A traveler returns with fever and periodic parasitemia; fever recurs every 48 hours. Which malaria species is most likely?

• A. Plasmodium vivax or Plasmodium ovale
• B. Plasmodium falciparum
• C. Plasmodium malariae
• D. Plasmodium knowlesi

Answer: (A)

Periodic fever in malaria is driven by the parasite’s synchronized red blood cell cycle. After merozoites invade and mature, they rupture the cells at regular intervals, releasing more merozoites and toxins that trigger the fever. The length of this cycle determines how often fever spikes occur. A 48-hour cycle, meaning fever every two days, is the classic pattern for tertian malaria caused by Plasmodium vivax and Plasmodium ovale. In contrast, Plasmodium malariae produces a 72-hour (quartan) pattern, and Plasmodium knowlesi tends to cause a daily (24-hour) fever pattern. Plasmodium falciparum often presents with irregular fever without a reliable rhythm. Thus, the described 48-hour fever pattern most strongly points to infection with Plasmodium vivax or Plasmodium ovale, which can also relapse due to dormant liver stages.