especially by the influx of Liberian refugees.

[Dynamics of malaria transmission in Kafiné, a rice growing village in a humid savannah area of Côte d'Ivoire]. / La dynamique de la transmission du paludisme à Kafiné, un village rizicole en zone de savane humide de Côte d'Ivoire.

A study on malaria transmission based on samples of mosquitoes caught on human subjects was conducted from February to August 1995 in the rice growing area of Kafine, a village located in the Niakaramandougou district of northern Côte d'Ivoire. The village is surrounded by 117,500 acres of rice fields. Irrigation is sub-permanent in the rice field and harvests number two a year. During the 6 months of the study, 12.353 mosquitoes were caught. The average biting rate was 118.8 bites per man per night (b/m/n). Mansonia, Culex and Aedes represented only 17.5% of the total number of mosquitoes caught. Anopheles accounted for 82.5% of the number of anthropophilic mosquitoes. Anopheles gambiae s.s. represented 83.7% of the total Anopheles species. As a whole, the average biting rate recorded for the Anopheles was 98 b/m/n. The average biting rate of An. gambiae was 90.4 b/m/n. The highest rate (121.5 b/m/n) was recorded in April. During the dry and rainy season, the indoor biting cycle per hour of An. gambiae s.s. was studied from 6 p.m. to 6 a.m. In both seasons, a marked biting activity was noticed between 10 p.m. and 5 a.m. The average annual parity rate reached 40.2% but it ranged from 59.8% (n = 82) in February to 19% (n = 63) in May. The mean sporozoitic index of An. gambiae throughout the study period was 1.1% (14 positive salivary glands/1.251 dissected). The index ranged from 0 in April, May and June to 6.2 (n = 192) in July. The rate did not vary with rainfall but with the different stages of rice growing. The non-synchronisation of agricultural practises for each growing cycle seemed to be a conclusive factor in the transmission of malaria in this locality. Malaria transmission at Kafine can be characterised by 3 main elements: transmission is intensive with an estimated inoculation rate of 1 ib/m/n; transmission is more related to double phase rice cultivation (regardless of synchronisation on plots) than to rainfall; transmission shows particular variations linked to rice cultivation cycles with an increase during periods of ripeness and harvest. The nuisance caused by higher mosquito density has brought people to comply with use of pyrethroid impregnated bed nets advocated for wide use by the National Malaria Control Program.

[Antimalarial guidelines and therapy practices of the population of Bouake, Ivory Coast]. / Itinéraires et pratiques thérapeutiques antipaludiques chez les citadins de Bouaké, Côte d'Ivoire.

This survey of 162 households in the city of Bouaké, Côte d'Ivoire was undertaken to study the behavior of the population in diagnosing and treating malaria. Findings indicate that awareness of symptoms and ability to evaluate the severity of malaria is high. In most cases, mild malaria is treated at home. In case of presumptive diagnosis of malaria, 87.6% of households undertake self-treatment, 9.3% seek institutional healthcare, 1.2% go to traditional healers, and 1.9% use traditional remedies. The most frequent drug for primary treatment is chloroquine (68.3%) which is generally obtained from pharmacies (98.8%). However, proper dosages are rarely used. If primary treatment fails, behavior is complex depending on the estimated severity of disease. Although many causes of malaria are mentioned, most people implicate mosquitoes (75.6%). In 95.1% of households surveyed, chloroquine prophylaxis was used for newborns. Most households (89.5%) practice mosquito bite protection but use of mosquito nets is low (4.9%). These results showing the preference for family-based management suggest that informational campaigns are needed to promote effective and consistent home treatment. Education is also needed to increase knowledge about mosquito nets and insecticides.

[Aspects of malaria in a village of the humid savannah of the Ivory Coast]. / Aspects du paludisme dans un village de savane humide de Cote d'Ivoire.

Malaria is a major cause of morbidity and mortality in Ivory Coast. This fact justifies further epidemiological investigations to define regional features and allow implementation of the most suitable control measures. To this end, a study focusing on transmission of malaria was conducted between January and May 1993 concurrently with malarial parasite identification in Allokoukro, a village in the humid savannah in the central region of Ivory Coast. Two vectors of malaria were found in the village, i.e. Anopheles gambiae s.l. and Anopheles funestus. These two species accounted for 53.7% of Culicides captured during the study with important monthly variations depending on rainfall. Anopheles gambiae s.l. accounted for 92.2% of the anopheles captured and thus was the main vector identified in the village. As a result of its persistence and high density, this species ensured uninterrupted transmission of malaria. Anopheles funestus was scarce and thus played a limited role in infection at the beginning of the rainy season. Plasmodium falciparum and Plasmodium malariae were the main parasite species identified in the population of the village. The incidence of malarial infection was high in children between the ages of 0 and 14 years. Plasmodium indices stood at 45.5% in March and 82.2% in May. The prevalence of malarial infection in may was associated with an increase in mean serum parasite levels in children. Clinical studies showed that malaria motivated 64.4% of consultations during the rainy season and was one of the mean causes of morbidity in particular among children.

[Malaria surveys in a humid savannah region in Côte d'Ivoire]. / Enquêtes paludométriques en zone de savane humide de Côte d'Ivoire.

The purpose of this report is to describe six surveys carried out from March 1993 to March 1994 to assess seasonal variations in parasite indexes and malaria morbidity rates in children between the ages of 0 and 14 years living in the village of Alloukoukro in the wet Savannah region of Cote d'Ivoire. Results demonstrated the presence of both Plasmodium falciparum and Plasmodium malariae. No case of infection only by Plasmodium malriae was observed. Parasite indexes were greater than 50% in all newborns and preschoolers. Wide seasonal variations were observed with the highest indexes (91.9%) occurring at the end of the rainy season. The lowest indexes were always observed in children between the ages of 10 and 14 years. There was not a significant proportional relationship between parasite index and daily mosquitoes inoculation rates. However highest parasite indexes were always measured after periods of intense transmission. Overall findings showed that gametocyte index increased during the rainy season and peaked at the beginning of the dry season in December. Strong recrudescence of malarious disease during the rainy season corresponded to an increase in the mean parasite density. The seasonal rises in malaria incidence occurred a few weeks after the first rains of the year with the greatest incidence occurring in May. Curves for maximum mean parasitemia rate and peak parasite incidence crossed at the end of the rainy season in October. The results of this study indicate that malaria is the most common parasitic disease year round in children living in the wet Savannah region of Cote d'Ivoire and that it is one of the main causes of morbidity.

[Efficacy of permethrin-impregnated Olyset Net mosquito nets in a zone with pyrethroid resistant vectors. I--Entomologic evaluation]. / Efficacité des moustiquaires pré-imprégnées de perméthrine Olyset Net en zone de résistance des vecteurs aux pyréthrinoïdes. I--Evaluation entomologique.

The efficacy of permethrin-treated Olyset Net mosquito nets on malaria transmission and morbidity was studied in Kafine, a village located in the savanna region of the Cote d'Ivoire in Africa. After collecting sociodemographic, entomological, and parasitological data, bednets were distributed first in the southern half of the village and then in the whole village. Throughout the study period, mosquito specimens were captured on the skin of inhabitants at four points in the village between 6 PM and 6 AM both inside (but outside bednets) and outside houses. Prior to distribution of bednets, the mean biting rate (MBR) by Anopheles gambiae was 77.4 bites per man per night (b/m/n). The mean parturity rate (MPR) was 40.6 p. 100, the sporozootic index (SI) was 0.99 p. 100, and the mean entomological inoculation rate (MEIR) was 0.7 infectious bites per man per night (b+/m/n). Six months after distribution of bednets in the southern half of the village, MBR was 80.2 b/m/n, MPR was 32 p. 100, SI was 1.8 p. 100, and MEIR was 0.83 b+/m/n. After extending distribution to the whole village, data from November 1996 to July 1997 were as follows: MBR, 67.8 b/m/n; MPR, 20.1 p. 100; SI, 0.65 p. 100; and MEIR, 0.66 p. 100. From August 1977 to July 1998, data were as follows: MBR, 102.6 b/m/n; MPR, 26.2 p. 100; SI, 1.15 p. 100; and MEIR, 0.74 b+/m/n. Comparative analysis of these data showed that use of bednets had no effect on the bite or entomological inoculation rate. This is in agreement with the documented resistance of vectors in the study zone to permethrin. Despite the known stimulation/repulsion effect of permethrin, use of treated bednets had no real impact on transmission. This inefficacy could be related to the high prevalence (80 p. 100) of the Kdr gene (responsible for resistance) in the savanna form of Anopheles gambiae.

Differential effects of Bacillus sphaericus strain 2362 on Culex quinquefasciatus and its competitor Culex cinereus in West Africa.

The larval susceptibility to Bacillus sphaericus strain 2362 of the non-man-biting mosquito Culex cinereus and the urban filariasis vector Culex quinquefasciatus, two competitor mosquitoes in polluted habitats, was compared. In the laboratory, both species ingested a similar amount of B. sphaericus spores when fed c. 2 x 10(5) spores per ml for 30 min. However, in the same experiment, third-instar larvae of Cx quinquefasciatus were reduced by 98% at 24 h exposure while Cx cinereus larvae were only reduced by 6% at 72 h. In the field, preimaginal populations of Cx cinereus ingested, within a week, more than 99% of the applied spores, but showed no significant decrease through 14 days in cesspools treated at 10 g/m2 of a flowable concentrate of B. sphaericus 2362, containing 2 x 10(10) spores/g. It is proposed that specific biological control of Cx quinquefasciatus could result from appropriate treatment of breeding-sites with larvicidal B. sphaericus and competitive displacement by Cx cinereus or other mosquitoes with larvae that are more tolerant of B. sphaericus.

Malaria in Côte d'Ivoire wet savannah region: the entomological input.

A two years study has been carried out in Alloukoukro, a traditional wet savannah village in the central region of Côte d'Ivoire. The productive breeding sites of malaria vectors are natural puddles and some man-made shelters around the village. 576 man-nights of capture have identified Anopheles gambiae s.l. and An. funestus as vectors of malaria in the study area. The low densities of An. phaorensis and An coustani implies that their possible role in transmission is very negligible. An. gambiae s.l. was the predominant species throughout the year with a mean of 19.2 b/m/n in 1991 and 13.6 b/m/n in 1992. The densities of An. funestus increased gradually during the rainy season and reached its peak values towards the end of the season. An. gambiae s.l. assures transmission throughout the year. An. funestus maintains a seasonal transmission which is spread over seven months. In 1991, each person would have received an average of 264.5 infected bites altogether with 204.5 infected bites from An. gambiae s.l. and 62 infected bites from An. funestus. In 1992, there would have been 196.5 infected bites per man with 160 and 36.5 infected bites respectively from An. gambiae s.l. and An. funestus. This study has shown that in wet savannah areas, the rainy season spreading almost all over the year, allows the breeding sites to retain water much longer and thus, to keep alive a more important residual vector populations capable to ensure malaria transmission even during the dry season. The great majority of infected glands (96.7%) were observed between 11 p.m. and 04 a.m. So, the large scale use of treated bednets has been therefore strongly recommended as key measure against malaria transmission in this area.

[Factors affecting the efficacy of 2 growth regulator compounds, OMS 3010 (phenoxycarb) and OMS 3019 (ethoxypyridine), on larvae of the Simulium damnosum complex]. / Etude de facteurs conditionnant l'efficacité de deux composés régulateurs de croissance, OMS 3010 (phenoxycarb) et OMS 3019 (ethoxypiridine), sur les larves du complexe Simulium damnosum (Diptera: Simuliidae).

Two insect growth regulators (IGR'S) acting as juvenile hormone analogs (JHA'S), OMS 3010 (phenoxycarb) and OMS 3019 (ethoxypyridine) were selected after a screening of several compounds proposed by industry on black fly larvae of the Simulium damnosum complex (Diptera: Simuliidae) the vector of onchocerciasis in West Africa. Bioassays were designed to study two parameters: larval age and exposure time. The results showed that these compounds are more efficient on old larvae (6th and 7th instars) than young larvae (3rd, 4th and 5th instars). However, exposure time seems essential. The black fly larvae live in fast running water courses. Thus, it is difficult to insure a prolonged exposure time in natural conditions. Though being active on black fly larvae, three factors are limiting the prospects for operational use of these two compounds: high dosages, limited effectiveness on young instar larvae and exposure time.

[Small-scale evaluation of the efficacy of growth-regulating insecticides on larvae of the Simulium damnosum complex (Diptera: Simuliidae)]. / Evaluation à échelle réduite de l'efficacité d'insecticides régulateurs de croissance sur les larves du complexe Simulium damnosum (Diptera: Simuliidae).

The efficacy of insect growth regulators was assessed in small scale tests on larvae of the Simulium damnosum complex (Diptera: Simuliidae) in the Ivory Coast. Three compounds [OMS 2015 (triflumuron), OMS 3009 (teflubenzuron), OMS 3013 (chlorfluazuron)] belong to the group of benzoylphenyl-urea substitutes; these IGR's are supposed to inhibit chitin synthesis. Two other compounds are Juvenile Hormone Analogs (JHA's) (OMS 3007 and OMS 3019). The last compound (OMS 3010) is a phenoxycarbamate. The first three compounds had a low efficacy on blackfly larvae, which is consistent with the literature data for another compound of this group: diflubenzuron. The other three compounds (OMS 3007, OMS 3010 and OMS 3019) were much more efficient, OMS 3010 and OMS 3019 showing high activity at low concentrations. These results would justify further studies on the effect of larval age and exposure parameters, and eventually full scale river tests.

Molecular evidence of incipient speciation within Anopheles gambiae s.s. in West Africa.

We karyotyped and identified by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) analysis Anopheles gambiae s.s. samples collected in several African countries. The data show the existence of two non-panmictic molecular forms, named S and M, whose distribution extended from forest to savannahs. Mosquitoes of the S and M forms are homosequential standard for chromosome-2 inversions in forest areas. In dry savannahs, S is characterized mainly by inversion polymorphisms typical of Savanna and Bamako chromosomal forms, while M shows chromosome-2 arrangements typical of Mopti and/or Savanna and/or Bissau, depending on its geographical origin. Chromosome-2 inversions therefore seem to be involved in ecotypic adaptation rather than in mate-recognition systems. Strong support for the reproductive isolation of S and M in Ivory Coast comes from the observation that the kdr allele is found at high frequencies in S specimens and not at all in chromosomal identical M specimens. However, the kdr allele does not segregate with molecular forms in Benin.