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Intestinal parasites

How do we contract parasites?

Parasites can inhabit every tissue of the human body and infection can be via a number of routes including:
  • Drinking water that contains parasites or their eggs
  • Skin contact with contaminated water
  • Skin contact with contaminated soil or sand (barefoot on the beach)
  • Eating foods which are undercooked or not cooked properly (e.g Sushi and Pork)
  • Contact with insects such as lice, fleas, mites and ticks
  • Via airborne viruses and bacteria
  • Via pets - Dogs, cats and other some animals carry tapeworm parasites at certain stages in their life cycle which infect humans and are transferred by an animal licking or "kissing" the face


Intestinal parasites are not normal inhabitants of a healthy gastro-intestinal tract. They survive in the gut by living off the hosts food supply and have the potential to cause harm.

In general, symptoms of parasitic infection can include diarrhoea with or without mucus and/or blood, fever, nausea, or abdominal pain. However, these symptoms do not always occur and can vary from person to person. Parasitic infections should not be left untreated, as chronic parasitic infections can cause damage to the intestinal lining and can be the cause of illness and fatigue. Chronic parasitic infections can also be associated with increased intestinal permeability, irritable bowel syndrome, irregular bowel movements, malabsorption, gastritis or indigestion, skin disorders, joint pain, allergic reactions, decreased immune function and fatigue.

Blastocystis hominis

Blastocystis hominis is a common protozoan found throughout the world. Blastocystis is transmitted via fecal/oral transmission or by ingestion of contaminated food or water.

Patients with B Hominis commonly have fatigue. Some patients will have abdominal pain, nausea, vomiting, diarrhoea, weight loss as well as anorexia, flatus and eosinophilia.  Typical symptoms include diarrhoea, crampy abdominal pain, nausea, vomiting, low grade fever, gas, malaise and chills.  Fecal leukocytes are sometimes seen.  B Hominis can cause colitis.

Giardia Lamblia

Giardia is associated with abdominal pain, diarrhoea, constipation, bloating, chronic fatigue, food allergy and intolerance as well as exacerbating IBS, rheumatoid arthritis, food allergy or multiple chemical sensitivity.  Some infections are relatively asymptomatic.

Dientamoeba Fragilis

Infection with D Fragilis does not necessarily cause obvious symptoms, or it can cause Diarrhoea and a painful abdomen in some people. Occasionally there may be some blood seen in the stool. It is transmitted via contaminated water or in food containing pinworm eggs.

Citrobacter Freundii

This is also known as Citrobacter rodentium, its a gram negative anaerobe and facultative anaerobe and can cause gastroenteritis in humans.  Animal studies have shown that this bacterium can cause an intense inflammatory response in the gastro-intestinal tract which can resemble inflammatory bowel disease.  Most Citrobacter freundii produce hydrogen sulphide gas which interferes with mitochondrial function and can contribute to colitis.

Entamoeba coli

Infection often is free of symptoms, or mild diarrhoea.  Occasionally this ‘bug’ can cause symptoms not limited to the gastro-intestinal tract.  Patients have reported that they felt strange all over. Transmission is also via contaminated food or water.

Endolimax Nana

Endolimax Nana is a protozoa with world-wide distribution and commonly considered to be harmless.  However infection with E Nana can cause a peripheral arthropathy which is clinically similar to rheumatoid arthritis and which remits when the parasite is eradicated.  Intestinal colonization by E Nana has been seen in patients presenting with chronic fatigue, myalgia, eczema and refractory chronic vaginitis.

Entamoeba Histolytica

E Histolytica can induce tissue damage, amebic colitis and liver abscess.  Amoebic colitis can be misdiagnosed as ulcerative colitis and can manifest as IBS, rheumatoid arthritis, fibromyalgia, food allergy or multiple chemical sensitivities.  Some infections are asymptomatic.


Holford, P. Improve your digestion (Optimum Nutrition Handbook) Hachette Digital, 2010.


If you are at all concerned that you may have a parasite then stool testing is strongly recommended.  Also remember that you do not have to travel to tropical locations to contract a parasite as many are prevalent in the UK and can be picked up from contaminated food, water or even your pets!