The importance of wild fish in the epidemiology of Clonorchis sinensis in Vietnam

Abstract

Preliminary findings of a high prevalence of Clonorchis sinensis in wild-caught fish in a North Vietnam reservoir (Thac Ba reservoir, Yen Bai Province) prompted a longitudinal epidemiological study of fish infections. Monthly collections of fish from September 2014 to August 2015 were processed for recovery of metacercariae; 1219 fish, representing 22 species, were examined. Seven species were infected with C. sinensis metacercariae. Four species, Toxabramis houdemeri, Hemiculter leucisculus, Cultrichthys erythropterus, and Culter recurvirostris, had high prevalence (31.1 to 76.7 %); metacercarial intensities ranged from 3.9 to 65.7 metacercariae/fish. A seasonal variation of C. sinensis prevalence was observed in T. houdemeri. Variation in intensity of infection occurred in C. erythropterus and H. leucisculus. Intensity and prevalence of C. sinensis in the most highly infected species, T. houdemeri, varied by fish size; prevalence was higher in fish weighing more than 3 g, and intensity was higher in fish weighing more than 5 g. The distribution of metacercariae in the body region of T. houdemeri was significantly higher in the caudal fin (14.7 metacercariae/g), compared to the body and head regions (0.7 and 1.4 metacercariae/g, respectively). Further epidemiological investigations on C. sinensis in this reservoir region should include assessing the relative risk of the different fish species for humans based on the latter's food preferences, and the prevalence of C. sinensis in the community. The snail intermediate host(s) in the reservoir should also be identified along with the ecological factors influencing its exposure to C. sinensis eggs and its subsequent transmission of cercariae to fish. Also needed are investigations on the relative importance of wild and domestic reservoir hosts as sources of egg contamination of the reservoir.

Prevalence and risk factors associated with Clonorchis sinensis infections in rural communities in northern Vietnam

“…In this study, the fish species reported as being used to prepare raw fish dishes are known to be infection sources of C . sinensis in Vietnam [ 24 , 32 – 35 ]. A significant association was observed between the source of raw fish dishes and province.…”

“…We selected these two provinces because recent studies suggested a high endemicity of clonorchiasis: a prevalence of 17% was reported in a commune in Thanh Hoa [18], a coastal province, and more than 36% in a mountainous area of Yen Bai province [23]. Moreover, in these two provinces, raw fish consumption is common [18,24].…”

“…In Yen Bai, the communes Phuc An and Vu Linh were selected on the basis of their location close to the Thac Ba lake, one of the biggest artificial lakes in Vietnam, and the main source of fish in the province. Bui et al [24] recorded a high prevalence (31.1-76.7%) of C. sinensis infection in four wild-caught fish species originating from the lake. The consumption of raw fish in both communes, bordering the eastern part of Thac Ba lake, is common.…”

Prevalence of Clonorchis sinensis infection in fish in South‐East Asia: A systematic review and meta‐analysis

“…Some studies suggest that temperature is the most important regulating factor in China (Li, Yang, & Wang, 2014; Xu et al., 2005). Additionally, there is a significant difference in C. sinensis infection in fish between the dry‐cool and rainy‐warm seasons at the Thac Ba Reservoir in Vietnam (Bui et al., 2016). In summer and autumn, the temperature and humidity are beneficial to C. sinensis transmission between intermediate hosts (Li et al., 2014).…”

“…Pungtungia herzi and Zacco platypus have a higher infection rate of C. sinensis metacercariae and are popularly eaten raw in Korea. Approximately 45 species of freshwater fish are known to carry C. sinensis metacercariae in Vietnam (Bui et al., 2016; De, Le, & Murrell, 2012; Hung et al., 2015; Kino, Inaba, De, Chau, & Sano, 1998; Phan, Bui, Nguyen, & Murrell, 2016; Phan, Ersboll, et al, 2010; Phan, Ersbøll, et al, 2010). These species include Hypophthalmichthys molitrix , Ct. idella , Labeo rohita and Cirrhinus mrigala , all eaten raw by local people.…”