Giardiasis Infection

Giardiasis Infection: Overview

Giardiasis is a diarrheal illness caused by Giardia intestinalis (also known as Giardia lamblia), a one-celled, microscopic protozoan parasite that lives in the intestine of people and animals.  Giardia has become recognized as one of the most common causes of waterborne disease (both through drinking water and through recreational use of water) in humans in both developing and industrialized countries.

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The giardia parasite lives in the intestine of infected humans or animals and is passed in stools.  The dormant form – a 'cyst' – is protected by an outer shell, making it exceptionally hardy and able to tolerate extremes of both pH and temperature.  It can survive outside the body and in the environment for long periods of time.  Giardia may be found in soil, food, water, or surfaces that have been contaminated with the feces from infected humans or animals.

Causes and Development

Early human research demonstrated that ingestion of fewer than 10 cysts failed to cause infection, whereas more than 100 cysts resulted in infection.

Once ingested, these cysts pass into the stomach, where they are exposed to gastric acid.  The low pH in the stomach and pancreatic proteases found in the proximal small intestine promote rapid breakdown of the cysts' outer walls within minutes of reaching the duodenum.  Typically, each cyst gives rise to two 'trophozoites', which are the vegetative form of giardia; they are able to colonize and rapidly replicate in the gastrointestinal tract as well as cause gastrointestinal symptoms.

Signs and Symptoms

Symptoms generally begin within 1 to 2 weeks of infection and include watery diarrhea, vomiting, stomach cramps, upset stomach, loss of appetite, dehydration, nausea and fatigue.  Less common symptoms include low-grade fever, chills, headaches, urticaria, and polyarthritis.  Mucous- and blood-tinged feces are rarely found.  Signs include weight loss, abdominal distension and tenderness, bad-smelling flatulence and burps, pale watery stools, frothy, foul-smelling stools.  Symptoms usually persists from 2 to 6 weeks in otherwise healthy individuals.

Symptoms range in severity from mild to extreme; however, a significant proportion of infected individuals are completely asymptomatic.  In some individuals giardiasis is short-lasting and resolves spontaneously, whereas in others infection can be prolonged and debilitating.

Diagnosis and Tests

Giardiasis is diagnosed by signs and symptoms, as well as the presence of giardia cysts and trophozoites in the stool.  Stool examination can be unreliable, however, as organisms may be excreted at irregular intervals, which can produce a false negative test result.  Hence, definitive diagnosis may require repeated stool examinations, fecal immunoassays, or even sampling of the upper intestinal contents.  Two stool examinations will detect 80-90% of infections, while three samples will detect over 90%.

Giardiasis can often be distinguished from viral or bacterial gastrointestinal (GI) infections by the longer duration of illness (often 7-10 days by the time of first presentation) and weight loss.  In addition, careful history taking may uncover recent travel to tropical or sub-tropical environments, wilderness exposure, or situations involving pool fecal-oral hygiene.

Treatment and Prevention

The most beneficial way to treat giardiasis naturally may be through a combination approach, utilizing both nutritional interventions and other natural agents.  Numerous medicinal herbs show promise in the treatment of giardiasis.  Blending nutritional interventions and phytotherapeutic agents can minimize giardia symptoms and aid in clearing the parasite, without significant ill effects.  As such, this therapeutic strategy is considered by many natural doctors as being the first-line approach.

The main aims of dietary modification in giardiasis should be to reduce the acute symptomatology, promote host defense mechanisms, and inhibit growth and replication of giardia trophozoites.  These aims can be achieved by consuming a whole-food, high-fiber, low simple-carbohydrate, low-fat diet.

This diet will ensure adequate amounts of lignins and insoluble and soluble fibers are consumed, which can increase mucin production in the small bowel, sequester bile acids, and help to mechanically sweep trophozoites out of the small intestine.  Consuming foods low in simple carbohydrates limits the amount of sugars available in the intestinal lumen, which may lessen the osmotic draw of water into the intestinal lumen, and reduce diarrhea.

Conditions that suggest Giardiasis Infection:

Symptoms - Gas-Int - General

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Risk factors for Giardiasis Infection:

Symptoms - Gas-Int - General

Giardiasis Infection suggests the following may be present:


Recommendations for Giardiasis Infection:


Pippali rasayana

Researchers Agarwal et al investigated the antigiardial and immunostimulatory effects of Pippali rasayana (PR).  Agarwals' research team conducted a double-blind, placebo-controlled trial with 50 subjects, all of whom had clinical signs and symptoms of giardiasis, as well as giardia trophozoites and cysts in the stool.  Twenty-five subjects received active treatment (1gm PR three times daily), while the others received a placebo.  Alter 15 days of treatment, complete disappearance of G. lamblia from the stools was seen in 92% of the PR group and 20% in the placebo group.  Diarrhea and the presence of mucous in the stool were also significantly reduced.  There was also an improvement in cell-mediated immune status, as assessed by the leukocyte migration inhibition test.

Botanical / Herbal

Grapefruit Seed Extract

In a series of almost 200 patients treated for giardia or entamoeba histolytica by a Dr. Parish and his associates over a two month period, grapefruit seed extract gave symptomatic relief more than any other treatment that was tried.


Garlic has traditionally been used as an antiparasitic and antimicrobial agent.  Recent research has substantiated its traditional uses and discovered probable active constituents and possible mechanisms of action.  Harris et al demonstrated the antigiardial activity of both whole raw garlic and some of its constituents.

Whole garlic extract demonstrated an I[C.sub.50] (the concentration that inhibits growth of parasites by 50%) of 0.3mg/ml, while the allicin breakdown products diallyl disulfide, diallyl sulfide, and allyl mercaptan demonstrated I[C.sub.50] values of 0.1mg/ml, 1.3mg/ml, and 0.037mg/ml, respectively.  Other garlic constituents, such as allyl alcohol and dimethyl disulfide were also strongly inhibitory (with I[C.sub.50] values of 0.007mg/ml and 0.2mg/ml, respectively).

Researchers Soffar and Mokhtar performed an open trial investigating the use of garlic in giardiasis.  Twenty-six children infected with G. lamblia took 5ml crude extract (fresh garlic blended with distilled water and then centrifuged and filtered to remove the solids) in 100ml water twice daily or a commercial garlic preparation two capsules (0.6mg capsules) twice daily for three days.  Both preparations were given on an empty stomach two hours before meals.  Clinical symptoms subsided in all cases within 36 hours.  Parasitic cure (according to stool examinations) occurred within three days of beginning treatment.


Wormwood has antiprotozoal activity and is especially effective against giardia, but caution is advised as it can cause a worsening of symptoms and mild intestinal irritation initially.  It may be used with other herbs known for their antiparasitic activity.

Oregon Grape Root

Berberine, from oregon grape or golden seal, has been found effective against diarrheas caused by giardia lamblia (giardiasis).

Indian Long Pepper

Researchers Tripathi et al assessed the antigiardial action of Indian long pepper in vitro, and found aqueous extracts (250mcg/ml) and ethanol extracts (125mcg/ml) demonstrated 100% giardicidal activity.

Berberine-containing Herbs

Berberine salts and extracts have demonstrated in vitro inhibitory activity against Giardia trophozoites, and berberine sulfate has been shown to induce morphological damage to trophozoites, including the appearance of irregularly-shaped vacuoles, swollen trophozoites, and the development of glycogen deposits.

In a placebo-controlled clinical trial, 40 subjects received either a vitamin B-complex syrup (as a placebo), berberine hydrochloride (5 mg/kg/day), or metronidazole for six days.  Berberine administration resulted in a marked decline in gastrointestinal symptoms (superior to that of metronidazole) and a 68% reduction in Giardia-positive stools.  Metronidazole-treated patients were 100% parasite free, and patients on placebo had a 25% reduction in Giardia-positive stools.  The authors speculated that an increase in the dose or a longer duration of treatment would increase berberine's treatment efficacy.

In an uncontrolled trial of 137 children ranging from five months to 14 years, berberine was administered in one of four regimens.  Group 1 received 5 mg/kg/day for five days, group 2 received 5 mg/kg/day for 10 days, group 3 received 10 mg/kg/day for five days, and group 4 received 10 mg/kg/day for 10 days.  The number of individuals with Giardia-negative stool samples was 47% in group 1, 55% in group 2, 68% in group 3, and 90% in group 4. The cure rate in group 4 was comparable to that obtained with furazolidone (92%) and metronidazole (95%).  A small number of subjects in group 4 and in the metronidazole-treated group experienced a relapse one month after treatment ceased.  The authors suggested either re-infection occurred or that a longer duration of treatment or multiple treatment periods may be necessary to improve overall outcomes in some patients.


High/Increased Fiber Diet

Nutritional intervention aims to reduce the acute symptoms of giardia and help clear the infection.  This can best be achieved by consuming a whole-food based, high-fiber diet that is low in fat, lactose, and refined sugars.

Dietary fiber probably plays an important role in the clearance of giardia infection.  One study found that animals consuming a low-fiber diet were found to be significantly more likely to contract giardiasis than were animals on a high-fiber diet.  When infected animals on the low-fiber diet were put on the high-fiber diet, trophozoites were cleared from the small bowel.  The number of trophozoites attached to the jejunal epithelium decreased, while the number associated with the mucous layer increased.  The authors of the study concluded that the fiber induced an increase in mucous secretion and, in combination with the bulk movement of insoluble fiber, reduced trophozoite attachment to the intestinal mucosa and decreased the probability of trophozoites establishing and maintaining mucosal colonization.

Sugar Avoidance / Reduction

See the link between Giardia and High-Fiber Diet.

Dairy Products Avoidance

Studies have shown that giardia infection, whether symptomatic or asymptomatic, can reduce the production of lactase in the small intestine, resulting in lactose malabsorption and its resultant diarrhea.  Therefore, minimizing consumption of lactose-containing dairy products may improve diarrhea and the abdominal bloating and pain commonly associated with giardiasis.  Studies have shown that reducing the consumption of lactose-containing foods to less than 6gm of lactose in a single dose should relieve symptoms.  A 100-150gm serving of yogurt (about 12 cup) contains 3.0-5.3gm of lactose, and thus should be a safe amount to consume.

Low/Decreased Fat Diet

Reducing the intake of fat might reduce the nausea, steatorrhea, and diarrhea often associated with giardiasis.  Dietary fat is also the main stimulator for the release of bile acids into the intestinal lumen, which giardia trophozoites depend on for survival in the small bowel.

Wheat Germ

N-acetyl-D-glucosamine (NAG) residues are major structural components of both giardia cysts and trophozoites.  Wheat germ contains a lectin (wheat germ agglutinin – WGA) that specifically binds to NAG residues.  Commercial wheat germ preparations contain between 13-53mcg of WGA per gm.  In vitro research has demonstrated that pre-exposure of giardia cysts to WGA inhibits excystation by more than 90%.  Wheat germ agglutinin appears to inhibit excystation by interfering with proteolysis of the cyst wall glycoproteins.  In addition, WGA can inhibit the growth of giardia trophozoites in vitro.  Wheat germ agglutinin arrests the trophozoite growth cycle in the G2/M phase, thus preventing Giardia growth, replication, and encystation.

Recommended dose: 2 Tbsp of wheat germ three times daily.

Digestive Aids


Probiotics may interfere with giardia infection through a number of mechanisms, including competition for limited adhesion sites; competition for nutrients that would otherwise be utilized by pathogens (e.g. glucose); and stimulation of the immune response.  Orally-administered probiotics have great potential to affect the microflora of the proximal small intestine as this area is sparsely populated when compared to the colon or distal small bowelProbiotic attachment, subsequent growth, and metabolic activity may have dramatic effects on host immune responses and the local micro-ecology.

Probiotics may also directly inhibit giardial growth and induce innate and immunological antigiardial mechanisms.  For example, Lactobacillus johnsonii strain La1 has demonstrated the ability to produce substances that inhibit growth of G. intestinalis in vitro.  Substances found in L. johnsonii La1 supernatant impaired the ability of giardia to replicate and encyst.  The La1 extracellular products have also been found to cause dramatic alterations in the morphology of giardia trophozoites.

Probiotics can also enhance intestinal IgA immune responses and increase intestinal mucin production.  The actions and qualities of probiotics appear to be strain-specific.  Even closely-related bacterial strains within the same species may have significantly different actions.

Taking sauerkraut or kim chi throughout the day is a dietary measure that often helps.


Prebiotics, such as fructooligosaccharides, may play a minor role in the management of giardiasis, since they primarily affect the large intestine.  Prebiotics possess limited ability to alter the small bowel ecosystem and most likely have no effect in the proximal section of the small bowel where giardia resides.  Prebiotic fermentation increases short-chain fatty acid production in the colon, and subsequent increased mucin production in the GI tract, which may enhance giardial clearing.  Only minimal dosages of prebiotics can be used (e.g. 2gm twice daily), as symptoms such as abdominal bloating and flatulence may increase.



Antibiotic use may best be reserved for cases that fail to respond to initial treatment with natural measures.  Because of the increased risk of side-effects and the possible emergence of antibiotic-resistant organisms, metronidazole, tinidazole, or benzimidazole antibiotics may best be reserved for cases in which the primary non-antibiotic treatment program is ineffective.  In particular, metronidazole has been associated with recurrence rates as high as 90%, and the prevalence of clinical metronidazole-resistance may be as high as 20%.


MSM (Methyl Sulfonyl Methane)

Oregon Health Sciences University researchers have found that MSM has anti-parasitic properties against giardia.

Oxygen/Oxidative Therapies

Ozone / Oxidative Therapy

Cuban doctors are using capsules filled with ozonated oil to treat gastroduodenal ulcers, gastritis, giardia and peptic ulcers.

In 50 cases of giardiasis which did not respond to conventional treatment, ozonated water was administered.  Each patient drank four glasses of ozonated water per day for ten days, followed by a 7-day period without treatment.  This cycle was then repeated a second time.  46% experienced a remission during the first cycle of treatment while an additional 48% became asymptomatic by the end of the second cycle.  There were no adverse side-effects reported. [Revista CENIC Ciencias Biologicas, pp. 61-4]

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