Int. J. Environ. Res. Public Health 2011, 8 915 habitat is a function of the ambient temperature [12,19]. Rainfall rises the abundance of the breeding habitat while higher temperature increases the malaria risk by shortening the malaria parasites development-cycle [20]. The average life span of a mosquito carrying malaria parasites is about 21 days. It takes 19 days for the malaria parasite to mature inside the mosquito at 22 degrees Celsius and 8 days to mature at 30 degrees Celsius. Apart from the African highlands and the farthest southern and northern African regions, the annual mean temperature on the African continent is above 25 degrees Celsius [19]. Therefore, the projected increase in mean temperature of about 1.4 to 5.8 degrees Celsius under climate change [21] may result in a faster parasite development and a potentially higher incidence of malaria. Recent studies have attempted to estimate the impact of climate change on malaria prevalence. Ebi et al. [22] studied climate suitability for stable malaria transmission in Zimbabwe under various climate change scenarios based on MARA/ARMA (Mapping Malaria Risk in Africa/Atlas du Risque de la Malaria en Afrique) decision rules. They indicate that changes in temperature and precipitation could alter the geographic distribution of malaria in Zimbabwe, with previously unsuitable regions with dense human populations becoming suitable. Thomson et al. [23] investigated the effect of rainfall and sea surface temperature on malaria incidence in Botswana finding that variability in rainfall and sea temperature accounts for more than two-thirds of the inter-annual variability in malaria incidence. Ndiaye et al. [24] studied relationships between climate variability and malaria mortality in a small region of Senegal from 1984 to 1996. They found that 89.1% of the malaria mortality was observed in August and December which are relatively rainy and warmer months. They found high correlation between rainfall variability and malaria mortality but did not find significant correlation with temperature and humidity variability. Jaenisch and Patz [25] find that malaria prevalence is sensitive to short-term fluctuations in temperature and rainfalls in a way that extreme precipitation events could wash away anopheles mosquito larvae from breeding sites and lead to reduced incidence. This argument means that the relationship between malaria cases and climatic factors is of a nonlinear nature and using linear functions to study such relationship will be misleading. Wandiga et al. [8] found significant correlation between malaria cases and climatic factors in Uganda but implicitly assumed a linear relationship [25]. Zhou et al. [7] pursued a nonlinear relationship study and found that climatic factors were the driving forces behind malaria’s resurgence in highlands of Africa explaining 65 to 81 percent of the variation in number of cases. They also found a statistically significant synergy effect between temperature and precipitation in determining the number of malaria cases in all the regions studied. The study in this paper builds on these previous studies to improve our understanding of the climate-malaria relationship and the potential economic consequences from climate change. We employ socio-economic variables to study how they might affect malaria prevalence along with temperature and precipitation. Some of these variables may exhibit linear relationships while others might involve nonlinearities. To accommodate this we use semi-parametric methods that allow nonlinearity without assuming a priori knowledge of the functional forms governing the process [10,26-28]. Also, semi-parametric methods offer a way to test the validity of the non-linear relationship between climate and malaria prevalence claimed in previous literature [7,23,25] using a nonparametric statistical test [27].