Epidemiology

Endemic areas for Clonorchis sinensis are in Asia including Korea, China, Taiwan, and Vietnam. Clonorchiasis has occasionally been reported in non-endemic areas (including the United States). In such cases, the infection is usually found in Asian immigrants, or following ingestion of imported, undercooked or pickled freshwater fish containing metacercariae.


Geographic distribution.

The trematode responsible for clonorchiasis is found throughout much of East Asia from Indochina to Japan as a common parasite of man and fish-eating mammals. An estimated 19 million people are infected in the heavily populated regions of China (especially the southern provinces), Taiwan, Hong Kong, the Red River delta in Indochina, Korea and Japan.

The incidence in China and Japan has been decreasing in recent decades, but Hong Kong still has a very high incidence, as well as the adjacent Kwangtung Province of South China where fish farming is a major industry. Although it may persist in immigrants for decades, the disease has not become endemic in the United States because suitable intermediate hosts are lacking in America.

Several Hawaiians have acquired clonorchiasis by eating infected raw, frozen, or salted fish shipped from China or Japan. More commonly, however, it is modern day immigrants from China and East Asia who are occasionally seen in Hawaiian and mainland U.S. hospitals with cholangiohepatitis caused by C. sinensis.

Public Health and prevention strategies focus on controlling the use of "night soil" (fertilizer contaminated with human feces), which is used to fertilize fish ponds to increase fish production; unfortunately, this practice also stimulates snail growth with an increased number of secondary hosts for C. sinensis. The other obvious countermeasures are to avoid eating raw fish and using contaminated water for consumption.