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- Malaria is caused by intraerythrocytic Plasmodium protozoa belonging to the Apicomplexa group, transmitted by night-time or pre-dawn biting female Anopheles sp. mosquitoes.
- CDC confirmed 1,517 U.S. cases in 2015, a decrease of 208 cases from 2014.
- P. falciparum (67% of U.S. cases)
- Invades RBCs of all stages
- Causes the most severe and lethal illness
- RBCs rosette and sequester in microvasculature and damage heart, brain, kidney, lung, placenta.
- P. vivax
- Most common type outside of sub-Saharan Africa, survives at lower temperatures and higher elevations.
- Preferentially invades reticulocytes and requires Duffy antigen for RBC entry
- Less prevalent in sub-Saharan Africa, as population lacks the Duffy antigen
- Persists in hepatocytes as hypnozoites for months to years
- Eradication requires treatment of both liver (hypnozoite) and blood (schizont) stages.
- P. ovale
- Can persist in hepatocytes as hypnozoites for months to years
- Eradication requires treatment of both liver and blood stages.
- P. malariae
- Infects older RBCs and causes low-level parasitemia and chronic, low-grade infection
- P. knowlesi: a monkey malaria parasite, causes human malaria in Southeast Asia, morphologically resembles P. malariae
- Both uncomplicated and severe disease occur at low parasitemia. IV artesunate recommended for parasitemia > 15,000/μL.
- Life cycle: female 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.
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