Animal Reservoir Hosts and Fish-borne Zoonotic Trematode Infections on Fish Farms, Vietnam

Abstract

Fish-borne zoonotic trematodes (FZT) pose a risk to human food safety and health and may cause substantial economic losses in the aquaculture industry. In Nghe An Province, Vietnam, low prevalence of FZT for fi sh farmers but high prevalence for fi sh indicate that reservoir hosts other than humans may play a role in sustaining transmission. To determine whether domestic animals may be reservoir hosts, we assessed prevalence and species composition of FZT infections in dogs, cats, and pigs in a fi sh-farming community in Vietnam. Feces from 35 cats, 80 dogs, and 114 pigs contained small trematode eggs at 48.6%, 35.0%, and 14.4%, respectively; 7 species of adult FZT were recovered from these hosts. These results, combined with data from previous investigations in this community, imply that domestic animals serve as reservoir hosts for FZT and therefore must be included in any control programs to prevent FZT infection in humans. In Asia, fi sh-borne zoonotic trematodes (FZT), including liver and intestinal fl ukes, are widely reported (1-3). FZT not only pose risks to food safety and human health but also may cause substantial economic losses in the aquaculture industry, resulting from to restrictions on exports and reduced consumer demand because of food safety concerns (4). A range of mammals and birds serve as defi nitive hosts for FZT (2). Although information on infection levels and species distribution in humans and fi sh is becoming increasingly available, similar information for reservoir hosts such as wild and domestic animals and fi sh-eating birds is scarce (1).Recent studies conducted in Nghe An Province, a major area for freshwater aquaculture in Vietnam, found prevalence of FZT in humans to be low (0.6%) and prevalence in fi sh from farms to be high (>35%) (5,6). These fi ndings suggest that reservoir hosts other than humans play a major role in sustaining transmission of FZT in this community. We therefore investigated the role of the domestic animals on these fi sh farms. We determined prevalence and species composition of FZT infections in dogs, cats, and pigs in the community and analyzed potential risk factors for the transmission of FZT to animals and animals' role in sustaining FZT infections in cultured fi sh. Materials and Methods Study Design, Sampling, and Laboratory AnalysisThe study was conducted in November 2005 in Nghe An Province, northern Vietnam (Figure 1), in fi sh-farming households previously investigated for human and fi sh FZT infections (5,6). From a total of 1,281 households, 50 were randomly selected in proportion to farm numbers in 5 districts: Hung Nguyen (n = 8), Nam Dan (n = 15), Yen Thanh (n = 9), Thanh Chuong (n = 10), and Tan Ky (n = 8). Another fi sh farm previously found to have cases of FZT in humans (5) was included, yielding a total of 51 fi sh-farming households in the study.

A Review of Foodborne Bacterial and Parasitic Zoonoses in Vietnam

“…7/10 species of fresh water fish infected with metacercariaKino et al (1998)1997Ninh Binh province (Red River Delta)Faeces from healthy individuals; tissues of farmed fish30613.7% FZT egg-positive for C. siniensis ; Males higher prevalence than females (23 vs. 1.5%); prevalence increase with age; prevalence of metacercaria in silver carp >56%; prevalence of cercaria among Melanoides tuberculatus snails (13%)Dang et al (2008)1999/2000Ninh Binh province (Red River Delta)Faeces from healthy individuals1,11526.1% FZT egg-positive; males higher prevalence than females; All adult parasites recovered were C. sinensis; association between FZT positivity and consumption of raw fishOlsen et al (2006)2004Nghe An (north-central VietnamFaeces of fish farmers9640.6% FZT egg-positive for FZT; 0.7% for Fasciolopsis buski ; infection prevalences of Ascaris lumbricoides , Trichuris trichiura and hookworm were 34.8, 50.7 and 51.3%, respectivelyTrung et al (2007)2005Nam Dinh province (Red River Delta)Faeces of healthy individuals; positive individuals examined for adult parasites after treatment with praziquantel615 (33 examined twice)65% FZT egg-positive; Among treated and re-examined patients: 51% positive with C. sinensis. Other species identified were Haplorchis pumilio (100%) ; H. taichui (70%) ; H yokogawai (3%); Stellantchasmus falcatus (6%) ; Fascilopsis buski (3%)Chi et al (2008)2005North-central VietnamTissues of tilapia and 6 carp species from 53 fish farms71612–61% FZT metacercaria positive species included FZT H. pumilio , H. taichui , H. yokogawai , Centrocestus formosanus , S. falcatus and Echinochasmus japonicus ; similar prevalence in nursery and grow-out pondsLan-Anh et al (2009)2005Nghe An (north-central Vietnam)Faeces of terrestrial farm species35 domestic cats, 80 domestic dogs, and 114 pigs48% egg FZT positive (cats); 35% (dogs); 14% (pigs)Nguyen et al (2007a, b)2005–2006Nghe An (north-central VietnamTissues of tilapia and carp fish reared on wastewater-fed ponds…”

Prevention and Control of Fish-borne Zoonotic Trematodes in Fish Nurseries, Vietnam

“…Animals in which eggs were found were given 1 dose of praziquantel at 40 mg/kg ( 22 , 23 ). Fecal examinations were repeated every 30 days during the production cycle, and animals with positive results were again treated.…”

Foodborne trematodes

“…Recently there have been a number of reports about domestic animals infected with foodborne trematodes; also poultry and other domestic animals have been found to be reservoir hosts of fish borne zoonotic trematodes in Vietnamese fish farms (Anh et al, 2009(Anh et al, , 2011. Many trematodes are zoonotic parasites that are able to infect both animals and humans.…”