LYCOS RETRIEVER 
Giardia: Cysts
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Historically known as "beaver fever", 40 species of Giardia are now known to affect many kinds of rodents, amphibians, and mammals, including domestic cats and dogs, and humans. The common methods of infection are through contaminated water and inadvertent transmission of animal feces via the mouth. Giardiasis, was once thought of as a camper's disease. Campers under primitive conditions, such as lack of hygiene or water and contact with Giardia cysts through the droppings of wildlife, were often the ones that contracted the disease. Today, Giardia, is a disease most common in children under five, commonly thought to contract it through public swimming areas (pools, lakes, water parks) and day care centers. Each year there a thousands of hospitalizations and estimates are as high as 2.5 million cases of giardiasis in the US.
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Giardia alternates between two different forms — a hardy, dormant cyst that contaminates water or food and an active, disease-causing form that emerges after the parasite is ingested. National Institute of General Medical Sciences grantee Dr. Frances Gillin of the University of California, San Diego and her colleagues cultivated the entire life cycle of this parasite in the laboratory, and identified biochemical cues in the host's digestive system which trigger Giardia's life cycle transformations.[6][7] They ... uncovered several ways in which the parasite evades the defences of the infected organism. One of these is by altering the proteins on its surface, which confounds the ability of the infected animal's immune system to detect and combat the parasite (called antigenic variation). Gillin's work reveals why Giardia infections are extremely persistent and prone to recur. In addition, these insights into Giardias biology and survival techniques may enable scientists to develop better strategies to understand, prevent, and treat giardia infections.
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A few basic facts about Giardia should be mentioned. The life cycle of Giardia alternates between trophozoite and cyst. Giardia lacks mitochondria and peroxisomes and until recently (see below) was reported to ... lack a Golgi apparatus and endoplasmic reticulum. The dormant water-resistant cyst causes infection while the rapidly dividing trophozoite causes the symptoms of giardiasis. The processes of encystation and excystation are both problems in cell differentiation. Giardia is relatively easy to culture and work with in the laboratory.
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Giardia occurs in two forms: a motile feeding stage that lives in the intestine, and a non-motile cyst stage that passes in the feces. Encystment occurs as the parasite travels to the large intestine. The cysts are fairly resistant, and can survive for several months as long as sufficient moisture is provided. Mature cysts are usually found in the feces of infected animals. Animals become infected by ingesting cysts. These cysts break open in the intestine to release the motile feeding stage (trophozoite).
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Giardia exists in 2 forms; trophozoites and cysts. The active and motile form, called trophozoites, are the stage which lives in the intestines of an affected mammal. These trophozoites produce non-motile cysts which are shed into the environment. The cysts remain viable in the environment for months, especially in cool and moist areas. They thrive in clear and cool water, a good reason not to drink running water in the outdoors, no matter how pristine it looks. The cysts are killed by freezing, boiling, and extended contact with disinfectants.
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Giardia infection (giardiasis) can cause a variety of intestinal symptoms that begin one to two weeks after ingestion of cysts and frequently recur. These include diarrhea, gas or flatulence, greasy stools that tend to float, stomach cramps and upset stomach or nausea, which may lead to weight loss and dehydration. Some people with giardiasis have no symptoms at all. In otherwise healthy persons, symptoms of giardiasis may last two to six weeks.
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