Sunday, 27 January 2008

Water borne protozoa_elaine(2nd blogging)

Protozoa: single-celled parasites
--> they are unicellular eukaryotes, meaning that they are charactistics organelles. They are relatively large and some are visible with the naked eye. They occupy a vast array of habitats and niches and have organelles similiar to those found in other eukaryotes cells as well as specialized organelles. Protozoa usually reproduce asexually by binary fission. (3)

Infection with parasites is a major cause of morbidity and mortality in tropical and semitropical countries
-->arthropod vectors
-->intermediate hosts e.g. fishes or snail
-->Treat drinking water with high efficiency filtration and/or chemical disinfection such as chlorination or ozonation (4)

1) Giardia Lamblia (giardiasis):
--> A flagellated protozoon and an important cause of diarrhea worldwide. (1)
--> is a flagellated protozoan parasite that colonises and reproduces in the small intestine, causing giardiasis.
--> Giardiasis does not disseminate haematogenously, nor does it spread to other parts of the gastro-intestinal tract, but remains confined to the lumen of the small intestine. Giardia trophozoites absorb their nutrients from the lumen of the small intestine, and are anaerobes.
[Route of infection]: Faecal-oral

[Pathogenesis]: cysts of Giardia Lamblia have been demonstrated in the drinking water. Ingestion of cysts—the resistance, infective stage—is followed by the production of trophozoites in the upper small intestine. Trophozoites cause irritation, which leads to gastrointestinal symptoms.

[Clinical features]
Symptoms: diarrhea, mild to severe, with characteristic light-coloured fatty tools; abdominal pain: cramps, with flatulence and epigastric tenderness; anorexia
Malabsorption: steatorrhoea is not common and may lead to the full-blown malabsorption syndrome.

2) Cryptosporidium Parvum (Cryptosporidiosis): (1)
-->Cryptosporidium is a protozoan pathogen of the Phylum Apicomplexa and causes a diarrheal illness called cryptosporidiosis.
-->Human infection is often acquired as a result of animal slurry contaminating water supplies.
The infective stage is the oocyst, passed in faeces: transmitted person-to-person, animal-to-person or via contaminated water.

[Clinical features]
Symptoms: self-limiting diarrhea in the immunocompetent individual.

3) Isospora Belli:
--> humans seem to be the only host of this parasite, which infects the small intestine. (2)
Faecal-contaminated food and water

[Clinical Features]
In the immunocompetent infection is often asmptomatic and the diarrhea, when present, tends to be mild.
In the immunocompetent, infection is generally asymptomatic or a self-limiting gastro-enteritis. However, in chronic infections, severe diarrhoea and fat malabsorption can occur.
Infection in immunocompromised individuals ranges from a self-limiting enteritis to severe diarrhoeal illness resembling that of cryptosporidiosis.

4) Cyclospora Cayetanensis (Cyclosposiasis): infect the small intestines (1)
The infective stage is the oocyst passed in faeces (waterborne)

[Clinical features]
Symptoms: diarrhea, remitting and relapsing, sometimes lasting as long as 6 weeks; malabsorption in some cases; weight loss

5) Entamoeba Histolytica (amoebiasis): a common infection in tropical countries such as Indonesia where the sanitation is poor. (2)
[Route of infection]
Faecal-oral, owing to contaminated water

[Clinical features]
Diarrhea, progressing rapidly to bloody diarrhea accompanied by fever and painful abdominal cramps, symptoms may pesist into a chronic relapsing state. Sometimes progresses to dilatation of the colon, with the risk of intestinal perforation.

Amoebic absecess owning to spread to the liver causing painful enlargement and accompanied by high fever, raised white cell count and high ESR.


(1) Medical microbiology 4th edition. written by patrick R. Murray, Ken S. Rosenthal, George S. Kobayashi, Micheal A. Pfaller

(2)Book: microbiology of waterborne disease. written by S L Percival, R M Chalmers

(5) Carlo Denegri Foundation. Intestinal parasites. html>iso1.htm/">>hTML>iso1.htm

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