Epidemiologic characteristics of Clonorchiasis sinensis in Guandong Province, China.

Extensive survey of the distribution of the liver fluke Clonorchis sinensis in Guandong Province, China, has revealed high frequencies in human populations in some areas and absence in others. The distribution relates in part to the demography of first and second intermediate hosts and animal reservoir hosts, but it relates more clearly to the differing food habits of various populations in particular geographic areas. Thus clonorchiasis is concentrated in the Zhu Jiang (Pearl River) delta and along the Han Jiang (Han River) but is absent in the Leizhou Peninsula and in the western region of the province. Males tend to have higher infection rates than females. Age distribution is not uniform: in some communities infection rates increase with age where adults eat raw or undercooked fish, while in other infections reaches its peak in early teenage children and declines thereafter where children eat small raw fish but the habit does not persist into adult life. While there is some evidence that high C. sinensis rates correlate with high liver cancer rates and vice versa, this issue requires in depth investigation at community level to differentiate hepatocellular carcinoma and early cholangiocarcinoma, since it is possible that C. sinensis infection promotes higher risk of the latter form of liver cancer.