Immunity

Lack of immunity or low immunity to malaria in the human population makes epidemics more likely. In areas of unstable transmission, such as Ethiopia, population immunity is generally low, so epidemics are more likely. Indeed, malaria is a risk in 75% of the villages in Ethiopia and epidemics can occur in those villages.

Migration

Movements of people can contribute to malaria epidemics in two ways. First, people with malaria moving into an area where malaria has been controlled or eliminated can be sources of Plasmodium parasites for local mosquitoes, precipitating an epidemic. Second, non-immune people moving to areas where malaria is highly endemic can cause an apparent epidemic, as they are more susceptible than the local population to malaria.

Interruption of vector control efforts

In Study Sessions 9, 10 and 11 you learned that larval control, indoor residual spraying (IRS) of households with insecticides, and use of insecticide treated nets (ITNs), are important malaria prevention tools. If the implementation of these measures is stopped, vector populations and thus malaria transmission may increase dramatically. Similarly, epidemics can occur if vectors become resistant to insecticides and are no longer killed by spraying.