Detection of giardia antigen in stool samples by a semi-quantitative enzyme immunoassay (EIA) test

A semi-quantitative enzyme immunoassay (EIA) test for the detection of Giardia intestinalis antigen in faeces was developed. In order to avoid unspecific reactions due to anticalf serum activity, IgG fractions of anti-giardia rabbit and sheep sera were purified from antibovine antibodies by immunoadsorption. Faecal specimens tested in the assay were mixed with normal horse serum to avoid unspecific and proteolytic effects of stool components. Out of a range of bacterial and parasitic antigens tested, only high concentrations of Ascaris suum egg antigen and Shigella sonnei gave slight unspecific reactions. During an outbreak of waterborne giardia infection faecal samples from 49 individuals were tested. Giardia cysts were found by microscopy in 22 individuals and specimens from 24 persons were positive by EIA. The estimated amount of antigen found in the positive samples ranged from 50 to 5,000 ng giardia protein/ml. After filtration through a 0.45 microns filter antigenic activity was found in the filtrate of 10 samples. In 3/6 samples with no cysts detected by microscopy, mainly soluble giardia antigen was found.