| General Features | External Features Body is soft and oval in outline, dorso-ventrally flattened and leaf like. Anterior end of body has a prominent oral projection, bearing a triangular aperture (mouth). Suckers are devoid of hooks and spines. Single excretory pore at the posterior end. Alimentary canal is incomplete with no anus. Body is covered by cuticle, from which numerous backwardly directed scales project. These anchor the body to the walls of the host’s bile duct, protect the body and help in locomotion. Parasitic Adaptations Tegument is thick, permeable to water but enzyme resistant. (So that the parasite is not digested by digestive juices of the host). Locomotory organs are absent as not required by adult. Free living larvae have cilia. Oral sucker, acetabulum and spines serve to attach to body of host. Alimentary canal without anus, as there is no undigested food for excretion. Highly branched intestine helps in distributing food to all parts of the body. Lack circulatory, respiratory and nervous system. Also lack sense organs. Respiration is anaerobic as free oxygen is not available. Reproductive system is highly developed. Number of eggs produced is enormous. Resistant egg shells around zygotes. Hermaphrodites: ensures self-fertilisation. |
| Life History | Adult fluke lays eggs within an egg shell. Leave the fluke’s body through Gonopore and into the host’s intestine, and are finally ejected out with its faeces. Further development takes place when the capsule comes in contact with humid soil / water and slightly acidic environment, temperature 22-25ºC. Thus, the encapsulated embryo enables survival till the intermediate host (snail) is encountered. Encapsulated embryo develops into Miracidium larva — has sense organs, nervous tissue and protonephridia. Enables it to have a free-living existence till it finds a host. It does not feed and only tries to swim about trying to attach to a host. Apical papilla of miracardium enables it to bore into the host body. Miracardium makes its way to digestive glands of snail and forms Sporocyst larva. Glands, brain, apical papillae, eye spots degenerate. Sporocyst develops into Rediae, which emerge by rupture of Sporocyst. 2nd generation Rediae develop into Cercaria larvae which leave the body through birth pore. After an active life for 2-3 days it forms metacercaria larva by undergoing encystment on aquatic plants. When the host ingests leaves with metacercaria larva, it gets infected. Cyst wall dissolves and liberates the larva. The larva moves to bile duct where it attains sexual maturity. |
| Pathogenicity | Opisthorchiasis Caused by Opisthorchis sinensis Due to eating raw or undercooked fish which contain metacercariae. Inhabit the bile ducts, causing thickening of duct walls. Severe cases may lead to cirrhosis and death. Treatment: Gentian Violet and Chloroquine |