Spatial and temporal variation of malaria entomological parameters at the onset of a hydro-agricultural development in central Côte d'Ivoire.
BACKGROUND
A deeper understanding of the ecology and small-scale heterogeneity of malaria transmission is essential for the design of effective prevention, control and elimination interventions. The spatial and temporal distribution of malaria vectors was investigated in five villages in close proximity to a hydro-agricultural system in Côte d'Ivoire over the course of construction and the early phase of irrigated rice farming.


METHODS
The study was carried out in five villages (Raffierkro, N'Douakro, Ahougui, Kpokahankro, Koffikro) near Bouaké, central Côte d'Ivoire, between early 2007 and late 2009. In each village, mosquitoes were collected by human landing catches and identified morphologically at genus and species level, and entomological parameters were determined. Plasmodium infection was assessed by dissection and an enzyme-linked immunosorbent assay.


RESULTS
A total of 19,404 mosquitoes belonging to the genus Anopheles were sampled during 328 human-night catches. Before the construction of the hydro-agricultural system, comparable densities of Anopheles gambiae were observed in all villages. In subsequent years, densities in Raffierkro and Ahougui were significantly higher than the other villages [Kruskal-Wallis (KW) test = 31.13, p < 0.001]. The density of Anopheles funestus in the five villages was comparable in the early stage of the project, while a high density was reported in Koffikro at the end (KW test = 11.91, p = 0.018). Transmission of Plasmodium falciparum is perennial in the study area. Over the course of the study, high entomological inoculation rates (EIRs) were found: 219-328 infectious bites per person per year with An. gambiae. For An. funestus considerably lower EIRs were observed (5.7-39.4). Changing patterns of An. gambiae were not correlated with malaria transmission.


CONCLUSIONS
In this study setting, located in the bioclimatic transition zone of Côte d'Ivoire, rice cultivation was not observed to increase malaria transmission. The entomological parameters recorded until the onset of rice-growing activities in a hydro-agricultural system presented considerable heterogeneity both in space and time; a strong increase of Anopheles mosquitoes was observed in two of the five villages located in close proximity to the dam and irrigated rice fields. Malaria still is a main public health problem in all villages that require adequate control measures.
Unité de Formation et de Recherche Biosciences, Université Félix Houphouët-Boigny, 22 BP 522, Abidjan 22, Côte d'Ivoire. diaknarose@yahoo.fr.
Nana R
NR
Diakité
Unité de Formation et de Recherche Biosciences, Université Félix Houphouët-Boigny, 22 BP 522, Abidjan 22, Côte d'Ivoire. coulnegno1@yahoo.fr.
Négnorogo
N
Guindo-Coulibaly
Unité de Formation et de Recherche Biosciences, Université Félix Houphouët-Boigny, 22 BP 522, Abidjan 22, Côte d'Ivoire. akremaurice@yahoo.fr.
Akré M
AM
Adja
Unité de Formation et de Recherche Biosciences, Université Félix Houphouët-Boigny, 22 BP 522, Abidjan 22, Côte d'Ivoire. mamadou_ouatt@yahoo.fr.
Mamadou
M
Ouattara
Unité de Formation et de Recherche Biosciences, Université Félix Houphouët-Boigny, 22 BP 522, Abidjan 22, Côte d'Ivoire. couljeanvae@yahoo.fr.|Département Environnement et Santé, Centre Suisse de Recherches Scientifiques en Côte d'Ivoire, 01 BP 1303, Abidjan 01, Côte d'Ivoire. couljeanvae@yahoo.fr.|Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, P.O. Box, 4002, Basel, Switzerland. couljeanvae@yahoo.fr.|University of Basel, P.O. Box, 4003, Basel, Switzerland. couljeanvae@yahoo.fr.
Jean T
JT
Coulibaly
Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, P.O. Box, 4002, Basel, Switzerland. juerg.utzinger@unibas.ch.|University of Basel, P.O. Box, 4003, Basel, Switzerland. juerg.utzinger@unibas.ch.
Jürg
J
Utzinger
Unité de Formation et de Recherche Biosciences, Université Félix Houphouët-Boigny, 22 BP 522, Abidjan 22, Côte d'Ivoire. eliezerngoran@yahoo.fr.|Département Environnement et Santé, Centre Suisse de Recherches Scientifiques en Côte d'Ivoire, 01 BP 1303, Abidjan 01, Côte d'Ivoire. eliezerngoran@yahoo.fr.
Eliézer K
EK
N'Goran
D000383:Agriculture / Q000706:statistics & numerical data*; D000818:Animals; D000852:Anopheles / Q000502:physiology*; D007560:Cote d'Ivoire / Q000453:epidemiology; D003430:Cross-Sectional Studies; D006801:Humans; D007299:Insect Bites and Stings / Q000453:epidemiology; D007303:Insect Vectors / Q000502:physiology*; D008288:Malaria / Q000453:epidemiology* / Q000635:transmission*; D062211:Spatio-Temporal Analysis