The acanthocephala are thought to be intermediate between the cestodes and nematodes.
Thorny-headed worms (acanthocephalins) – the adult forms of these worms reside in the gastrointestinal tract.Flatworms (platyhelminths) – these include the trematodes (flukes) and cestodes (tapeworms).There are three main groups of helminths (derived from the Greek word for worms) that are human parasites: In their adult form, helminths cannot multiply in humans. Like protozoa, helminths can be either free-living or parasitic in nature. Helminths are large, multicellular organisms that are generally visible to the naked eye in their adult stages. Sporozoa – organisms whose adult stage is not motile e.g., Plasmodium, CryptosporidiumĪn adult Ascaris lumbriocoides worm.Ciliophora – the ciliates, e.g., Balantidium.Mastigophora – the flagellates, e.g., Giardia, Leishmania.The protozoa that are infectious to humans can be classified into four groups based on their mode of movement: Protozoa that live in the blood or tissue of humans are transmitted to other humans by an arthropod vector (for example, through the bite of a mosquito or sand fly). Transmission of protozoa that live in a human’s intestine to another human typically occurs through a fecal-oral route (for example, contaminated food or water or person-to-person contact). They are able to multiply in humans, which contributes to their survival and also permits serious infections to develop from just a single organism.
Protozoa are microscopic, one-celled organisms that can be free-living or parasitic in nature. A microscope is necessary to view this parasite.
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