The ELISA-based detection of anti-Opisthorchis viverrini IgG and IgG₄ in samples of human urine and serum from an endemic area of north–eastern Thailand

Abstract

The levels of correlation between the number of Opisthorchis viverrini eggs excreted in the faeces and levels of anti-Opisthorchis IgG and IgG₄ in the serum and urine (as indicated by absorbances in ELISA) have recently been evaluated in north–eastern Thailand. The 225 subjects investigated in detail, all of whom came from an endemic village in Chaiyaphum province, were selected on the basis of the numbers of O. viverrini eggs that they were excreting. ELISA based on a crude antigen extract of the trematode were then used to determine the levels of specific IgG and IgG₄ in serum and urine samples. Compared with the egg-negative, the villagers who were found to be egg-positive for O. viverrini had significantly higher levels of specific IgG in their urine and serum and significantly higher levels of specific IgG₄ in their serum. The serum levels of specific IgG and IgG₄ and the urine levels of specific IgG all correlated with the numbers of O. viverrini eggs/g faeces [with correlation coefficients (r) of 0.251, 0.121 and 0.142, respectively]. Although the serum levels of IgG were positively correlated with the urine levels of IgG (r=0.098), there was no significant relationship between the serum and urine levels of specific IgG₄ (r=0.051).

When the 225 subjects investigated in the ELISA were divided according to whether they had no detectable Opisthorchis eggs in their faeces (N=57), or 1–100 (N=154), 101–1000 (N=5), 1001–1500 (N=5) or >1501 (N=4) eggs/g faeces, the serum and urine levels of specific IgG and the serum (but not urine) levels of specific IgG4 were also found to correlate significantly with the infection-intensity categories (with r-values of 0.550, 0.146 and 0.578, respectively). When the results of the faecal examinations were treated as the 'gold standard', the ELISA for the detection of (Opisthorchis-specific) serum IgG, serum IgG₄, urine IgG and urine IgG₄ had sensitivities of 99.2%, 23.1%, 43.0% and 45.9% and specificities of 93.0%, 29.6%, 45.9% and 67.2%, respectively. Although the study was limited by the small number of subjects with intense infections, it appears worth investigating urine samples for subclasses of specific IgG other than IgG₄.