The diagnosis of malaria is established by the identification oforganisms on stained smears of peripheral blood. In nonimmune persons, symptoms typically occur 1 to 2 days beforeparasites are detectable on blood smear. Although P. falciparumis most likely to be identified from blood during a febrile paroxysm, the timing of the smears is less important than obtainingsmears several times each day over 3 successive days. Both thickand thin blood smears should be examined. The concentration of erythrocytes on a thick smear is approximately 20 to 40 times greater than that on a thin smear. Thick smears are used to scan large numbers of erythrocytes quickly. Thin smears allow for positive identification of the malaria species and determinationof the percentage of infected erythrocytes, which also is usefulin following the response to therapy. Rapid diagnostic tests mayemerge as point of care tests in the near future.
The most important aspect of diagnosing malaria in children isto consider the possibility of malaria in any child who has fever,chills, splenomegaly, anemia, or decreased level of consciousness with a history of recent travel or residence in an endemicarea, regardless of the use of chemoprophylaxis. The differential diagnosis is broad and includes many infectious diseases,such as typhoid fever, tuberculosis, brucellosis, relapsing fever,infective endocarditis, influenza, poliomyelitis, yellow fever,trypanosomiasis, kala-azar, and amebic liver abscess.
Table 123-1 Characteristics of Plasmodium Species Causing Malaria CHARACTERISTIC P. FALCIPARUM P. VIVAX P. OVALE P. MALARIAE P. KNOWLESI Exoerythrocytic cycle 5.5–7 days 6–8 days 9 days 12–16 days 8-9 days Erythrocytic cycle 48 hours 42–48 hours 49–50 hours 72 hours 24 hours
Erythrocyte Young erythrocytes, Reticulocytes Reticulocytes Older erythrocytes Older erythrocytes preference but can infect all
Duration of untreated 1–2 years 1.5–4 years (includes 1.5–4 years (includes 3–50 years Unknown infection
Usual periodicity of None 48 hours 48 hours 72 hours 24 hours febrile attacks
Duration of febrile 16–36 hours (may be 8–12 hours 8–12 hours 8–10 hours Unknown paroxysm longer)
Adapted from Strickland GT: Malaria. In Strickland GT, editor: Hunter’s Tropical Medicine, ed 7, Philadelphia, 1991, WB Saunders, p 589.
Oral chloroquine is the recommended treatment except for chloroquine-resistant P. falciparum. Either atovaquone-proguanil (Malarone) or artemether-lumefantrine (Coartem) is an appropriate first-line therapy for malaria acquired in areas of chloroquine resistance. Specific treatment should be guided by where the patient acquired the infection and the local resistance patterns. Patients with malaria usually require hospitalization and may require intensive care unit admission. Quinidine gluconate is the only drug available in the United States that is used for parenteral treatment.
Cerebral malaria is a complication of P. falciparum infection and a frequent cause of death (20% to 40% of cases), especially among children and nonimmune adults. Similar to other complications, cerebral malaria is more likely to occur among patients with intense parasitemia (>5%). Other complications include splenic rupture, renal failure, severe hemolysis (blackwater fever), pulmonary edema, hypoglycemia, thrombocytopenia, and algid malaria (sepsis syndrome with vascular collapse).