OVERVIEW: What every practitioner needs to know

Are you sure your patient has giardiasis? What are the typical findings for this disease?

Infection with Giardia typically presents with insidious symptoms developing over 1 to 2 weeks. Symptoms of acute giardiasis include:

Watery diarrhea, frequently foul smelling with fatty stools

Abdominal cramps and bloating

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Acute infection may be self-limited but up to one half of symptomatic patients go on to experience chronic infection with ongoing loose stools, steatorrhea, abdominal cramping, borborygmus, weight loss, malabsorption, malaise, and fatigue lasting many months.

Asymptomatic infection occurs frequently and may contribute to transmission.

Additional clinical observations

Fever occurs in only 10%-15% of cases.

Untreated symptoms generally persist for 2-4 weeks or more and significant weight loss may occur.

Up to one half of symptomatic cases progress to chronic disease, with continued loose stools, stomachache, malaise, weight loss, and malabsorption.

Up to 40% of patients experience acquired lactose intolerance, which can persist for months, even after the infection resolves.

What other disease/condition shares some of these symptoms?

Other protozoan infections (e.g., Cryptosporidium, Cyclospora)

Malabsorption syndrome

Lactose intolerance (which may be part of the disease state or occur independently)

Inflammatory bowel disease

What caused this disease to develop at this time?

The peak of giardiasis cases occur in early summer through fall (reflecting outdoor activities with potential exposure to contaminated water and animals) and in children younger than 5 years of age.

Risk factors for acquiring Giardia infection include:

Recreational water exposure, swimming or drinking untreated water from streams or lakes

International travelers and children adopted internationally

Attendance at child care facilities

Institutionalization (e.g., nursing home)

Unprotected anal intercourse

Contact with infected animals

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

Examination of fresh stool for Giardia cysts and trophozoites; evaluation of three stools increases sensitivity from 50%-70% for a single stool to approximately 90%.

Giardia antigen detection assays (enzyme-linked immmunosorbent assay, direct-fluorescent antibody assay) are commercially available and have increased sensitivity compared with microscopic examination with a specificity of ≥98%.

Rarely the diagnosis is made by duodenal biopsy if noninvasive tests do not reveal the diagnosis.

Would imaging studies be helpful? If so, which ones?

Imaging studies are not routinely indicated in the evalutaion of giardiasis.

If you are able to confirm that the patient has giardiasis, what treatment should be initiated?

See Table I for Giardia treatment regimens.

Table I.
Dosage Advantages Disadvantages/Side Effects
Primary Agents
Metronidazole 5 mg/kg/dose × 5-7 d(maximum dose = 250 mg) Most commonly used drug in United States80%-95% cure rate Metallic taste, nausea, vomiting, dizziness, headache, disulfaram-like effectNeutropenia
Tinidazole 2 g × 1 dose Single-dose therapy ~90% efficacySame drug class (nitroimidazole) as metronidazole Same as metronidazole, although less common overall
Nitazoxanide Age 1-2 y: 100 mg BID × 3 dAge 4-11 y: 200 mg bid × 3 d>11 y: 500 mg bid × 3 d Pediatric efficacy 70%-85% Abdominal pain; diarrhea; dizziness; ↓ appetite; nausea; vomiting; yellow discoloration of urine, skin, sclerae; exfoliative dermatitis, psychosis
Secondary Agents
Mebendazole 200 mg tid × 5 d ~80% positive cure rateAvailable in tablets or suspension Not approved for giardiasis in United StatesFewer side effects than metronidazole or tinindazole
Albendazole 15 mg/kg/dose × 5-7 d(maximum dose = 400 mg) As effective as metronidazoleFewer adverse reactions Abdominal discomfort, nausea, vomiting, headache, dizziness, ↑ transaminase levels; leukopeniaAvailable in tablets only
Paromomycin 10 mg/kg/dose TID × 5-10 d (maximum dose = 500 mg) Nonabsorbable aminoglycoside: safe in second and third trimesters of pregnancy Less effectiveAbdominal pain, nausea, diarrhea, dizziness, rash, ototoxicity and nephrotoxicity

Furazolidone and quinacrine are other drugs available for treating giardiasis, but they are not currently available in the United States.

If symptoms recur after therapy, consideration should be given to possible ongoing exposure with reinfection or drug resistance. In such cases after addressing sources of reinfection, one could consider a longer course of the original agent or an alternative drug.

Combination therapy (e.g., albendazole and metronidazole), especially in patients with underlying immunodeficiency or cystic fibrosis, might be considered.

Patients requiring more than one course of treatment should be evaluated for immunodeficiency if not done previously.

Treatment of asymptomatic individuals with giardiasis is controversial, although it could be considered in an outbreak to help control spread.

What are the adverse effects associated with each treatment option?

See Table I.

What are the possible outcomes of giardiasis?

Giardiasis is typically a self-limited infection that responds well to therapy.

International adoptees should be screened for Giardia on initial evaluation and treated if positive to eliminate any possible contribution to poor weight gain in the child.

With chronic infection, response to treatment may be slower and residual lactose intolerance may persist for weeks to months after the infection has cleared.

Treatments for the infection have some side effects (see Table I) but the courses are relatively short so that the reactions are generally manageable.

What causes this disease and how frequent is it?

The flagellated protozoan Giardia duodenalis (also known as G. intestinalis and previously G. lamblia) is the most commonly identified diarrheal parasite in the United States. The organism also has a worldwide distribution and has been found in a number of other mammalian species (e.g., beavers, dogs, cattle, and sheep) as well as in people.

The protozoan is shed in feces and can survive in fresh water such as mountain streams or lakes. Untreated well water and fecally contaminated food and water are the most common sources of infection. Person-to-person transmission through the fecal-oral route can also occur.

Giardiasis is a nationally reportable gastrointestinal illness with approximately 20,000 cases/year noted in the United States. Reported cases of giardiasis likely greatly underestimate the burden of disease, as many cases are asymptomatic or may be mild enough not to require medical attention or have stools for analysis.

How do these pathogens/genes/exposures cause the disease?

Giardia is not an invasive organism, but when ingested the cysts of the organism can attach to the duodenum and jejunum and release trophozoites that are capable of dividing by binary fission.The trophozoites then pass to the large intestine where they revert to cyst forms that are excreted in the feces.The exact mechanism by which the organism causes disease is not completely understood. Since Giardia is noninvasive, peripheral eosinophilia or leukocytosis and white blood cells are not seen on stool examination.

What complications might you expect from the disease or treatment of the disease?

Chronic giardiasis may be associated with significant malabsorption and weight loss.

How can giardiasis be prevented?

Strict handwashing in child care and institutional settings

Clean surfaces after diaper changes

Water purification (boiling ≥ 1 minute, filtration [0.2- to 1-micron filter or iodine treatment]) before drinking surface or untreated well water

Avoid swallowing water while swimming in lakes, streams

Safe sexual practices, especially with anal sex

Wash, peel, or cook raw fruits and vegetables before eating

Drink only pasteurized milk, juices, cider

What is the evidence?

Pickering, LK. ” infections (giardiasis)”. Red Book: 2009 Report of the Committee on Infectious Diseases. vol. 303. 2009. pp. 784

Huang, DB, White, AC. “An updated review on Cryptosporidium and Giardia”. Gastroenterol Clin North Am. vol. 35. 2006. pp. 291-314.

“Drugs for Parasitic Infections”. 2010.

Munoz, FM. “Treatment and prevention of giardiasis”. . 2011.

Ongoing controversies regarding etiology, diagnosis, treatment

The main controversies regarding giardiasis management relate to the optimal agent for therapy and optimal duration of therapy.