Introduction
Background
Giardiasis is a major diarrheal disease found throughout the world. The flagellate protozoan Giardia lamblia, its causative agent, is the most commonly identified intestinal parasite in the United States and the most common protozoal intestinal parasite isolated worldwide.
Giardiasis usually represents a zoonosis with cross-infectivity between animals and humans. Giardia have been isolated from the stools of beavers, dogs, cats, rodents, sheep, and cattle.
Pathophysiology
Giardiasis is caused by ingestion of Giardia cysts, which retain viability in cold water for as long as 2-3 months. The infective dose is low in humans; 10-25 cysts are capable of causing clinical disease in 8 of 25 subjects. Ingestion of more than 25 cysts results in a 100% infection rate. After ingestion of cysts, excystation, trophozoite multiplication, and colonization of the upper small bowel occur.
The exact pathophysiology of giardiasis is unclear. Postulated mechanisms include damage to the endothelial brush border, enterotoxins, immunologic reactions, and altered gut motility and fluid hypersecretion via increased adenylate cyclase activity. Adhesion of trophozoites to the epithelium has been demonstrated to cause increased epithelial permeability. Giardia- induced loss of intestinal brush border surface area, villus flattening, inhibition of disaccharidase activities, and eventual overgrowth of enteric bacterial flora appear to be involved in the pathophysiology of giardiasis but have yet to be causatively linked to the disease's clinical manifestations.
Most infections result from fecal-oral transmission or ingestion of contaminated water. Contaminated food is a less common etiology. Person-to-person spread is common, with 25% of family members with infected children themselves becoming infected.
Most infections are asymptomatic, and the attack rate for symptomatic infection in the natural setting varies from 5-70%. Giardia is found in healthy people in endemic areas and in asymptomatic carrier states with high numbers of cysts excreted in stools common.
Predisposing factors to symptomatic infection include hypochlorhydria, various immune system deficiencies, blood group A, and malnutrition. The incubation period averages 1-2 weeks, with a mean of 9 days. The average duration of symptoms in all ages ranges from 3-10 weeks.
Frequency
United States
Giardiasis is found throughout the United States; however, the incidence appears greatest in northern states. Carrier rates as high as 30-60% have been documented among children in day care centers, institutions, and on Native American reservations. Endemic infection occurs most commonly from July through October among children younger than 5 years and adults aged 25-39 years. Between 1964 and 1984, 90 outbreaks (24,000 cases) of giardiasis in the United States were linked epidemiologically to water. These outbreaks typically occurred in small water systems using untreated or inadequately treated surface water.
Most water-borne outbreaks in the United States have occurred in western mountain regions (Rocky Mountains, Sierra Nevada, Cascades) where giardiasis must be considered endemic. However, since water-borne giardiasis outbreaks have been reported in every region in the United States, the diagnosis must be considered anywhere in the country. Areas and populations with poor hygiene and close physical contact tend to have higher rates of infection. Venereal transmission has been reported among homosexuals through direct fecal-oral contamination.
International
Giardiasis is prevalent throughout the world. Giardia is one of the first enteric pathogens to infect infants in the developing world, with peak prevalence rates of 15-20% in children younger than 10 years.
A recent study demonstrated a Giardia infection rate of 19.6 per 100,000 population per year in Canada.1 While the yearly incidence of the disease was stable, a significant seasonal variation was observed, with a peak in late summer to early fall, which correlates with the pattern found in the United States.1
Giardiasis accounts for a relatively small percentage of traveler's diarrhea. It is more likely to be found as the cause of diarrhea that occurs or persists after returning home from travel to developing regions of the world due to its relatively long incubation period and persistent symptoms. Giardia has been identified as the causative agent in a large percentage of cases among travelers in the region of St. Petersburg, Russia, where tap water is the primary source.
Mortality/Morbidity
Giardiasis is not associated with mortality except in cases of extreme dehydration and malnourishment, primarily in infants. Morbidity is moderate and involves primarily GI symptoms.
Race
Giardiasis does not have any race predilection. Native American populations residing on reservations can have high carrier rates.
Sex
Males have been noted to be at higher risk for infection than females. A Canadian population study demonstrated infection rates of 21.2 per 100,000 per year versus 17.9 per 100,000 per year for males and females, respectively, resulting in a relative risk of 1.19.1
Age
Giardiasis occurs in all ages but is most common in early childhood, possibly through exposure at daycare centers.
Clinical
History
A broad spectrum of clinical syndromes may occur. The vast majority of symptoms are GI in nature.
- Gastrointestinal
- A small number of persons develop abrupt onset of explosive, watery diarrhea, abdominal cramps, foul flatus, vomiting, fever, and malaise; these symptoms last 3-4 days before transition into the more common subacute syndrome.
- Most patients experience a more insidious onset of symptoms, which are recurrent or resistant.
- Stools become malodorous, mushy, and greasy. Watery diarrhea may alternate with soft stools or even constipation. Stools do not contain blood or pus because dysenteric symptoms are not a feature of giardiasis.
- Upper GI symptoms, often exacerbated by eating, accompany stool changes or may be present in the absence of soft stools. These include upper and midabdominal cramping, nausea, early satiety, bloating, sulfurous belching, substernal burning, and acid indigestion.
- Constitutional symptoms
- Anorexia, fatigue, malaise, and weight loss are common.
- Weight loss occurs in more than 50% of patients and averages 10 pounds per person.
- Chronic illness may occur with adults presenting with long-standing malabsorption syndrome and children with failure to thrive.
- Lactose intolerance
- Miscellaneous: Unusual presentations include allergic manifestations such as urticaria, erythema multiforme, bronchospasm, reactive arthritis, and biliary tract disease.
Physical
- Physical examination generally is unremarkable.
- Abdominal examination may reveal nonspecific tenderness without evidence of peritoneal irritation.
- Rectal examination should reveal heme-negative stools.
- In severe cases, evidence of dehydration or wasting may be present.
Causes
- Giardiasis is caused by the ingestion of infective cysts.
- Person-to-person transmission, often associated with poor hygiene and sanitation, is a primary means of infection.
- Diaper changing and inadequate hand washing are risk factors for transmission from infected children.
- Children attending day care centers, as well as day care workers, have a higher risk of infection secondary to fecal-oral transmission.
- Water-borne transmission is responsible for a significant number of epidemics in the United States, generally following ingestion of unfiltered surface water. Giardia was implicated in 90 waterborne outbreaks in the United States from 1964-1984, affecting 23,500 persons.
- Venereal transmission occurs through fecal-oral contamination.
- Food-borne epidemics have been reported, most commonly secondary to contamination by infected food-handlers.
- Pets frequently harbor Giardia in their GI tracts, but they are not thought to be a significant cause of outbreaks in humans.
More on Giardiasis |
 Overview: Giardiasis |
| Differential Diagnoses & Workup: Giardiasis |
| Treatment & Medication: Giardiasis |
| Follow-up: Giardiasis |
| Multimedia: Giardiasis |
| References |
| Further Reading |
| Next Page » |
References
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Further Reading
Clinical guidelines
Practice guidelines for the management of infectious diarrhea. Guerrant RL, Van Gilder T, Steiner TS, Thielman NM, Slutsker L, Tauxe RV, Hennessy T, Griffin PM, DuPont H, Sack RB, Tarr P, Neill M, Nachamkin I, Reller LB, Osterholm MT, Bennish ML, Pickering LK; Infectious Diseases Society of America. Clin Infect Dis. 2001 Feb 1;32(3):331-51.
Keywords
giardiasis, traveler's diarrhea, Giardia, Giardia lamblia, lambliasis, Giardia intestinalis, Giardia duodenalis, backpacker's diarrhea, beaver fever
