Résumé
La dengue sévit au Vietnam depuis 50 ans sur un mode endémoépidémique. Le Sud Vietnam connaît chaque année d’importantes épidémies pendant la saison des pluies, avec une morbidité et une mortalité élevées, notamment chez les jeunes enfants. La seule mesure de prévention est la lutte antivectorielle, mais elle est souvent mise en oeuvre trop tard ou sans discernement. L’objectif de ce travail était de rechercher, en phase pré-épidémique, l’existence de variations significatives des indices vectoriels permettant de prévoir les flambées de dengue. C’est une étude descriptive transversale, répétée une fois par mois pendant quatre mois (de mars à juin) dans le village de Locthuan (province de Ben Tre) dans le delta du Mékong. Les moustiques adultes ont été capturés dans 30 maisons et les larves dans les réservoirs d’eau de 50 maisons. Les densités vectorielles ont été calculées selon les indices recommandés par l’OMS. Une analyse virologique a été effectuée sur les lots d’Aedes femelles et de larves afin de déterminer les taux d’infection virale. Les captures de moustiques adultes ont rapporté 496 spécimens dont 329 Aedes, 139 Culex et 28 anophèles. Aedes aegypti était présent dans 63 % des maisons visitées avec une densité moyenne de 1,8 moustique par maison. L’augmentation des indices imaginaux au cours des quatre mois n’était pas significative. L’enquête sur les gîtes larvaires d’Ae. aegypti a identifié 1292 réservoirs d’eau dans lesquels 71 569 spécimens de larves ont été collectés. La valeur des indices « maison », « récipients » [IR] et Breteau [IB] augmentait chaque mois, ce dernier passant de 166 à 442. Cette augmentation était significative pour IR et IB. Les gîtes larvaires étaient surtout intradomiciliaires, constitués de jarres en terre. La densité des larves d’Ae. aegypti dans les réservoirs augmentait aussi de façon significative au cours des quatre mois. Elle était corrélée à l’absence de couvercle et de prédateurs. La mise en culture de 15 lots de femelles adultes et de 29 lots de larves d’Ae. aegypti n’a pas permis d’isoler de virus de la dengue. Le haut niveau des indices stégomyiens d’Ae. aegypti dans ce village du Sud Vietnam et leur augmentation avant la saison des pluies décrivent une situation à haut risque épidémique, mais ne permettent pas de prévoir la survenue d’une flambée en l’absence d’isolement viral chez les moustiques. Ils justifient la conduite d’une stratégie intégrée de lutte antivectorielle tout au long de l’année.
Abstract
Dengue has emerged in Vietnam 50 years ago and since has become endemo-epidemic throughout the whole country. Each year, major epidemics of dengue fever (DF) and dengue hemorrhagic fever (DHF) hit South Vietnam during the rainy season, causing significant morbidity and mortality, especially among young children. The only preventive measure is vector control, but it is often implemented too late or indiscriminately. The aim of this study was to investigate, in the pre-epidemic stage, the existence of significant changes in vector indices, which will predict DF/DHF outbreaks. We conducted a descriptive transversal study, repeated once a month for four months (March to June) in the village of Locthuan (province Ben Tre) in the Mekong’s delta. Adult mosquitoes were caught in 30 houses, and larvae were collected in water holding containers of 50 houses. The houses were randomly selected. Vector densities were calculated according to the indices recommended by WHO. Virological analysis was carried out on lots of female Aedes and larvae in order to determine viral infection rates. Catches of adult mosquitoes collected 496 specimens including 329 Aedes, 139 Culex and 28 Anopheles. Aedes aegypti was present in 63% of visited homes that is an average density of 1.8 mosquitoes per house. The increase in imaginal indices during the 4 months was not significant. The survey of breeding sites of Ae. aegypti identified 1292 water containers in which 71,569 larval specimens were collected. The values of house index, container index [CI] and Breteau index [BI] increased each month, the latter from 166 to 442. This increase was significant for CI and BI. Breeding sites were mostly intra-home, mainly consisting of large and small ceramic jars. Larval density of Ae. aegypti in the containers also increased significantly over the 4 months. It was correlated with the lack of cover and predators such as Mesocyclops spp., Micronecta spp. and larvivorous fishes. Cultivation of 15 pools of 10 adult females and 29 pools of larvae (ie 1088 specimens) of Ae. aegypti failed to isolate dengue virus. The high Stegomyia indices measured in this South Vietnamese village and their increase before the rainy season reflect a situation at high risk of epidemics but cannot predict the occurrence of an outbreak in the absence of virus isolation from mosquitoes. They justify conducting an integrated vector control throughout the year.
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Nguyen, T.P.Q., Luu, L.L., Vu, T.Q.H. et al. Augmentation des indices vectoriels en période pré-épidémique de dengue à Ben Tre, Sud Vietnam. Bull. Soc. Pathol. Exot. 104, 313–320 (2011). https://doi.org/10.1007/s13149-011-0154-4
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DOI: https://doi.org/10.1007/s13149-011-0154-4