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

Van Thi Phan,Annette Kjær Ersbøll,Anders Dalsgaard,Khue Viet Nguyen,Henry Madsen,Banchob Sripa

doi:10.1371/journal.pntd.0000742

Van Thi Phan, Annette Kjær Ersbøll + Show 4 more

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https://doi.org/10.1371/journal.pntd.0000742

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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.

Highlights

Fish-borne zoonotic trematodes (FZT) belonging to the Opisthorchiidae and Heterophyidae families are important emerging and re-emerging pathogens causing liver and intestinal fluke diseases in human [1,2]
There are no such estimates available of the number of people infected with intestinal flukes worldwide [4], but the prevalence of infection is believed to be high, e.g. the Red River Delta, Northern Vietnam is endemic for fish-borne zoonotic trematodes (FZT), including both liver and intestinal trematode infections in humans and animals [7,8,9]
Three risk factors associated with the development of the prevalence of FZT infection in fish were identified including presence of snails in the pond, feeding fish with green vegetation collected outside fish farms, and mebendazole medication by the household members

Summary

Introduction

Fish-borne zoonotic trematodes (FZT) belonging to the Opisthorchiidae and Heterophyidae families are important emerging and re-emerging pathogens causing liver and intestinal fluke diseases in human [1,2]. Humans and animals acquire the FZT infection through consumption of raw, inadequately cooked, dried, salted or pickled fish that harbor infective metacercariae stages [4,5,6]. Keiser and Utzinger [4,5] estimated that about 681 million people worldwide are at risk of infection and more than 46 million people are infected with liver flukes (Clonorchis sinensis and Opisthorchis sp.) There are no such estimates available of the number of people infected with intestinal flukes worldwide [4], but the prevalence of infection is believed to be high, e.g. the Red River Delta, Northern Vietnam is endemic for FZT, including both liver and intestinal trematode infections in humans and animals [7,8,9]. Interventions in aquaculture should be based on knowledge of the main risk factors associated with FZT transmission

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