Epidemiological study on Clonorchis sinensis infection in Shenzhen area of Zhujiang delta in China.

To study the transmission route and epidemiological features of Clonorchis sinensis infection in Shenzhen area, which is the biggest immigration city in the south of China, we examined 1,473 individuals (710 males and 763 females) to assess the current status of C. sinensis infection among the people in a village of Shenzhen in Zhujiang delta of Guangdong province, China. Freshwater snails, 630, of different species known as the first intermediate host of C. sinensis were collected and examined for cercaria infection, and 430 freshwater fishes of different species as the second intermediate host were examined for metacercaria infection. Among 1,473 people examined, 70 (4.75%) were found infected with C. sinensis. By counting eggs per gram feces (EPG), it was found that the intensity of infection in males was stronger than that of females, and the average EPG was 41.87 in all population. Snails, 1.15%, were infected with cercariae of C. sinensis. The average infection rate of freshwater fishes of 15 species with metacercariae of C. sinensis was 16.97%, and the carps reached the highest infection rate (40.74%). A questionnaire was designed with 12 questions covering socioeconomic conditions and human behavior, contamination of the environment, and fishponds. Of 1,473 interviewees, 54% did not know about fluke disease or its transmission route, 12% of those who knew about the fluke believed that the infection causes no harm or only slight harm to their health. Of the interviewees, 27%, ate raw fish at least one to two times per month. Of families, 5% used the same utensils for both raw fish and cooked food. Of the fishpond owners, 40% fed their fishes with feces of domestic animals and humans. All these factors of unhealthy behaviors, poor knowledge, inappropriate farming/fishery practices, and eating raw fish have made the prevalence of clonorchiasis increase in humans in the Shenzhen area. It is urgent to perform a control program, including health education, environmental modification, reform of traditional farming/fishery practice, mass screening, and chemotherapy for humans, and the management of domestic animals to decrease C. sinensis infection in the human population in Shenzhen.