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===Example of a Protozoal Life Cycle===
===Example of a Protozoal Life Cycle===
See [[Coccidia]]
See [[Coccidia]]
==Types==
===Protozoa===
Protozoa are single-celled eukaryotes that can act as extracellular or intracellular parasites. While their medical importance is very high, only a small number are pathogenic for man and some, such as ''Toxoplasma'', are only a concern in the immunodeficient.
{| border="1"
|+ Important protozoa
! !! Extracellular !! Intracellular
|-
! Insect-borne
| African trypanosome || ''Plasmodium'', ''Leishmania''
|-
! Water-borne
| ''Giardia'', ''Cryptosporiudium'', ''Trichomonas'', ''[[Isospora spp.|Isospora]]''
| ''Toxoplasma''
|}
[[Image:Malaria.jpg|thumb|right|100px|Life cycle of malaria]]
*'''Malaria''': The malaria parasite ''Plasmodium'' grows in the gut of female mosquitoes of the Anopheles genus, eventually moving to the salivary glands. They are then transferred to a human host when she next feeds. In man, there are phases in the blood and the liver, after which the protozoa is transferred back to another feeding mosquito. There are four species of ''Plasmodium'' that can infect man, the most important in terms of mortality being ''P. falciparum'' (at least 1 million deaths a year). The major complications with this species are anaemia and cerebral malaria (a process known as ''sequestration''- infected cells attach to vessel endothelium in the brain).
*'''Leishmania''': Transmitted by the bite of the sandfly, this parasite is taken up by macrophages and forms either cutaneous (skin) or visceral (spleen or liver) infection. Dogs and rodents are the main reservoir.
*'''Trypanosomes''': African trypanosome, such as ''T. brucei'', infect many warm-blooded animals, causing 'sleeping sickness'. The South American types live for a brief period in the blood, becoming predominantly intracellular and infecting the heart and nerve fibres.
*'''Toxoplasma''': can infect any warm blooded animal, although sexual reproductive cycles only occur in the cat. Most infections are symptomless, although this protozoa is a concern for the immunodeficient and pregnant women, causing CNS and congenital defects.