The present study developed and
standardized an enzime-linked immunosorbent assay (ELISA) to detect
Giardia
antigen in feces using rabbit polyclonal antibodies.
Giardia cysts were
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 isolates to
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 cysts,
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 antigen detection
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.
