Human Health And Disease

Malaria is caused by protozoans of the genus Plasmodium, and among the species infecting humans, Plasmodium falciparum produces the most severe and potentially fatal disease, known as malignant malaria. The parasite is introduced into the human bloodstream as sporozoites through the bite of an infected female Anopheles mosquito, after which it multiplies in liver cells and then in red blood cells, causing their rupture along with the release of the toxin haemozoin that triggers the characteristic recurring chills and high fever. Plasmodium vivax causes a milder tertian malaria and is rarely fatal, so it does not fit the description of the most lethal form. Plasmodium malariae causes quartan malaria with a longer fever cycle and is also far less dangerous. Entamoeba histolytica is not even a malarial parasite; it causes amoebiasis affecting the intestine, so it is irrelevant here. As described in NCERT Class 12, Chapter 8 (Human Health and Disease), the female Anopheles acts as the vector while the human is the host where asexual multiplication occurs. As a biological consistency check, only Plasmodium falciparum among the listed options is both a malarial agent and the species linked with cerebral and malignant malaria, confirming it as the correct answer.