Giardiasis

What is Giardiasis

Giardiasis is an infection of the small intestine with the parasite Giardia intestinalis.

The parasite is often found in unclean (contaminated) water or areas with poor sanitation. It usually takes 1–3 weeks after swallowing the parasite to become sick. The illness usually lasts 1–2 weeks, but it may last longer.

What causes Giardiasis?

This condition is caused by swallowing the parasite. This can occur by:

  • Drinking contaminated water or eating ice that was made with contaminated water.
  • Eating contaminated food. This can include raw food that was washed with contaminated water.
  • Coming into contact with the feces of a person who is infected and then passing the parasite from your hands to your mouth. This can happen after coming in contact with a surface that contains feces, such as bathroom handles or diaper changing tables.
  • Swallowing contaminated water when swimming in lakes, ponds, or rivers.

What increases the risk?

This condition is more likely to develop in people who:

  • Do not have access to clean water.
  • Are the parent of a young child.
  • Work at a daycare or long-term care facility.
  • Have anal sex without a condom with someone who is infected.
  • Live with or care for someone with giardiasis.
  • Frequently camp or hike and drink unclean water.
  • Travel to areas that to do not have access to clean water.
  • Have certain digestive or gastric disorders, such as pancreatitis.

What are the symptoms?

Symptoms of Giardiasis include:

  • Bad-smelling and watery diarrhea.
  • Nausea.
  • Stomach cramps and pain.
  • Gas or bloating.
  • Greasy stools (feces) that float.
  • Fatigue.
  • Weight loss.
  • Fever.
  • Dehydration. Signs of dehydration can include:
    • Dry mouth and sticky tongue.
    • Headaches.
    • Dizziness.
    • Irritability.
    • Dry skin.
    • Weakness.
    • Dark yellow urine or a decrease in urination.
    • Constipation.

Some people do not develop symptoms, but they can still infect other people.

How is this diagnosed?

This condition is diagnosed based on:

  • Your medical history.
  • Your symptoms.
  • A physical exam.
  • Your travel history.
  • Tests, including:
    • A stool sample test. You may need to submit several stool samples taken over the course of a few days.
    • Blood tests.

How is this treated?

This condition is treated with antibiotic medicines or medicines that kill the parasite (antiparasitics). If you are pregnant, you may need to take different medicines. For mild symptoms, you may not need medicine. It is important to discuss treatment options with your health care provider.

Follow these instructions at home:

  • Take over-the-counter and prescription medicines only as told by your health care provider.
  • If you were prescribed an antibiotic medicine, take it as told by your health care provider. Do not stop taking the antibiotic even if your condition improves.
  • Always wash your hands after going to the bathroom or changing diapers, and before preparing food. Use soap and water when washing your hands. If soap and water are not available, use hand sanitizer.
  • Follow your health care provider’s instructions about what you can or cannot eat or drink, such as dairy products.
  • Drink enough fluid to keep your urine clear or pale yellow.
  • Keep all follow-up visits as told by your health care provider. This is important.

How is this prevented?

  • Boil your water or drink bottled water in areas of giardiasis contamination.
  • Do not eat ice that was made from poorly treated water. Do not drink beverages with ice that was made from poorly treated water.
  • Do not swallow water while swimming in pools, hot tubs, ponds, lakes, or the ocean.
  • Use safe, clean water to wash all foods.
  • Avoid eating raw or undercooked foods from areas with poorly treated water.
  • Always wash your hands after going to the bathroom, changing diapers, or gardening, and before preparing food. Use soap and water when washing your hands. If soap and water are not available, use hand sanitizer.
  • Practice safe sex and use condoms.

Make sure to clean and disinfect areas in the house that may have been contaminated with feces from an infected person. These include hard surfaces, furniture, bedding, and toys.

Contact a health care provider if:

  • Your symptoms get worse.
  • Your symptoms come back after you finish treatment.
  • You have symptoms of dehydration, including:
    • Dry mouth and sticky tongue.
    • Headaches.
    • Dizziness.
    • Irritability.
    • Dry skin.
    • Weakness.
    • Dark yellow urine or a decrease in urination.
    • Constipation.
  • You have a fever.
  • You continue to lose weight after treatment.
  • You have joint pain.

Get help right away if:

  • You have blood in your stool.
  • You have symptoms of severe dehydration, including:
    • Rapid heartbeat.
    • Sunken eyes.
    • Inability to sweat or produce tears.
    • No urination for more than 8 hours.
    • Extreme thirst.
    • Low blood pressure.
    • Confusion.
    • Fever.

Summary

  • Giardiasis is an infection of the small intestine with the parasite Giardia intestinalis.
  • This parasite is often found in unclean (contaminated) water or areas with poor sanitation.
  • You can develop this condition after swallowing the parasite.
  • This condition is treated with antibiotic medicines or medicines that kill the parasite (antiparasitics).
  • Handwashing is an important part of preventing giardiasis. Always wash your hands after going to the bathroom, changing diapers, or gardening, and before preparing food. Use soap and water when washing your hands. If soap and water are not available, use hand sanitizer.

Detailed Info of Giardiasis

7 Interesting Facts of Giardiasis

  1. Giardiasis is an intestinal infection by the protozoan parasite Giardia
  2. Common symptoms include diarrhea, flatulence, abdominal cramps, and bloating
  3. Diagnosis is established by detection of Giardia in stool immunoassay, ova and parasites stool examination, or examination of upper intestinal contents
  4. Antiprotozoal agents most commonly used for treatment include metronidazole, tinidazole, and nitazoxanide; paromomycin is recommended for pregnant or nursing patients
  5. Comorbid infection with amebiasis may require increased dosing and treatment time
  6. Complications include lactose intolerance, irritable bowel syndrome, and a number of extraintestinal sequelae including ocular and nutritional complications
  7. With treatment, symptoms should clear in 5 to 7 days, but infection may last several months if untreated

Pitfalls

  • Carriers of Giardia may be asymptomatic and the infection may not be recognized, facilitating inadvertent spread
  • Giardiasis is an intestinal infection by the protozoan parasite Giardia 
    • Responsible species is most often referred to as Giardia lamblia; also known as Giardia duodenalis or Giardia intestinalis
    • May cause either acute self-limited diarrhea or chronic diarrhea with or without malabsorption; may also be asymptomatic

Classification

  • Acute
    • Symptoms, if they occur, appear 7 to 14 days after infection 
    • Symptomatic infection typically lasts 7 to 14 days, but it may persist several months and become chronic 
  • Chronic
    • Symptoms can occur continuously, intermittently, recurrently, or sporadically 
    • Stools may be normal between bouts of diarrhea
    • Often results in malabsorption 

Clinical Presentation

History

  • Many patients are asymptomatic 
  • Typical symptoms are gastrointestinal in nature
    • Diarrhea is the predominant symptom, occurring in about 89% of patients, ranging from acute self-limiting to chronic 
      • Loose, foul-smelling, and greasy stools occur in about 72% of patients 
    • Other symptoms
      • Malaise is common (about 84% of patients), particularly in more severe cases 
      • Flatulence is characteristic (about 74% of patients) 
      • Abdominal cramps (about 70% of patients) 
      • Bloating (about 69% of patients) 
      • Weight loss occurs in 64% of patients; it may be significant (4.5 kg or more in adults) 
      • Anorexia and nausea occur in 64% to 68% of patients 
  • Additional symptoms in chronic disease
    • Stools may be frothy, yellow, and of small volume
      • Constipation is possible between bouts of diarrhea
    • Chronic abdominal discomfort, which may increase after eating
    • Severe weight loss and debilitation in children may result from malabsorption associated with chronic diarrhea; poorly absorbed nutrients include vitamin A, vitamin B₁₂, protein, D-xylose, and iron 
    • Failure to thrive in children 
    • Inanition
    • Headache

Physical examination 

  • Fever is rare and is low grade if present
  • Mild abdominal distention, possibly with tympany on percussion
  • Increased bowel sounds may be noted
  • Mild abdominal tenderness on palpation, without peritoneal signs

Causes

  • Infection by protozoan parasite Giardia lamblia 

Risk factors and/or associations

Age
  • Higher incidence in children aged 1 to 9 years 
Sex
  • Reported slightly more often in men 
Other risk factors/associations
  • Situations that increase risk for contracting Giardia infection
    • Contaminated water
      • Consumption of unsterilized freshwater from streams, rivers, or lakes 
      • Recreation in contaminated water, resulting in inadvertent ingestion (eg, swimming in public swimming pool, lake, or river; white-water rafting) 
    • Recent travel to areas with poor sanitation and unsafe water 
    • Attendance in day care or school where Giardia infection is common 
    • HIV or other causes of immunodeficiency
    • Oral-anal sexual practices
    • Poor hygiene

Diagnostic Procedures

Primary diagnostic tools

  • Detection of Giardia in stool
    • Traditional method involves direct observation of trophozoites or cysts in stool 
      • Requires an experienced microscopist
    • Because the level of Giardia in the stool can be highly variable, more sensitive and specific detection methods may be necessary to make or confirm diagnosis
      • Immunoassays to detect Giardia antigens in stool include immunofluorescence ELISAs and direct fluorescence antibody tests
  • In cases in which Giardia infection is strongly suspected but results of repeated stool analyses are negative, examination of the duodenum, in which Giardia exist at the highest level, may yield positive results
    • String test is a noninvasive means of obtaining duodenal contents
    • Endoscopic aspiration with biopsy also allows examination for other enteric parasites and for noninfectious causes; this is not routine but can help if other results are unclear

Laboratory

  • Ova and parasites examination of stool for cysts or trophozoites
    • Trophozoites
      • Can be identified using direct smears or fecal wet mounts of fresh, watery stools
    • Cysts
      • Must be stained with iodine (fresh) or with trichrome or iron hematoxylin staining
      • Can be identified in both formed and unformed stools
      • Examination of 3 stool samples from 3 different days increases sensitivity to more than 90%, compared with 1 sample (60%-80%) or 2 samples (80%-90%)
  • ELISA or direct fluorescence immunoassays that recognize antigens specific to Giardia 
    • Various commercial kits are available
    • Sensitivity and specificity are as good as or better than microscopic examination ; sensitivities and specificities above 94%
    • Faster and more reproducible compared with the ova and parasites examination

Procedures

  • String with gelatin capsule is swallowed by the patient; the string is later retrieved, and duodenal contents adhering to the string are examined for Giardia trophozoites
  • Often referred to by trade name Entero-Test
  • Giardiasis is suspected but stool examination results are consistently negative
  • Identification of Giardia trophozoites from bile-stained mucus on retrieved string indicates infection
  • Endoscopy to obtain tissue specimen and a sample of the upper intestinal contents
  • Giardiasis is suspected but stool examination results are consistently negative
  • Other causes, including noninfectious ones, are considered
  • Presence of Giardia in duodenal aspirates or tissue samples is diagnostic

Differential Diagnosis

Most common

  • Other infections that cause diarrhea
    • Bacterial and viral gastroenteritis
      • Characterized by gastrointestinal symptoms including diarrhea and abdominal cramps, as with giardiasis
      • Duration of illness is generally shorter (5-7 days); presence of fever depends on the organism, but generally it is more common with bacterial diarrhea than with giardiasis
      • Differentiate by stool culture result positive for recognized enteric pathogens
    • Viral gastroenteritis
      • Characterized by gastrointestinal symptoms including watery diarrhea and abdominal cramps, as with giardiasis
      • Nausea and vomiting may be more prominent in viral infection than in giardiasis; viral infections usually resolve spontaneously and more quickly than giardiasis (3-5 days)
      • Differentiate by rapid antigen tests if due to a virus for which assays are available (eg, rotavirus, norovirus) or by clinical context in typical community outbreak situations
    • Cryptosporidiosis
      • Diarrheal disease, similar to giardiasis
      • Stools are frequent, watery, and may occur in large volume
      • Low-grade fever is more common in cryptosporidiosis than in giardiasis
      • Differentiate from giardiasis by presence of acid-fast cryptosporidial oocysts in stool
    • Cyclospora infection
      • Intestinal infection by Cyclospora cayetanensis spread by oral-fecal route
      • As with giardiasis, diarrhea and abdominal cramps are characteristic
      • Explosive diarrhea and nonspecific flulike symptoms are more prevalent than in giardiasis
      • Differentiate from giardiasis by presence of Cyclospora oocytes in stool 
  • Irritable bowel syndrome
    • Chronic functional condition characterized by alternating diarrhea and constipation; bloating and abdominal discomfort are usually prominent features
    • Fever is absent
    • Differentiate from giardiasis by chronicity and by absence of laboratory demonstration of Giardia
    • Diagnosis may be complicated by the fact that giardiasis can precipitate irritable bowel syndrome, in which case symptoms may be mistaken for apparent relapse

Treatment Goals

  • Eliminate parasitic infection

Disposition

Admission criteria

Dehydration or electrolyte imbalances may require hospital admission; may require oral or IV fluid supplementation

Criteria for ICU admission
  • Severe dehydration and electrolyte imbalances can lead to need for ICU admission, but giardiasis rarely leads to such severe illness

Recommendations for specialist referral

  • Refer to a gastroenterologist if elusive diagnosis requires endoscopy and intestinal biopsy

Treatment Options

Asymptomatic infection

  • If Giardia is detected and there is little chance of reinfection, treatment is warranted
  • If Giardia is detected and there is a strong chance of reinfection, treatment can be withheld
  • If Giardia is associated with failure to thrive in children, treatment is called for even when reinfection is likely
  • For asymptomatic children who risk infection of family members and other students: treat
  • For asymptomatic patients with likelihood of transmission to others (eg, food handlers): treat

Symptomatic infection 

  • Treat all symptomatic patients

Treatment consists of drug therapy and, if diarrhea warrants it, fluid and electrolyte management

  • Metronidazole, tinidazole, and nitazoxanide are the most common drugs used to treat giardiasis
    • Metronidazole is usually first line therapy for giardiasis (off-label use but widely implemented)
    • Tinidazole is associated with fewer adverse events compared with metronidazole. Outside the United States, it is sometimes considered first line therapy when single-dose administration is important 
  • Quinacrine, furazolidone, albendazole, and paromomycin are used less frequently and are associated with significant adverse effect profiles
    • Quinacrine is no longer produced in the United States but may be obtained from select pharmacies
    • Furazolidone is available in liquid suspension and may be used for pediatric patients
    • Use caution with paromomycin in those with impaired renal function, because of potential for nephrotoxicity

Drug therapy

  • Nitroimidazoles
    • Metronidazole
      • Giardiasis is off-label use
        • Metronidazole benzoate Oral powder; Infants, Children, and Adolescents: 15 mg/kg/day (Max: 750 mg/day) PO divided every 8 hours for 5 to 7 days.
        • Metronidazole Oral capsule; Adults: 250 mg PO 3 times daily for 5 to 7 days.
      • Not to be taken with alcohol, owing to potential for disulfiram-like reactions
    • Tinidazole
      • Less toxic than metronidazole, but equally or more effective 
        • Tinidazole Oral tablet; Children and Adolescents 4 to 17 years: 50 mg/kg/dose (Max: 2 g/dose) PO as single dose.
        • Tinidazole Oral tablet; Adults: 2 g PO as single dose.
      • Although disulfiram-like reactions have not been reported, avoidance of alcohol is prudent based on the chemical similarity to metronidazole
  • 5-nitrothiazole derivatives
    • Nitazoxanide
      • Nitazoxanide Oral suspension; Children 1 to 3 years: 100 mg PO every 12 hours with food for 3 days.
      • Nitazoxanide Oral suspension; Children 4 to 11 years: 200 mg PO every 12 hours with food for 3 days.
      • Nitazoxanide Oral tablet; Adults: 500 mg PO twice daily for 3 days.
  • Benzimidazoles
    • Albendazole
      • Giardiasis is off-label use
      • Albendazole Oral tablet; Children and Adolescents: 10 mg/kg (Max: 400 mg/dose) PO daily for 5 days.
      • Albendazole Oral tablet; Adults: 400 mg PO once daily for 3 days.
  • Aminoglycosides
    • Paromomycin 
      • Use in pregnant or lactating patients
      • Giardiasis is off-label use
      • Paromomycin Sulfate Oral capsule; Adults, Adolescents, and Children: 30 mg/kg/day PO for at least 5 days.
  • Resistance of Giardia to drug treatment has been reported
    • Alternative treatments include:
      • Quinacrine 
        • NOTE: This drug is discontinued in the United States. Some pharmacies may compound quinacrine capsules from supplies of bulk powder
        • Quinacrine Oral capsule; Children and Adolescents: 7 mg/kg/day PO in 3 divided doses for 5 to 7 days. Max: 300 mg/day.
        • Quinacrine Oral capsule; Adults: 100 mg PO 3 times per day for 5 to 7 days.
      • Furazolidone
        • Not available in the United States
        • Furazolidone Oral suspension; Children and Adolescents: 2 mg/kg PO 4 times per day for 10 days.
        • Furazolidone Oral tablet; Adults: 100 mg PO 4 times per day for 7—10 days.

Nondrug and supportive care

  • Fluid and electrolyte management, if diarrhea warrants it 

Comorbidities

  • Amebiasis
    • Doses and duration of antiprotozoal agents are increased to treat concurrent amebiasis in the presence of giardiasis
  • Immunodeficiency (eg, HIV infection)
    • Prolonged therapy may be required

Special populations

  • Pregnant or lactating patients
    • For patients who are asymptomatic, have mild disease, or are in their first trimester of pregnancy: avoid treatment
    • Paromomycin is generally considered safe during pregnancy and nursing because it is not absorbed from the gastrointestinal tract
    • Metronidazole may be used in the second and third trimester if necessary

Complications

  • Dehydration requiring oral or IV fluid supplementation may occur 
  • Lactose intolerance requiring dietary adjustment occurs in 20% to 40% of patients 
    • May persist for weeks despite successful elimination of infection
  • Postinfectious irritable bowel syndrome
    • Chronic abdominal discomfort and altered bowel habits may be precipitated by Giardia infection despite clearance of pathogen
    • Risk is higher in females and in younger age groups, and it increases with duration of symptomatic infection
  • Long-term extraintestinal consequences of giardiasis
    • Ocular pathologies including iridocyclitis, choroiditis, and retinal hemorrhages
      • Young children are more susceptible than adults
    • Enteric infection–related arthritides
      • Inflammatory arthritis is seen in association with enteric infections and may manifest 2 to 4 weeks after infection
    • Hypokalemic myopathy
      • Correlates with duration and severity of disease
      • Occurs more often in hospitalized elderly women
      • Usually improves slowly with repletion of potassium
    • Nutritional consequences
      • Malnutrition, both micronutrient and protein-energy types
        • May result in growth failure and stunting and result in poor cognitive function in infected children

Prognosis

  • With treatment
    • Clearance of parasites from stool occurs in approximately 3 to 5 days
    • Symptoms resolve in 5 to 7 days
  • Without treatment
    • Infection can last for several months 

Prevention

  • Good handwashing and hygiene are essential to avoid fecal-oral contamination, especially after using the bathroom, changing diapers, playing with pets, and before eating or preparing food 
  • Exclude children who have diarrhea from day care until the diarrhea has ended 
  • Children and adults with giardiasis should avoid swimming until a week after diarrhea has ended 
  • Advise travelers and campers to treat drinking water appropriately, if safety of water is not known 
    • Drink bottled water, or
    • Disinfect ground water or tap water before using it
      • Most effective way to disinfect water is by heating to a rolling boil for 1 minute
      • Halogenation is less effective against Giardia and other parasites than against bacteria
      • Filtration requires a pore size of less than 0.1 µm to remove water-borne viruses, which are often co-contaminants

References

1: Center for Food Security and Public Health, Iowa State University: Giardiasis. Iowa State University website. Updated December 2012. Accessed October 7, 2020. http://www.cfsph.iastate.edu/Factsheets/pdfs/giardiasis.pdf Reference 

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