Abstract:
Opisthorchiasis remains a major public health problem in Southeast Asia, particularly in Thailand, Laos PDR, Cambodia and Vietnam. Human and animals are infected with metacercariae of O. viverrini by consumption of traditional raw or uncooked freshwater cyprinid fish. The objectives of this research were to study the infection rates of silver bard fish, Barbodes gonionotus that were infected by cercariae from Cambodias snails, and the development of metacercariae in fish. The experiment was performed in laboratory by 3 replications. Collected fish were divided into 4 groups, namely one control group, and three experimental groups, which were injected with 100, 200, and 400 cercariae respectively. The post infection, infection rates and development of metacercariae in the fish were observed in 7, 14, 21, 28, 35 and 42 days. The metacercariae from the fish organs were examined. The results were recorded and analyzed by statistical methods. In this study, metacercariae from the experimental fish were identified using molecular techniques. Amplification by polymerase chain reaction (PCR) of cytochrome c oxidase subunit 1 (cox1) gene of mitochondrial DNA region was performed. Out of 241 experimental fish, 200 were found to be infected by cercariae, equivalent to an 82.99% infection rate. The highest infection rate was in the fourth group, which was significantly different from the other groups (p<0.05). The average number was 10.08 (S.D.=9.27) metacercariae per infected fish. The most metacercariae were found in the tail of 91.5 % samples (183 fish), followed by those in the dorsal fins and pelvic fins of 70.0% samples (140 fish) and 44.0% samples (88 fish) respectively. The least infected area was the muscle of pectoral fins of 4.5% samples (9 fish). It was also found that the metacercariae started to develop in the second week after the infection. At this stage, they would be able to survive and fully develop.