Parasitol Res (2012) 111:1045–1048 DOI 10.1007/s00436-012-2929-3 ORIGINAL PAPER Evaluation of the role of rats as reservoir hosts for fishborne zoonotic trematodes in two endemic northern Vietnam fish farms Nguyen Lan Anh Thi & Henry Madsen & Dao Thanh Ha & Eric Hoberg & Anders Dalsgaard & K. Darwin Murrell Received: 16 November 2011 /Accepted: 16 April 2012 /Published online: 17 May 2012 # Springer-Verlag 2012 Abstract Fishborne zoonotic trematodes (FZTs) pose a nematode infection was significantly higher in commensal food safety risk for the aquaculture industry in Vietnam. rats (p<0.05). The only FZTs recovered were the intestinal The risk of being infected from eating raw fish applies not flukes Echinostoma cinetorchis and Centrocestus formosanus, only to humans but also to domestic animals which can both at low prevalence. Because the most common FZTs serve as reservoir hosts in fish farms. The role of rodents, found in fish from these communes are Haplorchis pumilio commonly found in fish farms, as reservoir hosts has not and Haplorchis taichui, neither of which were found in the been adequately evaluated. To study this question, commen- rats, we conclude that rats are not significant reservoir hosts for sal and rice field rats were collected from fish farms in FZT in these Vietnamese fish farms. Nghia Lac and Nghia Phu communes, Nam Dinh province, Vietnam and examined for FZT infection. A total of 250 rats (Rattus norvegicus, Rattus argentiventer,andBandicota Introduction indica) were collected and examined; the rats were trapped in the farm households (commensal) and in rice fields ad- Rats have been shown in Asia to be hosts for various parasites joining the fish ponds (field). The total prevalence of all including zoonotic species of trematodes (Kiitipong et al. 2010; parasites was 52.8 %: nematodes, 42.4 %; trematodes Kataranovski et al. 2011; Seo et al. 1981). In Vietnam, rats are 18.0 %; and cestodes, (3.6 %), including two zoonotic abundant around farm households, fish ponds, and adjoining cestode species, Raillietina celebenisis and Hymenolepis farm fields. Because of the high prevalence of fishborne zoo- diminuta. Although overall prevalence and intensity of notic trematodes (FZT) in fish reared in Vietnamese farms (Chi parasite infection did not differ significantly among rat Tran et al. 2008;Phanetal.2010; Thien et al. 2007),theroleof species or between the two communes, the intensity of rats as reservoir hosts for these parasites is of interest. An understanding of reservoir host epidemiology is necessary for N. Lan Anh Thi : D. Thanh Ha programs designed to prevent and control of FZT infection in National Institute for Veterinary Research, aquaculture. Previous research has shown that cats, dogs, and 86 Truong Chinh, pigs have important roles as reservoir hosts in Vietnamese Hanoi, Vietnam aquaculture (Anh et al. 2009). The results of this investigation H. Madsen : A. Dalsgaard : K. D. Murrell (*) increase the understanding of the relative importance of differ- Department of Veterinary Disease Biology, ent species of reservoir hosts of FZT in Vietnamese aquaculture. Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark e-mail: [email protected] Materials and methods E. Hoberg Study design US National Parasite Collection, Animal Parasitic Diseases Laboratory, Beltsville Agricultural Research Center, Agricultural Research Service, The study was conducted from November 2010 to January Beltsville, MD, USA 2011 in Nghia Lac and Nghia Phu communes in Nam Dinh 1046 Parasitol Res (2012) 111:1045–1048 province, located in the Red River Delta of northern in Hanoi. Species of rats were identified according to Corbet Vietnam, an area endemic for FZT (Phan et al. 2010). and Hill (1991, 1992). Rats were trapped either in rice fields adjoining fish farms or from around farm households (commensal) with Data analysis working fish ponds, and examined for FZT infection. Commensal rats were caught using traps baited with corn Data from the study were double entered into Excel files and or fried fish. For the collection of field rats from their transferred to STATA for analysis. Prevalence of infections burrows, a fire was created at a burrow entrance, and the in rats (positive/negative) and intensity of infection (number rats were caught as they emerged from another entrance. per infected host) were compared among rat species, between Small rats (<10 cm in body length) were excluded from communes and origin (rice field/commensal) using logistic the study. regression analysis (Hilbe 2009) and negative binomial regression, respectively. Recovery, isolation, and identification of FZT Ethical review Rats were killed in the field by anesthesia in an enclosed bottle containing 1–5 ml diethyl ether. The livers and intes- The study was approved by the National Institute for tines were immediately removed and placed in separate, Veterinary Research. Before the study started, all selected labeled plastic containers. The liver was opened, and any households were given information about the study, and worms observed were picked out and placed in a Petri dish their consent to participate was obtained. An ethical review with water. The liver was then crushed in warm water and and approval of the study was obtained from the project poured through a tea strainer to recover any remaining para- management of the FIBOZOPA project in Vietnam, which sites. All recovered worms were preserved in 70 % ethanol. provided the funds. The intestine was opened and the contents washed by tap water into a large container. This was then poured through a tea strainer and sieve (100-μm mesh). The sediment left on Results the sieve was next washed into a sediment cup and near boiling hot water added to kill any worms present; the Prevalence of FZT contents were then poured into plastic tubes containing 70 % ethanol. The fluid passing through the sieves was also A total of 250 rats were obtained from both Nghia Lac and allowed to settle in a cup and then hot water poured into Nghia Phu communes (Table 1). The rodent species cap- cup to kill any worms present. This was then transferred tured were Rattus norvegicus, Rattus argentiventer,and to a plastic tube with 70 % ethanol. The intestine was Bandicota indica; the majority of all three species were then divided into small pieces and placed in a small trapped in the rice fields (Table 1). The prevalence of all bucket with warm water for 15 min, after which the parasites was 52.8 % (Table 2). Nematodes had the highest mucosa was scraped to dislodge any worms present. prevalence (42.4 %), followed by trematodes (18.0 %) and The entire sediment was transferred to large plastic tubes cestodes (3.6 %). Intensity of infection was highest for containing 70 % ethanol. trematodes. Although overall prevalence and intensity of In the laboratory, worms were removed from the tube infection did not differ significantly among rat species or contents and separated into basic groups, i.e., cestodes, between the two communes, the intensity of nematode in- trematodes, and nematodes. After counting, the trematodes fection was significantly higher in commensal rats trapped were transferred to fresh 70 % ethanol, stained (Anh et al. than in field rats (p<0.05). 2009), and identified using published keys (Yamaguti 1971; Pearson and Ow-Yang 1982; Scholtz 2008). Cestodes were Table 1 Distribution of rat species trapped around households and rice preserved in ethanol and were stained as for the trematodes fields in Nghia Lac and Nghia Phu communes, Nam Dinh Province and identified at the National Parasite Collection by one of Rat species Origin of rats examined Total no. of the authors (EH). Nematodes were preserved in 70 % rats trapped ethanol and cleared in a drop of 5 % glycerin; identification Field Households was aided by published keys (Yorke and Maplestone 1969) (%) (%) and by comparison with specimens in the helminth collection Rattus norvegicus 72.7 27.3 44 at the National Parasite Collection, Beltsville Agricultural Bandicota indica 55.6 44.4 9 Research Center, in Beltsville, Maryland. Rattus argentiventer 89.9 10.2 197 The rat carcasses were kept in 60 % ethanol for identifi- Total 85.6 14.4 250 cation at the Institute of Ecology and Biological Resources Parasitol Res (2012) 111:1045–1048 1047 Table 2 Comparison of helminth prevalence and intensities between Table 3 Nematode, trematode, and cestode species recovered from rat host species the rats Host Parasites recovered (%) No. pos. Prev (%) Intensity Nematodes Trematodes Cestodes Mean Max Rattus norvegicus 47.7 15.9 2.3 Nematodes Bandicota indica 22.2 33.3 11.1 Nippostrongylus muris 104 41.6 3.18 28 Rattus argentiventer 42.1 18.3 3.6 Heligmosomoides polygyrus 6 2.4 1.00 1 Total 42.4 18.4 3.6 H. sedicimradiatus 1 0.4 1.00 1 P valuea ns ns ns Syphacia obvelata 2 0.8 1.50 2 Parasite mean intensity Trematodes Rattus norvegicus 5.14 11.57 2.00 Echinostoma spp.a 18 7.2 4.11 15 Bandicota indica 4.00 21.33 1.00 E. hortense 11 4.4 1.73 4 Rattus argentiventer 2.71 4.17 1.14 E. cinetorchis 27 10.8 6.26 38 Total 3.22 6.41 1.22 Centrocestus formosanus 9 3.6 2.67 7 P valueb ns nd nd Notocotylus sp. 4 1.6 2.25 4 Maximum recovery (in one rat) Cestodes Rattus norvegicus 28 60 2 Raillietina celebensis 9 3.6 1.22 2 Bandicota indica 6331 The table shows the combined data from all the host species Rattus argentiventer 13 52 2 a Specific identification not made due to poor preservation Total 28 60 2 nd not done because of limited sample size or the model was overdispersed, ns not significant hosts have a minimal role in the transmission of fishborne a Comparing the three species by cross-tabulation trematodes in these farm pond environments.