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 Giardia Lamblia 

Giardia Lamblia is a single-celled parasite that can cause a gastrointestinal illness called Giardiasis. Giardia cysts are generally found in the faeces of infected animals or humans.

 If you have a Giardia infestation, you may have no symptoms

To become infected, you must consume contaminated food or water including drinking from streams or rivers.  Direct or hand-to-mouth transfer of the parasite from human or animal faeces can also cause infection.

If you have symptoms, they will probably go away by themselves in a week or so. Or they can vanish suddenly and then reappear.  They may hide for months.  They may not appear at all. If you develop serious persistent symptoms, you should seek advice and treatment. If you’re even unfortunate enough to contract Giardiasis, you can develop an immunity to it.

Symptoms usually appear between one to four weeks after the cysts are ingested and can present themselves as mild to moderate abdominal discomfort, abdominal distention as a result of increased intestinal gas, sulfurous or “rotten egg” burps, highly offensive flatulence, diarrhoea, IBS, chronic fatigue, blood sugar imbalances or weight loss.  These symptoms can last for years. Even without any symptoms, infected people can remain contagious for months.

Stools are soft (but not liquid), bulky, and foul smelling.  They have been described as greasy and frothy, and they float on the surface of water.  Nausea, weakness, and loss of appetite can occur. 

If you have symptoms, you may not have Giardia

The diarrhoea being blamed on Giardia from that hiking trip a week ago may instead be due to some spoiled food eaten last night or Campylobacter in undercooked chicken four days ago.  Other possible offenders are Cryptosporidium, Salmonella and Escherichia coli.  If you’re in the high-risk groups for Giardia (see below), look within your family and friends as a more likely source.

The type of diarrhoea can also help in the diagnosis:  If it is liquid and mixes readily with water rather than floating on top and is not particularly foul smelling, the problem is likely something other than Giardiasis.  Diarrhoea which lasts less than a week, untreated, is probably not from Giardiasis.

Institutions for the mentally retarded can have high infection rates, as do hikers, promiscuous male homosexuals, international travellers, and patients with cystic fibrosis.  Young children in nurseries are particularly susceptible because they put so many things into their mouths.  The family members of these individuals are highly likely to become infected.


The Facts:

 Giardia lamblia, was first observed in 1681 by Anton van Leeuwenhoek, inventor of the microscope.  The parasite was named in 1915 after two scientists who studied it:  Prof. A. Giard in Paris and Dr. F. Lambl in Prague.

 In the USA, 30% of daycare workers and 60% of children have been found to be infested with Giardia.

 A study of blood samples chosen at random in an American hospital showed that 20% harboured Giardia parasites.

 The number of cysts shed in faeces is highly variable but has been estimated as high as 900 million per day for humans.  

 When 16 people got sick from the salad at a Connecticut picnic, the Center for Disease Control tracked the source to a woman who had mixed the salad with her hands.  She didn’t have Giardiasis, but one of her children did—without any symptoms.

Common sense precautions

Most of the ‘How To Avoid Giardia’ precautions border on the paranoid.  If you really want to eliminate the possibility of Giardia, the only certain ways are by boiling and filtration. Boil water for a minimum of 10 minutes; 15 minutes if you’re in the mountains.  Filters should be no greater than 3 microns.  A micron is one millionth of a metre; Giardia cysts measure 5 microns.  Coffee makers never get hot enough to kill Giardia.  Even more important than filtering is washing your hands regularly – you can wash your hands in a natural antiseptic like tea-tree oil (diluted) or carry a waterless antiseptic cream with you.  

Drink and Think Smart

On hiking trips drink from large fast-flowing streams whenever possible.

Giardia cysts can be destroyed by iodine-based compounds which are used in water purification kits.  Iodine has drawbacks as it can cause accidental poisoning and may be contraindicated in sensitive or allergic people.  Practicing common-sense wilderness sanitary habits—defecating at least 100 feet away from the water’s edge, burying faeces and toilet paper makes good sense.

Internet Search

If you look up Giardia on the internet you’ll see a host of websites that give either flawed or anecdotal information that all rivers are teeming with Giardia.  You get the wrong impression that if you drink from them and you’ll catch Giardia.  Yes Giardia are likely to be present but Bob Rockwell a US wildlife expert writes:

Neither health department surveillance nor the medical literature supports the widely held perception that Giardiasis is a significant risk to backpackers in the United States.  In some respects, this situation resembles the threat to beachgoers of a shark attack:  an extraordinarily rare event to which the public and press have seemingly devoted inappropriate attention.”

I don’t imagine that rivers and streams in the UK or Europe are too different.

A 1990’s study in New York of over 400 Chronic Fatigue sufferers evidenced that an incredible 93% had one or more forms of parasitic infection.  Environmental toxins are often claimed to be the cause of Chronic Fatigue but we forget to consider the toxins parasites expel within our digestive tract.  These are re-absorbed causing significant dysfunctions in our biochemistry.  Single celled organisms such asGiardia, Cryptosporidium and Blastocystisis Hominis, wreak havoc with the intestine causing leaky-gut syndrome.

What Doctor’s Don’t Tell You’s Dr Leo Galland first reported the link between chronic fatigue and Giardia infection.  Most of his patients with so-called IBS in fact have parasites. Dr Galland believes that anyone with immune or gastro-intestinal disturbance of any kind should be thoroughly investigated for the presence of parasites.

Giardia in more detail:


Giardia lamblia trophozoites as they appear with the scanning electron microscope 
Original image: 
Arturo Gonzalez

Giardia is a single-celled microscopic protozoan that, in its active form, attaches itself to the gut lining of the host animal.  There, it feeds and reproduces.  They divide by binary fission about every 12 hours.  Thus, a single parasite can theoretically result in more than a million in 10 days and a billion in 15 days.

At some time in its active life, it releases its hold on the bowel wall and floats in the fecal stream.  As it makes its journey, it transforms into an egg-like structure called a cyst, which is eventually passed in the stool.  Duration of cyst excretion, called shedding, may persist for months.  Once outside the body, the cysts can be ingested by another animal.  Then, as a result of stomach acid action and digestive enzymes, they hatch into a stage called ‘trophozoite’.  The cycle then repeats.

A significant infestation can leave millions of trophozoites stuck tight to the intestinal lining.  There, they cripple the gut’s ability to secrete enzymes and absorb food, especially fats, folic acid and Vitamin B12, thereby producing a variety of symptoms and anaemia.  

Stool Tests

About 8000 Giardia can squeeze onto a pinhead making it difficult to detect them, unless with an electron microscope.  To have any chance of finding Giardia in stool samples, the stool must be tested within 6-7 hours of being formed.  Even then tests using specific antigen (a substance that stimulates an immune response) must be made and Giardia are adapt at evading detection by changing their antigen.  Past studies have evidenced that even at the height of acute infection, stool samples have returned showing no evidence of Giardia.

There is a specific test (enzyme-linked immunosorbent assay, or ELISA) for the detection of Giardia antigens in stool samples.  ELISA is a big improvement over the microscopic search, with detection sensitivities of 90 percent or more. 

The Bottom Line

Whether at home or on a mountain trail, all cooks must pay special attention to cleanliness, washing hands thoroughly, especially before handling utensils and preparing meals.  If you contract Giardiasis as a result of hiking through the Pennines, the Alps or the Rockies, check the cook first, then your friends; don’t blame the water.  So drink confidently: personal hygiene is far more important in avoiding Giardiasis than treating the water.

Graeme Dinnen

With particular thanks to Bob Rockwell for his invaluable contribution.  Bob has climbed the Sierra Nevadas all his life and has never filtered or treated the water.  He has never contracted symptoms of Giardiasis.

Precaution is infinitely better than an after-the-event struggle to recover from the effects of Giardia, or any other parasite infestation.  We carry Natural Cleanse with us as our health insurance.  



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