Giardiasis or beaver fever is an infection of the small bowel by a single-celled organism called Giardia lamblia. People become infected with the Giardia parasite after swallowing Giardia cyst often found in water contaminated by raw sewage or animal waste.

-Giardiasis can be found among 2-5% of people in industrialized nations such as the United States. In developing countries, 20-30% of the population may have giardiasis.

-Travelers to foreign countries may develop diarrhea often caused by Giardia.


Giardia cysts are transmitted to humans in various ways.

Contaminated water supplies: Giardia is one of the most common causes of water-borne diarrhea outbreaks. Sources of contaminated water include public facilities that improperly filter and treat water, water in developing countries, or rivers and lakes used by hikers. Overseas travelers and hikers are at a high risk for infection.

Contaminated food: Food that may have been washed in contaminated water, exposed to manure, or prepared by an infected person can transmit the disease.

Person-to-person contact: Infection may be caused by poor hygiene and most commonly occurs in daycare centers, nursing homes, and in sexually active homosexual males. Up to 50% of children infected with Giardia in daycare centers, and up to 20% of infected sexually active homosexual males, pass cysts in their stool. Family members, daycare workers, and others in contact with infected stool may then themselves become infected.


Giardiasis can show itself in different ways. Some people can be carriers of the parasite and have no symptoms of the disease, but they pass cysts in their stool and pass the disease to others. Others may develop acute or chronic diarrheal illnesses in which the symptoms occur 1-2 weeks after swallowing the cysts.

Acute diarrheal illness

Diarrhea: Up to 90% of people with giardiasis complain of diarrhea. Stool is usually described as profuse and watery early in the disease. Later in the disease, stools become greasy, foul smelling, and often float. Blood, pus, and mucus are usually not present. Symptoms may last for 1 to several weeks.

Weight loss, loss of appetite

Bloating, abdominal cramping, passing excessive gas, sulfur-tasting burps

Occasional nausea, vomiting, fever, rash, or constipation

Chronic diarrheal illness

Diarrhea: Stools are often greasy, foul smelling, yellowish, and may alternate between diarrhea and constipation.

Abdominal pain worsens with eating

Occasional headaches

Weight loss

Giardiasis Treatment

Self-Care at Home
Drink fluids such as sports drinks, diluted fruit juices, flat soda (such as 7-Up or ginger ale, none with caffeine), broth, soups, or preparations such as Pedialyte for children. Fluids should be taken in small amounts frequently throughout the day. Avoid fluids containing caffeine.
Suck on ice chips to keep from becoming dehydrated if you cannot keep fluids down.
After 12 hours, the diet can be advanced to bland foods such as potatoes, noodles, rice, toast, cereal, crackers, and boiled vegetables. Avoid spicy, greasy, and fried foods.
After stools become formed, return to a regular diet. Avoid milk for several weeks.
If you do not have fever or bloody diarrhea, you may take over-the-counter medications (along with antimicrobial prescription medications from your doctor). Loperamide is usually effective and should be taken as instructed on the label. Common nonprescription medications containing loperamide are Imodium, Kaopectate, and Pepto Diarrhea Control.


Medications are used effectively to treat giardiasis.

Metronidazole (Flagyl)

Treatment is 80-95% effective with these pills given 3 times a day for 5 days.

Side effects may include nausea, vomiting, headache, dry mouth, or a metallic taste in the mouth. Urine may turn dark or reddish-brown. Metronidazole brings on nausea and vomiting when alcohol is consumed while on the medication. Avoid alcohol 24 hours before starting the drug and for 48 hours after the last dose.


Treatment is 90% effective with these pills given over 5 days. Side effects may include nausea, vomiting, yellow skin and eyes, dark urine, and a rash.


Treatment is 80% effective. It is used with children because it is available as a liquid. Side effects may include loss of appetite, nausea, and vomiting.

Nitazoxanide (Alinia)

This drug was approved by the FDA in November 2002 for use in children with giardiasis. It is available in liquid form and must be taken with food. Side effects may include stomach pain, diarrhea, vomiting, or headache.

Pregnant women with giardiasis are treated somewhat differently because of the possible risk to the fetus by some of the medications.

If the disease is mild and dehydration can be avoided, treatment may be postponed until after delivery.

If treatment is necessary, paromomycin may be used but is less effective. The effects of metronidazole on the fetus appear to be minimal and occur mostly in the first trimester.

If therapy is necessary, metronidazole is probably safe to use in the second and third trimesters.