Malaria environmental risk assessment in Eritrea

Agroclimactic data and growing degree day-water balance spatial analysis were used to describe potential risk of malaria based on climate suitability for the Plasmodium falciparum-Anopheles arabiensis (Patton) system in Eritrea. A model based on monthly accumulation of the product of two climate gradients, growing degree days (mean temperature-16°C base temperature) and the ratio of monthly rain/potential evapotranspiration (R/PET) was most significantly correlated with infection prevalence data from a 2000-2001 survey of malaria at 173 sites in Eritrea. Results indicate: 1) optimum conditions for malaria transmission occur at sites with moderate temperatures (20-30°C) and 6-11 potential malaria generations per year during months in which soil moisture exceeds a threshold of 20% of holding capacity, 2) additional consideration of a hydrologic gradient (R/PET), with thermal factors, most accurately reflected field malaria risk, 3) there is a need to systematically account for heat stress at high temperatures that result in decreasing suitability for propagation and transmission of malaria, and 4) marked differences in seasonality of transmission pattern found in Eritrea can be predicted, using growing degree day-water balance models. As a regional-scale component of more comprehensive risk assessment methods, the climate-based models developed ay enable future near real-time disease prediction and intervention by health system managers.