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Giardiasis - Causes, Symptoms, Diagnosis, and Treatment

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Giardiasis is an infection that affects the intestine caused by giardia, resulting in diarrhea, stomach cramps, and vomiting. Read the article below to know more.

Medically reviewed by

Dr. Kaushal Bhavsar

Published At September 7, 2022
Reviewed AtFebruary 20, 2023


Giardiasis is a waterborne disease found worldwide, especially in places with poor sanitation and contaminated water. Swallowing contaminated or recreational water from lakes, rivers, or pools is the most common cause of the disease.

What Is Giardiasis?

Giardiasis affects the small intestine and is a parasitic infection. Giardia is the causative organism of the disease and can spread through direct person-to-person contact or by consuming contaminated food and water. The infection is marked by diarrhea, stomach cramps, nausea, and vomiting.

What Is the Cause of Giardiasis and How Is It Spread?

Giardiasis is caused by a microscopic parasite that infects the intestine - giardia and is found in human and animal feces and can contaminate anything. Once the parasite enters a person’s body, it lives in the intestine and is passed in stools. However, giardia can live outside the body for an extended time, for weeks or months.

Giardiasis can be spread by:

  • Consuming food contaminated by giardia.

  • Drinking unsafe water.

  • Person-to-person contact; being in close contact with a person infected by the parasite.

  • Traveling to places with poor sanitation.

  • Having unprotected anal sex with an infected person.

  • Touching surfaces that may be contaminated with Giardia (like doorknobs, diaper changing tables, stair rails), and then touching the mouth.

  • Being in close contact with animals that may have been infected.

What Are the Risk Factors?

Giardiasis is a common illness and can affect anybody; however, some are at a higher risk of contracting the disease.

  • Children are at the most risk of giardiasis, as they are likely to come in contact with feces, especially in a child care center.

  • Parents and caretakers who change diapers.

  • People who stay in places without access to safe drinking water: giardiasis spreads in places with poor sanitation and without access to safe water.

  • Travelers and backpackers travel to different places and may not have access to safe water and food.

  • People who engage in unprotected anal or oral-anal sex

What Are the Symptoms and Signs of Giardiasis?

The clinical symptoms in a person would depend on many factors, including the parasite load, the immune response of the person, etc. Some people may not show symptoms. Symptoms may appear one to two weeks after the infection and may last for two to six weeks. However, in people with weaker immunity, it may last longer.

The symptoms include:

  • Diarrhea.

  • Weakness.

  • Stomach cramps.

  • Headache.

  • Gas or flatulence.

  • Nausea and vomiting.

  • Greasy stools that float.

  • Anorexia (an eating disorder represented by abnormally low body weight).

  • Low-grade fever.

  • Weight loss.

  • Dehydration.

  • Itchy skin.

  • Swelling of eyes and joints.

Over time giardiasis can also prevent the body from absorbing nutrients that are necessary for the body.

How Is Giardiasis Diagnosed?

The diagnosis of giardiasis is made by testing the person’s stool sample. However, not all samples might contain Giardia; hence multiple stool tests are done. The doctor may also perform an endoscopy, where a thin, flexible tube is placed through the mouth to inspect the small intestine, followed by which a tissue sample is obtained from the small intestine for biopsy.

What Are the Treatment Options Available for Giardiasis?

Most people do not require treatment as the infection subsides in a few weeks unless they are likely to spread the disease. The doctor would advise antiparasitic medication for mild cases of giardiasis. However, in case of severe symptoms, antibiotics may be prescribed, like Metronidazole, Tinidazole, and Nitazoxanide. One must follow the healthcare provider’s instructions and take the medications in time. If the medication is not taken properly or stopped abruptly, this may lead to another infection as the previous one was not cleared, and the second course of medication.

What Are the Complications of Giardiasis?

Giardiasis symptoms usually go away after a few weeks of the infection; however, some serious complications linger even after the infection subsides:

  • Dehydration: This results from severe diarrhea when the body does not have enough water to function normally.

  • Malnutrition: Severe and chronic diarrhea due to giardiasis can lead to malnutrition in children and harm their mental and physical development.

  • Lactose Intolerance: Some people develop lactose intolerance following a giardiasis infection.

What Is the Long-Term Outlook for Giardiasis?

Giardiasis usually subsides two to six weeks after the infection and in severe cases, may subside with appropriate medications. However, a few complications like lactose intolerance may linger.

Can Pets Get Giardiasis?

Animals can acquire the disease from feces or another infected animal. Still, the chances of a pet spreading it to a person are relatively small, as the type of Giardia that infects humans is often different from the one in animals.

How to Prevent Giardiasis?

Currently, no medications can prevent giardiasis, but some simple precautions can save one from giardiasis.

  • Washing Hands Often: This could not only protect one from giardiasis but most infections can be prevented by washing hands often. Wash the hands with soap after a diaper change, using the toilet, before preparing food, and before eating. Alcohol-based sanitizers can also be used if necessary instead of soap and water.

  • Avoid Drinking Unsafe Water: Do not directly drink water from rivers or lakes; these may be contaminated. Make sure to drink filtered or boiled, or treated water only.

  • Avoid Swallowing Water While Swimming: Avoid swallowing water in pools, hot tubs, splash pads, etc. when swimming, and keep your mouth closed.

  • Wash Fruits and Vegetables: Wash all produce well before consuming or using them to prepare food.

  • Practice Safe Sex: Use condoms and perform only safe and protected sex.


Giardiasis is an infection that affects the small intestine caused by and causes diarrhea, stomach cramps, nausea, vomiting, malaise, etc. Most symptoms tend to subside a few weeks after the infection and are more likely to require no treatment. However, in severe cases, antibiotics are prescribed. The disease has never been fatal and has often been resolved by taking appropriate treatment as prescribed by the doctor.

Frequently Asked Questions


What Causes Giardiasis?

Giardia duodenalis, sometimes known as "Giardia," is a tiny parasite that causes the diarrheal disease giardiasis. Once Giardia infection has occurred in a human, the parasite dwells in the intestines and is expelled in the stool. Giardia can occasionally survive after leaving the body for several weeks or even months. A few sources of pollution are diapers, agricultural runoff, and animal waste. Giardiasis is less frequently acquired from food since heat destroys the parasites. However, the parasite can spread by improper food handling or consuming vegetables in polluted or contaminated water.


What Happens When Giardia Is Not Treated?

Giardiasis can occasionally cause long-term side effects if left untreated, such as reactive arthritis, irritable bowel syndrome, and persistent diarrhea that can linger for years. Giardiasis in children can impair development, hinder physical and mental growth, and can result in malnutrition.


What Is the First-Line Treatment of Giardia?

Giardiasis is most commonly treated with Tinidazole, which typically only needs one dosage to be effective. The related antibiotic Metronidazole is as effective, but it needs to be taken three times daily for five to seven days.


How Can Giardia Be Diagnosed?

Fluorescence microscopy is a standard test for the diagnosis of giardiasis. Since it offers more sensitivity than non-fluorescent microscopy techniques, microscopy with direct fluorescent antibody testing (DFA) is preferred for diagnosing giardiasis.


Can Giardia Be Naturally Killed in Humans?

Soda crackers, toast, plain rice or noodles, prepared cereal, applesauce, bananas, and easily digestible food, including acidic foods (such as tomatoes or oranges), spicy or fatty foods, meats, and fresh vegetables are all healthy options in case of giardiasis. Wormwood, a herb that has anti-parasitic effects, and Oregano oil, which naturally includes antibacterial and antiparasitic compounds that have a variety of detoxifying benefits, are also believed to be good intake for giardiasis. However, there are no reports that these could kill giardia in humans.


What Does Stool Look Like in People with Giardia?

Soft, greasy stools may alternate with diarrhea that is occasionally foul and watery. Moreover, giardiasis symptoms often start with two to five loose stools (poop) each day.


How Can Giardia Affect the Body?

Giardia is spread either directly through the fecal or oral route or through the consumption of cysts in contaminated food or water. Giardiasis, disease-causing intestinal malabsorption, and diarrhea are caused by cyst ingestion in humans.


What Is the Incubation Period of Giardia?

Acute giardiasis typically lasts between one and three weeks and occurs after an incubation period of one to fourteen days (an average of seven days). Diarrhea, stomach discomfort, bloating, nausea, and vomiting are some of the symptoms of giardiasis.


How Many Days Should Giardiasis Be Treated?

Usually, within two to six weeks, giardiasis patients often feel better and stop experiencing symptoms. However, in other circumstances, symptoms could appear to have subsided but come back after a few days or weeks. Therefore, the healthcare provider would treat it with Tinidazole or Metronidazole based on the condition.


What Two Life Phases Does Giardia Have?

A vegetative trophozoite and an infectious cyst with resistance to extreme environmental circumstances make up the two different phases of the Giardia life cycle. The infectious cysts are responsible for the spread of giardiasis. Each infective cyst releases two trophozoites in the small intestine when ingested or transmitted through the fecal-oral route, which eventually attaches to the mucosa of the small intestine.


Can Giardia Be Detected in Urine?

No, giardia cannot be found in urine. Stool tests are more useful for diagnosis since the parasite's cysts are expelled in feces. On the other hand, specialist testing may occasionally identify Giardia antigens in urine. However, the mainstay for a precise diagnosis of Giardia infections is still stool testing. 


How Can Giardiasis Be Prevented?

Engaging in good hand hygiene, consuming clean and good water and non-contaminated food, using safer sex techniques, and using proper disinfection techniques are some ways to prevent giardiasis infection. Avoid consuming untreated water sources and always consume safe, pure water. Avoid ingesting water from lakes or streams when swimming to ensure safety. To lessen the chance of Giardia transmission, handle food properly and keep a distance from sick people.


Which Food Should People Avoid to Prevent Giardiasis?

Drinking untreated water or water possibly contaminated by feces and eating crops washed in polluted water, such as fruit or vegetables, should be avoided. Eat nothing uncooked or undercooked to prevent Giardiasis, especially meats and seafood that may contain the Giardia parasite. Fruits and vegetables should be handled carefully; ensure they are well-cleaned and peeled.


What Probiotic Helps Giardia?

Giardia infections were shown to be less severe and to last less time when probiotics (Lactobacillus rhamnosus, Lactobacillus casei) were given either before or at the beginning of the infections. Giardia infection symptoms may be lessened by taking certain probiotics, such as Saccharomyces boulardii. The ability of S. boulardii to lessen the length and intensity of diarrhea linked to giardiasis has been investigated.


Can Giardia Be Cured?

Giardiasis commonly causes mild symptoms that go away independently, and the person might not require therapy. The doctor can recommend an antibiotic with an antiparasitic action to destroy the parasite if the individual has more severe parasite symptoms. Several treatments are available to treat giardiasis. Tinidazole, Metronidazole, and Nitazoxanide are reported to be efficient treatments. Paromomycin, Quinacrine, and Furazolidone are other drugs. And yes, giardiasis can be cured with proper medical attention.


Is Giardia a Lifelong Condition?

Giardiasis can occasionally cause long-term side effects such as reactive arthritis, irritable bowel syndrome, and persistent diarrhea that can linger for years. Some patients have a recurrence after receiving treatment for Giardia and seeing their symptoms improve. This may occur due to ongoing Giardia infection or intestinal alterations that increase a person's sensitivity to specific meals.


Is Giardia a Type of Worm?

Giardiasis is a diarrheal disease caused by a microscopic parasite (germ) called Giardia. Giardia is a parasite that may be found in food, water, soil, and surfaces that have come into touch with infected human or animal feces. Giardiasis can develop if a person consumes contaminated food or water. The parasitic Giardia organisms are tiny and impossible to spot without a microscope.
Dr. Kaushal Bhavsar
Dr. Kaushal Bhavsar

Pulmonology (Asthma Doctors)


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