**2.1 Study sites**

The study described here was carried out in the villages of Tiemelekro (geographical coordinates: 6500 N, -4170 W) and Zatta (6880 N, -5390 W), located in central Côte d'Ivoire (Figure 1). A detailed description of Tiemelekro, including climatic conditions, current health care delivery structures and key demographic and socioeconomic indicators, has been presented recently (Girardin et al., 2004). Zatta is located 7 km north-west of Yamoussoukro, the capital city of Côte d'Ivoire. The mean annual temperature in this village is 26.5C and the mean annual precipitation is 1280 mm. There is a long rainy season between April and July and a shorter one in October/November. A dispensary, run by two local nurses, is located in Zatta and also covers nearby settlements. Two small dams were constructed in this village in the mid-1970s. Since 1997, a very large irrigated rice field has been cultivated on an estimated surface area of 36 ha, in close proximity to human habitations. However, due to unstable socio-political conditions and a farmers' conflict over land, rice irrigation was interrupted in 2000 and again in 2003/2004.

Living conditions and several of the investigated household characteristics are comparable between the two study villages. For example, similar proportions of houses utilized ironcorrugated sheets as roofing material (93.8% in Tiemelekro vs. 92.9% in Zatta), and had running water at home (74.1% vs. 65.4%). On the other hand, improved sanitation facilities were less prominent in Tiemelekro than in Zatta (17.0% vs. 47.6%). With regard to personal protective measures against mosquito bites, the proportion of people sleeping under a bednet was similarly low in both villages (8.4–11.2%), whereas use of fumigating coils was much more pronounced in Zatta (47.3%) when compared to Tiemelekro (9.1%).
