The present study developed and
standardized an enzime-linked immunosorbent assay (ELISA) to detect Giardia
antigen in feces using rabbit polyclonal antibodies. Giardia
purified from human fecal samples by sucrose and percoll gradients. Gerbils (Meriones
unguiculatus) were infected to obtain trophozoites. Rabbits were inoculated with
either cyst or trophozoite antigens of 14 Colombian Giardia
develop antibodies against the respective stages. The IgG anti-Giardia
were purified by sequential caprylic acid and ammonium sulfate precipitation.
A portion of these polyclonal antibodies was linked to alkaline phosphatase (conjugate).
One hundred and ninety six samples of human feces, from different patients, were
tested by parasitologic diagnosis: 69 were positive for Giardia
56 had no Giardia
parasites, and 71 revealed parasites other than Giardia
The optimal concentration of polyclonal antibodies for antigen capture was 40
µg/ml and the optimal conjugate dilution was 1:100. The absorbance cut-off
value was 0.24. The parameters of the ELISA test for Giardia
were: sensitivity, 100% (95% CI: 93.4-100%); specificity, 95% (95% CI: 88.6-97.6%);
positive predictive value, 91% (95% CI: 81.4-95.9%); and negative predictive value,
100% (95% CI: 96.1-100%). This ELISA will improve the diagnosis of Giardia
infections in Colombia and will be useful in following patients after treatment.