Fish-borne zoonotic trematode infections in humans are prevalent in Asia. Clinical signs result from liver and intestinal flukes,which can result in widespread human morbidity.A total of 51 households from a fish-farming Vietnamese community were examined to quantify prevalence of zoonotic trematode infection in household humans, dogs, cats, and pigs.Trematode eggs were detected in 35% of dogs, 48.6% of cats, and 14.4% of pigs. Previous human prevalence in this province measured 0.6%, and prevalence of eggs in the fish from these farms was greater than 35%.A formula was developed for total daily egg excretion for each species—egg intensities of shedding were highest for cats, lowest for pigs, and intermediate for dogs. However, the relative transmission index was highest in pigs. Infection in pigs resulted in the highest proportion of egg contamination to the community, presumably because of the large quantities of feces and fecal contamination.Trematodes identified in this study were fishborne zoonotic intestinal flukes, and the most commonly identified species were Haplorchis pumilio,H taichui, and H yokogawai. Domestic animal infection could have been facilitated by consumption of raw and dead fish, catching fish from canals, and free-roaming behaviors in companion animals. Study data suggest that domestic animals examined in this study could serve as reservoir hosts for zoonotic trematode infection given the high prevalence of infection in this area among fish and domestic animals, the relative transmission index in domestic animals, and the similarity of trematode species in animals and infected fish.

COMMENTARY: Zoonotic fish-borne trematode infections are not a current problem in the United States.However, they pose significant human health, public health, and food-borne safety hazards in southeast Asia.This study identified the potential for domestic animals to serve as potential reservoir hosts for fish infection.This could have significant economic implications for the global export of fish and meat from southeast Asia. Prevention should include avoiding feeding rawfish meals to domestic animals,minimizing fecal egg contamination of water to avoid infection of fish, and deworming treatments in all reservoir hosts.—Indu Mani, DVM, DSc (infectious disease)

Animal reservoir hosts and fish-borne zoonotic trematode infections on fish farms, Vietnam.Anh NTL, Phuong NT,Murrell KD, et al. EMERG INFECT DIS 15:540-546, 2009