Sporozoans – Protozoan
Sporozoans of the genus Plasmodium are responsible for causing a serious human disease, malaria. They are among, the best known parasites which live in the fixed tissues of the body and circulating red blood cells of their vertebrate host. More than 100 species of Plasmodium parasitise a wide variety of vertebrates - lizards, birds and mammals, primates and rodents in particular. Four species of Plasmodium which mainly occur in man and have no other natural vertebrate host are the cause of human malaria. These are Plasmodium vivax, p. falciparum, p. malariae and p. ovale most prevalent in tropical and subtropical regions of the world.
All malarial parasites require two hosts, one a vertebrate host in which asexual cycle of the parasite (involving schizogony and early gametogony) occurs, and the other a mosquito in which sexual phase of life cycle (involving completion of gametogony and sporogony) is completed.