Genetic and household risk factors for Schistosoma japonicum infection in the presence of larger scale environmental differences in the mountainous transmission areas of China.

Schistosoma japonicum egg excretion and kinship relationship data from 13 endemic villages in the mountainous transmission area near Xichang, in Sichuan province, China, were analyzed via a variance components methodology to assess the relative contribution of kinship, shared household, and shared village to the risk of infection. Large intervillage differences in egg counts exist in this region due to differences in transmission potential related to environmental differences in snail density and agricultural practices. After accounting for these intervillage differences, there was no kinship or household effect on egg excretion. This reinforces earlier findings that suggest environmental factors dominate risk in this region.