Quantitative post-mortem study of Opisthorchis viverrini in man in north-east Thailand.

The results of an autopsy study of Opisthorchis viverrini infection in 181 accident subjects in northeast Thailand are presented. The age-prevalence profiles were similar whether determined by faecal examination for parasite eggs or by recovery of worms from the liver. The prevalence increased rapidly with age and reached a plateau at 70-80% in adults. The overall prevalence estimated by faecal examination was 69.2%, while that measured by worm recovery was 79.2%. The average intensity of infection, as indicated by eggs per gram of faeces, rose with age and became relatively stable in groups over 20 years of age. Worm burden also increased rapidly with age, reaching a peak in the 31-40 year groups and slightly declining in the 2 oldest age groups. Fluke distribution between individual subjects was highly dispersed; most people harboured no or low worm burdens (0-200 worms) while a small group of subjects (16.5%) carried 66% of the total worms recovered. The distribution of flukes within the liver appeared to be homogeneous. The results of the present study were similar to those from field studies, and possible mechanisms that generate these observed patterns of infection are discussed.