Giardiasis

Giardiasis (JEE-are-DYE-uh-sis) is a diarrheal illness of humans and animals. It is caused by a one-celled, microscopic parasite, Giardia intestinalis (also known as Giardia lamblia). Once an animal or person has been infected with Giardia, the parasite lives in the intestine and is passed in the stool. Because the parasite is protected by an outer shell, it can survive outside the body and in the environment for a long time.

Giardia infection is one of the most common causes of waterborne disease (found in both drinking and recreational water) in humans in the United States.^[1] Giardia parasites are found worldwide.

Other Names

• "Beaver fever" (slang, referring to one of the many animals whose contaminated stool can spread the disease)

Signs and Symptoms

Giardia cysts: A: G. intestinalis cyst. 1000× magnification. B: Two G. intestinalis cysts; 1000× magnification. Giardia intestinalis cysts are oval to ellipsoid and measure 8-19 µm (average 10-14 µm). Mature cysts have 4 nuclei, while immature cysts have two. Source: CDC

Giardia infection can cause a variety of intestinal symptoms, which include

• Diarrhea, which is often foul-smelling
• Gas or flatulence
• Greasy stools that tend to float
• Stomach cramps
• Upset stomach or nausea

These symptoms may lead to weight loss and dehydration. Some people with giardiasis have no symptoms at all.

Symptoms of giardiasis normally begin one to two weeks (average, seven days) after a person becomes infected. In otherwise healthy persons, symptoms of giardiasis last about two to six weeks. Occasionally, symptoms last longer.

This scanning electron microscopy image shows a Giardia parasite attached to the carpet-like microvilli of a layer of cultured human intestinal cells. Source: Wendy R. Hansen^[2]

Cause

Giardiasis is caused by infection by the Giardia intestinalis or Giardia lamblia parasite. Giardia is a type of protozoa called a diplomonad. Diplomonads have two nuclei in each cell, but lack the energy factories of eukaryotic cells (mitochondria) and some other hallmarks of eukaryotic cells. Giardia and other diplomonads are thought by some to be the most primitive type of eukaryotic cell.

People contract giardia by ingesting it. They may drink contaminated water; eat contaminated food; or ingest small amounts of feces, as with small children or during sexual contact.

Diagnosis

Giardia infects the gut and causes diarrhea. Diagnosis of giardiasis involves finding evidence of the Giardia parasite in feces (stool) by seeing the organism under the microscope. Immunological tests (immunoassays) are also used. These look for evidence of proteins that coat the parasite's surface.

There are no recommended blood tests for Giardia and no imaging tests that can help its diagnosis. Three stool specimens are needed to increase the chances of detected infection if it is present. These must be collected over several days. Since the Giardia parasite is difficult to see in the blood, the immunoassay is the best test. This means that Giardia is frequently only detected when doctors suspect it to be the cause of illness and request the special Giardia immunoassay; it isn't generally discovered by accident.

Treatment

Several prescription drugs are available to treat Giardia. Since Giardiasis is an infection, these treatments are antimicrobials. The drugs tinidazole and metronidazole are most frequently prescribed. Tinidazole is preferable since it can be given just once and cures the majority of cases, whereas metronidazole must be given several times a day for a week to achieve successful eradication of the infection. Since the infection is difficult to eradicate, everyone who undergoes treatment must be tested afterwards to make sure they do not still have the infection. As well as preventing their disease from coming back, this also stops people from carrying the disease and spreading it to others.

As well as eradicating the infection, the clinician must treat the problems the parasite causes. Dehydration due to diarrhea is one. Although Giardia can infect all people, young children and pregnant women may be more susceptible to dehydration resulting from diarrhea and should, therefore, drink plenty of fluids while ill.

Once definitively free of the parasite, a person is considered cured, although re-infection from a new contamination can occur.

Prevention

One of the main methods of preventing giardiasis is to prevent people from becoming exposed to others who are infected. A Giardia infection can be very contagious. The following are steps that can be taken by people with Giardia infection to avoid spreading it to others:

• Washing hands with soap and water after using the toilet, changing diapers, and before eating or preparing food.

• Not swimming in recreational water (pools, hot tubs, lakes or rivers, the ocean, etc.) during Giardia infection or for at least 2 weeks after diarrhea stops. Giardia passed in the stool can contaminate water for several weeks after symptoms have ended. This has resulted in outbreaks of Giardia among recreational water users.
• Avoiding fecal exposure during sexual activity.

There are a number of steps that can be taken by people who are not known to be infected to avoid succumbing to giardiasis.

Practicing good hygiene

• Washing hands thoroughly with soap and water.
  • Washing hands after using the toilet and before handling or eating food (especially for persons with diarrhea).
  • Washing hands after every diaper change, especially in people who work with diaper-aged children, even when wearing gloves.
• Protecting others by not swimming when experiencing diarrhea (essential for children in diapers).

Avoiding water that might be contaminated

People should:

• Not swallow recreational water
• Not drink untreated water from shallow wells, lakes, rivers, springs, ponds, and streams
• Not drink untreated water during community-wide outbreaks of disease caused by contaminated drinking water
• Not use untreated ice or drinking water when traveling in countries where the water supply might be unsafe.

In the United States, nationally distributed brands of bottled or canned carbonated soft drinks are safe to drink. Commercially packaged non-carbonated soft drinks and fruit juices that do not require refrigeration until after they are opened (those that are stored unrefrigerated on grocery shelves) also are safe.

When drinking water not known to be safe, people should:

• Heat the water to a rolling boil for at least 1 minute.
• Use a filter that has an absolute pore size of 1 micron or smaller, or one that has been NSF rated for "cyst removal."
• Chemically treat the water by chlorination or iodination. Using chemicals may be less effective than boiling or filtering because the amount of chemical required to make the water safe is highly dependent on the temperature, pH, and cloudiness of the water.

Avoiding food that might be contaminated

People should:

• Wash and/or peeling all raw vegetables and fruits before eating.
• Use safe, uncontaminated water to wash all food that is to be eaten raw.
• Avoid eating uncooked foods when traveling in countries with minimal water treatment and sanitation systems.

Testing well water for Giardia

Well-water testing may be recommended in one of the following circumstances:

• A patient or members of his/her family are becoming ill after consuming water from a particular well
• The well is located at the bottom of a hill, or is considered shallow. If so, runoff from rain or flood water may be draining directly into the well causing contamination.
• The well is in a rural area where animals graze. Well water can become contaminated with feces if animal waste seepage contaminates the ground water. This can occur if the well has cracked casings, is poorly constructed, or is too shallow.

Tests used to specifically identify Giardia are often expensive and difficult, and usually require hundreds of gallons of water to be pumped through a filter. Often the first step to be taking involves testing the well water for fecal contamination by testing it for the presence of coliforms or E. coli (a bacteria found abundantly in feces) instead of Giardia. Although tests for fecal coliforms or E. coli do not specifically say whether Giardia is present, these tests will show whether the well water has been contaminated by fecal matter. These tests are only useful if the well is not routinely disinfected with chlorine, since chlorine kills fecal coliforms. If the tests are positive, it is possible that the water may also be contaminated with Giardia or other harmful bacteria and viruses.

People whose well water is contaminated should contact their county health department, county cooperative extension service, or a local laboratory to find out who offers water testing in their area. If the fecal coliform test comes back positive, indicating that the well is fecally contaminated, no one should drink the well water. The local water authority should be contacted for instructions on how to disinfect the well.

Chances of Developing Giardiasis

Anyone can get giardiasis. There are at least 100,000 cases of giardia in the United States per year and at least 5,000 cases are bad enough to require hospitalization. Persons more likely to become infected include:

• Children who attend day care centers, including diaper-aged children
• Child care workers
• Parents of infected children
• International travelers
• People who swallow water from contaminated sources
• Backpackers, hikers, and campers who drink unfiltered, untreated water
• Swimmers who swallow water while swimming in lakes, rivers, ponds, and streams
• People who drink from shallow wells

Contaminated water includes water that has not been boiled, filtered, or disinfected with chemicals. Several community-wide outbreaks of giardiasis have been linked to drinking municipal water or recreational water contaminated with Giardia.

How Giardiasis is Spread

Giardia Life Cycle. Cysts are resistant forms and are responsible for transmission of giardiasis. Both cysts and trophozoites can be found in the feces (diagnostic stages)(1). The cysts are hardy and can survive several months in cold water. Infection occurs by the ingestion of cysts in contaminated water, food, or by the fecal-oral route (hands or fomites)(2). In the small intestine, excystation releases trophozoites (each cyst produces two trophozoites)(3). Trophozoites multiply by longitudinal binary fission, remaining in the lumen of the proximal small bowel where they can be free or attached to the mucosa by a ventral sucking disk (4). Encystation occurs as the parasites transit toward the colon. The cyst is the stage found most commonly in nondiarrheal feces (5). Because the cysts are infectious when passed in the stool or shortly afterward, person-to-person transmission is possible. While animals are infected with Giardia, their importance as a reservoir is unclear. Source: CDC

The giardia parasite lives in the intestine of infected humans or animals. Millions of cysts can be released in a bowel movement from an infected human or animal. Giardia is found in soil, food, water, or surfaces that have been contaminated with the feces from infected humans or animals. This is termed fecal-oral spread. Infection with Giardia results from accidentally swallowing the parasite. This means that it can be spread by:

• Accidentally putting something into the mouth or swallowing something that has come into contact with feces of a person or animal infected with Giardia
• Swallowing recreational water contaminated with Giardia. Recreational water includes water in swimming pools, hot tubs, jacuzzis, fountains, lakes, rivers, springs, ponds, or streams that can be contaminated with sewage or feces from humans or animals.
• Eating uncooked food contaminated with Giardia
• Accidentally swallowing Giardia picked up from surfaces contaminated with feces from an infected person. Such surfaces include bathroom fixtures, changing tables, diaper pails, or toys.

Giardia cannot be spread by blood contact or blood transfusion.

Clinical Trials

For a list of government-sponsored clinical trials in the US that are investigating giardiasis, click here.

Research

Research on Giardia and giardiasis centers on two very different areas: the primitive nature (from an evolutionary point of view) of Giardia; and the public health problem of giardiasis.

History

Etymology

The protozoan was initially named Cercomonas intestinalis by F. Lambl of Prague in 1859 and renamed Giardia lamblia by Stiles in 1915, in honor of Professor Alfred Giard of Paris and Dr. Lambl. However, many consider the name Giardia intestinalis to be the correct name for this protozoan. The International Commission on Zoological Nomenclature is reviewing the issue.

Epidemiology

Giardiasis is widespread geographically in the United States, although the diagnosis and/or transmission of giardiasis might be higher in northern states. It is found all over the world, with an especial burden of disease in Africa, Asia, and Latin America.

Giardia Incidence in the United States, 2005. Source: CDC^[3]

Although giardiasis affects persons in all age groups, the number of reported cases was highest among children aged one to nine years and adults aged 35–44 years. Because fecal-oral contact is more likely in young children, their incidence of giardiasis is higher, and so is that of the people who care for them (e.g., day care staff, family members, and other household contacts). Investigation of a giardiasis outbreak in a day care facility determined that 47% of ill children transmitted the infection to more than one household contact.^[3]

The illness begins most commonly in early summer through early fall, probably due to increased outdoor activity (e.g. swimming and camping).

The importance of water and food in the transmission of Giardia is highlighted by recent giardiasis outbreaks. In 2003, a communitywide outbreak of giardiasis in Massachusetts was traced to use of a wading pool at a membership club.^[3] In addition to the 30 case-patients with primary exposures to the pool, an additional 105 cases were caused by secondary person-to-person transmission. Also in 2003, a communitywide outbreak in Iowa implicated a wading pool at a day care center that was filled with water from the municipal water supply. From the child care center, illness spread into the community via secondary transmission, sickening an estimated 100 persons with giardiasis, cryptosporidiosis, or both.^[4]

Among patients for whom data on sex were reported, a majority of cases occurred among males. This sex-related difference might be attributable in part to sexual contact among men who have sex with men.^[3]

Giardiasis is highly underreported because:

1) not all infected persons are symptomatic,

2) those who are symptomatic do not always seek medical care,

3) health-care providers do not always include laboratory diagnostics in their evaluation of non-bloody diarrheal diseases, and

4) case reports are not always completed for positive laboratory results or forwarded to public health officials.

References

1. ↑ Centers for Disease Control and Prevention, Giardiasis Fact Sheet
2. ↑ PLoS Neglected Tropical Diseases Issue Image | Vol. 2(2) February 2008. PLoS Neglected Tropical Diseases 2(2):ev02.i02
3. ↑ ^{3.0 3.1 3.2 3.3} Yoder JS, Beach MJ; Centers for Disease Control and Prevention (CDC). Giardiasis surveillance--United States, 2003-2005. MMWR Surveill Summ. 2007 Sep 7;56(7):11-8. Full Text
4. ↑ Dziuban EJ, Liang JL, Craun GF, et al. Surveillance for waterborne disease and outbreaks associated with recreational water--United States, 2003-2004. In: Surveillance Summaries, December 22, 2006. MMWR Morb Mortal Wkly Rep. 2006;55:1-30. Full Text

External Links

CDC: Healthy Swimming

Food and Drug Administration's Bad Bug Book: Giardia

New York State Dept. of Health: Giardiasis

For information on choosing a water filter or bottled water, see the CDC fact sheet entitled Preventing Cryptosporidiosis: A Guide to Water Filters and Bottled Water.

Microbe Wiki: Diplomonads