plasmodium

Plasmodium is a genus of intracellular parasitic protists in the phylum Alveolata. Members cause malaria in humans and other vertebrates. Transmission occurs when an infected female Anopheles mosquito bites a person, injecting sporozoites into the bloodstream. The parasites first invade hepatocytes in the liver, where they multiply and form merozoites. Merozoites then enter red blood cells, initiating the blood-stage infection characterized by cycles of invasion, growth, and rupture of erythrocytes. Some parasites differentiate into gametocytes, which are taken up by a feeding mosquito, where they fuse to form zygotes and develop into ookinetes and oocysts, completing the life cycle in the vector.

Species commonly infecting humans include Plasmodium falciparum, P. vivax, P. ovale, P. malariae, and P. knowlesi. Plasmodium falciparum is the most deadly form, capable of causing cerebral malaria through sequestration of infected red blood cells. Vivax and ovale species can form dormant liver stages (hypnozoites) that cause relapses.

Diagnosis relies on microscopic examination of stained blood smears, rapid diagnostic tests for parasite antigens, and, when needed, molecular methods such as PCR. Treatment depends on species and resistance patterns; artemisinin-based combination therapies are first line for uncomplicated P. falciparum in most regions, while chloroquine remains effective in some areas. Primaquine is used to eradicate hypnozoites but requires assessment for G6PD deficiency to avoid hemolysis.

Prevention focuses on vector control, including insecticide-treated nets and indoor residual spraying. Plasmodium species possess apicomplexan features, including an apicoplast, with a nuclear genome of roughly 23–32 Mb and a small mitochondrial genome.