Abstract
BackgroundFish-borne zoonotic trematodes (FZT) are a food safety and health concern in Vietnam. Humans and other final hosts acquire these parasites from eating raw or under-cooked fish with FZT metacercariae. Fish raised in ponds are exposed to cercariae shed by snail hosts that are common in fish farm ponds. Previous risk assessment on FZT transmission in the Red River Delta of Vietnam identified carp nursery ponds as major sites of transmission. In this study, we analyzed the association between snail population density and heterophyid trematode infection in snails with the rate of FZT transmission to juvenile fish raised in carp nurseries.Methodology/Principal FindingsSnail population density and prevalence of trematode (Heterophyidae) infections were determined in 48 carp nurseries producing Rohu juveniles, (Labeo rohita) in the Red River Delta area. Fish samples were examined at 3, 6 and 9 weeks after the juvenile fish were introduced into the ponds. There was a significant positive correlation between prevalence of FZT metacercariae in juvenile fish and density of infected snails. Thus, the odds of infection in juvenile fish were 4.36 and 11.32 times higher for ponds with medium and high density of snails, respectively, compared to ponds where no infected snails were found. Further, the intensity of fish FZT infections increased with the density of infected snails. Interestingly, however, some ponds with no or few infected snails were collected also had high prevalence and intensity of FZT in juvenile fish. This may be due to immigration of cercariae into the pond from external water sources.Conclusions/SignificanceThe total number and density of potential host snails and density of host snails infected with heterophyid trematodes in the aquaculture pond is a useful predictor for infections in juvenile fish, although infection levels in juvenile fish can occur despite low density or absence infected snails. This suggests that intervention programs to control FZT infection of fish should include not only intra-pond snail control, but also include water sources of allochthonous cercariae, i.e. canals supplying water to ponds as well as snail habitats outside the pond such as rice fields and surrounding ponds.
Highlights
Production of fish for human consumption from aquaculture, have expanded rapidly and it is estimated that 48.2% of fish for human consumption originates from aquaculture, a number that is expected to rise further [1]
Risks of fishborne zoonotic trematodes (FZT) infections in humans [2,3] has been linked to the increase in aquaculture production [4,5] and WHO added Fish-borne zoonotic trematodes (FZT) to their list of emerging infectious diseases, i.e. clonorchiasis and opistorchiasis where it is estimated that these two diseases result in 275,370 and 74,367 ‘‘disability-adjusted life years’’ (DALY’s) globally, with Vietnam accounting for 26,366 DALY’s [5]
Control programs to prevent FZT infections in fish produced from aquaculture are needed for limiting or preventing these neglected fishborne diseases
Summary
Production of fish for human consumption from aquaculture, have expanded rapidly and it is estimated that 48.2% of fish for human consumption originates from aquaculture, a number that is expected to rise further [1]. Risks of fishborne zoonotic trematodes (FZT) infections in humans [2,3] has been linked to the increase in aquaculture production [4,5] and WHO added FZT to their list of emerging infectious diseases, i.e. clonorchiasis and opistorchiasis where it is estimated that these two diseases result in 275,370 and 74,367 ‘‘disability-adjusted life years’’ (DALY’s) globally, with Vietnam accounting for 26,366 DALY’s [5]. Integrated household-based culture systems that combine fish culture, raising pigs and horticulture are common in Vietnam and have been shown to have high risk for FZT transmission [11]. We analyzed the association between snail population density and heterophyid trematode infection in snails with the rate of FZT transmission to juvenile fish raised in carp nurseries
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