Malaria is a serious disease which can lead to death. This sometimes fatal disease is caused by a parasite that infects some types of mosquitos, which feed on human blood. People who suffer from malaria have very high fevers, chills and often look like they have the flu.
You avoid the mosquito bites by using a mosquito net or insect repellents with mosquito control (which is basicly spraying insecticides). For tourists and travellers to ares where malaria is common it is advised to use these. A vaccine for malaria does not exists, although they are trying to make one.