[High proliferation of An. gambiae and An. funestus larvae in irrigated and non-irrigated rice fields in the Western forest region of Côte-d'Ivoire]. / Forte prolifération de larves d'An. gambiae et An. funestus en milieux rizicoles irrigués et non irrigués dans la région forestière ouest de la Côte-d'Ivoire.

Entomological surveys were conducted in the forest region of western Côte-d'Ivoire from November 1998 to December 1999 in order to study the ecology of mosquito breeding sites and bioecology of Culicidae. Three following agro-systems were considered: landscaped lowland (R0), the lowland with one growing season of rice per year (R1) and the lowland with two seasonal production of irrigated rice field per year (R2). Two villages were selected by agro-system, and cross-sectional entomological surveys were conducted every six weeks in each village. A total of 5,839 larvae of mosquitoes were collected in the different categories of breeding sites surveyed. From these larvae, 2,199 imagos emerged, giving an emergence rate equal to 37.7%. Nine species belonging to three genera were identified. The genus Anopheles with 1,828 larvae represented 83.1% of the total. Five anophelinae species were identified. An. ziemanni was the most abundant species with 751 larvae (32.5% of the total). An. funestus with 531 larvae represented 24.1% of the total. Larvae from this species were collected in river with raised vegetation and in irrigated rice field at transplanting and cut stages. About 559 larvae of An. gambiae representing 25.4% of the total were collected from artificial breeding sites, particularly in rice fields after the planting stage. Additionally, 38,626 anthropophilic mosquitoes were collected on 936 mannight catches in the study area. Thirty species belonging to seven genera were identified in the three agro-systems. In the villages of the agro-system R0, 2,675 mosquitoes were collected on landing catches. In the villages of the agro-ecosystem R1, 11,311 mosquitoes were collected, which was 4.2 higher than the number collected in the village of agro-system R0 for the same sampling effort. In the village of the agro-system R2, 24,640 mosquitoes were collected, which was 9.2 higher than the number collected in the agro-system R0 and 2.2 higher than the number collected in the agro-system R1. In the villages of agrosystems R0, R1 and R2, An. gambiae represented respectively 72.1%, 56% and 58.3% of anophelinae species collected, whereas An. funestus represented 25.6%, 40% and 31.9% of anophelinae species collected, in the same agrosystems, respectively. These results showed that areas of irrigated rice fields favoured the development of larvae from An. gambiae and An. funestus.

Contribution of Anopheles funestus, An. gambiae and An. nili (Diptera: Culicidae) to the perennial malaria transmission in the southern and western forest areas of Côte d'Ivoire.

The involvement of members of the Anopheles gambiae complex Giles and An. funestus Giles and An. nili Theobald groups in the transmission of Plasmodium falciparum was recently investigated in the villages of Gbatta and Kpéhiri, which lie, respectively, in forest areas in the west and south of Côte d'Ivoire. Adult female mosquitoes were collected, using human landing catches, inside and outside dwellings. After identification and dissection, the heads and thoraces of all the anopheline mosquitoes were tested, in an ELISA, for circumsporozoite protein (CSP). All the female anopheline mosquitoes collected and identified to species using PCR were found to be An. gambiae s.s., An. nili s.s. or An. funestus s.s., with An. gambiae s.s. and An. funestus s.s. predominant in Gbatta but An. nili s.s. the most common species in Kpéhiri. In Gbatta, 3·1% of the female An. gambiae collected, 5·0% of the female An. funestus and 1·8% of the female An. nili were found CSP-positive. The corresponding values in Kpéhiri were even higher, at 5·9%, 6·2% and 2·4%, respectively. The estimated entomological inoculation rates (EIR) were very high: 302 infected bites (139 from An. gambiae, 146 from An. funestus and 17 from An. nili)/person-year in Gbatta and 484 infected bites (204 from An. gambiae, 70 from An. funestus and 210 from An. nili)/person-year in Kpéhiri. In Gbatta, An. gambiae s.s. was responsible for most of the rainy-season transmission while An. funestus became the main malaria vector in the dry seasons. In Kpéhiri, however, An. nili appeared to be the main vector throughout the year, with An. gambiae of secondary importance and An. funestus only becoming a significant vector during the rainy season. Although, in both study sites, intense transmission was therefore occurring and the same three species of anopheline mosquito were present, the relative importance of each mosquito species in the epidemiology of the human malaria at each site differed markedly.

[Bio-ecological characteristics of Anopheles gambiae s.s. in irrigated rice fields of central Côte d'Ivoire]. / Caractéristiques bioécologiques d'Anopheles gambiae s.s. en zones de riziculture irriguée au centre de la Côte d'Ivoire.

This longitudinal entomological survey was conducted between September 2008 and September 2009 in the villages of Abokro and Yaokoffikro located in an irrigated rice farming area of central Côte d'Ivoire. The purpose was to investigate the bio-ecological characteristics of Anopheles gambiae s.s. during the gonotrophic cycle. In both villages, adult mosquitoes were captured in 72 light traps, collected on humans subjects at a rate of 72 man-night from 6 p.m. to 6 a.m., and knocked down using pyrethroid spray inside 60 sentinel houses in the early morning. A total of 10,312 adult mosquitoes were collected in Abokro and 7,662 in Yaokoffikro. Anopheles was the dominant genus at both locations. Light traps were three times more efficient in Abokro than in Yaokoffikro. In both places, An. gambiae s.s. biting rates increased gradually up to a peak observed between midnight and 1 a.m. In Abokro, most An. gambiae s.s. were collected inside sleeping rooms. The endophagic rate and indoor resting density was 67.4% (n = 4798) and 14.9 females per bedroom per night, respectively, in Abokro as compared to 49.3% (n = 6775) and 2.9 females per bedroom per day, respectively, in Yaokoffikro.

Spatial dispersion and characterisation of mosquito breeding habitats in urban vegetable-production areas of Abidjan, Côte d'Ivoire.

Although urban agriculture (UA) in the developing world may enhance nutrition and local economies, it may also lead to higher densities of mosquito breeding sites and, consequently, to increased transmission of malarial parasites. If targeted interventions against malaria vectors are to be successful in urban areas, the habitats that support Anopheles breeding need to be identified and detected. Mosquito breeding sites have recently been characterised, and the factors associated with productive Anopheles habitats identified, in market gardens of Abidjan, Côte d'Ivoire. Two surveys were conducted in seven vegetable-production areas, one towards the end of the rainy season and one during the dry season. A standardized methodology was used for habitat characterisation and the detection of Anopheles larvae and mosquito pupae. Overall, 454 and 559 potential mosquito-breeding sites were recorded in the rainy-season and dry-season surveys, respectively. In the rainy season, Anopheles larvae and mosquito pupae were found in 29.7% and 5.5% of the potential breeding sites, respectively, whereas the corresponding percentages in the dry season were 24.3% and 8.6%. The potential breeding sites in an agricultural zone on the periphery of Abidjan were those least likely to be positive for Anopheles larvae and mosquito pupae whereas 'agricultural trenches' between seedbeds were the sites most likely to be positive. In a spatially-explicit Bayesian multivariate logistic-regression model, although one out of every five such wells was also found to harbour Anopheles larvae, irrigation wells were found to be the least productive habitats, of those sampled, for pupae. In the study area, simple and cost-effective strategies of larval control should be targeted at agricultural trenches, ideally with the active involvement of local stakeholders (i.e. urban farmers and urban agricultural extension services).

Effects of seasonality and irrigation on malaria transmission in two villages in Côte d'Ivoire.

The seasonality of malaria transmission was investigated in two villages in central Côte d'Ivoire: one usually with irrigated rice farming (Zatta) and one without (Tiémélékro). Adult mosquitoes were collected, from February 2002 to August 2005, inside and outside sentinel houses. In Tiémélékro, the biting rate of Anopheles gambiae s.s. showed a significant difference between the dry and rainy season only in 2003 (P<0.001). The corresponding rates for An. funestus s.s. showed significant seasonal differences in both 2002 and 2003 (P<0.001 for each year). In Zatta in 2003-2004, when irrigated rice farming was interrupted, there was no significant difference between the An. gambiae s.s. biting rates recorded in the dry and rainy seasons. In both 2002 and 2005, however, when irrigated rice farming was practised, the An. gambiae s.s. biting rate recorded in Zatta during the rainy season was significantly higher than that seen in the dry season (P<0.001 for each year). With just one exception (in Tiémélékro in 2005, the prevalence of Plasmodium infection in the An. funestus was significantly higher in the rainy season than in the dry season), no significant seasonal differences were seen in the prevalences of Plasmodium infection among the An. gambiae or An. funestus. In conclusion, although malaria transmission is quite stable in central Côte d'Ivoire throughout the year, it can be distinctly modified by irrigated rice farming.

[Malaria transmission in an area of high coverage with long lasting insecticidal nets in central Côte d'Ivoire]. / Transmission du paludisme en zone de haute couverture en moustiquaires imprégnées d'insecticide de longue durée, au centre de la Côte d'Ivoire.

The purpose of this study was to assess malaria transmission in an area of high coverage with long-lasting insecticidal nets (LLINs) in central Côte d'Ivoire. Two four-day larva collections were carried out in April and July 2008. Adult mosquito samples were collected by conducting human bait catches during a total of 80 man-nights. Vector infection rates were determined using an ELISA circumsporozoite antibody test. A total of 1582 mosquitoes were captured. Mansonia was the dominant genus in the culcidian fauna followed by Anopheles that was dominant in the anopheline fauna. The only Plasmodium vector was An. gambiae s.l. The high household bednet coverage rate probably accounted for the relatively low biting rate: 0.75 to 4.15 bites per person per night (b/p/n). Households not using bednets appear to have benefited from a passive protection effect associated with high LLIN coverage. Biting and entomological inoculation rates were 2.25 to 4.1 b/p/n (range) and 0.184 ib/p/n respectively in households that did not use LLINs and 0.75 to 4.15 b/p/n (range) and 0.341 ib/p/n respectively in households using LLINs.

[Agricultural activities and malaria transmission in two eco-epidemiological settings in central Côte d'Ivoire]. / Pratiques agricoles et transmission du paludisme dans deux zones éco-épidémiologiques au centre de la Côte d'lvoire.

We comparatively studied the dynamics of malaria transmission in the villages of Zatta (located in close proximity to an irrigated rice perimeter) and Tiémélékro (rural area with traditional agriculture), central Côte d'Ivoire. In the former village, the irrigated rice farming had been interrupted in 2003/2004 due to a farmers' conflict over land. In each village, mosquitoes were collected by human landing catches at night in sentinel houses. Anopheles gambiae was the predominant malaria vector, followed by An. funestus. In Zatta, the return to an irrigated rice farming in January 2005 was paralleled by a significant increase of the entomological inoculation rate (EIR) ranging from 38 infective bites per person per year (ib/ply) in 2003 to 295 ib/ply in 2005. In Tiémélékro high EIRs were found in 2003 (342 ib/ply) and 2005 (572 ib/ply). Our findings confirm that changes in irrigated rice agriculture influence malaria transmission dynamics, and call for control measures that are readily adapted to local eco-epidemiological settings.

Effect of an armed conflict on human resources and health systems in Côte d'Ivoire: prevention of and care for people with HIV/AIDS.

In September 2002, an armed conflict erupted in Côte d'Ivoire which has since divided the country in the government-held south and the remaining territory controlled by the 'Forces Armées des Forces Nouvelles' (FAFN). There is concern that conflict-related population movements, breakdown of health systems and food insecurity could significantly increase the incidence of HIV infections and other sexually-transmitted infections, and hence jeopardize the country's ability to cope with the HIV/AIDS epidemic. Our objective was to assess and quantify the effect this conflict had on human resources and health systems that provide the backbone for prevention, treatment and care associated with HIV/AIDS. We obtained data through a questionnaire survey targeted at key informants in 24 urban settings in central, north and west Côte d'Ivoire and reviewed relevant Ministry of Health (MoH) records. We found significant reductions of health staff in the public and private sector along with a collapse of the health system and other public infrastructures, interruption of condom distribution and lack of antiretrovirals. On the other hand, there was a significant increase of non-governmental organizations (NGOs), some of which claim a partial involvement in the combat with HIV/AIDS. The analysis shows the need that these NGOs, in concert with regional and international organizations and United Nations agencies, carry forward HIV/AIDS prevention and care efforts, which ought to be continued through the post-conflict stage and then expanded to comprehensive preventive care, particularly antiretroviral treatment.

Malaria transmission dynamics in central Côte d'Ivoire: the influence of changing patterns of irrigated rice agriculture.

The dynamics of malaria transmission was studied comparatively in the villages of Zatta and Tiemelekro, central Cote d'Ivoire, from February 2002 to August 2003. Prominent agroecosystems in these villages are irrigated rice growing and vegetable farming, respectively. Mosquitoes (Diptera: Culicidae) were collected on human bait at night and by pyrethrum knock-down spray sheet collections at four randomly selected sentinel sites in each village. In 2002, for a total of 96 man-nights per village, 7716 mosquitoes were collected in Zatta and 3308 in Tiemelekro. In 2003, with half the sampling effort, 859 and 2056 mosquitoes were collected in Zatta and Tiemelekro, respectively. Anopheles gambiae Giles s.l. was the predominant mosquito and the key malaria vector throughout, followed by An. funestus Giles. Anthropophily among adult female Anopheles exceeded 95% in both villages. Comparison between years revealed that the biting rate of An. gambiae s.l. in Zatta decreased several-fold from 49.3 bites per person per night (b/p/n) in 2002 to 7.9 b/p/n in 2003 (likelihood ratio test (LRT) = 1072.66; P < 0.001). Although the biting rate remained fairly constant in Tiemelekro, the difference between years was significant (16.1 vs. 18.2 b/p/n; LRT = 148.06; P < 0.001). These observations were paralleled by a marked decrease in the infective rate of An. gambiae s.l. in Zatta (4.6-1.2%), and an increase in Tiemelekro (3.1-7.6%). Meanwhile, the entomological inoculation rate of An. gambiae s.l. decreased 21-fold in Zatta, from 789 to 38 infective bites per person per year (ib/p/y), whereas it remained high in Tiemelekro (233 vs. 342 ib/p/y). The interruption of irrigated rice growing in Zatta in 2003, consequential to a farmers' conflict over land, might be the underlying cause for the significant reduction in malaria transmission, whereas more stable conditions occurred in Tiemelekro.