Major variations in malaria exposure of travellers in rural areas: an entomological cohort study in western Côte d'Ivoire

Abstract

Background: Malaria remains a major threat, to both travellers and military personnel deployed to endemic areas. The recommendations for travellers given by the World Health Organization is based on the incidence of malaria in an area and do not take the degree of exposure into account. The aim of this article is to evaluate the exposure of travellers by entomologic methods, which are the commonly used measures of the intensity of malaria transmission.

Methods: From February 2004 to June 2004, five groups of 30 military personnel were stationed in up to 10 sites in western Côte d'Ivoire, from one week to several months. Adult mosquitoes were collected by human landing catches at each site during the five months and the level of exposure to malaria transmission of each group was estimated.

Results: The level of transmission varied from one site to another one from less than one to approximately more than 100 infective bites per month. In the majority of sites, at least two anopheline species were involved in transmission. The cumulative EIR over the study period varied according to the groups from 29 infected bites per person/per mission to 324.

Conclusion: The level of malaria transmission and malaria risk varies widely (varying by a factor of eleven) between groups of travellers travelling in the same region and at the same time. Physicians involved in travel medicine or supporting expatriated populations or refugees should consider this heterogeneity and emphasize the importance of combining appropriate measures, such as chemoprophylaxis and protective measures against mosquitoes.

Figure 1

Schematic map of Côte d'Ivoire showing the study area.

Figure 2

Distribution of Anopheles gambiae s.s. molecular forms populations and respective CSP rates. Sample percentage of the M and S molecular forms in each population are indicated in black and white respectively. * represents the presence of one hybrid M/S CSM: CSP rates of M molecular form An. gambiae s.s. CSS: CSP rates of S molecular form An. gambiae s.s.

Figure 3

The nocturnal biting cycle of An. gambiae s.l., An. funestus s.l. and An. nili s.l. by permanent sites. Black represents the percentage of bites by hour of An. gambiae s.l., and white and grey bars represent the percentage of bites by hour An. funestus s.l. and An. nili s.l, respectively.

Figure 4

The average accumulated number of infected anopheline bites sustained by a platoon of French military personnel.