Giardiasis is the infection of the intestines caused by Giardia lamblia, and although many infected individuals have no symptoms, some patients present with diarrhea, gas or bloating, lack of appetite and headache. The infection is acquired by drinking water or eating food contaminated with the microorganism. Diarrheal stools are the most common patient specimens used to diagnose giardiasis.
Microscopy
Giardia lamblia exists in an dormant form known as a cyst. However, when it enters the human body, it changes into an active, motile and non-infective form known as trophozoite. According to "Mackie and McCartney Manual of Practical Medical Microbiology," if a small amount of the patient's stool is placed in a drop of saline on a glass slide and observed under a microscope within 15 minutes of the passage of the stool, pear-shaped, rapidly moving and tumbling trophozoites can be observed.
If this is not possible, the patient's specimen should be collected into a solution of polyvinyl alcohol. A small amount of the patient's sample is placed on a glass slide and stained with a dye known as the Giemsa stain. Cysts of Giardia lamblia can be observed as small circular structures with a single longitudinal fibre extending from one side.
Immunological Tests
A patient with giardiasis will have anti-giardia antibodies in his blood. These antibodies can be detected using techniques such as ELISA and immunofluorescence, where a component of the Giardia cell is coated with a marker such as a dye and made to react with the patient's blood sample. If the patient has the infection, the giardia antibodies and cell components react and markers in the solution help to visually display the reaction.
Giardia antigens or cell components can also be detected in the patient's feces in a similar manner by making them react with anti-giardia antibodies. A study published in the November 2008 issue of "Clinical Microbiology and Infection" states that antigen detection tests provide results quickly and are 96 percent as specific as other tests.
Enteroscopy
Enteroscopy is a procedure during which a small, flexible tube is inserted through the patient's mouth into the intestines in order to examine and observe them. Changes in the normal structure of the intestine may indicate giardiasis. Medline Plus warns that patients may feel like gagging when the tube is inserted through the mouth and may receive a sedative to diminish that feeling.
References
- "Mackie and McCartney's Manual of Practical Medical Microbiology"; J. G. Collee, A. G. Fraser, B. P. Marmion and A. Simmons; 1996
- "Clinical Microbiology and Infection"; Sensitivity of a Giardia antigen test in persistent giardiasis following an extensive outbreak; E. A. Strand; November 2008
- MedlinePlus: Enteroscopy
