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Giardiasis

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Giardiasis 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 cysts often found in water contaminated by raw sewage or animal waste. 11

Giardia species are endemic in areas of the world that have poor sanitation. In developing countries, the disease is an important cause of morbidity, and water- and food-borne outbreaks are common. Because of the small inoculum of organisms necessary to cause infection, giardiasis is common in daycare center attendees and institutionalized patients in developed countries. G lamblia is a particularly significant pathogen for people with malnutrition, immunodeficiencies, or cystic fibrosis. Beavers may be an important reservoir host for G lamblia. 2

This case illustrates how giardiasis can be present in patients with no suspicion of the disease. Giardiasis is an infection of the small intestine caused by the flagellated protozoan Giardia lamblia. Giardia lamblia has the distinction of being the first microscopic organism to be recognized as a cause of infection, when Van Leeuwenhoek had diarrhea, examined his own stool with a primitive microscope and described the organisms in 1681. Giardiasis is present in all climates, but is especially common in developing countries with tropical or subtropical climates. Giardiasis is very common. There are estimated to be 2.5 million cases of giardiasis per year in the United States and Giardia lamblia can be identified in approximately 4% of stool specimens submitted to laboratories in the United States. 46

Consumers’ Research Magazine; 4/1/1993; Hunter, Beatrice Trum; 997 words; However, during the next decade, human giardiasis infections produced by G. lamblia increased within periods of five years. At present, giardiasis has become the most common parasitic infection has been treated. 8

There are several different species of Giardia. Recently, taxonomists (scientists who specialize in placing related organisms into ordered species groupings) have proposed changing the name of the Giardia species that causes human disease from Giardia lamblia to G. intestinalis. Currently, discussions and publications regarding this organism occur under both names. Dogs often become ill with related species of Giardia. It is not yet known whether humans are easily infected with this organism. It is not known whether animals play an important role in human infection with Giardia. Beavers, deer, and elk may contaminate surface water such as lakes and streams with Giardia, but how often this results in human infection is not clear. 41

G lamblia trophozoites attach to the epithelium and distort microvilli at the site of attachment. The trophozoite has a convex dorsal surface and a flat ventral surface containing a disk, which is often referred to as the sucking or adhesive disk. The parasite has powerful adhesion, catching, and holding abilities with its disk. In the murine model of giardiasis, the ventral disk adhesion imprints are marked but less impressive than in the human small intestine. However, this direct injury is an unlikely cause of the more extensive reduction in microvillus surface area, the reduction in disaccharidase activities, and the more pronounced abnormalities of villous architecture. 2

The pathogenesis of the diarrhea and malabsorption that can occur in giardiasis is incompletely understood since Giardia are not invasive organisms. The major structural and functional abnormalities associated with giardiasis are found in the small intestine. Human infection may be associated with a spectrum of light microscopic changes that range from no abnormalities, to mild or moderate partial villous atrophy, to subtotal villous atrophy in severe cases. An increase in crypt depth may also be seen. Even in the absence of changes in villous and crypt architecture, shortening and disruption of microvilli may occur. In addition to these microscopic changes, deficiencies in epithelial brush border enzymes (eg, lactase) can develop. These alterations in epithelial structure and function probably play a role in pathogenesis. 12

A person has to eat or drink the Giardia lamblia cyst form. Drinking directly from contaminated lakes or streams can cause illness, even if the water appears clean. Infection can occur after ingestions of as few as 10-25 cysts. Once an animal or person has been infected with Giardia the parasite lives in the intestine and is passed into the environment in the stool. Both cysts and trophozoites can be found in the feces. Ingestion of one or more cysts may cause disease. 42

This organism remains the most commonly identified intestinal parasite. From 1964-1984, G lamblia caused at least 90 water-borne outbreaks of diarrhea, affecting more than 23,000 people. Groups most at risk for infection include travelers, children, homosexual men, and individuals with immunoglobulin deficiency states (inherited or acquired). 3

G lamblia is the parasite most commonly identified in stool specimens. The age-specific prevalence of giardiasis is highest in childhood and adolescence and begins to decline thereafter. Overall, the asymptomatic carriage rate of G lamblia is estimated to be 3-7%. The asymptomatic carriage rate in children may be as high as 20% in southern regions and in children younger than 36 months who attend daycare centers. Asymptomatic carriage may persist for several months. Many children with giardiasis are symptomatic, have been shown to spread the disease within their homes, and may contribute to high endemic rates in their communities. 2

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. 11

Conventional treatment of giardiasis consists of drugs, such as metronidazole (flagyl) and fenbendazole (panacur). Both of these drugs carry direct side-effects and neither is highly effective, as the parasites have become resistant to them. Ronidazole is another drug that may be used for giardiasis. After the use of a conventional drug, symptoms of infection may subside for a couple of months only to return with a greater vengeance. Successive treatments with an antiparasitical drug are often needed at set intervals. Multiple courses of treatment may be needed if the bird�s nutritional status is low prior to and during treatment. 10

For additional information concerning giardia please call the DES Water Supply Engineering Bureau at (603) 271-3139. If you have questions concerning the disease giardiasis please call Health Risk Assessment unit of the Department of Public Health at 271-4664. For a full listing of drinking water supply fact sheets, please request WD-WSEB-15-2. 40

It has been recognized only recently that Giardia infection may be transmitted by sexual activity, particularly among homosexual men, but also heterosexually. Physicians should attempt to determine if giardiasis is being acquired in this way so that they can distinguish from failure of drug treatment and prompt reinfection. Perhaps more important, a Giardia infection that may have been acquired in this way should alert the physician to the possible presence of more serious fecal-oral infections such as amebiasis, syphilis, gonorrhea, or hepatitis. 26

The most common way to diagnose giardiasis is by the visualization of the Giardia cysts by experienced professionals. The cysts are detected 50-70% of the time in the first stool specimen examined. Over 90% of the time the cysts are detected after 3 stool specimens have been examined. So more than 1 specimen may be required. 11

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