How many different species of human parasites are there?
Helminths (worms) species reported from human hosts.
By Taxonomic Group
Source: Journal of Parasitology 85:379-403 Dr. D.W.T. Crompton (Crompton, D.W.T.  How much human helminthiasis is there in the world?)
Protozoa species reported from human hosts.
Protozoa are the single celled organisms. There are 30,800 described species Protozoa living on planet Earth, but less then 70 are known to be parasitic inside human body.
In general, the protozoans are unicellular animals (although some have some plant or fungal features) that must be in liquid to be active. Many can survive drying by sealing themselves in protective coverings, but they aren't really active in those stages. This means that protozoans are found in water - they can be found in the oceans, in fresh water, or even really wet land environments like the undersides of thick leaf litter - and inside the watery environment of multicellular organisms. It is likely that you right now have protozoans living somewhere on you, although not as certain as having Monerans on or in you. Many of these "hitchhiker" protozoans do no or hardly any harm to their larger hosts, although some can produce various kinds of diseases. ...more
The protozoa comprise many different organisms with four classes that are of interest to us. These are the Sarcodina (amoebae), Ciliophora (ciliates, ) Zoomastigophora (flagellates) and the Apicomplexa (sporozoa). In each of these, individuals can be readily differentiated microscopically using a variety of anatomical and morphologic characteristics. One major difference between each class is the type of locomotion employed. In amoebae, movement is by pseudopodia or false feet, while ciliates utilize cilia and flagellates posses flagella. There is no notable means of movement in the Apicomplexa with most members being intracellular parasites .However, limited movement can be accomplished by contraction of intracellular microfilaments. http://www.cvm.okstate.edu/instruction/kocan/vpar5333/5333iia.htm
At least seven species of amoebae belonging to three genera are known to parasitize humans. These include Entamoeba histolytica, E. hartmanni, E. coli, E. polecki, E. gingivalis, Endolimax nana, and Iodamoeba butschlii. All inhabit the large intestine except E. gingivalis which is found in the mouth. At least three genera (Naegleria, Acanthamoeba, and Hartmannella) usually free-living organisms, are known to also parasitize humans and other mammals.
The Apicomplexa are a taxonomic group that possess structures known collectively as an apical complex. The apical complex is found in the sporozoite and merozoite stage of all genera of malaria, piroplasms, coccidia (and related organisms) and Pneumocystis carinii.
The amoebae are common protozoa in most free-living situations. Most species posses both a trophozoite and cyst stages although exceptions occur. Some species have developed a parasitic mode of existence in various tissues and organs of animals and it is these that we will discuss in the next section.
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