Parasite Wiki


Giardia is a microscopic parasite that causes the diarrheal illness known as giardiasis. Giardia (also known as Giardia intestinalis, Giardia lamblia, or Giardia duodenalis) is found on surfaces or in soil, food, or water that has been contaminated with feces from infected humans or animals. Giardia is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it tolerant to chlorine disinfection. While the parasite can be spread in different ways, water (drinking water and recreational water) is the most common method of transmission.


What is giardiasis?

Giardiasis is a diarrheal disease caused by the microscopic parasite Giardia. A parasite is an organism that feeds off of another to survive. Once a person or animal (for example, cats, dogs, cattle, deer, and beavers) has been infected with Giardia, the parasite lives in the intestines and is passed in feces . Once outside the body, Giardia can sometimes survive for weeks or months. Giardia can be found within every region of the U.S. and around the world.

How do you get giardiasis and how is it spread?

Giardiasis can be spread by:

  • Swallowing Giardia picked up from surfaces (such as bathroom handles, changing tables, diaper pails, or toys) that contain stool from an infected person or animal
  • Drinking water or using ice made from water sources where Giardia may live (for example, untreated or improperly treated water from lakes, streams, or wells)
  • Swallowing water while swimming or playing in water where Giardia may live, especially in lakes, rivers, springs, ponds, and streams
  • Eating uncooked food that contains Giardia organisms
  • Having contact with someone who is ill with giardiasis
  • Traveling to countries where giardiasis is common
  • Anything that comes into contact with feces from infected humans or animals can become contaminated with the Giardia parasite. People become infected when they swallow the parasite. It is not possible to become infected through contact with blood.

    What are the symptoms of giardiasis?

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

  • Diarrhea
  • Gas or flatulence
  • Greasy stool that can float
  • Stomach or abdominal cramps
  • Upset stomach or nausea
  • Dehydration
  • These symptoms may also lead to weight loss. Some people with Giardia infection have no symptoms at all.

    How long after infection do symptoms appear?

    Symptoms of giardiasis normally begin 1 to 3 weeks after becoming infected.

    How long will symptoms last?

    In otherwise healthy people, symptoms of giardiasis may last 2 to 6 weeks. Occasionally, symptoms last longer. Medications can help decrease the amount of time symptoms last.

    Who is most at risk of getting giardiasis?

    Though giardiasis is commonly thought of as a camping or backpacking-related disease and is sometimes called "Beaver Fever," anyone can get giardiasis. People more likely to become infected include:

  • Children in child care settings, especially diaper-aged children
  • Close contacts (for example, people living in the same household) or people who care for those sick with giardiasis
  • People who drink water or use ice made from places where Giardia may live (for example, untreated or improperly treated water from lakes, streams, or wells)
  • Backpackers, hikers, and campers who drink unsafe water or who do not practice good hygiene (for example, proper handwashing)
  • People who swallow water while swimming and playing in recreational water where Giardia may live, especially in lakes, rivers, springs, ponds, and streams
  • International travelers
  • People exposed to human feces through sexual contact
  • What should I do if I think I may have giardiasis?

    Contact your health care provider.

    How is a giardiasis diagnosed?

    Your health care provider will ask you to submit stool samples to see if you are infected. Because testing for giardiasis can be difficult, you may be asked to submit several stool specimens collected over several days.

    What is the treatment for giardiasis?

    Many prescription drugs are available to treat giardiasis. Although the Giardia parasite can infect all people, infants and pregnant women may be more likely to experience dehydration from the diarrhea caused by giardiasis. To prevent dehydration, infants and pregnant women should drink a lot of fluids while ill. Dehydration can be life threatening for infants, so it is especially important that parents talk to their health care providers about treatment options for their infants.

    My child does not have diarrhea, but was recently diagnosed as having Giardia infection. My health care provider says treatment is not necessary. Is this correct?

    Your child does not usually need treatment if he or she has no symptoms. However, there are a few exceptions. If your child does not have diarrhea, but does have other symptoms such as nausea or upset stomach, tiredness, weight loss, or a lack of hunger, you and your health care provider may need to think about treatment. The same is true if many family members are ill, or if a family member is pregnant and unable to take the most effective medications to treat Giardia. Contact your health care provider for specific treatment recommendations.

    If my water comes from a well, should I have my well water tested?

    Giardia and Well Water Testing

    What can I do to Prevent and Control giardiasis?

    To prevent and control infection with the parasite, it is important to:

  • Practice good hygiene
  • Avoid water (drinking or recreational) that may be contaminated
  • Avoid eating food that may be contaminated
  • Prevent contact and contamination with feces during sex

    Giardiasis is a diarrheal illness caused by the parasite Giardia intestinalis (also known as Giardia lamblia or Giardia duodenalis). A parasite is an organism that feeds off of another to survive.

    Giardiasis is a global disease. It infects nearly 2% of adults and 6% to 8% of children in developed countries worldwide. Nearly 33% of people in developing countries have had giardiasis. In the United States, Giardia infection is the most common intestinal parasitic disease affecting humans.

    People become infected with Giardia by swallowing Giardia cysts (hard shells containing Giardia) found in contaminated food or water. Cysts are instantly infectious once they leave the host through feces. An infected person might shed 1-10 billion cysts daily in their feces and this might last for several months. However, swallowing as few as 10 cysts might cause someone to become. Giardia may be passed person-to-person or even animal-to-person. Also, oral-anal contact during sex has been known to cause infection. Symptoms of giardiasis normally begin 1 to 3 weeks after a person has been infected.Giardia infection rates have been known to go up in late summer. Between 2006-2008 in the United States, known cases of giardiasis were twice as high between June-October as they were between January-March.Anyone may become infected with Giardia. However, those at greatest risk are :

  • Travelers to countries where giardiasis is common
  • People in child care settings
  • Those who are in close contact with someone who has the disease
  • People who swallow contaminated drinking water
  • Backpackers or campers who drink untreated water from lakes or rivers
  • People who have contact with animals who have the disease
  • Men who have sex with men

    Causal Agent:

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

    Life Cycle:

    Life cycle of Babesia microti

    Cysts are resistant forms and are responsible for transmission of giardiasis. Both cysts and trophozoites can be found in the feces (diagnostic stages). 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). In the small intestine, excystation releases trophozoites (each cyst produces two trophozoites). 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. Encystation occurs as the parasites transit toward the colon. The cyst is the stage found most commonly in nondiarrheal feces. 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.

    Life cycle image and information courtesy of DPDx.


    Giardiasis is the most frequently diagnosed intestinal parasitic disease in the United States and among travelers with chronic diarrhea. Signs and symptoms may vary and can last for 1 to 2 weeks or longer. In some cases, people infected with Giardia have no symptoms.

  • Diarrhea
  • Gas
  • Greasy stools that tend to float
  • Stomach or abdominal cramps
  • Upset stomach or nausea/vomiting
  • Dehydration (loss of fluids)
  • Other, less common symptoms include itchy skin, hives, and swelling of the eye and join. Sometimes, the symptoms of giardiasis might seem to resolve, only to come back again after several days or weeks. Giardiasis can cause weight loss and failure to absorb fat, lactose, vitamin A and vitamin B12.

    In children, severe giardiasis might delay physical and mental growth, slow development, and cause malnutrition.


    Because Giardia cysts can be excreted intermittently, multiple stool collections (i.e., three stool specimens collected on separate days) increase test. The use of concentration methods and trichrome staining might not be sufficient to identify Giardia because variability in the concentration of organisms in the stool can make this infection difficult to diagnose. For this reason, fecal immunoassays that are more sensitive and specific should be used.

    Rapid immune-chromatographic cartridge assays also are available but should not take the place of routine ova and parasite examination. Only molecular testing (e.g., polymerase chain reaction) can be used to identify the subtypes of Giardia.


    Pactice good hygiene

  • Wash hands with soap and clean, running water for at least 20 seconds; rub your hands together to make a lather and be sure to scrub the backs of your hands, between your fingers, and under your nails.
  • Before, during, and after preparing food
  • Before eating food
  • Before and after caring for someone who is sick
  • Before and after treating a cut or wound
  • After using the toilet
  • After changing diapers or cleaning up a child who has used the toilet
  • After blowing your nose, coughing, or sneezing
  • After touching an animal or animal waste
  • After handling pet food or pet treats
  • After touching garbage
  • Help young children and other people you are caring for with handwashing as needed
  • At child care facilities
  • To reduce the risk of spreading the disease, children with diarrhea should be removed from child care settings until the diarrhea has stopped
  • At recreational water venues (for example, pools, beaches, fountains)
  • Protect others by not swimming if you have diarrhea (this is most important for children in diapers)
  • Shower before entering the water
  • Wash children thoroughly (especially their bottoms) with soap and water after they use the bathroom or after their diapers are changed and before they enter the water
  • Take children on frequent bathroom breaks and check their diapers often
  • Change diapers in the bathroom, not by the water
  • Around animals
  • Minimize contact with the feces of all animals, especially young animals
  • When cleaning up animal feces, wear disposable gloves and always wash hands when finished
  • Wash hands after any contact with animals or their living areas
  • Thoroughly washing your hands after gardening can help prevent exposure to parasitic diseases.
  • Wash hands after gardening, even if wearing gloves
  • Avoid water (drinking and recreational) that may be contaminated

  • Do not swallow water while swimming in pools, hot tubs, interactive fountains, lakes, rivers, springs, ponds, streams or the ocean
  • Do not drink untreated water from lakes, rivers, springs, ponds, streams, or shallow wells
  • Do not drink poorly treated water or ice made from water during community outbreaks caused by contaminated drinking water
  • Do not use or drink poorly treated water or use ice when traveling in countries where the water supply might be unsafe
  • If the safety of drinking water is in doubt (for example, during or after an outbreak, in a place with poor sanitation or lack of water treatment systems), do one of the following:
  • Drink bottled water
  • Disinfect tap water by heating it to a rolling boil for 1 minute
  • Use a filter that has been tested and rated by National Safety Foundation (NSF) Standard 53 or NSF Standard 58 for cyst and oocyst reduction; filtered tap water will need additional treatment to kill or weaken bacteria and viruses
  • Avoid eating food that may be contaminated

  • Use safe, uncontaminated water to wash all food that is to be eaten raw
  • After washing vegetables and fruit in safe, uncontaminated water, peel them if you plan to eat them raw
  • Avoid eating raw or uncooked foods when traveling in countries with poor food and water treatment
  • Prevent contact and contamination with feces during sex

  • Use a barrier during oral-anal sex
  • Wash hands right after handling a condom used during anal sex and after touching the anus or rectal area

    For more information view the source:Center for Disease Control

    Recommended Test:Full GI Panel

    Recommended Product:Freedom Cleanse Restore Parasite Cleanse

    << Back to Wiki