Two-year intervention trial to control of fish-borne zoonotic trematodes in giant gourami (Osphronemus goramy) and striped catfish (Pangasianodon hypophthalmus) in nursery ponds in the Mekong Delta, Vietnam

Fish-borne zoonotic trematode parasites (FZT) pose a food safety and public health problem in Vietnam. The transmission cycle is complex as domestic animals, especially dogs, cats, fish-eating birds and pigs together with humans serve as reservoir hosts and contribute to FZT egg contamination of aquaculture ponds and the environment. This intervention trial was conducted to determine the effectiveness of various on-farm interventions, including reduction in FZT egg contamination through treatment of infected people and domestic animals, reduction in snail density through mud removal from aquaculture ponds prior to fish stocking, and various other measures in reducing FZT infection in juvenile striped catfish (Pangasianodon hypophthalmus) and giant gourami (Osphronemus goramy). Interventions were implemented on 5 farms for each fish species during production cycles in 2009 and 2010 while 5 similar farms for each species served as control. For both fish species, both prevalence and intensity of infection did not differ significantly between intervention and non-intervention farms prior to the interventions. The interventions significantly reduced both prevalence and intensity of FZT infection in the juvenile fish compared to control ponds. For giant gourami, odds of infection in intervention ponds was 0.13 (95% CL: 0.09–0.20; p<0.001) of that in non-intervention ponds after the 2009 trial and 0.07 (0.03–0.14; p<0.001) after the 2010 trial. For striped catfish, these figures were 0.17 (0.08–0.35; p<0.001) after the 2009 trial while after the 2010 trial all ponds with interventions were free from infection. Metacercariae intensity (no. of metacercariae/fish) in giant gourami from intervention ponds was 0.16 (0.11–0.23; p<0.001) of that in fish from non-intervention ponds after the 2009 trial and 0.07 (0.04–0.15; p<0.001) after the 2010 trial; for striped catfish these figures were 0.18 (0.09–0.36; p<0.001) and 0.00 (confidence limits not estimated), respectively. The aquaculture farm pond intervention approaches taken in this trial have the potential to reduce or eliminate FZT infections in fish and may be implemented across the entire region if adjusted to local conditions and fish species.