Originally the laboratory diagnosis of parasitic infections has been based on the demonstration of the organism such as eggs, larvae, adults, cysts, and trophozoites in feacal specimens, tissue, and body fluids. To find and identify the parasite is the definitive proof of infection. In many instances it is not possible or very difficult to find the organism because of low/irregular excretion or their hiding in the tissue. To facilitate the laboratory diagnosis, indirect methods have been developed. These methods rely on detection of antibodies directed against the organism or antigens secreted by the organisms. Lately also detection of nucleic acid-based probe tests (PCR) have been developed. It is important to be aware of sensitivity and specificity and the purpose of the investigation when deciding methods to be utilized. Under certain circumstances, a method with high specificity and less sensitivity is preferable, but opposite can be as likely. The criteria for diagnosis of individuals may differ from the criteria needed for screening of populations.

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