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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.

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.

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.

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.

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.