Plasmodium

MICROBIOLOGY

• 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.[14]
  
  • 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.[14]
    • Preferentially invades reticulocytes and requires Duffy antigen for RBC entry
      • Less prevalent in sub-Saharan Africa, as population lacks the Duffy antigen[14]
    • 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.[13]
• 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.