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- Malaria is caused by Plasmodium parasites belonging to the Apicomplexa group of protozoa, transmitted by night-time or pre-dawn biting female Anopheles sp. mosquitoes.
- CDC reported 1,864 U.S. cases in 2010, a 14% increase from 2009, by species:
- P. falciparum (58%)
- P. vivax (19%)
- P. ovale (2%)
- P. malariae (2%)
- Unreported or undetermined (18%)
- P. knowlesi: a monkey malaria parasite, noted to cause human malaria in Southeast Asia, morphologically resembles P. malariae.
- Life cycle: anopheline mosquito bites human host and injects sporozoites, which invade hepatocytes and mature into schizonts (exo-erythrocytic schizogony), which rupture and release merozoites that invade RBCs. In RBCs, ring stage trophozoites mature into schizonts (erythrocytic schizogony), followed by rupture of RBCs and a new cycle of RBC invasion.
- Pathophysiology differs by species:
- P. falciparum invades RBCs of all ages, causes most severe and lethal illness as RBCs rosette and sequester in microvasculature, and damage heart, brain, kidney, lung, placenta.
- P. vivax and P. ovale can persist in hepatocytes as hypnozoites for months to years. Eradication requires treatment of both liver and blood stages. P. vivax preferentially invades reticulocytes and requires Duffy antigen for RBC entry.
- P. malariae infects older RBCs and causes low level parasitemia and chronic, low-grade infection.
- P. knowlesi may cause rapidly progressive, severe disease.