Farm-Level Risk Factors for Fish-Borne Zoonotic Trematode Infection in Integrated Small-Scale Fish Farms in Northern Vietnam

Abstract

BackgroundNorthern Vietnam is an endemic region for fish-borne zoonotic trematodes (FZT), including liver and intestinal flukes. Humans acquire the FZT infection by eating raw or inadequately cooked fish. The production of FZT-free fish in aquaculture is a key component in establishing a sustainable program to prevent and control the FZT transmission to humans. Interventions in aquaculture should be based on knowledge of the main risk factors associated with FZT transmission.Methodology/Principal FindingsA longitudinal study was carried out from June 2006 to May 2007 in Nam Dinh province, Red River Delta to investigate the development and risk factors of FZT infections in freshwater cultured fish. A total of 3820 fish were sampled six times at two-month intervals from 96 fish farms. Logistic analysis with repeated measurements was used to evaluate potential risk factors based on information collected through questionnaire interviews with 61 fish farm owners. The results showed that the FZT infections significantly increased from first sampling in June to July 2006 (65%) to sixth sampling in April to May, 2007 (76%). The liver fluke, Clonorchis sinensis and different zoonotic intestinal flukes including Haplochis pumilio, H. taichui, H. yokogawai, Centrocestus formosanus and Procerovum varium were found in sampled fish. Duration of fish cultured (sampling times), mebendazole drug self-medication of household members, presence of snails in the pond, and feeding fish with green vegetation collected outside fish farms all had a significant effect on the development of FZT prevalence in the fish.Conclusions/SignificanceThe FZT prevalence in fish increased by 11 percentage points during a one-year culture period and the risk factors for the development of infection were identified. Results also highlight that the young fish are already highly infected when stocked into the grow-out systems. This knowledge should be incorporated into control programs of FZT transmission in integrated small-scale aquaculture nursery and grow-out systems in Vietnam.

Studies on some fish parasites of public health importance in the southern area of Saudi Arabia

“…Poor sanitation and traditional methods of food preparation have accelerated the spread of food-borne trematode infection (PHAN et al, 2010).…”

Exceptionally High Prevalence of Infection of Bithynia siamensis goniomphalos with Opisthorchis viverrini Cercariae in Different Wetlands in Thailand and Lao PDR

“…(3) Although human fecal material is not deliberately used for fertilizing rice fields, the drainage system present in rural villages leads directly to the contamination of fields with human and animal feces. 16,37 The surprisingly high prevalence that we detected has important implications for the transmission potential of O. viverrini and therefore, the possible increases in opisthorchiasis and CCA in the lower Mekong Region. Our results showing that there is a higher ratio of infected snails in Lao PDR compared with Thailand fit the epidemiological findings that humans in the Nam Ngum wetland have very high prevalence of O. viverrini, whereas control efforts have been underway in Thailand for several decades, possibly reducing the contamination of the environment with infected feces.…”

Prey species and size choice of the molluscivorous fish, black carp (Mylopharyngodon piceus)

“…M. tuberculata is the primary host for intestinal trematodes in aquaculture ponds i.e., mainly Haplorchis spp., Stellantchasmus falcatus, and C. formosanus (Phan et al 2010a). The black carp is primarily molluscivorous and most fish ponds have a dense population of viviparid snails, in particular, A. polyzonata.…”

“…Trematodes, particularly intestinal trematodes of family Heterophyidae, but also to some extent liver trematodes (Opisthorchis viverrini Stiles & Hassall, 1896 and Clonorchis sinensis Looss, 1907) of family Opisthorchiidae, may be found in aquaculture ponds in Vietnam (Le 2000;De 2004;Dung et al 2007;Phan et al 2010a) where eating raw fish is a common practice (Chi et al 2009;Phan et al 2011). Dung et al (2007) found from fecal examination that 64.9% of the adult people in Nam Dinh were positive for small trematode eggs (Heterophyidae and Opisthorchiidae) and expulsion of adult trematodes from 33 people with high egg counts (>1000 eggs/g feces) showed that 51.5% were infected with C. sinensis.…”