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Classification and external resources
Giardia lamblia SEM 8698 lores.jpg
Giardia cell, SEM
ICD-10 A07.1
ICD-9 007.1
DiseasesDB 5213
MedlinePlus 000288
eMedicine emerg/215
MeSH D005873

Giardiasis (popularly known as beaver fever[1]) is a parasitic disease caused by the flagellate protozoan Giardia lamblia (also sometimes called Giardia intestinalis and Giardia duodenalis).[2] The giardia organism inhabits the digestive tract of a wide variety of domestic and wild animal species, as well as humans. It is a common cause of gastroenteritis in humans, infecting approximately 200 million people worldwide.

Signs and symptoms[edit]

Symptoms include loss of appetite, diarrhea, hematuria (blood in urine), loose or watery stool, stomach cramps, upset stomach, projectile vomiting (uncommon), bloating, excessive gas, and burping (often sulfurous). Symptoms typically begin one to two weeks after infection and may wane and reappear cyclically. Symptoms are caused by Giardia organisms coating the inside of the small intestine and blocking nutrient absorption. Most people are asymptomatic; only about a third of infected people exhibit symptoms. Untreated, symptoms may last for six weeks or longer.

Symptomatic infections are well recognized as causing lactose intolerance,[3] which, while usually temporary, may become permanent.[4][5] Although hydrogen breath tests indicate poorer rates of carbohydrate absorption in those asymptomatically infected, such tests are not diagnostic of infection.[6] It has been suggested that these observations are explained by symptomatic giardia infection allowing for the overgrowth of other bacteria.[6][7]

Some studies have shown giardiasis should be considered as a cause of vitamin B12 deficiency as a result of the problems caused within the intestinal absorption system.[8]


Giardiasis is passed via the fecal-oral route. Primary routes are personal contact and contaminated water and food. The more susceptible are institutional or day-care workers, travelers, those eating improperly treated food or drink, and people who have contact with individuals already infected.

It is a particular danger to people hiking or backpacking in wilderness areas worldwide, especially if they have no immediate access to medical supplies. Giardia is also suspected to be zoonotic—communicable between humans and other animals. Major reservoir hosts include beavers hence its nickname, beaver fever, dogs, cats, horses, humans, cattle and birds.


Giardia are flagellated protozoans that cause decreased expression of brush-border enzymes, morphological changes to the microvillus, and apoptosis of small intestinal epithelial cells. There is no invasion of giardia trophozoites, and small intestinal morphology may appear normal in light microscopy.

The attachment of trophozoites causes villus flattening and inhibition of disaccharidase activities. Ultimately, the enteric microbiota of the intestine overgrow and may be the cause of further symptoms, though this idea has not been fully investigated. The alteration of the villi leads to an inability of nutrient and water absorption from the intestine, resulting in diarrhea, one of the predominant symptoms. In the case of asymptomatic giardiasis, there can be malabsorption with or without histological changes to the small intestine. The degree to which malabsorption occurs in symptomatic and asymptomatic cases is highly varied.

Interestingly, the species Giardia intestinalis has proteinases that attack the villi of the brush border and appear to increase crypt cell proliferation and crypt length of crypt cells existing on the sides of the villi.

On an immunological level, activated host T lymphocytes attack endothelial cells that have been injured in order to remove the cell. This occurs after the disruption of the tight junctions between endothelial cells that make up the brush border. The result is heavily increased intestinal permeability.

There appears to be a further increase in apoptosis by Giardia intestinalis, which further damages the intestinal barrier to permeability. There is significant up-regulation of the apoptotic cascade by the parasite, and, furthermore, substantial down-regulation of the anti-apoptotic proteins Bcl-2 and upregulation of the proapoptotic protein Bax. These connections suggest a role of caspase-dependent apoptosis in the pathogenesis of giardiasis.

Giardia protects its own growth, reducing the formation of nitric oxide by consuming all local arginine, which is the necessary substrate for the production of nitric oxide. Arginine starvation is known to be a cause of programmed cell death, and local removal is a strong apoptotic agent.[9]


  • The mainstay of diagnosis of giardiasis is stool microscopy. This can be for motile trophozoites or for the distinctive oval G.lamblia cysts.
  • The entero-test uses a gelatin capsule with an attached thread. One end is attached to the inner aspect of the patient's cheek, and the capsule is swallowed. Later, the thread is withdrawn and shaken in saline to release trophozoites which can be detected microscopically.
  • A new immunologic test, enzyme-linked immunosorbent assay (ELISA), is now available. These tests are capable of a 90% detection rate or more.[10]
  • Because Giardia lamblia is difficult to detect, often leading to misdiagnoses, several tests should be conducted over a one-week period.[11]


Treatment is not always necessary as the infection usually resolves by itself. But in others, the illness is acute or symptoms persist and medications are needed to treat it. Usually metronidazole, albendazole, and tinidazole are used.

In most countries, the drug used to treat giardiasis is metronidazole. The current research evidence suggests albendazole is probably as effective, but has fewer side effects (gastrointestinal and neurological) and is more convenient to take or administer. Both need a five to 10 day long course; albendazole is taken once a day, while metronidazole needs to be taken three times a day. There is very little evidence to support using any other drugs (tinidazole, quinacrine, furazolidone and nitazoxanide) in preference to these two main options[12][13] but a single dose of tinidazole is considered a first-line agent outside the United States. [14]


Some intestinal parasitic infections may play a role in irritable bowel syndrome.[15]


  1. ^
  2. ^ Huang DB, White AC (June 2006). "An updated review on Cryptosporidium and Giardia". Gastroenterol. Clin. North Am. 35 (2): 291–314, viii. doi:10.1016/j.gtc.2006.03.006. PMID 16880067. 
  3. ^ Pettoello Mantovani M, Guandalini S, Ecuba P, Corvino C, di Martino L (1989). "Lactose malabsorption in children with symptomatic Giardia lamblia infection: feasibility of yogurt supplementation". J. Pediatr. Gastroenterol. Nutr. 9 (3): 295–300. doi:10.1097/00005176-198910000-00006. PMID 2614615. 
  4. ^ Wolfe MS (1975). "Giardiasis". JAMA 233 (13): 1362–5. doi:10.1001/jama.233.13.1362. PMID 1174208. 
  5. ^ Vega-Franco L, Meza C, Romero JL, Alanis SE, Meijerink J (1987). "Breath hydrogen test in children with giardiasis". J. Pediatr. Gastroenterol. Nutr. 6 (3): 365–8. doi:10.1097/00005176-198705000-00010. PMID 3430245. 
  6. ^ a b Moya-Camarena SY, Sotelo N, Valencia ME (2002). "Effects of asymptomatic Giardia intestinalis infection on carbohydrate absorption in well-nourished Mexican children" (PDF). Am. J. Trop. Med. Hyg. 66 (3): 255–9. PMID 12139217. 
  7. ^ Tomkins AM, Wright SG, Drasar BS, James WP (1978). "Bacterial colonization of jejunal mucosa in giardiasis". Trans. R. Soc. Trop. Med. Hyg. 72 (1): 33–6. doi:10.1016/0035-9203(78)90294-8. PMID 635972. 
  8. ^ Cordingley, FT; Crawford, GP (1986). "Giardia infection causes vitamin B12 deficiency". Australian and New Zealand journal of medicine 16 (1): 78–9. doi:10.1111/j.1445-5994.1986.tb01127.x. PMID 3458451. 
  9. ^ Muhkerjee, Sandeep. "Giardiasis". Medscape Reference. Retrieved 21 November 2012. 
  10. ^ Giardia Lamblia and Giardiasis by Robert L. Rockwell, PhD
  11. ^ Center for Disease Control - Parasite division -Giardia
  12. ^ Granados, CE; Reveiz, L; Uribe, LG; Criollo, CP (Dec 12, 2012). "Drugs for treating giardiasis". In Granados, Carlos E. Cochrane database of systematic reviews (Online) 12: CD007787. doi:10.1002/14651858.CD007787.pub2. PMID 23235648. 
  13. ^ Solaymani-Mohammadi, S; Genkinger, JM; Loffredo, CA; Singer, SM (May 11, 2010). "A meta-analysis of the effectiveness of albendazole compared with metronidazole as treatments for infections with Giardia duodenalis". In Keiser, Jennifer. PLOS Neglected Tropical Diseases 4 (5): e682. doi:10.1371/journal.pntd.0000682. PMC 2867942. PMID 20485492. 
  14. ^ Medscape Emedicine - Giardiasis Medication
  15. ^ Stark D, van Hal S, Marriott D, Ellis J, Harkness J (January 2007). "Irritable bowel syndrome: a review on the role of intestinal protozoa and the importance of their detection and diagnosis". Int. J. Parasitol. 37 (1): 11–20. doi:10.1016/j.ijpara.2006.09.009. PMID 17070814. 

Further reading[edit]

Kathleen Meyer, How to Shit in the Woods: An Environmentally Sound Approach to a Lost Art, Ten Speed Press (1989). A practical guide to wilderness waste disposal to prevent giardiasis.

External links[edit]