Last week, you went camping, with lots of water activities—swimming in a lake and hiking by a stream that was so clear that you had to take a sip from it—and now, you’ve had diarrhea for days. What happened? You might have had an encounter with Giardia duodenalis, a parasite that causes an illness called giardiasis.
Giardiasis is the most common parasitic infection globally. In developing countries, about a third or more of the population has experienced giardiasis due to poor sanitary conditions and lack of clean water. In the United States, it likely affects more than a million people each year, though not every state tracks or reports cases.
UNC Health infectious disease expert Luther Bartelt, MD, explains the condition.
Symptoms of Giardiasis
If you have diarrhea caused by a bacteria or virus, as in the case of food poisoning or a stomach virus, you can usually expect the diarrhea to resolve in about two to three days. Not so with giardiasis.
“The diarrhea is prolonged,” Dr. Bartelt says. “We would highly suspect giardiasis if the diarrhea is foul or greasy, but it doesn’t have to be. If you’ve had diarrhea for a week or longer, it should increase your suspicions of giardiasis.”
Other symptoms include abdominal cramping and bloating. While giardiasis is sometimes colloquially known as “beaver fever,” due to the beaver’s presence at freshwater sources that harbor the parasite, it’s unlikely that you would run a temperature (though you will be running to the bathroom several times a day).
Dr. Bartelt says that the parasite is detectable in the body about three to seven days following exposure to the parasite, as it replicates rapidly, and that symptoms start appearing within five to 10 days after exposure.
How Giardiasis is Transmitted
Giardiasis may start with a sip of water. If you’re camping and don’t treat your drinking water, or if you get a mouthful of lake or river water as you’re swimming, you may swallow a microscopic cyst that contains the parasite.
“It only takes 10 cysts to establish an infection, and there could be billions of cysts in contaminated water,” Dr. Bartelt says. “That infection leads to tens of millions of cysts in the gut.”
Cysts could be present in any lake or river worldwide, but in places where sanitation systems are not adequate, they can also be present in the drinking water. If you’re traveling internationally to regions without adequate water sanitation capabilities, you should brush your teeth with factory-sealed bottled water and peel raw fruits and vegetables before eating if they were washed with tap water.
The cysts are eventually expelled from the body through your stool, so contact with stool can also spread the disease. Day cares are associated with giardiasis cases because of the high number of diapers changed. If someone doesn’t practice good hand hygiene after touching infected stool, and then prepares food or touches a common surface, the parasite can be transmitted. Sexual acts that involve contact with stool, such as anal intercourse, are a risk factor for giardiasis as well, Dr. Bartelt says.
While pets like dogs and cats can get giardiasis and pass it to each other, Dr. Bartelt says it’s very uncommon for people to get it from animals at home. People can get giardiasis from the stool of wild animals, which is why it’s so important for nature enthusiasts to take precautions when hiking or camping.
“When humans are in contact with contaminated water sources, there’s always a risk for exposure,” Dr. Bartelt says. “That’s why it’s so important not to drink from rivers, lakes or streams. Bring your own water, or bring the equipment to treat your water, such as a filtration system or a heater to boil the water for three minutes.”
Diagnosing and Treating Giardiasis
Giardiasis is diagnosed by testing the stool to detect the presence of the parasite. If it’s detected, there are a few medication options: tinidazole, which is administered in a single dose but is not always available; metronidazole, which is the same medication but administered in multiple doses; and nitazoxanide, which is the only drug approved by the FDA for children under the age of 3.
Broad-spectrum antibiotics are not effective for parasites, and taking them unnecessarily contributes to the problem of antibiotic-resistant bacteria. They also disrupt the gut microbiome and could actually lead to an increased presence of giardia in the gut.
“The nature of the test is unpleasant and inconvenient, but we shouldn’t empirically treat diarrhea with antibiotics without a test,” Dr. Bartelt says.
While receiving treatment, you should practice good hand hygiene and use disinfectant, particularly in the bathroom and on high-touch surfaces—especially if you live with others. Do not swim with diarrhea; while Dr. Bartelt says that giardia outbreaks related to swimming pools are rare, sharing the pool with an infected person increases others’ risk.
It is possible for the parasites to clear your body via your stool, but it will take a while.
“If it runs its natural course, we’d expect symptom resolution within four to eight weeks,” Dr. Bartelt says. “Even when it clears on its own, some will experience prolonged post-infection irritable bowel symptoms.”
In the developing world, giardia is associated with restricted growth in children. That’s much less common in the United States, but the parasite is worth considering if a child isn’t growing and may have been exposed through travel, outdoor activity or in a child care setting.
“People should be aware of giardiasis as a global health concern and understand potential giardia exposure,” Dr. Bartelt says.
If you’re experiencing concerning gastrointestinal symptoms, talk to your doctor. If you need a doctor, find one near you.