Protozoa

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Protozoa

 [pro″to-zo´ah]
a subkingdom (formerly a phylum) comprising the unicellular eukaryotic organisms; most are free-living, but some lead commensalistic, mutualistic, or parasitic existences. According to newer classifications, the Protozoa are divided into seven phyla: Sarcomastigophora, Labyrinthomorpha, Apicoplexa, Microspora, Acetospora, Myxozoa, and Aliophora. Pathogenic protozoa include Plasmodium species, the cause of human malaria; Trypanosoma gambiense, the cause of African trypanosomiasis; Toxoplasma gondii, of which house cats are the reservoir and humans the intermediate host; Entamoeba histolytica, the cause of amebic dysentery; and Balantidium coli and Isospora belli, both of which cause diarrhea in humans.

Protozoa can be ingested and transmitted through contaminated feces. Prevention of transmission is extremely important; handwashing and stool precautions are recommended. Other necessary precautions (see infection control) should be carried out according to directions from the Centers for Disease Control and Prevention. Protozoal infections are occurring more frequently in North America and other industrialized countries because of increased world travel.

protozoa

 [pro″to-zo´ah]
plural of protozoon.

Pro·to·zo·a

(prō'tō-zō'ă),
Formerly considered a phylum, now regarded as a subkingdom of the animal kingdom, including all of the so-called acellular or unicellular forms. They consist of a single functional cell unit or aggregation of nondifferentiated cells, loosely held together and not forming tissues, as distinguishes the Animalia or Metazoa, which include all other animals. Protozoa were formerly divided into four classes: Sarcodina, Mastigophora, Sporozoa, and Ciliata; new classifications employ higher taxa (phyla, subphyla, and superclasses) and a number of major subdivisions.
[proto- + G. zōon, animal]

Pro·to·zo·a

(prō'tō-zō'ă)
Formerly considered a phylum, now regarded as a subkingdomof the animal kingdom, including all of the so-called acellular or unicellular forms. Members consist of a single functional cell unit or aggregation of nondifferentiated cells, loosely held together and not forming tissues.
[proto- + G. zōon, animal]

Protozoa

(prōt″ă-zō′ă) [ proto- + -zoa]
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The phylum of the kingdom Protista that includes unicellular, animal-like microorganisms. Many protozoa are saprophytes that live on dead matter in water and soil. Many parasitic protozoa infect only humans without adequate immunological defenses although a few infect the immunocompetent. Infections are spread by the fecal-oral route, through ingestion of food or water contaminated with cysts or spores, or by the bite of a mosquito or other insect that has previously bitten an infected person. Common protozoan infections include malaria (Plasmodium vivax, P. malariae); gastroenteritis (Entamoeba histolytica, Giardia lamblia); leishmaniasis, an inflammatory skin or visceral disease (Leishmania species); sleeping sickness (Trypanosoma brucei gambiense, T. b. rhodiense); and vaginal infections (Trichomonas vaginalis). Pneumocystis jiroveci, previously classified as a protozoon, is now categorized as a fungus. Opportunistic protozoan infections caused by Cryptosporidium parvum and Toxoplasma gondii are seen in patients who are immunosuppressed by disease or drug therapy. See: illustration; table
SubphylumGenus and SpeciesDisease Caused
Zoomastigophora (Mastigophora)Giardia lambliaGastroenteritis
Locomotion by flagellaLeishmania donovaniKala azar
Leishmania braziliensisAmerican leishmaniasis
Leishmania tropicaOriental sore
Trichomonas vaginalisTrichomoniasis
Trypanosoma brucei gambiense, Sleeping sickness
T. b. rhodiense
Trypanosoma cruziChagas' disease
Rhizopoda (Sarcodinae)Acanthamoeba castellaniAmebic meningoencephalitis
Locomotion by pseudopodiaA. culbertsonii
A. astromyxis
Dientamoeba fragilisDiarrhea, fever
Entamoeba histolyticaAmebic dysentery
Naegleria fowleriAmebic meningoencephalitis
Apicomplexa (Sporozoa)Babesia microtiBabesiosis
No locomotion in adult stageB. divergens
Cryptosporidium parvumCryptosporidiosis
Cyclospora cayetanensisDiarrhea, gastroenteritis
Isospora belliDiarrhea
Microspora(multiple spp.)Diarrhea, chronic
Plasmodium malariaeQuartan malaria
Plasmodium falciparumMalignant tertian malaria
Plasmodium vivaxTertian malaria
Plasmodium ovaleTertian malaria
Toxoplasma gondiiToxoplasmosis
CiliophoraBalantidium coliBalantidiasis
Possession of cilia in some stage of life cycle

protozoa

Primitive, single-celled, microscopic animals able to move by amoeboid action or by means of CILIA or whip-like appendages (flagella). Many protozoa are parasitic on humans and are of medical importance. These include the organisms that cause AMOEBIASIS, BALANTIDIASIS, CRYPTOSPORIDIOSIS, GIARDIASIS, ISOSPORIDIOSIS, LEISHMANIASIS, MALARIA, SLEEPING SICKNESS, TOXOPLASMOSIS and TRICHOMONIASIS.

Protozoa

Group of extremely small single cell (unicellular) or acellular organisms that are found in moist soil or water. They tend to exist as parasites, living off other life forms.
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