eMedicine Specialties > Gastroenterology > Intestine

Giardiasis

Author: Sandeep Mukherjee, MB, BCh, MPH, FRCPC, Associate Professor, Department of Internal Medicine, Section of Gastroenterology and Hepatology, University of Nebraska Medical Center; Consulting Staff, Section of Gastroenterology and Hepatology, Veteran Affairs Medical Center
Coauthor(s): Mark H Johnston, MD, Associate Professor of Medicine, Uniformed Services University of Health Sciences; Consulting Staff, Lancaster Gastroenterology Inc
Contributor Information and Disclosures

Updated: Nov 18, 2009

Introduction

Background

Giardia lamblia was originally identified by von Leeuwenhoek in the 1600s and was first recognized in human stool by Vilem Dusan Lambl (1824-1895) in 1859 and by Alfred Giard (1846-1908) after whom it is named. Although it was the first protozoan parasite described, its role as a pathogenic organism was not recognized until the 1970s, after community outbreaks and after the appearance of the disease in travelers returning from endemic regions. Prior to that time, the organism was thought to be a harmless commensal organism of the intestine. (See images below and Images 1-2.)

<em>Giardia lamblia</em>, cyst form.

Giardia lamblia, cyst form.

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<em>Giardia lamblia</em>, cyst form.

Giardia lamblia, cyst form.


<em>Giardia lamblia</em> trophozoites in culture.

Giardia lamblia trophozoites in culture.

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<em>Giardia lamblia</em> trophozoites in culture.

Giardia lamblia trophozoites in culture.


Giardiasis is the most prevalent protozoal infection of the human intestine. G lamblia is one of the most common causative agents of epidemic and endemic diarrheal illness throughout the world. It continues to be the most frequently identified water-borne intestinal pathogen in the United States.1,2,3,4 G lamblia has been found in as many as 80% of raw water supplies from lakes, streams, and ponds and in as many as 15% of filtered water samples.5,6

Pathophysiology

Giardia has one of the simplest life cycles of all human parasites. The life cycle is composed of 2 stages, as follows: (1) the trophozoite (see Image 2), which exists freely in the human small intestine, and (2) the cyst, which is passed into the environment. No intermediate hosts are required. Upon ingestion of the cyst (see Image 1) contained in contaminated water or food, excystation occurs in the stomach and the duodenum in the presence of acid and pancreatic enzymes. The trophozoites pass into the small bowel where they multiply rapidly, with a doubling time of 9-12 hours. As trophozoites pass into the large bowel, encystation occurs in the presence of neutral pH and secondary bile salts. Cysts are passed into the environment, and the cycle is repeated.

The trophozoite form of G lamblia is teardrop-shaped and measures 9-21 micrometers long by 5-15 micrometers wide. The trophozoite has a convex dorsal surface and a flat ventral surface that contains the ventral disk, a rigid cytoskeleton composed of microtubules and microribbons. The trophozoite also contains 4 pairs of flagella, directed posteriorly, that aid the parasite in moving. Two symmetric nuclei with prominent karyosomes produce the characteristic facelike image that appears on stained preparations.

The cyst form of the protozoan is smooth-walled and oval in shape, measuring 8-12 micrometers long by 7-10 micrometers wide. As the cyst matures, nuclear division occurs and readies the cyst to release 2 trophozoites upon excystation. Once the host is infected, trophozoites may appear in the duodenum within minutes.7 Excystation occurs within 5 minutes of exposure of the cysts to an environment with a pH between 1.3 and 2.7.

After infection, the trophozoites attach to the enterocytes via the ventral adhesive disk. This may occur through the presence of lectin on the surface of the trophozoite or through other mechanical means. Encystation is a continuous process during infection. As the trophozoites encounter neutral pH and/or secondary bile salts, encystation-specific secretory vesicles (ESVs) appear. After 15 hours, cyst wall proteins are visible. Within 24 hours after the appearance of ESVs, the trophozoite is covered with these cyst wall proteins, the form of the cyst has emerged, and new antigenic differences are present.

The mechanism of epithelial injury remains unclear.8 However, a study by Panaro et al demonstrated that Giardia trophozoites induce cell apoptosis by activation of both intrinsic and extrinsic apoptotic pathways, down-regulation of the antiapoptotic protein Bcl-2, and up-regulation of the proapoptotic Bax, suggesting a possible role for caspase-dependent apoptosis in the pathogenesis of giardiasis.9

Frequency

United States

This organism remains the most commonly identified intestinal parasite. From 1964-1984, G lamblia caused at least 90 water-borne outbreaks of diarrhea, affecting more than 23,000 people. Groups most at risk for infection include travelers, children, homosexual men, and individuals with immunoglobulin deficiency states (inherited or acquired). A study by Yoder et al reported that, although giardiasis occurs throughout the United States, the incidence is greatest in northern states with a peak onset from early summer through early fall.10 However, this may be related to the differences in individual state surveillance systems and may not necessarily reflect a true increased incidence in northern states.10

International

This organism has a worldwide distribution and is a major cause of epidemic childhood diarrhea in developing countries. Prevalence rates vary from 4-42%. It is the most common gut parasite in the United Kingdom, and infection rates are especially high in Eastern Europe.

Mortality/Morbidity

  • Most infected subjects are asymptomatic, and most infections are self-limited. However, chronic infections, marked by chronic diarrhea/steatorrhea and malabsorption, can occur and can last from weeks to months.
  • Death is rare and usually occurs in malnourished children.
  • G lamblia has been implicated as the chief cause of growth retardation in infected children, even after control of other agents that cause diarrhea.

Race

  • No racial predilection exists for infection.

Sex

  • Infection occurs equally in both sexes.

Age

  • Children are particularly at risk for infection through exposure at day-care centers. Many of the epidemics documented over the last 2 decades have originated in day-care centers.
  • Estimates of the prevalence of infection, defined by the presence of cyst passage, have been as high as 20-25% in children younger than 3 years.11,12

Clinical

History

  • Approximately 15% of cases of giardiasis are asymptomatic, with cyst passage only.
  • Approximately 50% of patients infected with Giardia may present with a variety of symptoms, including acute watery diarrhea, chronic diarrhea with malabsorption and weight loss, and abdominal cramping.
  • Acute diarrhea is the most common symptom of Giardia infection, occurring in 90% of symptomatic subjects.
    • Abdominal cramping, bloating, and flatulence occur in 70-75% of symptomatic patients.
    • The pathogenesis of diarrhea in giardiasis is unknown. Proposed mechanisms include occlusion of the mucosa by large numbers of the organisms, competition with the host for nutrients, epithelial damage, immune-mediated absorptive changes such as transient lactase deficiency, altered mucus secretion, and alterations in motility.
    • The parasite is known to invade the colonic epithelium, but the significance of invasion is not known. The most important result of invasion by the parasite is subsequent activation of host immune processes.
  • Steatorrhea, vitamin B-12, vitamin A, protein, and D-xylose malabsorption all have been documented in patients with chronic infection.
    • Symptoms of chronic infection include chronic diarrhea, malaise, nausea, and anorexia.
    • Weight loss, as extensive as 10-15 pounds in an adult, occurs in approximately 66% of symptomatic patients.
    • Chronic sporadic diarrhea may continue for months.
    • Postinfection lactose deficiency also is a common finding, occurring in 2-40% of cases.
  • Extraintestinal manifestations are rare.
    • Symptoms such as urticaria and reactive arthritis have been reported.
    • The etiology of such extraintestinal symptoms is likely a result of host immune system activation and cross-reactivity/molecular mimicry.

Physical

Physical examination does not contribute to the diagnosis of giardiasis. Some evidence of weight loss may be present, but no known unique physical findings are attributable to giardiasis.

Causes

  • Subjects become infected through ingestion of infectious G lamblia cysts,13 either in contaminated water or food or via direct person-to-person contact.
  • The infectious load required to produce disease may be as low as 10 cysts.
  • The protozoan is known to have multiple strains with varying abilities to cause disease, and several different strains may be found in one host during infection.

More on Giardiasis

Overview: Giardiasis
Differential Diagnoses & Workup: Giardiasis
Treatment & Medication: Giardiasis
Follow-up: Giardiasis
Multimedia: Giardiasis
References
Further Reading
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References

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  3. Eisenstein L, Bodager D, Ginzl D. Outbreak of giardiasis and cryptosporidiosis associated with a neighborhood interactive water fountain--Florida, 2006. J Environ Health. Oct 2008;71(3):18-22; quiz 49-50. [Medline].

  4. Nishi L, Baesso ML, Santana RG, Fregadolli P, Falavigna DL, Falavigna-Guilherme AL. Investigation of Cryptosporidium spp. and Giardia spp. in a public water-treatment system. Zoonoses Public Health. Jun 2009;56(5):221-8. [Medline].

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  9. Panaro MA, Cianciulli A, Mitolo V, Mitolo CI, Acquafredda A, Brandonisio O, et al. Caspase-dependent apoptosis of the HCT-8 epithelial cell line induced by the parasite Giardia intestinalis. FEMS Immunol Med Microbiol. Nov 2007;51(2):302-9. [Medline].

  10. Yoder JS, Beach MJ. Giardiasis surveillance--United States, 2003-2005. MMWR Surveill Summ. Sep 7 2007;56(7):11-8. [Medline].

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  13. Abdul-Wahid A, Faubert G. Characterization of the local immune response to cyst antigens during the acute and elimination phases of primary murine giardiasis. Int J Parasitol. May 2008;38(6):691-703. [Medline].

  14. Nagaty IM, Hegazi MM. Dot-ELISA copro-antigen and direct stool examination in diagnosis of giardiasis patients. J Egypt Soc Parasitol. Aug 2007;37(2):641-8. [Medline].

  15. Morken MH, Nysaeter G, Strand EA, Hausken T, Berstad A. Lactulose breath test results in patients with persistent abdominal symptoms following Giardia lamblia infection. Scand J Gastroenterol. 2008;43(2):141-5. [Medline].

  16. Busatti HG, Vieira AE, Viana JC, Silva HE, Souza-Fagundes EM, Martins-Filho OA, et al. Effect of metronidazole analogues on Giardia lamblia cultures. Parasitol Res. Dec 2007;102(1):145-9. [Medline].

  17. Monajemzadeh SM, Monajemzadeh M. Comparison of iron and hematological indices in Giardia lamblia infection before and after treatment in 102 children in Ahwaz, Iran. Med Sci Monit. Jan 2008;14(1):CR19-23. [Medline].

  18. Busatti HG, Santos JF, Gomes MA. The old and new therapeutic approaches to the treatment of giardiasis: Where are we?. Biologics. 2009;3:273-87. [Medline]. [Full Text].

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  20. Dizdar V, Gilja OH, Hausken T. Increased visceral sensitivity in Giardia-induced postinfectious irritable bowel syndrome and functional dyspepsia. Effect of the 5HT3-antagonist ondansetron. Neurogastroenterol Motil. Dec 2007;19(12):977-82. [Medline].

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  40. Zhou P, Li E, Shea-Donohue T, Singer SM. Tumour necrosis factor alpha contributes to protection against Giardia lamblia infection in mice. Parasite Immunol. Jul 2007;29(7):367-74. [Medline].

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Further Reading

Clinical guidelines
WGO practice guideline: acute diarrhea.
World Gastroenterology Organisation - Medical Specialty Society. 2008 Mar. 28 pages. NGC:006567

Parasitic infections. In: Guidelines for prevention and treatment of opportunistic infections among HIV-exposed and HIV-infected children.
Centers for Disease Control and Prevention - Federal Government Agency [U.S.]. 2004 Dec 3 (revised 2008 Jun 20). 17 pages. NGC:007350

Clinical trials

Efficacy of BIO-K+ CL1285® Prophylaxis in the Prevention of Traveler's Diarrhea in Adults

Parasitic Infections of the Gastrointestinal Tract


Related eMedicine topics

 Giardiasis (Emergency Medicine)

Giardiasis (Pediatrics: General Medicine)

Intestinal Protozoal Diseases

Malabsorption

Malabsorption Syndromes

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Keywords

giardiasis, lambliasis, Giardia, lamblia, Giardia lamblia, intestinal parasite,  G lamblia, Giardia treatment, giardiasis symptoms, giardiasis treatment, protozoan parasites, endemic diarrheal illness, epidemic diarrheal illness, intestinal parasites, gut parasites, protozoal infection

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Contributor Information and Disclosures

Author

Sandeep Mukherjee, MB, BCh, MPH, FRCPC, Associate Professor, Department of Internal Medicine, Section of Gastroenterology and Hepatology, University of Nebraska Medical Center; Consulting Staff, Section of Gastroenterology and Hepatology, Veteran Affairs Medical Center
Sandeep Mukherjee, MB, BCh, MPH, FRCPC is a member of the following medical societies: Royal College of Physicians and Surgeons of Canada
Disclosure: Nothing to disclose.

Coauthor(s)

Mark H Johnston, MD, Associate Professor of Medicine, Uniformed Services University of Health Sciences; Consulting Staff, Lancaster Gastroenterology Inc
Mark H Johnston, MD is a member of the following medical societies: American College of Gastroenterology, American College of Physicians, American Gastroenterological Association, and Christian Medical & Dental Society
Disclosure: Nothing to disclose.

Medical Editor

Manoop S Bhutani, MD, FACG, FACP, Professor, Department of Medicine, Division of Gastroenterology, Director, Center for Endoscopic Ultrasound, Co-Director, Center for Endoscopic Research, Training and Innovation, University of Texas Medical Branch at Galveston
Manoop S Bhutani, MD, FACG, FACP is a member of the following medical societies: American Association for the Advancement of Science, American College of Gastroenterology, American College of Physicians, American Gastroenterological Association, American Institute of Ultrasound in Medicine, and American Society for Gastrointestinal Endoscopy
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Oscar S Brann, MD, FACP, Associate Clinical Professor, Department of Medicine, University of California at San Diego; Consulting Staff, Mecklenburg Medical Group
Oscar S Brann, MD, FACP is a member of the following medical societies: American Gastroenterological Association
Disclosure: Nothing to disclose.

CME Editor

Alex J Mechaber, MD, FACP, Associate Dean for Undergraduate Medical Education, Associate Professor of Medicine, University of Miami Miller School of Medicine
Alex J Mechaber, MD, FACP is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians-American Society of Internal Medicine, and Society of General Internal Medicine
Disclosure: Nothing to disclose.

Chief Editor

Julian Katz, MD, Clinical Professor of Medicine, Drexel University College of Medicine; Consulting Staff, Department of Medicine, Section of Gastroenterology and Hepatology, Hospital of the Medical College of Pennsylvania
Julian Katz, MD is a member of the following medical societies: American College of Gastroenterology, American College of Physicians, American Gastroenterological Association, American Geriatrics Society, American Medical Association, American Society for Gastrointestinal Endoscopy, American Society of Law Medicine and Ethics, American Trauma Society, Association of American Medical Colleges, and Physicians for Social Responsibility
Disclosure: Nothing to disclose.

 
 
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