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Opisthorchiasis caused by Opisthorchis viverrini infection, is a serious public health problem in Lao PDR, Cambodia, Vietnam and Thailand. Cyprinid fish are required for the transmission of O. viverrini metacercariae to fish eating-mammal hosts including humans. The transmission of infective metacerariae is an important event, potentially resulting in the development of cholangiocarcinoma in cases of chronic opisthorchiasis. For a better understanding of the development of O. viverrini metacercariae in the second intermediate host, Barbonymus gonionotus (Cyprinidae), the immune response of infected B. gonionotus through fibrous tissue formation and superoxide dismutase (SOD) activity were investigated. The immunosuppressant (prednisolone) was administered to B. gonionotus infected with O. viverrini cercariae to study infectivity and development of the metacercariae. Additionally, the effects of prednisolone were studied by the investigation of fibrous tissue formation around the metacercariae, as well as SOD activity. In our study, prednisolone administered prior to infection in B. gonionotus had higher metacercarial recovery when compared to the non-administered control group. On the other hand, the administration of prednisolone after the O. viverrini infection allowed metacercariae to develop to the infective stage. Energy consumption from encystation to the infective stage required 443.9–463.7 degree-days. The results show that immunosuppression decreases fibrous tissue and SOD activity in infected fish, and also affects the ability of O. viverrini metacercariae to develop to the infective stage. The immune response to metacercarial development of O. viverrini in cyprinid fish should be further studied to gain a greater understanding of this process, and hence, a better understanding of the mechanism(s) involved in metacercarial wall formation. [ABSTRACT FROM AUTHOR]

Opisthorchis viverrini is an important public health problem, a major cause of cholangiocarcinoma in the Greater Mekong subregion including Lao PDR, Cambodia, Vietnam and Thailand. Humans acquire the infection by consumption of raw, fermented or partially cooked freshwater cyprinid fish containing infective metacercariae. This study examined the effect of cercarial infection dosage (25–200 cercariae), age (1–60 day) and size (1–24 mm) of Barbonymus gonionotus fish on infection success of O. viverrini cercariae. Additionally, the site of cyst formation of O. viverrini cercariae and subsequent development to the metacercariae was examined. The result showed that cercarial infection dose ( F 4,95 = 8.52, P < 0.001) age ( P < 0.001, ƛ L R 2 = 954.72 ) and size ( P < 0.001, ƛ L R 2 = 1204.84 ) were significantly associated with number of O. viverrini metacercariae recovery with in every additional fish age, the O. viverrini metacercarial recovery rate increased by 5.4% ( P < 0.001). Most metacercariae were found in the body of the fish (81.4%). We concluded that O. viverrini cercarial infection dosage, and age and size of fish were important determinants for a successful infection to fish. [ABSTRACT FROM AUTHOR]

Highlights: [•] Infection of Opisthorchis viverrini starts from day 1 in fish fry. [•] Age, size of fish and doses of cercariae are related to infection rate in fish. [•] Every additional age the infection rate increased 5.4%. [•] Most metacercariae encystin body of fish. [Copyright &y& Elsevier]

Abstract: Snails and fishes from ponds in an area endemic for human liver fluke (Opisthorchis viverrini) in Khon Kaen Province, northeast Thailand, were surveyed for the presence of zoonotic helminth parasites during May–November 2007. The surveys were performed to obtain information on the potential for transmission of these parasites to fish cultivated for human consumption. Sixteen species/subspecies of snails from 7 families and 14 species of fish from 6 families were collected for parasitological examination. Four species of snails were found to be infected with a range of trematode species. Bithynia siamensis goniomphalos, the first intermediate host of O. viverrini, was the most commonly infected with trematodes, with a prevalence of infection of 1.69–25.00% in 10 ponds. O. viverrini was found in 1 of 1065 (0.09%) B. siamensis goniomphalos individuals examined in one pond. Metacercariae of Echinostoma revolutum, another agent of human infection, was found in the snail Idiopoma umbilicata in one pond. The fish Luciosoma bleekeri was infected with the trematode Centrocestus caninus in one pond. An environmental management trial was conducted in selected ponds in the endemic area to measure the effects of exclusion of snails and thus trematode parasites. After modifications to the ponds and boundaries, including the exclusion of snails, the ponds were stocked with Barbonymus gonionotus fingerlings. Batches of the fingerlings from the same nursery farm were determined to be free of parasites prior to their introduction to the ponds. The experimental ponds were examined monthly for the presence of snails. Fish were also sampled monthly for parasites. After 8months, fish grown in environmentally managed ponds were larger than those of the control pond. However, fish in all ponds were found to be infected with the trematode Haplorchis taichui. The source of this zoonotic species is uncertain and will require further investigation and potential environmental management, both at farms and at hatcheries. [Copyright &y& Elsevier]