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

Abstract

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.

Thorsellia anophelis is the dominant bacterium in a Kenyan population of adult Anopheles gambiae mosquitoes

“…Since the bulk of the current global burden of malaria is borne by countries in Africa and since flooded rice paddies serve as larval habitats and are a known risk factor for malaria transmission (Koudou et al, 2005), we selected a rice-growing region in central Kenya (Mwea) as our study site. Rice paddy water and An.…”

Spatial Analysis of Malaria Transmission Parameters in the Rice Cultivation Area of Office Du Niger, Mali

“…These are also the most common species in western African rice cultivation areas. 19,20 Among these two species, An. gambiae s.l was predominant, accounting on average for 90% (n ‫ס‬ 366,657) and was particularly abundant during the rainy season of 1999 and 2000 and the dry hot season of 1999 (second agricultural cycle).…”

“…Whereas a negative association between adult density and HBI has been observed in the Office du Niger, Mali 6,19 and Burkina Faso, 23 a recent study conducted in Côte d'Ivoire suggested a positive association reporting HBI up to 95% during high-density periods. 20 The vectorial capacity was relatively low with a seasonal and village-to-village variation. The median vectorial capacity was higher in the non-renovated zone of Molodo than in the renovated zones of Niono and Ndebougou, but the statistical significance was borderline.…”

“…This is almost certainly due to the current cultivation methods, which are characterized by overlaps between several agricultural cycles. 20,21 In spite of the high densities during the rainy season, the potential for transmission was lower than in the dry season. This could be explained by the decreases in HBI (a measure of vector-human contact) and PR (a measure of vector longevity) during that period (Figure 2).…”

Pratiques agricoles et épidémiologie du paludisme en zone soudano-sahélienne du Cameroun

“…Cependant, même s'ils permettent une augmentation importante de l'énergie, de la production de céréales et de produits maraîchers, les barrages hydroagricoles ont parfois des répercussions profondes sur l'endémie palustre, du fait de la création des gîtes larvaires favorables aux vecteurs du paludisme [20,21,28]. Au Cameroun, l'État a réalisé la construction d'une dizaine de barrages hydrauliques dans les années 1980.…”