Geographic Distribution:
Malaria generally occurs in areas where environmental conditions allow parasite multiplication in the vector.  Malaria today is usually restricted to tropical and subtropical areas and altitudes below 1,500 m., although in the past malaria was endemic in much of North America, Europe and even parts of northern Asia, and today is still present on the Korean peninsula.  However, this present distribution could be affected by climatic changes and population movements.  Plasmodium falciparum is the predominant species in the world.  P. vivax and P. ovale are traditionally thought to occupy complementary niches, with P. ovale predominating in Sub-Saharan Africa and P. vivax in the other areas; but their geographical ranges do overlap.  These two species are not always distinguishable on the basis of morphologic characteristics alone, and the use of molecular tools will help clarify their diagnosis and exact distribution.  P. malariae has wide global distribution, being found in South America, Asia, and Africa, but it is less frequent than P. falciparum in terms of association with cases of infection.  P. knowlesi is found in southeast Asia.

Click here to see a map showing an approximation of the parts of the world where malaria transmission occurs.

Click here to see a table listing malaria risk information and Prophylaxis by Country

Clinical features:
The symptoms of uncomplicated malaria can be rather non-specific and the diagnosis can be missed if health providers are not alert to the possibility of this disease.  Since untreated malaria can progress to severe forms that may be rapidly (<24 hours) fatal, malaria should always be considered in patients who have a history of exposure (mostly: past travel or residence in disease-endemic areas).  The most frequent symptoms include fever and chills, which can be accompanied by headache, myalgias, arthralgias, weakness, vomiting, and diarrhea.  Other clinical features include splenomegaly, anemia, thrombocytopenia, hypoglycemia, pulmonary or renal dysfunction, and neurologic changes.  The clinical presentation can vary substantially depending on the infecting species, the level of parasitemia, and the immune status of the patient.  Infections caused by P. falciparum can progress to severe, potentially fatal forms with central nervous system involvement (cerebral malaria), acute renal failure, severe anemia, or adult respiratory distress syndrome.  Complications of P. vivax malaria include splenomegaly (with, rarely, splenic rupture), and those of P. malariae include nephrotic syndrome.