What is giardia and how can I get infected?

I’m a healthy 32-year-old female who has been experiencing digestive problems for several years. It has become gradually worse in the past year. I’ve experienced stomach upset such as nausea, vomiting, heartburn and diarrhea. I can’t trace this to any particular food I eat. I thought I might have had Irritable Bowel Syndrome. I make many return trips to the toilet because I constantly feel the need to void my bowels. Shortly after eating most foods I experience bloating and nausea. My physican tested me for giardia, but it was negative. Any suggestions?

Although it would be impossible for me to offer a diagnosis for the symptoms described by the writer of today’s letter, I was impressed that her doctor had thought of giardiasis, and decided to take the opportunity to discuss this rather common parasitic infection.

Giardia lamblia is a one-celled protozoan parasite which is found worldwide. Unlike many parasitic infections, it is common in temperate regions as well as in the tropics, and is quite commonly seen in this country.

Doc’s Advice: What is giardia and how can I get infected?

The infection is transmitted by means of giardia cysts, which are excreted in the stools of infected humans and animals, and which are infectious when they contaminate food or water. The number of cysts which can cause infection in humans is quite small; therefore, a relatively tiny contamination of a municipal water supply or well can infect many people. Routine chlorination of the water supply, which protects us from most bacterial infections, does not kill giardia cysts, or those of another parasite which has been in the news recently, cryptosporidium. Filtration of water, which is a more expensive option than chlorination, is required to remove these cysts.

Giardia is commonly seen in day care centers and other institutional settings where fecal hygiene may break down. Once a child is infected it is not uncommon for all other household members to catch the infection. The cysts are also excreted by many animals, including beavers, dogs, cats, and cows. Campers and hikers who drink from streams which appear to be perfectly clean may become infected in this way. The cysts can live from many months in cold, fresh water.

Giardia lives in the small intestine in humans, and may produce a wide variety of symptoms. Some people may carry the infection with few symptoms, while others have symptoms similar to those described by today’s writer: nausea, bloating, abdominal pain, excessive belching (particularly sulphurous belching) and diarrhea. In some the diarrhea is not prominent, and the other symptoms are more troublesome. Blood or mucus in the stools, or fever, are uncommon.

People with certain immune deficiencies such as AIDS may have much more severe and intractable symptoms. Some degree of immunity to the parasite seems to develop, particularly in the underdeveloped world where it is estimated that almost 100 percent of children are infected before they are two years old, and around 30 percent of adults are excreting cysts at any given time.

Examining the stools for giardia cysts will often identify the infection, but many stools may have to be examined, and infected people may not shed cysts continuously. A more accurate but more invasive and troublesome test can be done by aspirating some of the contents of the small intestine through a tube passed through the mouth, or by a string test, done by swallowing and then retrieving a string which picks up the parasites from the small intestine. An expensive test to detect parasite antigen in the stool can also be performed and may be the most accurate diagnostic test now available.

Treatment with metronidazole (Flagyl) and/or quinacrine (Atabrine) usually eradicates the parasite. If many people in the family have the infection, they should all be treated simultaneously to avoid reinfection.

The information contained in or made available through This Site cannot replace or substitute for the services of trained professionals in the medical field. We do not recommend any treatment, drug, food or supplement. You should regularly consult a doctor in all matters relating to physical or mental health, particularly concerning any symptoms that may require diagnosis or medical attention.

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