Opisthorchis felineus (Rivolta, 1884) Blanchard, 1895
ETYMOLOGY:Opistho = posterior and orchis = testis along with felineus = representing the feline host.
SYNONYMS:Distoma felineum Rivolta, 1884; Distoma sibiricum Winogradoff, 1892.
HISTORY: This trematode was originally described from the bile passages of a cat in Italy (1884). In 1892, it was found in 9 human beings in Siberia.
GEOGRAPHIC DISTRIBUTION:Opisthorchis felineus is found in Siberia, areas drained by the Danube in Europe and the Volga in Russia.
LOCATION IN HOST: Gall bladder and bile ducts; occasionally in the pancreatic duct or the small intestine.
PARASITE IDENTIFICATION:Opisthorchis felineus is similar to Clonorchis sinensis, the most obvious difference is the difference in the amount of branching of the testes. Those of Clonorchis are highly branched, while those of Opisthorchis are lobed. The adults of Opisthorchis felineus differ from those of Opisthorchis viverrini mainly in larval development and morphology; however, the eggs of O. felineus are 30 by 11 µm while those of O. viverrini are 27 by 15 µm.
Specimens of the genus Metorchis have much wider bodies and spherical testes. In the genus Parametorchis, the flukes have the vitellaria become confluent in the anterior body. In specimens of Pseudamphistomum the posterior end of the body is squared-off giving the ventral surface of the body the appearance of being a pseudo hold-fast structure.
LIFE CYCLE: The life cycle is very similar to that of Clonorchis sinensis. The eggs hatch only after they are ingested by the appropriate snail (Bithynia leachi). Ultimately a cercaria develops that has eyespots and a large tail fin. The cercaria penetrates a fresh-water fish, typically of the carp family, between the scales and encysts as a metacercaria within the muscles. Cats become infected by eating infected fish. Once eaten, the fluke migrates through the ampule of Vater into the bile ducts where it matures (Vogel, 1934).
CLINICAL PRESENTATION AND PATHOGENESIS: Little attention has been given the pathological manifestations that take place within the feline host. It is expected that the changes will be similar to those observed in human beings infected with this parasite. Besides cirrhosis due to periportal fibrosis, there have also been reports of bile stones forming around eggs causing cholecystitis. As the periportal fibrosis continues, there will be the development of edema and ascites.
TREATMENT: Praziquantel is likely to prove successful in eliminating these trematodes from many treated cases.
EPIZOOTIOLOGY: Cats are a major host of this pathogen. Throughout Europe, Siberia, and the Ukraine, infections of cats with Opisthorchis felineus are not uncommon. In some parts of the parasite's range, the infection in maintained mainly in the human population, and improved sanitation among the human hosts will reduce the transmission of the parasite. Other hosts that have been reported to support the development of this parasite includes dogs, foxes, pigs,m martens, wolverines, polecats, gray seals, and bearded seals.
HAZARD TO OTHER ANIMALS: Dogs and other fish-eating mammals can also be infected with this parasite.
HAZARD TO HUMANS: Large numbers of human beings are infected with this parasite in the geographical regions where it is found.
CONTROL/PREVENTION: Prevent the ingestion of infected raw, dried or pickled fish; these latter methods are not necessarily going to kill the metacercarial stage of the trematode.
Vogel H. 1934. Der Entwicklungszyklus von Opisthorchisfelineus (Riv.) nebst Bemerkungen über Systematik und Epidemioloie. Zoologica 33:1-103.
Figure 2-39.Opisthorchisfelineus from a cat. Note the slightly branched testes and the vitellaria that extend only to the anterior of the most anteriad testis.