Five species of the plasmodium parasite can infect humans: the most serious forms of the disease are caused by Plasmodium falciparum. Malaria caused by Plasmodium vivax, Plasmodium ovale and Plasmodium malariae causes milder disease in humans that is not generally fatal. A fifth species, Plasmodium knowlesi, is a zoonosis that causes malaria in macaques but can also infect humans.

Alas, poor plasmodium! I knew him, Horatio. Chlorquinine has borne me to the latrine as thousand times, or so it seemed at the time.