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SakariJokiranta
HeliSiikamäki
AnuKantele

Introduction to Intestinal Protozoal Diseases

Causative agents

  • Protozoans are unicellular parasites.
  • Only some of intestinal protozoans cause symptomatic infections. Of these, the most important protozoans are Dientamoeba fragilis, Giardia intestinalis, Entamoeba histolytica and Cryptosporidium parvum. Entamoeba histolytica may cause amoebic abscesses in addition to intestinal infections Amoebic Abscess. Other intestinal protozoans capable of causing symptoms include Cyclospora cayetanensis, Cystoisospora belli, Sarcocystis species and microsporidia. The latter group usually only cause significant symptoms in immunocompromised patients, Sarcocystis also in the previously healthy.
  • Some pathogenic intestinal protozoans colonise the small intestine, others the large intestine. Protozoans move within the intestines with the aid of flagella, cilia or pseudopods.

Distribution

  • Dientamoebiasis, giardiasis and cryptosporidiosis are encountered worldwide.
  • Amoebiasis is mainly encountered in tropical and subtropical regions, but it is capable of spreading in cooler regions too.

Transmission

  • Intestinal protozoal infections are transmitted through cysts or oocysts ingested in contaminated food or drink. The cystic structures are able to withstand adverse environmental conditions well. Once in the intestines, they release active protozoans, which will either attach themselves to the intestinal wall or penetrate the intestinal epithelial cells.
  • In human intestines, the protozoans divide, and they may develop into new cysts or oocysts. The cysts and oocysts may enter water supplies through faeces or to food through contaminated hands and subsequently infect a new host.

Significance worldwide

  • The most significant protozoan worldwide is E. histolytica. It is capable of causing serious or even life-threatening infections such as an intestinal haemorrhagic infection (amoebic dysentery) Amoebiasis or an amoebic abscess Amoebic Abscess.
  • According to the WHO, Cryptosporidium causes more deaths than E. histolytica. A significant share of these result from diarrhoea that HIV patients have got in the AIDS stage and that is difficult to manage.
  • Other intestinal protozoans can also act as significant pathogens capable of producing widespread epidemics, and infected individuals may suffer from chronic abdominal symptoms.

Symptoms

  • Diarrhoea and intermittent abdominal complaints are the most common symptoms.
  • Typical symptoms of dientamoebiasis include prolonged flatulence, abdominal pains, diarrhoea or constipation and sometimes weight loss and faecal incontinence.
  • Giardiasis is typified, in addition to diarrhoea, with upper abdominal cramps, nausea, loss of appetite and flatulence.
  • Fever and bloody diarrhoea may accompany amoebiasis.

Diagnosis

  • Diagnosis is based on detection of the protozoan from the faeces by nucleic acid detection or microscopy (see table T1). In addition, the presence of serum antibodies may be determined in amoebiasis.

Treatment

  • All infections should be treated with drug therapy. An exception to this rule is Dientamoeba, which is treated only in symptomatic persons. Diarrhoea caused by Cryptosporidium in a generally healthy person usually resolves spontaneously, and medication is used as necessary.

Prevention

  • Good general food and water hygiene is the best form of prevention, since intestinal protozoans are mainly transmitted though faecally contaminated food or drink.
  • Good toilet hygiene is essential to protect people living together.
  • A tourist should be aware that the usual chlorination of the water supply will not eradicate protozoal cysts or oocysts, but boiling or filtering the water will.

Intestinal protozoal diseases

Disease or disease groupMode of transmissionMain symptomsDiagnosisTreatment
Dientamoebiasis Dientamoebiasis in AdultsFaeces - intestineFlatulence, loose stools, diarrhoea, constipation, abdominal pain, weight loss, prolonged abdominal complaints, faecal incontinenceFaecal nucleic acid detection (analysis including Dientamoeba fragilis)Paromomycin1) or metronidazole
Giardiasis GiardiasisFaeces - intestineAbdominal pains, loose stools, flatulence, nausea, loss of appetite, weight loss, intermittent symptoms in the chronic formFaecal screening test for intestinal parasites or nucleic acid detection, or giardia staining from small bowel samplesTinidazole1) , metronidazole in a resistant case quinacrine (mepacrine)1)
Intestinal amoebiasis AmoebiasisFaeces - intestineSevere diarrhoea, bloody diarrhoea, abdominal pain, feverFaecal nucleic acid detection or detection of Entamoeba histolytica antigensMetronidazolefollowed byparomomycin1)
Cryptosporidiosis CryptosporidiosisFaeces - intestineWatery diarrhoeaFaecal nucleic acid detection or Cryptosporidium stainNitazoxanide1)
Cyclosporiasis CryptosporidiosisFaeces - intestineWatery diarrhoeaFaecal stain for CryptosporidiumTrimethoprimsulfamethoxazole
Cystoisosporiasis CryptosporidiosisFaeces - intestineDiarrhoea, prolonged symptoms in immunocompromised patientsFaecal stain for CryptosporidiumTrimethoprimsulfamethoxazole
MicrosporidiosisAn opportunistic infection in an immunocompromised patientDiarrhoea, abdominal complaintsFaecal stain for microsporidia
1) May require special license

    References

    • Torgerson PR, Devleesschauwer B, Praet N et al. World Health Organization Estimates of the Global and Regional Disease Burden of 11 Foodborne Parasitic Diseases, 2010: A Data Synthesis. PLoS Med 2015;12(12):e1001920. [PubMed]