Intestinal Parasites


Parasites can inhabit every tissue of the human body. They are not normal inhabitants of a healthy gastro-intestinal tract and can cause harm. They survive in the gut by living off the host’s food supply.

Parasites can enter your gut via a number of routes. Examples include:

  • Drinking water containing parasites or their eggs

  • Skin contact with contaminated water

  • Skin contact with contaminated soil or sand (barefoot on the beach)

  • Eating foods which are uncooked (eg sushi) or undercooked (eg 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. These can be transferred to humans by an animal licking the face



Symptoms of parasitic infection can include

  • Diarrhoea with or without mucus and/or blood

  • Fever

  • Nausea

  • Abdominal pain

However, these symptoms do not always occur and can vary from person to person. Parasitic infections should not be left untreated. Ignoring them can cause damage to the intestinal lining and cause illness.

Chronic parasitic infections can 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

  • 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.

Campylobacter jejune

C. jejune infection causes diarrhoea, which can be watery or sticky and can contain blood (usually occult) and leukocytes (white blood cells) may be found in the stool. Symptoms include: fever, abdominal pain, nausea, headache and muscle pain. The illness usually occurs 2-5 days after ingesting the contaminated food or water. Illness generally lasts 7-10 days, but relapses are not uncommon (about 25% of cases). Most infections are self-limiting and are not treated with antibiotics.

Citrobacter Freundii

Also known as Citrobacter rodentium, this bacterium can cause gastroenteritis in humans. Animal studies have shown that it can cause an intense inflammatory response in the gastro-intestinal tract which can resemble inflammatory bowel disease (Crohn’s, Ulcerative or Microscopic Colitis). Most Citrobacter freundii produce hydrogen sulphide gas which interferes with mitochondrial function and can contribute to colitis.

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.

Entamoeba coli

Not to be confused with the bacterium Escherida coli (E Coli – see below), people infected with the Entamoeba Coli protozoa can be symptom-free, or only experience mild diarrhoea. But occasionally this ‘bug’ can cause symptoms beyond the gastro-intestinal tract: some patients have reported that they felt “strange all over”. Transmission is 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, amoebic 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.

Escherida Coli (E Coli)

E Coli is a bacterium that colonises dairy and beef cattle, which is why ground beef is the most common infection vehicle. However, raw milk, sausage, roast beef, unchlorinated water, apple cider, and raw vegetables have also been implicated. The STEC strains cause a spectrum of illness that can present as mild non-bloody diarrhoea, severe bloody diarrhoea (hemorrhagic colitis), and haemolytic uremic syndrome.

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.

Heliobacter Pylori

H Pylori is found in the intestinal tract of mammals and birds. Mode of transmission is usually via the fecal-oral or oral-to-oral route. This bacterium causes chronic gastritis and predisposes to gastric and duodenal ulcers. Increased risk of gastric carcinoma is associated with infection. If you are infected with H. Pylori, you may develop acute gastritis with symptoms of abdominal pain, nausea and vomiting, usually within two weeks of infection. Many patients have recurrent abdominal symptoms (non-ulcer dyspepsia) without ulcer disease.

H Pylori is treated conventionally with multi-drug regimens along with antacid medications.


This causes a common type of food poisoning. Symptoms of salmonellosis include diarrhea, fever, and abdomen cramping. Symptoms develop 12 to 72 hours after infection, and the illness usually lasts 4 to 7 days. Most people recover without treatment. But diarrhea and dehydration may warrant hospitalisation as it can be severe. Older adults, infants, and those who have impaired immune systems are at highest risk. If you only have diarrhea, you usually recover completely, although it may be several months before your bowel habits are entirely normal.

Most infections are self-limiting and are not treated with antibiotics.


If you are at all concerned that you may have a parasite then stool testing is strongly recommended. 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!

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