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Fig. 21.2 Adult Clonorchis sinensis, stained gross specimen. The oral sucker is at the top, the uterus is in the middle and the testis and excretory pore are at the bottom (Courtesy of Dr. Herman Zaiman).

Fig. 21.3 Unstained Clonorchis sinensis egg in feces showing the shoulder at the rim of the operculum. x890. AFIP 55-2469.

Fig. 21.4 Clonorchis sinensis eggs and Trichuris trichiura egg (upper left) in the same smear from fecal concentrate. (Courtesy of Dr. Herman Zaiman).

Fig. 21.5 Clonorchis sinensis operculated eggs in an adult fluke within the bile duct. Egg morphology in tissue sections may help identify the species of fluke.

 

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Epidemiology and Pathology

The parasite, Clonorchis sinensis, inhabits the bile ducts of man (the definitive host) and several species of mammals and birds (reservoir hosts). The adult fluke is oblong, narrow, flat, tapered anteriorly, reddish-brown, and almost transparent (Fig. 21.2). It is 10-20 mm long, 3-5 mm wide and 1 mm thick. The operculated eggs of C. sinensis measure 30 Ám x 15 Ám and contain fully developed miracidia (Figs. 21.3, 21.4, 21.5). Eggs are laid in the smaller biliary ducts, from where they are swept down the common bile duct to the duodenum and are passed in the stool. Hatching of the miracidia occurs when the eggs are ingested by a snail (the first intermediate host) feeding in water polluted by feces from an infected person or animal. Only operculate snails of the family Bulimidae, including Bulimus, Bithynia, Melanoides, Assiminea, and Parafossarulus, are suitable hosts for C. sinensis. Development of miracidia within the snail into sporocysts, and later rediae and cercariae, requires 4-5 weeks, during which time asexual reproduction occurs, producing large numbers of cercariae from each egg and miracidium. The free-swimming cercariae emerge from the snail and, within 15 minutes after penetrating the musculature of fresh-water cyprinoid fish, often carp, the organisms encyst and become metacercariae. After several weeks of further development, the metacercariae become infective and, when raw or poorly cooked fish containing encysted metacercariae are eaten by a man or animal, the developmental cycle of the parasite is completed (Fig. 21.6).

Fig. 21.6 Life cycle of Clonorchis sinensis and Opisthorchis viverrini.

 

 

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