Three techniques for estimating the intensity of Opisthorchis viverrini infection in individuals from a Northeast That community are compared. Egg counts were determined using a quantitative formalin/ethyl acetate technique, worm burdens were estimated by expulsion chemotherapy and antibody levels were measured by ELISA. Log-transformed worm and egg counts were closely correlated (r = 0·80), suggesting that both measurements provide good assessments of relative intensity of infection. However, no Opisthorchis worms were recovered from 34 people with high egg counts; probably due to problems with the expulsion technique in some individuals. Examination of egg production per fluke indicated that each fluke contributed an average of 180 eggs per gram (epg) of faeces and fecundity was negatively associated with total worm burden. Serum IgG levels correlated significantly with Opisthorchis egg count (r = 0·61) at two independent assessments. Although significant associations were observed between antibody levels and echinostome infection, analysis suggested that these reflected independent associations between these two variables and Opisthorchis infection and age. We conclude that all three measurements are useful for epidemiological studies.

This paper describes patterns of infection with Opisthorchis viverrini within a human community assessed by egg count, parasite-specific antibody levels and worm burden determined by expulsion chemotherapy. All three measurements increased significantly with age, reaching a plateau in young adults. There were no significant sex-associated differences in the prevalence or intensity of infection, antibody levels, or in the frequency of heavy worm burdens. A striking 81·5% of the total Opisthorchis population and 74% of the total egg output were expelled by the most heavily infected 10% of the humans sampled. This extreme over-dispersion, together with recent findings that hepatobiliary disease frequently accompanies heavy infections, argues that the priority for community-based parasite control programmes should be to maximize treatment and health promotion efforts toward heavily infected individuals.

Anti-A and anti-B titers were measured in 60 twin pairs and their families. Family data shows high correlations of antibody titer values for first degree relatives but no significant spousal correlations.