tertian malaria, a form of malaria caused by the protozoan Plasmodium vivax or P. ovale, characterized by febrile paroxysms that occur every 48 hours. Vivax malaria, caused by P. vivax, is the most common form of malaria. Although it is rarely fatal, it is the most difficult form to cure. Relapses are common. Ovale malaria, caused by P. ovale, is usually milder and causes only a few short attacks. Both types of tertian malaria are treated with chloroquine. Compare falciparum malaria, quartan malaria. See also malaria.
