An infection initially presents in nonspecific symptoms including but not limited to; headache, fatigue, nausea, and fever. Untreated malaria especially caused by P. falciparum, can quickly develop to a lethal outcome. Therefore, it is important to obtain an etiological diagnosis as quickly as possible by microscopic detection of the parasites in the blood, and to initiate effective treatment. Prophylactic measures are essential for travelers to regions where malaria is endemic.
LIFE CYCLE: The life cycle of malaria plasmodia includes phases of asexual multiplication in the human host and sexual reproduction and formation of sporozoites in the vector, a female Anopheles mosquito. The developmental cycle within the human host is as follows:
Infection and exoerythrocytic development: Humans are infected through the bite of an infected female Anopheles mosquito that inoculates spindle-shaped sporozoites into the bloodstream. Only a small number of sporozoites are needed to cause an infection in humans (about 10 for P. falciparum). Within about 15–45 minutes of inoculation, the sporozoites of all Plasmodium species reach the liver in the bloodstream and infect hepatocytes, in which asexual multiplication takes place. In this process, the sporozoite develops into a multinuclear, large schizont (meront) described as a tissue schizont. Following cytoplasmic division 2000 (P. malariae) to 30 000 (P. falciparum) merozoites are produced. This development takes six (P. falciparum) to 15 (P. malariae) days.
Shortly thereafter, the tissue schizonts release the merozoites, which then infect erythrocytes.
Erythrocytic development: The merozoites produced in the liver are released into the bloodstream where they infect erythrocytes, in which they reproduce asexually.
PATHOPHYSIOLOGY: Fever is induced when the schizonts burst and when many red blood cells are destroyed at once, causing the typical, intermittent fever attacks (“malarial paroxysm”). After one or more schizogonic generations, some of the plasmodia in each generation develop into sexual forms, the male microgamonts, and female macrogamonts. These sexual forms (gametocytes) persist for a certain period in the blood, after which those not taken up by blood-sucking Anopheles females die.
CLINICAL MANIFESTATIONS: The clinical manifestations of malaria are caused by the asexual erythrocytic stages of the plasmodia and therefore commence shortly after parasitemia at the earliest. The incubation periods vary, depending on the Plasmodium species involved, from seven to 35 days after infection. These periods can, however, be extended by weeks or even months, particularly if the infection is suppressed by prophylactic medication. The clinical manifestations of malaria depend on a number of different factors, above all the Plasmodium species and immune status of the patient. The Plasmodium species with the most pronounced pathogenicity is Plasmodium falciparum, which causes “malignant tertian malaria” (malaria tropica), whereas the other Plasmodium species cause milder forms (“benign malaria”).
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