infectious diseases
Malaria
Symptoms and Signs of Malaria
Theincubation periodis usually 12 to 17 days forP. vivax 9 to 14 days forP. falciparum 16 to 18 days or longer forP. ovale About 1 month (18 to 40 days) or longer (years) forP. malariae However, some strains ofP. vivaxin temperate climates may not cause clinical illness for months to>1 year after infection. Manifestations common to all forms of malariainclude Fever and rigors—the malarial paroxysm Anemia Jaundice Splenomegaly Hepatomegaly Malarial paroxysm is caused by hemolysis of infected RBCs, released merozoites and other malaria antigens, and the inflammatory response they elicit. The classic paroxysm starts with malaise, abrupt chills and fever rising to 39 to 41°C, rapid and thready pulse, polyuria, headache, myalgia, and nausea. After 2 to 6 hours, fever falls, and profuse sweating occurs for 2 to 3 hours, followed by extreme fatigue. Fever is often hectic at the start of infection. In established infections, malarial paroxysms typically occur every 2 to 3 days depending on the species. Splenomegaly usually becomes palpable by the end of the first week of clinical disease but may not occur withP. falciparum. The enlarged spleen is soft and prone to traumatic rupture. Splenomegaly may decrease with recurrent attacks of malaria as functional immunity develops. After many bouts, the spleen may become fibrotic and firm or, in some patients, becomes massively enlarged (tropical splenomegaly). Hepatomegaly usually accompanies splenomegaly. P. falciparumcauses the most severe disease because of its microvascular effects. It is the only species likely to cause fatal disease if untreated; nonimmune patients may die within days of their initial symptoms. Temperature spikes and accompanying symptoms typically occur in an irregular pattern but can become synchronous, occurring in a tertian pattern (temperature spikes at 48-hour intervals), particularly in residents of endemic areas who are partially immune. Patients with cerebral malaria may develop symptoms ranging from irritability to seizures and coma. Acute Hypoxemic Respiratory Failure (AHRF, ARDS) (ARDS), diarrhea, icterus, epigastric tenderness, retinal hemorrhages, algid malaria (a shocklike syndrome), and severe thrombocytopenia may also occur. Renal insufficiency may result from volume depletion, vascular obstruction by parasitized erythrocytes, or immune complex deposition. Hemoglobinemia and hemoglobinuria resulting from intravascular hemolysis may progress to blackwater fever (so named based on the dark color of the urine), either spontaneously or after treatment withquinine. Hypoglycemia is common and may be aggravated byquininetreatment and associated hyperinsulinemia. Placental involvement may lead to low birth weight, spontaneous abortion, stillbirth, or congenital infection. P. vivax,P. ovale, andP. malariaetypically do not compromise vital organs. Mortality is rare and is mostly due to splenic rupture or uncontrolled hyperparasitemia in asplenic patients. The clinical course withP. ovaleis similar to that ofP. vivax. In established infections, temperature spikes occur at 48-hour intervals—a tertian pattern. P. malariaeinfections may cause no acute symptoms, but low-level parasitemia may persist for decades and lead to immune complex–mediated nephritis or nephrosis or tropical splenomegaly; when symptomatic, fever tends to occur at 72-hour intervals—a quartan pattern. P. knowlesiis associated with the full spectrum of malaria. In contrast toP. falciparum, infection is more likely in males over 15 years living close to or working in forested areas. There are typically daily temperature spikes. Severity increases with the patient's age. The short asexual replication cycle of 24 hours can lead to high rates of parasitemia, and if untreated, death. Thrombocytopenia is common, but it is typically not associated with hemorrhage. In patients who have been taking chemoprophylaxis (see table), malaria may be atypical. The incubation period may extend weeks to months after the drug is stopped. Those infected may develop headache, backache, and irregular fever, but parasites may initially be difficult to find in blood samples. 