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Parasite Biology - Protozoa
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Parasite Biology - Protozoa

Protozoan parasites
  • Single-celled, anaerobic protists.
  • Most reproduce asexually, but some can replicate via sexual reproduction, as well.
  • They have varied life cycles and stages, some of which are quite complicated.
– Trophozoite stage is the active feeding and replicating form; thus, it is most directly responsible for pathology. – Many protozoa have a cyst or cyst-like stage, in which the organism is in a relatively inactive state and is protected by a hard outer covering. This form provides protection during unfavorable environmental conditions and aids in transmission.
  • Intra- and extracellular parasites.
  • Some require multiple hosts – for example, plasmodia, the causative agents of malaria, spend a portion of their life cycles in mosquitos before infecting human hosts.
  • Parasitic protozoans are motile.
– Can be classified by type of motility.
  • Amoebozoa
Entamoeba
  • Use pseudopods for movement.
– These temporary cytoplasmic extensions produce “crawling” motility.
  • Flagellates
Giardia lamblia aka, Giardia duodenalis, aka, Giardia intestinalis which causes gastrointestinal illness.
  • Pear-like shape
  • Two nuclei at one end
  • Multiple hair-like flagella extend laterally from the midline
– These flagella make whip-like motions that produce movement
  • Ciliates
Balantidium coli is the only ciliate known to infect humans.
  • Ovoid shape
  • Cilia that wave in unison to produce movement.
Balantidium coli* has two nuclei: – One macronucleus and one micronucleus
  • Apicomplexa
Be aware that some authors refer to this group as the Sporoza. Plasmodium
  • Oblong shape with a slightly pointed end
  • “Apical complex” is a collection of organelles unique to the apicomplexa.
– Cytoskeletal components of the apical complex contribute to gliding motility in parasitic Apicomplexa.
Be aware that some texts state that apicomplexa are non-motile.
Image Credits:
“Apicomplexa.” Wikipedia, July 31, 2018. https://en.wikipedia.org/w/index.php?title=Apicomplexa&oldid=852786636.
“Balantidiasis,” December 4, 2017. https://www.cdc.gov/dpdx/balantidiasis/index.html.
“Entamoeba Histolytica.” Wikipedia, October 4, 2018. https://en.wikipedia.org/w/index.php?title=Entamoeba_histolytica&oldid=862443030.
“Giardia.” Wikipedia, October 9, 2018. https://en.wikipedia.org/w/index.php?title=Giardia&oldid=863190986. “Paragonimus Westermani.” Wikipedia, October 13, 2018. https://en.wikipedia.org/w/index.php?title=Paragonimus_westermani&oldid=863789457.
“Plasmodium Malariae.” Wikipedia, October 7, 2018. https://en.wikipedia.org/w/index.php?title=Plasmodium_malariae&oldid=862833538.
Erlandsen, Dr Stan. English: A Scanning Electron Micrograph of the Surface of the Small Intestine of a Gerbil Infested with Giardia Sp. Protozoa. The Intestinal Epithelial Surface Is Almost Entirely Obscured by the Attached Giardia Trophozoites. [object HTMLTableCellElement]. Public Health Image Library (PHIL) -- image #11632. https://commons.wikimedia.org/wiki/File:Giardia-spp.--infected--gerbil-intestine.jpg.

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