Geographic Distribution:

Malaria generally occurs in areas where environmental conditions allow parasite multiplication in the vector.  Thus, malaria is usually restricted to tropical and subtropical areas (see map) and altitudes below 1,500 m.  However, this distribution might be affected by climatic changes, especially global warming, and population movements.  Both Plasmodium falciparum and P. malariae are encountered in all shaded areas of the map (with P. falciparum by far the most prevalent).  Plasmodium 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; however these two species are not always distinguishable on the basis of morphologic characteristics alone; the use of molecular tools will help clarify their exact distribution.

Clinical features:
The symptoms of uncomplicated malaria can be rather nonspecific 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.