Giardia lamblia

Diagnosis of giardiasis relay on direct visualization of G. lamblia trophozoite cysts by direct microscopy of faecal specimens, which has a sensitivity between 50 and 70% (Buke, 1975). PCRs have had difficulties in detecting the organisms due to problems in lysis of the cysts and large amounts of inhibitory substances present in the faecal specimens (Butcher and Farthing 1989; Lewis et al. 1990). Only one study have applied PCR to the evaluation of human faecal specimens (Weiss et al. 1992). Using a small sub-unit rRNA PCR assay on formalin-fixed faecal specimens, the test found both false positive and false negative compared to microscopy. The PCR technique has been used to genomically differentiate G. lamblia and have found that there was genetic variation among the human isolates (Mahbubani et al. 1992).

In recent years, there has been an increase in the incidence of waterborne disease outbreaks caused by G.

lamblia (Ongerth et al. 1995). The PCR test has been used to screen environmental water samples (Mahbubani et al. 1992; Rochelle et al. 1997), and it was also possible to distinguish live from dead cysts which is of great importance for the surveillance of the water supplies (Mahbubani et al. 1991). This environmental screening will probably be the first place, where the PCR assay will have a place in detection of G. lamblia.

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