Giardiasis
Giardiasis is an intestinal infection caused by a microscopic parasite that can spread through contaminated water, food, and surfaces. While some people never develop symptoms, others may experience watery diarrhea, stomach cramps, and fatigue that can last for weeks or even months if left untreated.
Table of contents
- What is giardiasis?
- What causes giardiasis and how does it spread?
- Symptoms of giardiasis
- Who is at risk?
- How is giardiasis diagnosed?
- Treatment and recovery
- How to prevent giardiasis
What is giardiasis?
Giardiasis is an intestinal infection caused by a microscopic parasite (a tiny organism that lives in or on another organism) called Giardia duodenalis, also known as Giardia lamblia or Giardia intestinalis[1][2]. This parasite lives in the small intestine (the part of the digestive system where food is broken down and nutrients are absorbed) and can cause a variety of digestive symptoms[3].
Giardiasis is one of the most common parasitic infections in the United States, affecting over a million people each year[2][3]. Worldwide, it is found in every region, with infection rates as high as 7% in developed countries and 30% in developing countries[3][5]. The infection is more widespread in areas with poor sanitation and contaminated water supplies[4].
The parasite has two forms in its life cycle. The cyst form is like a protective shell that allows the parasite to survive outside the body for weeks to months in water, soil, and on surfaces[2][3]. Once swallowed, the cyst opens in the small intestine and releases the active form called a trophozoite, which feeds on nutrients and multiplies. The trophozoites then change back into cysts and pass out in feces, where they can infect others[4][13].
What causes giardiasis and how does it spread?
You become infected with giardiasis by accidentally swallowing Giardia cysts[1][2]. The parasite spreads easily because swallowing just a few Giardia cysts can cause infection[2]. Since the cysts are found in the feces of infected people and animals, anything contaminated by feces can potentially spread the infection[2][3].
Common ways people get infected include drinking or swimming in contaminated water from streams, lakes, rivers, public water supplies, swimming pools, or wells[1][2]. The parasite has been found in as many as 80% of raw water supplies from lakes, streams, and ponds[7]. Giardia cysts can survive in cold water and are resistant to normal chlorination levels used in swimming pools[5].
Other transmission routes include eating contaminated food, touching surfaces that an infected person has touched without proper handwashing, person-to-person contact in daycare centers or through oral-anal sexual contact, and touching infected animals or contaminated soil[2][3][10]. The infection spreads particularly easily in childcare settings where handwashing practices may be poor and children wear diapers[2][10].
Both humans and animals can carry and spread Giardia. While the type of Giardia that infects people is usually not the same type that infects dogs and cats, beavers and other wild animals may serve as reservoir hosts[2][7].
Symptoms of giardiasis
About half of people infected with Giardia never develop any symptoms, though they can still spread the parasite to others through their feces[1][3]. For those who do develop symptoms, they typically appear one to two weeks after becoming infected, though the incubation period can range from one day to several weeks[1][2][10].
The most common symptom is diarrhea, which is often watery and may occur two to five times per day[2]. The stools may be soft, greasy, float in the toilet, and have a particularly foul smell[1][3]. This happens because the parasite interferes with the body’s ability to absorb fats from food[3].
Other common symptoms include stomach pain and cramping, intestinal gas and bloating, nausea and loss of appetite, and increasing tiredness[1][2][3]. Some people also experience weight loss due to the combination of diarrhea, nausea, and poor nutrient absorption[1]. A low-grade fever may occur at the beginning of the infection[7].
Less commonly, people may develop itchy skin, hives, swelling around the eyes, or swollen joints[3].
Symptoms usually last for two to six weeks[1][2]. However, some people develop longer-lasting or recurring symptoms that can persist for months or even years[1][3]. Chronic infection can lead to dehydration (loss of body fluids) and significant weight loss from ongoing diarrhea and nausea[3]. Some people develop lasting digestive problems, such as lactose intolerance (difficulty digesting milk and dairy products)[3][5].
Who is at risk?
Anyone can become infected with Giardia, but certain groups of people are at higher risk[2]. Children are infected more often than adults, particularly those under the age of 4[3][4]. Children in daycare centers and their families have increased risk because the infection spreads easily in these settings[2][7].
Travelers to developing countries where giardiasis is common are at higher risk, as are people who drink untreated water from springs, lakes, rivers, or shallow wells[2][4]. Campers, hikers, and outdoor enthusiasts who drink unprocessed water are also at increased risk[4].
People who swallow water from swimming pools, splash pads, lakes, or rivers while swimming have higher risk[2]. People who have contact with infected animals or environments contaminated with animal feces may also be at increased risk[2].
Individuals with weakened immune systems may have more severe or prolonged symptoms[2][3]. People who are in close contact with someone infected with Giardia, especially in childcare or healthcare settings, face higher risk[2]. Sexually active individuals who engage in oral-anal contact may also be at increased risk[2][7].
How is giardiasis diagnosed?
Healthcare providers diagnose giardiasis by testing stool samples for the presence of Giardia[2][11]. Before ordering tests, your healthcare provider will ask about your symptoms, travel history, whether you might have had contact with contaminated water during outdoor activities, whether your home has well water, and for children, whether there have been recent outbreaks of diarrhea at their daycare center[3].
The most common diagnostic method involves examining stool samples under a microscope to look for Giardia cysts or the active form of the parasite[3][5]. Because Giardia cysts are shed intermittently in the stool and may not appear in every sample, healthcare providers often ask for several stool samples collected over a few days[3][11].
Another testing method looks for Giardia antigens, which are small proteins produced by the parasite. These tests can detect Giardia even when cysts are not being shed, making them more reliable in some cases[3][5].
If stool tests are negative but symptoms continue, healthcare providers may use other methods. A string test involves swallowing a capsule attached to a string that travels to the small intestine where Giardia lives. After several hours, the string is withdrawn and examined for parasites[3]. In some cases, doctors may perform an endoscopy (a procedure using a flexible tube with a camera) with tissue samples from the small intestine[3].
Treatment and recovery
Many people with giardiasis recover on their own within a few weeks without medication[1][15]. People without symptoms often do not need treatment[3][15]. However, treatment may be considered to prevent household transmission, particularly to pregnant women or people with weakened immune systems[14].
When treatment is needed, healthcare providers can prescribe antiparasitic medications that are highly effective[1][2]. The most commonly used medication is metronidazole, typically given three times daily for five to seven days, which can cure over 90% of cases[1][11][12]. Side effects may include upset stomach and a metallic taste in the mouth, and patients should avoid drinking alcohol while taking this medicine[11].
Tinidazole is another effective option that can be given as a single dose and works as well as metronidazole with similar side effects[11][12]. Nitazoxanide is taken twice daily for three days and may be easier for children to take because it comes in liquid form; side effects can include upset stomach, gas, and yellow-colored urine[11][14].
For pregnant women, treatment choices are more limited because some medications may harm the unborn baby. If symptoms are mild, healthcare providers may recommend waiting until after the first trimester before starting treatment[11]. Paromomycin may be used during early pregnancy because it is not absorbed into the bloodstream, though it is not as effective as other medications[12][14].
If diarrhea is present, it is important to drink plenty of water or other fluids to avoid dehydration[2][15]. Dehydration can be especially dangerous for infants and pregnant women[15]. If you have trouble digesting milk and dairy products during or after infection, talk to your healthcare provider about temporarily avoiding these foods or using lactase supplements[5].
Most people fully recover from giardiasis with proper treatment[1]. However, some people continue to have symptoms for weeks to months after the infection has cleared[1][3]. In rare cases where standard treatment fails, healthcare providers may prescribe a longer course or combination of medications[12][14].
How to prevent giardiasis
Proper handwashing is one of the most important ways to prevent giardiasis[2][19]. Wash your hands thoroughly with soap and water after using the toilet, changing diapers, touching animals or soil, and before preparing food or eating[2][10][19].
To protect yourself from contaminated water, avoid drinking untreated water from springs, lakes, rivers, shallow wells, or public sources[2][10]. If you are camping or hiking, boil water for at least one minute (or three minutes at elevations above 6,500 feet) to kill Giardia cysts, or use a water filter[2][10]. Standard chlorination used in swimming pools is not effective against Giardia[17].
When swimming, avoid swallowing water from pools, splash pads, lakes, or rivers[2][19]. Do not swim if you have diarrhea[19]. Shower before entering the water to reduce contamination[19].
When traveling to developing countries, drink only bottled water, avoid raw fruits and vegetables unless you can peel them yourself, and do not drink beverages with ice cubes[10].
If you have oral-anal sexual contact, wait several weeks after you or your partner stops having diarrhea before resuming this activity, as Giardia can still be present in feces for weeks after symptoms stop[2][19]. Washing hands, genitals, and anus with soap and water before and after sex and using condoms can help reduce risk[19].
Avoid touching animal feces, especially from young animals[2][19]. Always wash your hands after working with soil during gardening, landscaping, or field work, even if you wore gloves[19].
If someone in your household has giardiasis and has had diarrhea, clean and disinfect contaminated areas[2][19]. Remove any feces with disposable materials, clean the area with soap or cleaning product, rinse thoroughly, and then use a disinfectant appropriate for the surface following product directions[19]. Common household disinfectants and steam cleaning are effective at killing Giardia cysts[9][19].
In childcare settings, keep children home if they have diarrhea until symptoms have stopped[19]. Practice careful handwashing and proper diaper disposal, and regularly clean and disinfect toys and surfaces[10][19].
