It is caused by parasite, a single-celled organism called Giardia lamblia.
The Centers for Disease Control and Prevention (CDC) estimate that there are around 16,000 cases in the United States each year, but there may be more.
Giardiasis occurs all over the world, but it is more common in areas with poor sanitation. In developing countries, 20 to 30 percent of the population can be infected at any one time.
Here are some key points about giardiasis. More detail and supporting information is in the main article.
- Giardiasis is caused by a globally present parasite - Giardia intestinalis
- The majority of infected individuals do not show any symptoms
- An estimated 200 million people in Africa, Asia, and Latin America have symptomatic infections
- Keeping hands clean is essential to reduce transfer of the parasite
- When traveling abroad, avoid having ice in drinks
What is giardiasis?
Artist's impression of the parasite responsible for giardiasis - Giardia lamblia.
Poor hand-washing can significantly increase the spread of infection.
If an infected person does not wash their hands after using the bathroom, they can spread the disease by shaking someone's hand, touching a surface, or handling food.
Foodborne giardiasis epidemics can occur through food contamination by infected food handlers.
Infected infants can transmit infection if the person changing the diaper does not wash their hands properly.
In the U.S., giardiasis is more common during the summer. This may be due to people spending more time doing outdoor activities and traveling in the wilderness.
Not everyone with giardiasis has symptoms, but they can still spread the disease.
Symptoms can appear between 1 and 3 weeks after becoming infected.
Symptoms may include:
- slight fever
- foul flatus, or strong smelling gas
- abdominal bloating, pain and cramps
- belching and halitosis, or foul-smelling breath
- in some cases, lactose intolerance
- loss of appetite
- Weight loss, which can be severe.
Diarrhea can lead to dehydration. If water loss is severe, it can become serious, especially for infants. It is important to consume plenty of fluids, preferably water.
Symptoms normally improve within two to 6 weeks, but this may take longer. Medications can help speed up recovery.
The parasite that causes giardiasis can thrive in lakes and streams.
There are two types of Giardia, the active form which exists in the gut of the infected person or animal, or the inactive cyst form that can remain dormant in the environment for several months.
The microscopic parasite is called Giardia lamblia or Giardia intestinalis.
Parasites can leave their host's body when a person or animal has a bowel movement. Outside, they form a hard, protective shell and become a Giardia cyst which can survive for several months in the environment.
A gust of wind can pick up the parasite cysts from infected manure on farmland and blow it in any direction.
The infection spreads most commonly when people drink water that has been tainted by infected feces. This is common in countries with poor sanitation.
The infection can also spread if infected people do not wash their hands after going to the toilet, and then handle food and eating utensils. Streams and lakes can also be contaminated.
Touching the anus of an infected person significantly increases the risk of developing giardiasis.
An infant with giardiasis who wear diapers in a swimming pool can contaminate that water. Anybody who swims there is then at risk of becoming infected.
There is a small risk of catching giardiasis from a pet, but animals usually have a different kind that does not affect humans.
Diagnosis and treatment
A stool sample is taken and sent to the lab to check for Giardia cysts. Sometimes several samples are needed, because an infected person does not expel cysts every time they use the bathroom.
Metronidazole (Flagyl) is a very effective medication for treating giardiasis. The adult dosage is 250 milligrams, three times daily for 5 days. The pediatric dosage is 5 milligrams per kilogram of body weight per dose, 3 times daily for 5 days.
Side effects are very rare, but they may include convulsions, confusion, hallucinations, rash, nausea, dark/cloudy urine, vomiting, and drowsiness. Metronidazole is thought to interfere with alcohol dehydrogenase, an enzyme which breaks down alcohol. For this reason, alcohol should be avoided.
Other possible medications
Tinidazole (Fasigyn): Adult dosage is 2 grams, taken once, the pediatric dosage is 50 milligrams per kilogram of body weight, taken once, up to a maximim of 2 grams.
Nitazoxanide: Adult dosage is 500 milligrams twice daily for 3 days. The pediatric dosage for ages 1-3 years is 100 milligrams every 12 hours for 3 days, for those aged 4 to 11 years, it is 200mg every 12 hours for 3 days.
Giardiasis is widespread in sub-Saharan Africa, South and Southeast Asia, Central America, western parts of South America, Russia, Turkey, Romania, and Bulgaria.
Travelers to these areas should be aware of the symptoms of giardiasis, and they should especially careful to practice good hand hygiene.
An estimated 200 million people in Africa, Asia, and Latin America have symptomatic infections. Many others do not know they have it, because they do not have any symptoms.
Giardiasis risk can be minimized by following some simple safety advice:
Hand-washing: Wash hands before and after using the bathroom, before and after eating, before and after changing a diaper, and before and after handling food, whether cooking or preparing food.
Drinking water: Beware of water in rivers and lakes. When camping, people should take their own water supply or some means of boiling it.
Traveling abroad: If visiting a part of the world where clean water is scarce, only purified bottled water should be used. Ice should be avoided, as it is impossible to know what type of water was used to make it. When drinking straight from the bottle, wipe the rim with a tissue before drinking. Avoid eating raw foods, brush teeth with purified water, and keep hands spotlessly clean.