Basics
Description
Infection of small intestine (duodenum and jejunum) and biliary tract with flagellated protozoan Giardia intestinalis (formerly Giardia lamblia and Giardia duodenalis)
Epidemiology
Giardia is the most common parasitic enteric pathogen diagnosed across the world, including in the United States.
Incidence
- U.S. average is 7.3-7.6 cases per 100,000 and approximately 20,000 cases are reported each year.
- Affects all age groups, but peaks at 1-9 years and less so at 35-49 years of age
- Highest in early summer through early fall and among residents of northern United States
Prevalence
- In the United States, nondysenteric diarrheal stool specimens ranges from 5 to 7%, with higher rates in children (up to 15-30% in United States and developing countries, respectively).
- Acquired by ingestion of cysts directly from infected person (rarely animals) or ingestion of fecally contaminated water or food
- Cysts infectious for as long as person excretes them (weeks to months), and infectious dose is low (10 cysts can produce infection).
- Incubation period usually 1-3 weeks
- Direct person-to-person transmission accounts for the very high prevalence rates in institutions, day care centers, and family contacts.
- Waterborne transmission is an important source of endemic or epidemic spread, especially when water is supplied by surface source such as streams and reservoirs (outdoor recreation and international travel).
- Foodborne infection is less common and generally from food (lettuce) washed by contaminated water source.
Risk Factors
- Day care attendance (poor fecal-oral hygiene)
- Travel to endemic areas
- International adoption
- Contact with recreational fresh water, backpacking, camping, swimming (swallowing water)
- Contact with some animal species
- Certain sexual practices
- Hypochlorhydria (previous gastric surgery)
- Hypogammaglobulinemia, immunodeficiency
General Prevention
- Practice good hygiene (hand washing after toileting, changing diapers, handling animal waste, gardening, tending to a person with diarrheal illness, and when preparing food).
- Exclusion from child care and pool/recreational water during diarrheal illnesses
- Avoiding potentially contaminated water (recreational/drinking) and food
- Examine water source in endemic areas.
- Boiling (1 minute) or filter (National Sanitation Foundation [NSF] Standard 53 or 58) water treatments
- Prevent contact with feces during sex.
- Vitamin A given in children of developing countries may improve host defenses against Giardia infection.
Etiology
- G. intestinalis
- 2-form life cycle: cyst (transmission) and trophozoite (infection)
- Gastric acid and pancreatic enzymes initiate excystation of ingested cysts.
- Trophozoites divide asexually and adhere to brush border of proximal small bowel enterocytes.
- Cyst formation (encystation) occurs in the colon and is passed into the environment.
Pathophysiology
- Trophozoite causes direct damage to intestinal brush border and mucosa (but does not invade mucosa) leading to the following:
- Disruption of tight junctional zonula occludens
- Increased permeability via myosin light chain kinase dependent phosphorylation of F-actin
- Induction of epithelial apoptosis
- Induction of host immune response that results in secretion of fluid and damage to the gut
- Secondary lactase deficiency
Diagnosis
- Most (50-75%) infected individuals are asymptomatic, or have acute self-limiting diarrhea (25-50%) lasting 7-10 days.
- Clinical presentation (acute):
- Sudden-onset watery, foul-smelling diarrhea without blood/pus/mucus
- Malaise
- Bloating/flatulence
- Steatorrhea
- Abdominal cramps
- Anorexia/nausea
- Dyspepsia
- Clinical presentation (chronic):
- Loose, semiformed stool >14 days
- Steatorrhea
- Profound malaise
- Abdominal distention
- Weight loss
- Anorexia
- Flatulence
- Depression
- Alternation of diarrhea/constipation until spontaneous resolution or treatment begun
- Malabsorption syndrome may include the following:
- Steatorrhea
- Deficiencies of iron, d-xylose, vitamins A, B12, and E
- Protein-losing enteropathy
History
- Exposures:
- Habitation or adoption from endemic area
- Attendants of child care centers or inhabitants of institutions
- Camping or hiking near fresh water/recreational water exposure
- Exposure to infected individual
- Underlying immunodeficiency or irritable bowel syndrome (IBS)
- Previous gastric surgery
- Asymptomatic infection can occur.
Physical Exam
- Abdominal distention
- Aphthous ulcers in oral mucosa
- Urticaria
- Arthralgia/arthritis
Diagnostic Tests & Interpretation
Lab
Initial Lab Tests
- Identification of trophozoites or cysts in stool specimens (multiple [3] ova/parasite [O/P] samples collected every other day can be sent to microscopy to increase sensitivity) AND
- Direct fluorescent antibody staining (DFA)
- Real-time PCR is most sensitive and preferred test for diagnosis, as available.
- Other immunodiagnostic kits that do not require microscopy (enzyme immunoassay [EIA]) should not replace O/P and DFA.
- If immunodeficiency is suspected, evaluate humoral immunodeficiency (total immunoglobulins includes IgA).
- WBC usually normal and eosinophilia absent
Diagnostic Procedures/Other
- Consider duodenal aspiration or string test (Enterotest) and rarely biopsy.
Pathologic Findings
Mucosal lesions vary from normal to subtotal villous atrophy, with crypt hyperplasia and proliferation of intraepithelial and lamina propria lymphocytes. Trophozoites may be seen on biopsies.
Differential Diagnosis
- Celiac disease
- Cystic fibrosis
- Lactose intolerance
- Irritable bowel syndrome
- Inflammatory bowel disease
- Nonulcer dyspepsia
Treatment
Medication
- Metronidazole (not approved by FDA)
- Most effective and best tolerated
- Dose: 15 mg/kg/24 h divided t.i.d. PO for 5-10 days
- Tinidazole (approved for children ≥3 years)
- 50 mg/kg, max 2 g; single oral dose
- Available in tablet form only
- Fewer adverse effects than metronidazole
- Nitazoxanide (approved for ages 1-11 years)
- Furazolidone: lower efficacy but better tolerated than metronidazole
- Paromomycin (for symptomatic infection in pregnant women in the 2nd and 3rd trimesters)
- Asymptomatic giardiasis, in absence of risk factors, should not be treated.
- Treatment failures:
- High dose courses of original agent
- Combination of nitroimidazole plus quinacrine for at least 2 weeks
- Treatment of asymptomatic carriers in patients with IBS or in households of patients with cystic fibrosis or hypogammaglobulinemia may be considered.
Ongoing Care
Follow-up Recommendations
Patient Monitoring
- Symptom recurrence can be attributable to reinfection, secondary lactose intolerance, insufficient treatment, or drug resistance.
- Detailed exposure history and O/P and antigen detection with recurrence of symptoms
- If reinfection suspected, a course can be repeated with similar drug, otherwise alternative agent if resistance suspected.
- If symptoms persist, with negative diagnostic studies, consider alternative etiology or enteropathogen.
Diet
Consider lactose avoidance to prevent bloating and diarrhea for 1 month after treatment.
Prognosis
- Remains good for symptomatic patients
- Combination therapy with 2 medications has been successful when repeated courses of single drug have failed.
Complications
- Malabsorption syndrome
- Steatorrhea
- Lactose deficiency
- Deficiencies of iron, folic acid, and vitamins A, B12, and E
- Protein-losing enteropathy
- Urticaria
- Arthralgia
- In pediatric patients:
- Growth retardation
- Failure to thrive
- Lower IQ
- Urticaria
Additional Reading
- Ali SA, Hill DR. Giardia intestinalis. Curr Opin Infect Dis. 2003;16(5):453-460. [View Abstract]
- American Academy of Pediatrics. Giardia intestinalis (formerly Giardia lamblia and Giardia duodenalis) infections. In: Pickering LK, Baker CJ, Kimberlin DW, et al, eds. Red Book: 2012 Report of the Committee on Infectious Diseases. 29th ed. Elk Grove Village, IL: American Academy of Pediatrics; 2012:333-335.
- Huang DB, White AC. An updated review on Cryptosporidium and Giardia. Gastroenterol Clin North Am. 2006;35(2):291-314. [View Abstract]
- Katz DE, Taylor DN. Parasitic infections of the gastrointestinal tract. Gastroenterol Clin North Am. 2001;30(3):797-815. [View Abstract]
- Lima AA, Soares AM, Lima NL, et al. Effects of vitamin A supplementation on intestinal barrier function, growth, total parasitic, and specific Giardia spp infections in Brazilian children: a prospective randomized, double-blind, placebo-controlled trial. J Pediatr Gastroenterol Nutr. 2010;50(3):309-315. [View Abstract]
- Yoder JS, Gargano JW, Wallace RM, et al. Giardiasis surveillance-United States, 2009-2010. MMWR Surveill Summ. 2012;61(5):13-23. [View Abstract]
Codes
ICD09
ICD10
- A07.1 Giardiasis [lambliasis]
SNOMED
- 58265007 Giardiasis (disorder)
- 10679007 Infection by Giardia lamblia
FAQ
- Q: How is G. intestinalis likely contracted?
- A: Most community-wide epidemics occur from a contaminated water supply (drinking water), as well as person-to-person transmission in child care and institutional settings. Food and food handler-associated outbreaks are less reported.
- Q: What do I do if I suspect Giardia, but the stool sample is negative?
- A: 3 O/P samples are needed and should optimally be done every other day on a diarrheal stool specimen with a DFA to increase diagnostic sensitivity. Stool samples should be examined as soon as possible or placed immediately in a preservative, such as neutral buffered 10% formalin or polyvinyl alcohol. If endemic areas, it may be appropriate to treat empirically. If stool testing is negative and the diagnosis is strongly suspected, you can consider ordering a commercially available string test (designed to obtain bile-stained mucus from duodenum to reveal trophozoites on wet mount) or refer to a pediatric gastroenterologist, who can perform endoscopy with duodenal aspiration and biopsy.