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December 1993, Volume 43, Issue 12


Diagnosis of Giardiasis

Rakhshanda Baqai  ( PMRC Research Centre, Jinnah Postgraduate Medical Centre, Karachi. )

Giardia lamblia (GL), a frequent cause of diarrhoea has often been reported to be a pathogen1-4 and giardiasis, an important unresolved, health problem in developing countries. This is perhaps due to the absence of a simple but reliable test for its diagnosis. Choice of diagnostic tests depend on their simplicity, feasibility and acceptability to the patient. When suspected on symptomatology diagnosis can be done by detection of trophozoites or cysts of GL on routine stool examination5-7. Although simple and con­venient but some cases can be missed on direct micros­copy. Its positivity varies from 36-50% mainly due to periodicity of its excretion and delay in examination of stool8-10. To increase the yield of direct microscopy three consecutive stools should be examined within one hour after defaecation11. For detection of cysts yield of concentration method is better than direct microscopy. Immunofluorescence test for the detection of giardia antigen in&ecal samples picks up 12% more true positive cases than other methods (unpublished dat4 It detects both cysts and trophozoites and immediate examination is not essential. This should be done in patients with strong clinical suspicion of giardiasis and repeated negative routine stool tests. Other diagnostic tests for the detection of giardia antigen in stools is enzyme linked immunosorbent assay (ELISA) 12. It can detect both cyst and trophozoite and remains positive at dilutions at which GL are not directly visualized13-15. ELISA is not a substitute for direct micros­copy but it can rule out infection with GL and monitor response16 to therapy. Counter immunoelectrophoresis (CIE) is also used for diagnosing giardiasis as well as monitoring chemotherapeutic effect of anti- giardia agents17. Other tests are based on the knowledge of natural habitat of GL in the duodenum and upper jejunum. String18 test direct microscopy of fresh duodenal aspirate collected during endoscopy19. duodenal jejunal mucosal imprints and detection of parasites in the intestinal mucous in small intestinal biopsies have been reported witltvarious frequencies20,21. Although there are different methods for diagnos­ing giardiasis but no single method is 100% reliable. The best approach for the detection of GL should be three consecutive stool examinations, if found negative other methods of detection of giardia antigen like immunofluorescence test, ELISA or CIE methods should be used in patients having symptoms of giardiasis.


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