The true incidence is higher, since it is thought that only a third to one-half of cases are being reported. Symptoms can develop as early as 6-8 days after infection or as late as several months after leaving a malarious area, after antimalarial drugs are discontinued. All febrile patients should be asked about travel history. If they have been exposed to malaria, they should be assumed to have it until proven otherwise, and definitive laboratory assessment initiated. If diagnosis is delayed, malaria can progress from an asymptomatic state to death in as little as 36-48 hours.
Malaria is caused by protozoan parasites of the genus Plasmodium.
Four species of Plasmodium are known to be responsible for disease in humans - Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale and Plasmodium malariae. P. falciparum is the most widespread and severe form. If untreated it can lead to fatal cerebral malaria. The definitive diagnosis of malaria is currently made by the morphological demonstration and identification of malarial parasites in stained blood smears. The preparation of both thick and thin films is recommended.