Giardia and Waterborne Disease

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Recent changes in the EPA Drinking Water regulations and the development of the SOURCE Water Protection strategies have required water suppliers using springs or groundwater sources to evaluate drinking water sources for the presence of Giardia trophozoites (explained below). Giardia is the parasitic protozoan as opposed to giardiasis which is the disease it produces. The cyst stage is the stage responsible for the spread of the organism in the environment. Giardia (pronounced "gee-ar-dee-ah") cysts are elliptically shaped and range in size from 6 to 10 microns. The cyst stage could be thought of as the equivalent of a "seed" or "spore;” the structure of the cyst makes the organism very resistant to environmental factors and disinfection. After entering the host, stomach acid causes a reaction that causes the cyst to excyst, i.e., "hatch like an egg" when it reaches the intestines where they quickly subdivide and attach to the lining of the intestine. This is the second life stage - the trophozoite. The trophozoite stage for Giardia duodenalis, the species that infects humans, has a pointed elongated median body that is approximately 12 - 15 microns long by 6 - 8 microns wide; the trophozoites contain four pairs of flagella.

What are the Health Effects?

After viable cysts are ingested, there is an incubation period of 2 to 12 days. Typically the average incubation period is 7 days. The primary symptoms of giardiasis include: diarrhea, abdominal cramps, headaches, nausea, vomiting, and low-grade fever, which can lead to weight loss and dehydration. For the average human being in good health, the symptoms last approximately two weeks, but for immunocompromised individuals, the disease can last for months and can be fatal. The individuals most at risk to this disease, if exposed, include: AIDS patients, organ transplant recipients, malnourished children, and individuals receiving certain cancer treatment. Note: There are some people who have Giardia in their system, but do not get ill. These individuals are asymptomatic and could act as carriers or hosts and spread the disease or infect the other members of the household or family. This is why all members of the household should be tested.

Giardiasis Treatment Options

In adults, giardiasis is commonly treated with a drug called metronidazole (otherwise known as Flagyl). Usually the drug is taken 3 times a day for 5 to 10 days. For children less than 5 years old, the treatment is typically with a drug known as furazolidone (or Furoxone). Typically the drugs have side effects similar to the disease. (Note: This is not medical advice, just a summary of available information; you must seek advice from your physician.)

Detection of Giardia in Drinking Water

The procedure used for testing for Giardia in drinking water is known as the immunofluorescent antibody method. The procedure requires that a minimum of 100 to 1000 gallons of water be filtered through a 1-micron filter. The filtrate is cleaned and centrifuged, creating a pellet. The centrifuged pellet is then floated (leaving sediment particles behind) using a Percoll - Sucrose density gradient technique. The floated material (which includes any Giardia cysts) is then cleaned and centrifuged, creating another pellet which is then stained with a fluorescent antibody. A technique known as the immunofluorescent antibody method.

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Source: EPA Website

Slides of the pellet are prepared and the slides are examined for potential Giardia cysts. If a cyst is suspected, the slide is then examined using the Hoffman Modulation technique to confirm that the suspected cyst has the proper shape, size, and, at a minimum, two internal structures characteristic of a Giardia cyst.

For More information on Giardia MPA MET Testing, please complete this request form.