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LAB
NEWS Chairman: Peter Jatlow, MD Editor: Henry M. Rinder, MD Production Assistant: June D. Fisher Contributors:Pei Lin, M.D., J. Greg Howe, Ph.D., Marie Louise Landry, M.D., Howard P. Flitman, M.D., Stephen E. Edberg, Ph.D., Peter McPhedran, M.D. GIARDIA ANTIGEN TESTGiardia lamblia is the most commonly identified protozoan parasite found in fecal specimens submitted to U.S. public health laboratories. It is endemic within the U.S., with an estimated prevalence of 4 - 7% in adults and a higher rate in children and homosexual men. Children at day care centers are at greater risk of giardiasis, with reported prevalence rates of 15% and higher. Epidemics involving the parasite occur from time to time in the U.S. Giardia is a major public health problem worldwide as well.Giardiasis may also be asymptomatic but typical symptoms of acute infection include abdominal pain and diarrhea, whereas chronic disease is associated with malabsorption and steatorrhea. Chronic infection in children may resemble Crohn's disease. Chronic infection is often linked to treatment failure, which may result in recurring symptoms. The parasite is transmitted by the fecal-oral route. G. lamblia cysts enter the human water supply when there exists inadequate sewerage upstream and defective local water purification; cysts are ingested and subsequently give rise to trophozoites in the duodenum, where they proliferate and attach themselves to the small bowel wall. The etiology of clinical symptoms, however, is still unclear. Trophozoites and cysts are ultimately passed in feces: whereas the former quickly disintegrate, cysts are hardier and, if they are subsequently consumed by another individual as a result of poor sanitation practices, another infection may result. Traditionally, the microorganism was identified in the Clinical Microbiology Laboratory by microscopic examination of fecal specimens. Trophozoites and cysts have a characteristic appearance and, once either or both is recognized, the diagnosis is made. Unfortunately, multiple specimens need to be examined to ensure that a sufficiently high level of sensitivity for the microscopic test is achieved. The Microbiology Laboratory now offers Giardia testing using an immunologic method that demonstrates both sensitivity and specificity for G. lamblia of 96 - 100%; it requires the submission of only one specimen and the test result is available within one day. The test is a Microplate Assay, i.e. a solid phase immunoassay, for the detection of Giardia specific antigen 65 (GSA 65). The assay is sufficiently sensitive to detect as little as 3.9 ng/mL. This antigen, which is associated solely with Giardia infection, consists of a 65,000 MW glycoprotein that is produced in copious amounts by the microorganism as it multiplies within the small bowel. Especially pertinent is the fact that GSA 65 can be found even in fecal specimens when visible evidence of trophozoites or cysts is lacking. The in vitro anti-GSA 65 antibodies that coat the Microplate test wells have not been found to cross-react with antigens of other enteric parasites, thereby affirming the highly specific nature of the test. Furthermore, this antigen is stable to decomposition as it passes through the bowel and then through standard collection, transport and processing procedures, thereby rendering false negative results less likely. Fecal specimens should be submitted to the Laboratory in the usual manner, viz. by employing a "Para-Pak Stool System" collection kit. If a fresh, untreated specimen is submitted instead, this should be done as quickly as possible. Rectal swabs should be checked to ensure that fecal material is present. Fecal material from diapers constitutes an acceptable specimen. The Clinical Microbiology Laboratory will also perform a standard microscopic examination, in addition to the immunoassay, by request only (8-2460). References
Howard P. Flitman, M.D. Stephen E. Edberg, Ph.D. January 1999 . . . . . . . . . . Vol. 39 No. 1 Chairman: Peter Jatlow, MD Editor: Henry M. Rinder, MD Production Assistant: June D. Fisher Contributors:Pei Lin, M.D., J. Greg Howe, Ph.D., Marie Louise Landry, M.D., Howard P. Flitman, M.D., Stephen E. Edberg, Ph.D., Peter McPhedran, M.D. GIARDIA ANTIGEN TESTGiardia lamblia is the most commonly identified protozoan parasite found in fecal specimens submitted to U.S. public health laboratories. It is endemic within the U.S., with an estimated prevalence of 4 - 7% in adults and a higher rate in children and homosexual men. Children at day care centers are at greater risk of giardiasis, with reported prevalence rates of 15% and higher. Epidemics involving the parasite occur from time to time in the U.S. Giardia is a major public health problem worldwide as well.Giardiasis may also be asymptomatic but typical symptoms of acute infection include abdominal pain and diarrhea, whereas chronic disease is associated with malabsorption and steatorrhea. Chronic infection in children may resemble Crohn's disease. Chronic infection is often linked to treatment failure, which may result in recurring symptoms. The parasite is transmitted by the fecal-oral route. G. lamblia cysts enter the human water supply when there exists inadequate sewerage upstream and defective local water purification; cysts are ingested and subsequently give rise to trophozoites in the duodenum, where they proliferate and attach themselves to the small bowel wall. The etiology of clinical symptoms, however, is still unclear. Trophozoites and cysts are ultimately passed in feces: whereas the former quickly disintegrate, cysts are hardier and, if they are subsequently consumed by another individual as a result of poor sanitation practices, another infection may result. Traditionally, the microorganism was identified in the Clinical Microbiology Laboratory by microscopic examination of fecal specimens. Trophozoites and cysts have a characteristic appearance and, once either or both is recognized, the diagnosis is made. Unfortunately, multiple specimens need to be examined to ensure that a sufficiently high level of sensitivity for the microscopic test is achieved. The Microbiology Laboratory now offers Giardia testing using an immunologic method that demonstrates both sensitivity and specificity for G. lamblia of 96 - 100%; it requires the submission of only one specimen and the test result is available within one day. The test is a Microplate Assay, i.e. a solid phase immunoassay, for the detection of Giardia specific antigen 65 (GSA 65). The assay is sufficiently sensitive to detect as little as 3.9 ng/mL. This antigen, which is associated solely with Giardia infection, consists of a 65,000 MW glycoprotein that is produced in copious amounts by the microorganism as it multiplies within the small bowel. Especially pertinent is the fact that GSA 65 can be found even in fecal specimens when visible evidence of trophozoites or cysts is lacking. The in vitro anti-GSA 65 antibodies that coat the Microplate test wells have not been found to cross-react with antigens of other enteric parasites, thereby affirming the highly specific nature of the test. Furthermore, this antigen is stable to decomposition as it passes through the bowel and then through standard collection, transport and processing procedures, thereby rendering false negative results less likely. Fecal specimens should be submitted to the Laboratory in the usual manner, viz. by employing a "Para-Pak Stool System" collection kit. If a fresh, untreated specimen is submitted instead, this should be done as quickly as possible. Rectal swabs should be checked to ensure that fecal material is present. Fecal material from diapers constitutes an acceptable specimen. The Clinical Microbiology Laboratory will also perform a standard microscopic examination, in addition to the immunoassay, by request only (8-2460). References
Howard P. Flitman, M.D. Stephen E. Edberg, Ph.D. |
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