Fact Sheet: Giardiasis (Giardia)

Giardiasis (commonly called giardia) is recognized as a disease of travelers worldwide, mainly in the developing world. In the United States, giardiasis is the most common pathogenic intestinal protozoa diagnosed, particularly in campers and hikers or swimmers in public swimming pools from drinking contaminated water, in children in day care centers, and in homosexual males. Other persons at risk include close contacts of infected persons or those who have contact with infected animals.

Cause of giardiasis

Giardiasis is caused by a protozoan, Giardia lamblia (also known as G. intestinalis or G. duodenalis).

The life cycle of Giardia is comprised of two stages: trophozoite and cyst. The trophozoite stage is responsible for producing clinical disease in humans. The mature cysts are environmentally resistant and responsible for disease transmission. Cysts may remain viable for several months in cool, moist conditions, and have been detected in natural surface waters. They are also able to survive standard concentrations of chlorine used in water purification systems.

Giardiasis is spread by the fecal-oral route. Giardia cysts are ingested with contaminated food or water or are acquired by unwashed hands. Although humans are the main reservoir of the parasite, a variety of both domestic and wild animals such as dogs, cats, cattle, beaver or deer carry Giardia species, which can infect humans.

Risk factors

High infection rates have been reported in hikers and campers in the U.S. since areas are inhabited by infected wild animals. Travelers represent one of the largest risk groups for giardiasis infection in the U.S. Contaminated water sources include unfiltered surface waters, shallow wells, and household water from either of the mentioned sources.

Symptoms of giardiasis

The most common symptoms of infection include:

• Diarrhea greater than 10 days in duration
• Abdominal pain
• Flatulence
• Bloating
• Vomiting
• Weight loss

Symptoms vary from person to person, often depending on the how many cysts are ingested, size, duration of infection, and individual host and parasite factors.

Giardiasis has been associated with several gastrointestinal disorders such as irritable bowel syndrome, inflammatory bowel disease and biliary tract dysfunction. Case reports indicate that giardiasis may also be involved with other health complications such as reactive arthritis and urticaria/pruritus or other dermatologic disorders.

Prevalence of giardiasis

Giardiasis occurs worldwide but is more prevalent in areas with inadequate sanitary conditions and where water treatment facilities and procedures are outdated. Unbeknownst to some, giardiasis is also found among people living in developed countries where sanitation is adequate and water supplies are piped and purified. Worldwide, it is one of the most important non-viral infections causing diarrheal illness in humans. The highest prevalence of giardiasis occurs in the tropics and subtropics. In the United States, giardiasis is the most commonly reported pathogenic protozoan disease.

Prevalence rates range from 2-7% in developed countries and 20-30% in most developing countries. In 1987, U.S. state diagnostic laboratories found 7.2% prevalence in stool specimens. The CDC estimates that there are upwards of 2.5 million cases that occur annually.

Giardiasis is a common traveler's infection among tourists and business travelers to developing countries, namely the Soviet Union, Mexico, Southeast Asia, and western South America. One study of travelers to St. Petersburg, Russia reported a 95% incidence.

Clinical signs and symptoms of G. lamblia infection

Giardiasis was initially regarded as non-pathogenic and often found in asymptomatic patients. However, there is now copious evidence for the pathogenic nature of G. lamblia. The major symptom of acute giardiasis, mainly seen in travelers, is protracted diarrhea. The diarrhea can be mild and produce semi-solid stools or it can be intense and debilitating.

The most common symptoms of infection include diarrhea of greater than 10 days duration, abdominal pain, flatulence, bloating, vomiting and weight loss. Symptoms vary from person to person, often depending on the inoculum size, duration of infection, and individual host and parasite factors. Children generally become less ill than adults and frequently develop asymptomatic infection. It has been suggested that as many as 50% of infections are asymptomatic. The incubation period for infection is generally 9-15 days. The acute stage usually begins with a feeling of intestinal uneasiness followed by nausea and anorexia. Low grade fever and chills may occur. These symptoms are followed by watery, foul-smelling, explosive diarrhea, abdominal pain, passage of foul gas and belching. This stage lasts for 3-4 days, often resembling other causes of travelers' diarrhea, so giardiasis may go undiagnosed. If left untreated, symptoms may persist for months. Malabsorption due to chronic Giardia infection has also been reported.

Diagnosis of giardiasis

The diagnosis of giardiasis is based on the detection of cysts or trophozoites in the feces, trophozoite in the small intestine, or by the detection of Giardia antigens in the feces.

There is no current gold standard diagnostic test for detecting giardiasis. However, the introduction of Giardia stool antigen tests has improved the diagnostic capability of giardiasis. Immunodiagnositc assays are available for the detection of Giardia and are more sensitive than the traditional ova and parasite (O&P) examinations. A single antigen test is able to detect 50% more infections than O&P examinations. Antigen tests also require less time than an O&P exam and can be combined with antigen testing for diagnosing Cryptosporidium making the antigen test more cost-effective. Giardia specific antigen may be detected in stool specimens even during an absence of cyst passage or visible signs of trophozoites.

Treatment of giardiasis

Tindamax^® (tinidazole) is a well-tolerated, highly effective treatment for giardiasis. Tinidazole's average giardiasis cure rate is 90%.¹

For more information about giardiasis:

• www.giardiasis.org
• The Centers for Disease Control and Prevention: call (800) 232-4636 or visit www.cdc.gov/std
• American Social Health Association: call (919) 361-8400 or visit www.ashastd.org
• www.tindamax.com

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