Diagnostic Criteria and Clinical Characteristics
Malaria should be suspected in anyone who has previously visited a malaria-endemic area, including those that took prophylaxis. Human malaria can be caused by five species of Plasmodium (Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, Plasmodium malariae, and the simian parasite Plasmodium knowlesi) out of which infections by P falciparum and P vivax are most common. Human infection with P knowlesi is thought to be a zoonosis and has only been reported in Southeast Asia.
Incubation period can be as short as 6 days for naturally acquired infection. Most patients who have a P falciparum infection will present within 6 months of exposure. P vivax and P ovale may enter a hypnozoite stage in the liver with infections usually presenting more than 6 months, and occasionally years, after exposure. There is a risk of relapse if only the blood phase of the disease is treated and the hypnozoites are not cleared.
Symptoms are nonspecific and there are no pathognomonic features. Most patients complain of fever or sweats or rigors, myalgia, headache, and general malaise. Malaria may be misdiagnosed as influenza or another respiratory viral infection, or as gastroenteritis due to gastrointestinal symptoms and jaundice. The fever typically does not follow the classically described quotidian, tertian, or quartan patterns.
Signs are also nonspecific and reminiscent of many other conditions. A fever is not invariably present and hepatomegaly is uncommon in acute malaria. Children are more likely to have hepatosplenomegaly than adults.
Severe or complicated falciparum malaria may present with