Malaria Update for the Clinical Microbiology Laboratory: a New Species, Plasmodium knowlesi, and New Diagnostic Tests

Plasmodium vivax and Plasmodium falciparum are responsible for 95% of malaria infections. P. vivax has the widest distribution and is thought to be responsible for 80% of the infections throughout the tropics, subtropics, and temperate zones. As early as 2004, a fifth malaria species had been implicated in human disease. Plasmodium knowlesi, a malaria parasite of long-tailed macaque monkeys, has been confirmed in a number of human cases from Malaysian Borneo, Thailand, Myanmar, and the Philippines. It is now well established that P. knowlesi is emerging as an important zoonotic human pathogen. Malaria is considered to be immediately life-threatening, and a patient with the diagnosis of P. falciparum or P. knowlesi malaria should be considered a medical emergency because the disease can be rapidly fatal. While rapid malaria tests have been used in many parts of the world, currently one test is now FDA approved for use within the United States. The pros and cons of this rapid procedure compared with the “gold standard” thick and thin blood films are discussed for all five species of human malaria.