Malaria is an infectious illness caused by a parasite. The parasite is transmitted to humans by the bites of infected mosquitos. Malaria frequently causes severe illness, including a high temperature and trembling chills. In some cases, it can be fatal. The three main types of malaria are: falciparum malaria, which is the most serious type; vivax malaria, which can sometimes cause problems or become active again after years of inactivity; and benign tertian malaria, which occurs twice a month with no symptoms between episodes. Severe forms of malaria are treated with drugs called antimalarials. Milder cases require only rest and medication to reduce fever and other symptoms. People who recover from malaria remain immune to it for life. However someone who recovers from one form of malaria may become susceptible to another form if they do not develop resistance. Resistant strains of malaria exist but are not common. If you have recently recovered from malaria, avoid areas where there is active mosquito transmission of the disease. In endemic areas people often have repeated exposures to malaria without getting sick. This is because they have developed some degree of immunity to the disease. There are several ways in which people under 30 are more likely to get malaria than older people: 1 They make up a large proportion of the world's population.