Opisthorchis viverrini: Life cycle, intermediate hosts, transmission to man and geographical distribution in Thailand

• Main Authors: C. Harinasuta, T. Harinasuta
• Other Authors: Mahidol University
• Format: Article
• Published: 2018
• Subjects: Chemistry; Pharmacology, Toxicology and Pharmaceutics
• Online Access: https://repository.li.mahidol.ac.th/handle/123456789/30596

Opisthorchis viverrini has been found to be the only species of liver fluke in Thailand. The morphology is similar to that of O. felineus, but it has more deeply lobated testes, situated near the ovary. The appearance and distribution of the vitellaria with few granular clumps and the shorter and wider egg closely resemble that of C. sinensis. The adult worms live in the biliary system. Eggs pass out in the faeces. On reaching water the eggs are eaten by snails, the first intermediate host. In the snail the miracidia hatch and develop further through the stages of sporocysts, rediae and cercariae in 6 to 8 weeks. The cercariae then leave the snail, penetrate into susceptible fresh water fish, encyst in the muscle and develop into metacercariae, an infective stage, in 6 weeks. When ingested by man or animal the metacercariae excyst in the duodenum or jejunum and then migrate to the bile duct. They become mature within 4 weeks and begin to produce eggs. The life span of the fluke is over 10 years. The snail intermediate hosts are Bithynia goniomphalus, B. funiculata and B. siamensis. Many species of cyprinoid fish serve as second intermediate hosts. Cyclocheilichthys siaja is the most important. Cats, dogs and many fish eating mammals are definitive hosts. Man and animals acquire infection by eating raw fish containing metacercariae cysts. In Northeast Thailand 'Koi-Pla' is the most popular raw fish dish. In 1980-1981 the prevalence in the north, northeast, centre and south of Thailand was 5.59, 34.60, 6.34, and 0.01%, respectively, with an overall prevalence of 14% or 7 million people.