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.

Relationship between faecal egg count and worm burden of Opisthorchis viverrini in human autopsy cases.

The relationship between faecal examination for egg output and worm burden of Opisthorchis viverrini in man of 181 autopsy cases from Northeast Thailand is described. Diagnosis of the parasite infection by stool examination for the presence of eggs was less sensitive than the worm recovery technique. Using Stoll's dilution and formalin-ether technique, no eggs were detected in the faeces of 20 cases harbouring low worm burdens (less than 20 worms). The quantitative faecal egg count by Stoll's dilution technique showed a strikingly close positive correlation with the number of worms recovered (r = 0.96, P less than 0.001) indicating a strong linear association between eggs per gram of faeces (epg) and worm burden. The number of epg per worm was inversely correlated to the worm burden (P less than 0.001), suggesting that density-dependent constraints on fecundity could operate to restrict egg output in heavy infections. The accuracy of egg counts for estimating worm burden and its relevance to parasite epidemiological research are discussed.