malariae

Plasmodium malariae, commonly referred to as malariae, is one of the protozoan parasites that cause malaria in humans. It is transmitted by Anopheles mosquitoes and is associated with a quartan fever pattern, with fever spikes occurring approximately every 72 hours. Compared with the more common P. falciparum and P. vivax, P. malariae tends to produce lower levels of parasitemia and can be more challenging to detect in some settings.

Life cycle and pathology

Sporozoites injected by a mosquito infect liver cells, but unlike some other species, P. malariae does not form hypnozoites in the liver. After hepatic stages, merozoites enter red blood cells and develop through ring, trophozoite, and schizont stages. The trophozoite stage often appears as a distinctive band form across the red cell. Mature schizonts typically yield 6–12 merozoites and can be seen in thin blood films. Infected red cells are usually not enlarged. Gametocytes develop for transmission to mosquitoes. The parasite can persist at low levels for years and may recrudesce after many months or years, even without re-exposure.

Clinical features

Infection produces regular fevers with a 72-hour cycle, along with malaise, anemia, and possible splenomegaly. Complications can include nephrotic syndrome and other immune-mediated phenomena, particularly with chronic infection. Severe disease is less common than with P. falciparum but can occur, especially in young children or individuals with limited immunity.

Diagnosis and treatment

Diagnosis relies on microscopy of Giemsa-stained blood smears, with band-form trophozoites and rosette schizonts aids in identification. Rapid diagnostic tests may be less sensitive for P. malariae compared with other species; molecular methods (PCR) can confirm diagnosis. Treatment has traditionally relied on chloroquine in areas where the parasite remains susceptible. In regions with resistance, artemisinin-based combination therapies are used. Because P. malariae does not form hypnozoites, primaquine is not required for radical cure. Prevention focuses on vector control and prophylaxis tailored to local drug resistance patterns.

Epidemiology

P. malariae is found in tropical and subtropical regions, with varying prevalence and often coexisting with other Plasmodium species. Surveillance and region-specific treatment guidelines guide management and prevention efforts.