some protozoa and many helminthes have complex life cycles, with not one but two and sometimes more hosts, when more than one host species is necessary to the development of the parasite, that host in which sexual stages of protozoa or adult helminth occurs is called the definitive host: and that host in which larvae stages of helminth or asexual stages of protozoa occurs is called the intermediate host(they are usually designated first and second intermediate hosts if there is more than one).some protozoa and many helminthes have complex life cycles, with not one but two and sometimes more hosts, when more than one host species is necessary to the development of the parasite, that host in which sexual stages of protozoa or adult helminth occurs is called the definitive host; and that host in which larvae stages of helminth or asexual stages of protozoa occurs is called the intermediate host (they are usually designated first and second intermediate hosts if there is more than one)