Giardiasis is a communicable gastrointestinal disease characterized by acute diarrhea. It is caused by a parasite, Giardia lamblia, also known as Giardia intes-tinalis. Giardiasis is the most common water-borne infection of the human intestine worldwide, affecting as many as 200 million people each year. According to the Centers for Disease Control and Prevention (CDC), there were 90 major community outbreaks of giardiasis in the United States between 1964 and 1984, and 34 major outbreaks since 1985.
The organism that causes giardiasis, G. lamblia, is a protozoan, a single-celled organism formerly classified
as a member of the animal kingdom. It is a pear-shaped parasite with four flagella, which are long whip-like extensions of the cell that allow the organism to move. It was first seen under a microscope by the Dutch lens maker Antony van Leeuwenhoek in the 17th century. G. lamblia was found in human stool samples in 1859 by a Czech physician named Lambl, but was not identified as the cause of giardiasis until the 1970s. It was given its present name in 1915 to honor Alfred Giard, a French biologist, as well as Dr. Lambl.
Dietary treatment of patients with giardiasis has been a gradual process, dependent on better understanding of the causes of the disease as well as the development of nutritionally adequate rehydration solutions and anti-infective medications. A large part of dietary therapy for giardiasis, in fact, consists of measures to prevent the spread of the disease, not just to treat the symptoms after they appear.
Life cycle of G. lamblia
In order to understand the symptoms, treatment, and prevention of giardiasis, it is helpful to understand the life cycle of G. lamblia. The parasite that causes giardiasis has a simple two-stage life cycle that does not require an intermediate host; it can be spread directly among human beings. The cycle begins when a person swallows as few as 10 to 15 cysts of G. lamblia. The cyst is a protective shell that the organism forms around itself that enables it to survive outside a human or animal host. The cysts of G. lamblia are smooth
Barberry— A shrub native to southern Europe and western Asia that produces oblong red berries that have a sour taste. Barberry has been used as a natural treatment for giardiasis.
Beaver fever— An informal name for giardiasis, so called because beavers are a common animal reservoir of the parasite that causes giardiasis.
Carrier— A person who bears or carries a disease agent in or on their body and can transmit the disease to others, but is immune to the disease or has no symptoms of it. Some people can be carriers of the organism that causes giardiasis without developing diarrhea.
Cyst— The protective shell formed by G. lamblia that keeps the organism alive after it has been expelled from the host’s body.
Endoscope— A special tube-shaped instrument that allows a doctor to examine the interior of or perform surgery inside the stomach or intestines.
Flatulence— The passage of intestinal gas. Flatulence is a common symptom of giardiasis.
Gastroenterologist— A doctor who specializes in the diagnosis and treatment of diseases of the stomach and intestines.
Lactose— A sugar found in milk and milk products that requires an enzyme called lactase to digest it. Some people with giardiasis must avoid foods containing lactose for several weeks or months after they are treated for the disease because their bodies are temporarily unable to produce enough lactase to digest the milk sugar.
Malabsorption syndrome— A condition characterized by indigestion, bloating, diarrhea, loss of appetite, and weakness, caused by poor absorption of nutrients from food as a result of giardiasis, other bowel disorders, or certain surgical procedures involving the digestive tract.
Protozoan— Any member of a phylum of one-celled eukaryotes (organisms with nuclei) that are able to move but are not animals in the strict sense. The organism that causes giardiasis is a protozoan.
Reservoir— A term used for animals that can carry parasites that cause disease in humans without falling ill themselves. Beavers, dogs, cats, cattle, and horses are common reservoirs of G. lamblia.
Steatorrhea— The passage of large amounts of fat or grease in the stool, caused by failure to absorb it during digestion. Steatorrhea is often associated with chronic giardiasis.
Traveler’s diarrhea (TD)— A nonspecific term for a form of diarrhea that frequently affects tourists abroad. TD is the most common illness affecting visitors to other countries. Some cases of TD are caused by G. lamblia, but others result from infection with various bacteria, rotaviruses, and other intestinal parasites.
Trophozoite— The active feeding stage in the life cycle of G. lamblia. It is the trophozoites that multiply within the small intestine and cause the diarrhea and other symptoms of giardiasis.
walled and oval in shape, about 8–12 micrometers long and 5–15 micrometers wide. They are hardy and can survive for several months in cold water They usually enter the human body through the mouth. The cysts may be transferred to the mouth directly from unwashed hands that have touched fecal matter containing cysts, or through having oral sex with an infected person. They may also enter the mouth through eating food or swallowing liquids contaminated by fecal matter containing G. lamblia cysts. G. lamblia is not, however, transmitted through blood
Once inside the body, the cysts pass through the digestive tract until they reach the small intestine. Each cyst then opens—often within 5 minutes after arrival—and releases two trophozoites, which are the active feeding stage of the parasite. The trophozoites multiply rapidly, reproducing every 9 to 12 hours. They may remain free within the central cavity (lumen) of the small intestine or attach themselves to the mucous tissue lining the intestine by a sucking disk located on their ventral surface. It is the trophozoites that cause the violent diarrhea, nausea, intestinal gas, and cramping associated with giardiasis. As of 2007, however, researchers do not know the exact reason for the symptoms; some think that the parasites compete with the host for nutrients, while others think that they affect the host’s immune system, cause damage to the tissues lining the intestine, or block the functioning of the intestinal mucosa by their sheer numbers.
As the trophozoites are carried toward the colon, they begin to secrete proteins to form the walls of a new cyst. Within the next 24 hours, the trophozoite completes the construction of its cyst and is shed into the outside environment through the person’s feces.
About 15% of people who swallow cysts are asymptomatic. These cases are usually detected only if the person’s stool is tested during a community outbreak. They are significant, however, because persons carrying the cysts in their digestive tract, known as carriers, can still transmit giardiasis to others even if they do not develop the symptoms of the illness. It is estimated that between 30 and 60% of children in daycare centers and adults on Native American reservations are carriers of G. lambliaSome domestic and wild animals can also be carriers of G. lamblia,dogs and beavers being the most common animal reservoirs
Of the patients who have symptoms, 90% develop acute diarrhea within 7 to 10 days of ingesting the cysts; and 70-75% have abdominal cramps, bloating, vomiting, and flatulence (the passage of intestinal gas). A small percentage of patients develop symptoms within 3 days of swallowing the cysts, including violent diarrhea, extremely foul-smelling intestinal gas, severe vomiting, fever, and headache. Most patients lose their appetite, and 50% lose weight—an average of 10 pounds in adults. Without treatment, these symptoms can last for as long as 7 weeks or even longer
Between 20 and 40% of adults with giardiasis develop a temporary difficulty with digesting lactose, a sugar found in milk or milk products. This condition is called lactose intolerance and may last for a month or so after treatment with anti-parasite medications for giardiasis. Having lactose intolerance does not mean that the person has become reinfected
There is no universal pattern to recovery from giardiasis. It is rarely fatal except in severely dehydrated and malnourished children, but may develop into chronic forms—malabsorption syndrome in adults and failure to thrive in children. Chronic giardiasis in adults is characterized by episodes of diarrhea that come and go, alternating with periods of constipation and normal bowel movements. Other symptoms of chronic giardiasis in adults include:
- Ongoing weight loss apart from intentional weight reduction.
- Steatorrhea. Steatorrhea is the medical term for the passage of large amounts of fat or greasy-looking material in the stool.
- Discomfort in the stomach or abdomen that is worse after a meal.
- Persistent bad breath or burping that smells like sulfur.
- Ongoing bloating, flatulence, or abdominal cramping.
- Recurrent headaches.
- Malaise (general feeling of sickness), fatigue, or weakness.
The symptoms of chronic giardiasis in children include:
- Failure to grow and gain weight at a normal rate for the child’s age and sex.
- Recurrent episodes of pale, frothy, foul-smelling diarrhea.
- Loss of appetite.
- Abdominal pain and vomiting.
- Nutritional deficiencies caused by the inability to absorb nutrients in food.
In the United States and other developed countries, giardiasis is most likely to affect children, particularly children in daycare centers. About 20 to 25% of the children in daycare centers are infected with giardiasis even though they may not be symptomatic. Most of the community outbreaks in the United States since the 1980s, in fact, began in daycare centers.
Older adolescents and adults are more likely to be infected with giardiasis while hiking or traveling abroad. G. lambliais a common cause of so-called traveler’s diarrhea, although it is not the only organism that causes it. Giardiasis acquired its nickname of “beaver fever” because backpackers and hikers who drink water from or swim in streams close to beaver colonies are likely to ingest G. lambliacysts shed into the water by infected animals. The CDC reports that as many as 80% of water samples from lakes, streams, and ponds in the United States contain G. lambliacysts.
Outbreaks of giardiasis are most likely to occur in Canada and the United States during warmer weather, particularly in summer and fall. Race does not appear to be a factor in contracting giardiasis; however, males in all age groups are about 1.2 times more likely than females to develop the disease.
Some people are at increased risk of contracting giardiasis because of their location or lifestyle:
- Parents of infected small children.
- Employees (and their family members) of daycare centers in which some of the children are not yet toilet-trained.
- Employees (and their family members) of nursing homes or other custodial facilities.
- Male homosexuals, particularly those with several or many partners.
- People who swim in or boat on rivers, lakes, streams, or other bodies of water liable to contamination by fecal matter. The greatest risk of infection comes from accidentally swallowing a mouthful of water while swimming, diving, rafting, or water skiing.
- People who depend on well water for their household drinking supply.
Some people are at increased risk of a severe case of giardiasis because they have other health problems:
- An impaired immune system.
- Crohn’s disease, cystic fibrosis, or other diseases that weaken the intestines.
- Recent surgery on the stomach or taking medications to lower stomach acid secretion (stomach acid kills G. lamblia).
Most people with giardiasis can be diagnosed and treated by their primary care physician. Diagnosis is usually done by examining stool samples under a microscope for the characteristic cysts and trophozoites of G. lamblia(both forms of the organism may appear in the stool); by enzyme-linked immunosorbent assay (ELISA) tests; or by an Entero-test. The Entero-test, also called the string test, consists of a gelatin capsule containing a nylon string attached to a weight. The patient tapes one end of the string to the inside of the cheek and swallows the capsule. The string is left in place for 4 to 6 hours or overnight while the patient is fasting; it is then removed and the mucus on the string is examined for trophozoites.
Patients suspected of having chronic giardiasis may be referred to a gastroenterologist, who is a doctor with special training in digestive disorders. In some cases, the doctor may need to examine the patient’s small intestine through an endoscope or remove a sample of tissue from the lining of the patient’s intestine to make sure that the patient’s symptoms are caused by a parasite and not by some other disorder.
Giardiasis is most commonly treated with one of the following drugs, which cause the death of the disease organisms:
- Metronidazole (Flagyl). The most common drug given to treat giardiasis. Adults are usually given three doses per day over a 5-day period, while children are usually given a 10-day course.
- Furazolidone (Furoxone). Some doctors prefer to treat children with this drug because it is available in a liquid form.
- Nitazoxanide (Alinia). This drug is also preferred for treating children because it causes fewer adverse effects in younger patients.
- Tinidazole (Tindamax). Tinidazole is a relatively new anti-infective drug; it was approved by the Food and Drug Administration (FDA) only in 2004. It has the advantage of requiring only one dose of 2000 mg for treatment of giardiasis rather than several days of repeated doses.
- Paramomycin (Humatin). Paramomycin is the only drug effective against G. lambliathat is considered safe to give pregnant women.
Some herbalists and naturopaths recommend barberry (Berberis vulgaris)as an anti-infective agent in treating giardiasis
Children or adults who are carrying cysts are sometimes given anti-infective drugs even if they are not symptomatic, in order to lower the risk of transmission to other children in a daycare center or other family members.
People with mild cases of giardiasis may not need any special dietary therapy after they have started taking medications to kill the parasites.
Children and adults who have become dehydrated because of severe diarrhea may be given a rehydration drink (Lytren, Rehydralyte, or Pedialyte) to sip. Adults should drink 1 cup of water or rehydration drink for each large passage of watery stool. Children should be given 1/2 to 1 cup of rehydration fluid (or Pedialyte frozen pops) per hour, as dehydration is more dangerous to them than to adults. Children should not be given undiluted sports drinks, soda pop, or fruit juice, as these contain too much sugar and not enough electrolytes. If a commercial rehydration drink is not available and the diarrhea does not stop within 24 hours, the World Health Organization (WHO) formula for oral rehydration can be used. To make the WHO formula at home, combine 1 quart of boiled or purified water with 2 teaspoons table sugar, 1/2 teaspoon salt, and 1/2 teaspoon of baking soda (sodium bicarbonate).
Dietary therapy for adults recovering from giardiasis includes the following:
- Take clear liquids only (beef broth, soda, vegetable or chicken bouillon, etc.) for the first 24 hours of acute symptoms; do not try to eat solid foods.
- Begin eating mild foods without spices on the second day. These foods include plain boiled rice, dry toast, saltines, applesauce, and bananas.
- Avoid spicy foods, citrus fruits, caffeinated beverages, and alcohol until two days after the last symptoms of giardiasis have disappeared.
- Avoid milk and other dairy products for three days after the last symptoms of giardiasis.
Patients who have developed lactose intolerance as a result of giardiasis can usually treat the problem themselves by avoiding milk and dairy products for a full month (or longer) after the end of symptoms, and then add them to the diet in small amounts on a gradual basis. They may also wish to consider some alternative products such as soy milk, almond milk, oat milk, or rice milk, or try some of the lactose-free milk and cheese products that are now available.
Anti-infective medications benefit the patient by killing the parasites responsible for giardiasis, thereby lowering the risk of developing chronic giardiasis and malabsorption syndrome.
Dietary treatment for giardiasis benefits the patient by giving the digestive tract a rest and by replacing nutrients and electrolytes lost by acute diarrhea or vomiting.
Patients taking anti-infective drugs should tell their doctor about any other medications they may be taking, including over-the-counter drugs, to lower the risk of drug interactions.
Pregnant women should not take any anti-infective medication for giardiasis except paramomycin, and then only if they are severely ill.
Anti-infective medications should be taken with food to lower the risk of nausea or heartburn. They should, however, neverbe taken with alcohol, as they will interact to cause severe nausea and vomiting. Alcoholic beverages should be avoided for at least 48 hours after the last dose of the medication.
Preventive dietary and public health measures
The risk of contracting giardiasis can be lowered by simple dietary and personal cleanliness measures:
QUESTIONS TO ASK YOUR DOCTOR
- What can I do to prevent giardiasis in my household?
- What precautions would you advise before a family vacation trip?
- Avoid drinking untreated or unpurified water when hiking or camping. Boil the water for at least 1 full minute or add commercial purification tablets before drinking.
- When traveling in other countries known to have high rates of giardiasis, drink only bottled water and do not eat raw fruits or vegetables or drink beverages containing ice made from untreated water. The CDC maintains a frequently updated list of travelers’ advisories on its website.
- Wash hands often, particularly after using the toilet, changing diapers, helping someone else use the toilet, or before food preparation.
- Avoid swallowing water when swimming in lakes, rivers, or streams.
- Protect others by avoiding swimming pools, hot tubs, the ocean, or lakes and streams while infected with G. lamblia,and for at least 2 weeks after the diarrhea stops. It is possible to pass the organism in stool and contaminate water for several weeks after the symptoms have ended.
- Avoid exposure to fecal material during sexual activity.
The anti-infective drugs listed above cause some adverse effects in some patients, including nausea, constipation, headache, temporary discoloration of the urine, a metallic taste in the mouth, drowsiness, skin rashes or itching, dry mouth, or depression
Anti-infective medications interact with such other drugs as cimetidine, praziquantel, tricyclic antidepressants, selective serotonin reuptake inhibitors (SSRIs), lithium, phenytoin, and others. They counteract the effects of some of these medications and intensify the effects of others.
There are no risks associated with modifying the patient’s normal diet as part of recovery from giardiasis No adverse effects have been reported from the use of rehydration solutions in treating patients with giardiasis.
Anti-infective medications for the treatment for giardiasis have been tested and used for several decades as of 2007. The WHO formula for oral rehydration has been used in developing nations since the 1960s in treating people dehydrated by diarrhea resulting from cholera, giardiasis, and other intestinal disorders.
“Giardiasis.” Chapter 185, Section 14 in the Merck Manual of Diagnosis and Treatment, 18th ed. Edited by Mark H. Beers and Robert Berkow. Whitehouse Station, NJ: Merck, 2007.
Gavagan, Thomas, MD, and Lisa Brodyaga, JD. “Medical Care for Immigrants and Refugees.” American Family Physician 57 (March 1, 1998): 1061–1068
Kucik, Corry Jeb, MD, Gary L. Martin, MD, and Brett V. Sortor, MD. “Common Intestinal Parasites.” American Family Physician 69 (March 1, 2004): 1161–1168
Pennardt, Andre, MD. “Giardiasis.” eMedicine, February 22, 2006. Available online at http://www.emedicine.com/emerg/topic215.htm (accessed March 27, 2007)
Rana, S. V., D. K. Bhasin, and V. K. Vinayak. “Lactose Hydrogen Breath Test in Giardia lamblia-positive Patients.” Digestive Diseases and Sciences 50 (February 2005): 259–261.
Centers for Disease Control and Prevention (CDC). Parasites and Health: Giardiasis. Atlanta, GA: CDC, 2005. Available online at http://www.dpd.cdc.gov/dpdx/HTML/Giardiasis.htm (accessed March 27, 2007)
Dietz, Thomas E., MD. “Dietary Hygiene in the Prevention of Travellers’ Diarrhea.” High Altitude Medicine Guide, May 2000. Available online at http://www.high-altitude-medicine.com/diarrhea.html(accessed March 27, 2007)
North American Society for Pediatric Gastroenterology, Hepatology and Nutrition (NASPGHAN). Acute Diarrhea in Children. Flourtown, PA: NASPGHAN, 2007. Available online at http://www.naspghan.org(accessed March 27, 2007)
Surawicz, Christina M., MD, and Blanca Ochoa, MD. Diarrheal Diseases. Bethesda, MD: American College of Gastroenterology (ACG), 2007.
American College of Gastroenterology (ACG). 6400 Goldsboro Road, Suite 450, Bethesda, MD 20817. Telephone: (301) 263-9000. Website: http://www.acg.gi.org
Centers for Disease Control and Prevention (CDC). 1600 Clifton Road, Atlanta, GA 30333. Telephone: (404) 639-3311. Website: http://www.cdc.gov/
North American Society for Pediatric Gastroenterology, Hepatology and Nutrition (NASPGHAN).P.O.Box 6, Flourtown, PA 19031. Telephone: (215) 233-0808. Website: http://www.naspghan.org
Rebecca J. Frey, PhD
Giardiasis (pronounced GEE-are-DYE-uh-sis) is intestinal infection with the protozoan parasite Giardia lamblia (also called Giardia intestinalis or Giardia (gee-ARE-dee-uh). Protozoa are single-celled animals with more complex features and behavior than bacteria, which are also single-celled organisms. Giardiasis is a waterborne disease found almost everywhere in the world. Its symptoms include diarrhea, gas, stomach cramps, fatigue, weight loss, and nausea. Giardiasis is transmitted by ingestion of cysts—extremely small, dormant, seedlike objects—that have been shed in the feces of an infected person or animal. Several drugs can be used to treat giardiasis, but healthy individuals can usually overcome the disease without treatment. The symptoms of untreated giardiasis usually last from two to six weeks.
Giardiasis has probably been endemic since before modern humans evolved. Giardia were first described by the Dutch scientist Antony van Leeuwenhoek (1632–1723), who significantly improved the microscope and was the first person to observe single-celled organisms. He found Giardia living in his own feces. The organism was originally named Cercomonas intestinalis by the Czech physician Wilhelm Lambl (1814–1895) in 1859. It was renamed Giardia lamblia in 1915 to honor both Lambl and the French physician Alfred Giard (1846– 1908), another early researcher of Giardia. Today, the term Giardia intestinalis is usually preferred by scientists.
In the twentieth century, five species of Giardia were identified. Giardia intestinalis, the species that afflicts humans, can be hosted by mammals, reptiles, and possibly birds.
Giardia is a protozoan flagellate, that is, a one-celled animal that propels itself using tiny, rapidly-waving hairs called flagella. It exists in two forms, the trophozoite and the cyst. A Giardia cyst is a microscopic, oval object about 1 to 12 μm (millionths of a meter) long and 7 to 10 μm wide. A Giardia infection occurs when a sufficiently large number of these cysts are ingested by an animal or human.
In the duodenum, the part of the small intestine just below the stomach, each cyst hatches and divides into two trophic individuals or trophozoites. A Giardia trophozoite is shaped somewhat like a limpet with a short, pointed tail. It attaches its flat surface to the cells of the intestinal wall and feeds on them. In a few days, the trophozoites detach from the intestinal wall and divide into two identical individuals. Some are carried downstream through the digestive tract to the large intestine, where feces are formed. The harsh chemical conditions in the large intestine signal the trophozoites to become cysts. Cysts can survive for months in surface waters such as lakes and streams.
Giardia infection usually lasts two to six weeks. In some cases, however, the infection can become chronic or ongoing. Exactly how Giardia cause the symptoms of giardiasis is not known. Between 60% and 80% of people infected with Giardia have no symptoms.
During bouts of diarrhea caused by giardiasis, both trophozoites and cysts exit the body in the feces. The trophozoites die outside the body, but the cysts may be ingested by another animal and continue the life cycle. There can be from 1,000,000 to 100,000,000 cysts per gram in stool samples that test positive for Giardia, but many stool samples of infected persons do not contain detectable levels of Giardia at all.
Cysts are almost always transmitted by the fecal-oral route—that is, by the ingestion of fecal material, generally in very small or dilute amount, through the mouth. This may occur through feces-hand-oral contact (common among children or those caring for children) or in drinking water. The drinking water route is common worldwide, but less so in developed countries. A 2001 New Zealand study found that persons who were changing diapers were four times more likely to test positive for Giardia than others. Giardia cysts may also be foodborne, that is, transmitted through contact between food and infected workers or family members.
Whether pets and animals are significant in spreading Giardia is debated. Giardia is common in pets, wild mammals, and farm animals, but there is little evidence that these are important sources of human infection, despite the association in the United States of Giardia with drinking open waters containing fecal matter from beavers. (The disease is sometimes called “beaver fever” in the United States.)
Giardia is present in most surface waters of the world, at rates varying from 0.1 to over 1,000 cysts per 26 gallons (100 liters) of water. About 12% of the groundwater sources in the United States are contaminated either with Giardia or Cryptosporidium, another protozoan parasite.
Globally, about 200 million people, about 3% of the world's population, are infected with Giardia at any one time. Giardiasis is particularly common in children in poor countries. In industrialized countries, giardiasis is most common among children one to four years old, in adults caring for small children, and in those who have traveled recently to the developing world. It can also be contracted by people who drink untreated lake or stream water while visiting wilderness areas. However, drinking such water does not usually result in infection. The body can usually fend off infection if it has ingested only a small to moderate number of cysts.
WORDS TO KNOW
TROPHOZOITE: The amoeboid, vegetative stage of the malaria protozoa.
The primary public-health approach to preventing giardiasis is to keep Giardia cysts out of drinking water supplies. This is accomplished by keeping water sources used for drinking water from Giardia contamination by sewage or livestock waste, and by treating drinking water before distributing it. Because Giardia and other protozoan cysts are resistant to chemicals such as chlorine at the levels ordinarily used to treat water, the primary means of treating water is filtering. Portable, hand-operated filters can be used by persons in wilderness areas to filter out not only Giardia cysts, but other parasites and bacteria. The U.S. Centers for Disease Control (CDC) recommends not drinking recreational water, untreated surface water, or untreated ice or drinking water while traveling in developing countries.
For healthy individuals, treatment for giardiasis is usually not necessary, as the body is capable of freeing itself from the infection. Where treatment is needed or desired, a number of drugs are available, including albendazole, furazolidone, metronidazole, nitazoxanide, and quinacrine.
Infection with Giardia intestinalis is the most commonly reported protozoan parasite infection worldwide. In developing countries, about 20% of patients with diarrhea are positive for Giardia (the range is 5% to 43%). In developed regions such as the United States and Europe, about 3% of diarrhea patients have Giardia. Because untreated diarrhea can cause severe dehydration (loss of water and electrolytes from the body), it can be life endangering in persons with little access to medical care and with compromised immune systems, especially small children. Diarrhea causes 4% of all deaths worldwide. In 1998, for example, diarrhea killed some 2.2 million people, most of them children under the age of five. It is not known how many of these deaths are due to Giardia infection. Chronic Giardia infection may also cause failure to thrive in children due to impaired uptake of fats and vitamins A and B12.
IN CONTEXT: REAL-WORLD RISKS
The Centers for Disease Control and Prevention, National Center for Infectious Diseases, Division of Parasitic Diseases states that, “Anyone can get giardiasis. Persons more likely to become infected include:
- Children who attend day care centers, including diaperaged children
- Child care workers
- Parents of infected children
- International travelers
- People who swallow water from contaminated sources
- Backpackers, hikers, and campers who drink unfiltered, untreated water
- Swimmers who swallow water while swimming in lakes, rivers, ponds, and streams
- People who drink from shallow wells.”
- “Contaminated water includes water that has not been boiled, filtered, or disinfected with chemicals. Several community-wide outbreaks of giardiasis have been linked to drinking municipal water or recreational water contaminated with Giardia.”
SOURCE: Centers for Disease Control and Prevention (CDC)
Erlandsen, Stanley, and Ernest Meyer. Giardia and Giardiasis, Biology Pathogenesis, and Epidemiology. New York: Springer, 2001.
Parker, James N., and Philip M. Parker. The Official Patient's Sourcebook on Giardiasis. San Diego, CA: Icon Health Publications, 2002.
Casemore, David P. “Foodborne Illness: Foodborne Protozoal Infection.” Lancet. 336 (1990): 1427–1433.
Hawralek, Jason. “Giardiasis: Pathophysiology and Management.” Alternative Medicine Review. 8.2 (2003): 129–143.
Hoque, M. Ekramul, et al. “Nappy Handling and Risk of Giardiasis.” Lancet. 357 (2001): 1017.
Meng, Tze-Chiang, et al. “Inhibition of Giardia lamblia Excystation by Antibodies against Cyst Walls and by Wheat Germ Agglutinin.” Infection and Immunity. 64 (1996): 2151–2157.
Reiner, David S., et al. “Identification and Localization of Cyst-Specific Antigens of Giardia lamblia.” Infection and Immunity. 57 (1989): 963–968.
Vogel, Gretchen. “Searching for Living Relics of the Cell's Early Days.” Science. 277 (1997): 1604.
Centers for Disease Control (U.S. Government). “Parasitic Disease Information: Giardiasis.” September 14, 2004 <http://www.cdc.gov/ncidod/dpd/parasites/giardiasis/> (accessed February 1, 2007).
Giardiasis is a common intestinal infection spread by eating contaminated food, drinking contaminated water, or through direct contact with the organism that causes the disease, Giardia lamblia. Giardiasis is found throughout the world and is a common cause of traveller's diarrhea. In the United States it is a growing problem, especially among children in childcare centers.
Giardia is one of the most common intestinal parasites in the world, infecting as much as 20% of the entire population of the earth. It is common in overcrowded developing countries with poor sanitation and a lack of clean water. Recent tests have found Giardia in 7% of all stool samples tested nationwide, indicating that this disease is much more widespread than was originally believed. It has been found not only in humans, but also in wild and domestic animals.
Giardiasis is becoming a growing problem in the United States, where it affects three times more children than adults. In recent years, giardiasis outbreaks have been common among people in schools or daycare centers and at catered affairs and large public picnic areas. Children can easily pass on the infection by touching contaminated toys, changing tables, utensils, or their own feces, and then touching other people. For this reason, infection spreads quickly through a daycare center or institution for the developmentally disabled.
Unfiltered streams or lakes that may be contaminated by human or animal wastes are a common source of infection. Outbreaks can occur among campers and hikers who drink untreated water from mountain streams. While 20 million Americans drink unfiltered city water from streams or rivers, giardiasis outbreaks from tainted city water have been rare. Most of these problems have occurred not due to the absence of filters, but because of malfunctions in city water treatment plants, such as a temporary drop in chlorine levels. It is possible to become infected in a public swimming pool, however, since Giardia can survive in chlorinated water for about 15 minutes. During that time, it is possible for an individual to swallow contaminated pool water and become infected.
Causes and symptoms
Giardiasis is spread by food or water contaminated by the Giardia lamblia protozoan organism found in the human intestinal tract and feces. When the cysts are ingested, the stomach acid degrades the cysts and releases the active parasite into the body. Once within the body, the parasites cling to the lining of the small intestine, reproduce, and are swept into the fecal stream. As the liquid content of the bowel dries up, the parasites form cysts, which are then passed in the feces. Once excreted, the cysts can survive in water for more than three months. The parasite is spread further by direct fecal-oral contamination, such as can occur if food is prepared without adequate hand-washing, or by ingesting the cysts in water or food.
Giardiasis is not fatal, and about two-thirds of infected people exhibit no symptoms. Symptoms will not occur until between one and two weeks after infection. When present, symptoms include explosive, watery diarrhea that can last for a week or more and, in chronic cases, may persist for months. Because the infection interferes with the body's ability to absorb fats from the intestinal tract, the stool is filled with fat. Other symptoms include foul-smelling and greasy feces, stomach pains, gas and bloating, loss of appetite, nausea and vomiting. In cases in which the infection becomeschronic, lasting for months or years, symptoms might include poor digestion, problems digesting milk, intermittent diarrhea, fatigue, weakness, and significant weight loss.
Diagnosis can be difficult because it can be easy to overlook the presence of the giardia cysts during a routine inspection of a stool specimen. In the past, the condition has been diagnosed by examining three stool samples for the presence of the parasites. However, because the organism is shed in some stool samples and not others, the infection may not be discovered using this method.
A newer, more accurate method of diagnosing the condition is the enzyme-linked immunosorbent assay (ELISA) that detects cysts and antigen in stool, and is approximately 90% accurate. While slightly more expensive, it only needs to be done once and is therefore less expensive overall than the earlier test.
Acute giardiasis can usually be allowed to run its natural course and tends to clear up on its own. Antibiotics are helpful, however, in easing symptoms and preventing the spread of infection. Medications include metronidazole, furazolidone and paromomycin. Healthy carriers with no symptoms do not need antibiotic treatment. If treatment should fail, the patient should wait two weeks and repeat the drug course. Anyone with an impaired immune system (immunocompromised), such as a person with AIDS, may need to be treated with a combination of medications.
Giardiasis is rarely fatal, and when treated promptly, antibiotics usually cure the infection. While most people respond quickly to treatment, some have lingering symptoms and suffer with diarrhea and cramps for long periods, losing weight and not growing well. Those most at-risk for a course like this are the elderly, people with a weakened immune system, malnourished children, and anyone with low stomach acid.
The best way to avoid giardiasis is to avoid drinking untreated surface water, especially from mountain streams. The condition also can be minimized by practicing the following preventive measures:
- thoroughly washing hands before handling food
- maintaining good personal cleanliness
- boiling any untreated water for at least three minutes
- properly disposing of fecal material
Children with severe diarrhea (and others who are unable to control their bowel habits) should be kept at home until the stool returns to normal. If an outbreak occurs in a daycare center, the director should notify the local health department. Some local health departments require a follow-up stool testing to confirm that the person is no longer contagious. People not in high-risk settings can return to their routine activities after recovery.
Centers for Disease Control. 〈http://www.cdc.gov/ncidod/EID/eidtext.htm〉.
International Society of Travel Medicine. 〈http:www.istm.org〉.
Antibody— A specific protein produced by the immune system in response to a specific foreign protein or particle called an antigen.
Antigen— A substance (usually a protein) identified as foreign by the body's immune system, triggering the release of antibodies as part of the body's defense mechanism.
Enzyme-linked immunosorbent assay (ELISA)— A laboratory technique used to detect specific antigens or antibodies. It can be used to diagnose giardiasis.
Giardia lamblia — A type of protozoa with a whiplike tail that infects the human intestinal tract, causing giardiasis. The protozoa will not spread to other parts of the body.
Immunocompromised— A state in which the immune system is suppressed or not functioning properly.
Giardiasis is an infection of the small intestine by the Giardia lamblia parasite. It is spread from person to person or by contact with contaminated water or food. Its major symptom is diarrhea.
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Giardiasis (je-ar-DY-a-sis) is a common infection caused by the Giardia Umblia (je-AR-de-a LAM-bli-a) protozoan, which is a one-celled organism that lives as a parasite*. Giardia contamination can occur in any water source, from clear mountain streams to poorly filtered city water supplies. The most common carriers of giardiasis are dogs, beavers, and humans. Giardiasis is easily passed from person to person through poor hygiene.
- * parasites
- are creatures that live in and feed on the bodies of other organisms. The animal or plant harboring the parasite is called its host.
Giardiasis is found worldwide in both developed and developing countries and in both temperate and tropical climates. In developing nations, infection rates from 20 to 50 percent may occur. In the United States, it is estimated to affect up to 20 percent of the population, with toddlers in diapers at busy day care centers at particular risk.
It is estimated that more than 50 percent of people with giardiasis have no symptoms or only mild symptoms. When symptoms of giardiasis do occur, they may start gradually or suddenly, usually within one to three weeks after exposure to the parasite. The illness usually begins with frequent watery diarrhea without blood or mucus. Because giardiasis affects the body’s ability to absorb fats and carbohydrates from ingested foods (malabsorption), giardiasis often produces foul-smelling, oily stools that float. Symptoms also may include abdominal cramps, a swollen or large abdomen, excessive gas, nausea and vomiting, loss of appetite, and sometimes a low-grade fever. Persistent symptoms can lead to weight loss and dehydration.
Giardiasis is diagnosed by examination of stool samples under a microscope. Doctors look for evidence of trophozoites (tro-fo-ZO-ites), which are active Giardia protozoa inside the body, or for evidence of cysts, which are Giardia surrounded by a protective wall, the form of the protozoan during the resting stage of its life cycle. Detecting Giardia is difficult, so doctors often need to repeat the stool sample tests several times before they can confirm or rule out Giardia infection. Diagnostic tests may sometimes take as long as four or five weeks.
Several drugs are available for treatment of giardiasis, and some of them work well in a single dose. Sometimes a second round of drug treatment is required. There is some controversy among doctors about whether to treat people who carry the parasite but who do not have symptoms of giardiasis. Treatment is sometimes considered because these individuals may transmit the infection to others and may eventually show symptoms themselves.
There is no vaccine or prophylactic (disease-preventing) drug for giardiasis. Preventing giardiasis depends on maintenance of safe supplies of drinking water, the sanitary disposal of human and animal waste, washing of fruits and vegetables before eating or cooking, and proper hygiene, which includes thorough washing of hands after going to the bathroom and before eating.
The Giardia protozoan can be filtered from water but is otherwise difficult to destroy. It can survive in cold water for as long as two months, and it is resistant to chlorine levels used to purify municipal water supplies. When municipal water supplies have been approved by local health departments, the water may be considered safe to drink. But when camping or traveling, it is important to make sure that drinking water, cooking water, and ice come only from safe sources. Clear cold mountain streams may look safe and inviting but they may also carry the Giardia parasite.
The U.S. National Institute of Allergy and Infectious Diseases posts a fact sheet about giardiasis at its website. http://www.niaid.nih.gov/factsheets/GIARDIA.htm