The role of rice fields, fish ponds and water canals for transmission of fish-borne zoonotic trematodes in aquaculture ponds in Nam Dinh Province, Vietnam

Abstract

BackgroundFish-borne zoonotic trematodes (FZT), such as Clonorchis sinensis, Opistorchis viverini (Opisthorchiidae) and intestinal trematodes of the family Heterophyidae, constitute a public health hazard in Vietnam and infections with these trematodes has been linked to consumption of raw or undercooked fish from aquaculture. The FZT transmission pathways, however, are more complicated than just the presence of intermediate snail hosts in aquaculture ponds as ponds may exchange water with surrounding habitats such as rice fields and irrigation canals and thereby these surrounding habitats may be a source of snails and cercariae and contribute to FZT infection in cultured fish.MethodsThis is a longitudinal descriptive study on selected farms (n = 30) in Nam Dinh Province which is endemic for FZT. At each farm, we sampled one pond, a small irrigation canal used to supply the pond with water, and a nearby rice field. At each of these three sites, we estimated the density of the FZT intermediate snail hosts and determined their trematode infection status. Comparative analysis was performed for the prevalence and density of FZT infections in fish and snails.ResultsSpecies of the Thiaridae, and most notably Melanoides tuberculata, the most important host species for FZT belonging to the Heterophyidae, were particularly abundant in ponds and small canals, i.e. M. tuberculata was found in 27 ponds and 13 small canals. Bithynia fuchsiana, a potential host for both Heterophyidae and Opisthorchiidae, was rarely found in fish ponds but common in rice fields. A total of 12 types of cercariae were found in the snails and pleurolophocercous cercariae, primarily FZT, constituted about 40 % of all cercarial infections. The fish species cultured were mainly carp species and Haplorchis pumilio was the dominating trematode species infecting fish. Clonorchis spp. were not recorded in any of the ponds. FZT transmission to fish was intense during the summer period (May-June to November) but less intense during the winter months (December-January) partly because cercarial emergence ceases due to the low temperature.ConclusionOur findings highlight the complexity of FZT transmission within aquaculture farm settings and suggest that efforts to control these infections must take a holistic approach using interventions against all stages of the transmission cycle.

Prevalence of gastrointestinal helminth parasites of <i>Clarias gariepinus</i> in Abuja, Nigeria

“…But there is report of human trematodiasis in Egypt caused by the digenetic trematodes of the families Heterophyidae. Heterophyids constitute a public health problem wherever people eat raw, salted or otherwise undercooked fish containing metacercariae (Paperna 1996;Centers for Disease Control and Prevention, 2013;Madsen et al, 2015). Heterophyidae was reported frequently to infect humans in Egypt.…”

Prevalence, Species Distribution, and Related Factors of Fish-Borne Trematode Infection in Ninh Binh Province, Vietnam

“…Studies using molecular tools to identify the species of FBT for adult worms collected from infected persons have revealed inconsistent results [15, 18]. For a long time, much attention has focused on SLF [19, 22] but most of the metacercariae collected from fish in that region were MIF while the prevalence of SLF is very low [17, 23, 24]. With such divergent results, FBT infection among local people should be resituated.…”

Epidemiology of Opisthorchis viverrini in an endemic area of Thailand, an integrative approach

“…Chronic infection caused by the Southeast Asian liver fl uke (Opisthorchis viverrini) is a critical risk factor for the development of the bile duct cancer cholangiocarcinoma (CCA), what is a major health concern in South-East Asia (Thailand, Laos People's Democratic Republic, Cambodia and central Vietnam) Aunpromma et al, 2012;Miyamoto et al, 2014;Kaewpitoon et al, 2015;Khuntikeo et al, 2016). In Thailand at least 6 million people are estimated to be currently infected (Andrews et al, 2008).…”

“…In Thailand at least 6 million people are estimated to be currently infected (Andrews et al, 2008). Opisthorchis viverrini infection in humans and in dog and cat host reservoirs (Sithithaworn & Haswell-Elkins, 2003) occurs via the consumption of a raw or uncooked fi sh which contains infective metacercariae (Sripa et al, 2007;Donthaisong et al, 2014;Madsen et al, 2015;Onsurathum et al, 2016) In addition, fermented fi sh also contain high concentrations of nitrosamines that are known to be potent human carcinogens (Thamavit et al, 1993). Once metacercariae are ingested they migrate to the intrahepatic bile duct via the common bile duct and once the fl uke becomes gravid (in about 30 days) the eggs are excreted by feces .…”