a clinical rhythmicity reflected in periodic fevers and chills recurring at approximately 48-hour intervals in tertian malaria (Plasmodium vivax or P. ovale) or at 72-hour intervals in quartan malaria (Periodicity malariae); the rhythm of tertian or 48-hour cycles is frequently modified in malignant tertian or falciparum malaria (P. falciparum); associated with release of merozoites from red blood cells during erythrocytic schizogony, although the controlling mechanism for the synchronous release is unknown.