Plasmodiidae

Plasmodiidae is a family of unicellular, obligate intracellular parasites in the phylum Apicomplexa, within the order Haemosporida. The most prominent member is the genus Plasmodium, which encompasses the malaria parasites that infect humans and a wide range of nonhuman vertebrates. Members of this family are characterized by complex life cycles that involve an insect vector and a vertebrate host, with successive rounds of asexual replication in the liver and in red blood cells, followed by sexual development in the insect vector.

Transmission typically occurs when an infected mosquito injects sporozoites into a vertebrate host during a blood meal. Sporozoites migrate to the liver, invade hepatocytes, and multiply to form hepatic schizonts that release merozoites. Merozoites then invade red blood cells, initiating the erythrocytic cycle, where they develop into trophozoites and schizonts that cause clinical symptoms. Some parasites differentiate into sexual stages, gametocytes, which are taken up by a feeding mosquito. In the mosquito gut, gametocytes mature into male and female gametes, fuse to form a zygote, which becomes an ookinete and then an oocyst. The oocyst releases new sporozoites that migrate to the mosquito’s salivary glands, ready to infect another host.

Humans are primarily affected by Plasmodium falciparum, P. vivax, P. ovale, and P. malariae, with P. knowlesi recognized as a zoonotic example. Related Plasmodium species infect other primates, birds, and other vertebrates. Malaria remains a major global health issue in tropical regions, transmitted by Anopheles mosquitoes. Control strategies include vector management, chemoprophylaxis, and antimalarial drugs, though resistance and ecological factors pose ongoing challenges.