Cat liver fluke

Morphology and anatomy of the worm

The sexually mature adult (sarissa/marita) of the cat liver fluke has a characteristic leaf-like body shape, with the anterior end noticeably narrower than the posterior one. The parasite is small: the length is 8–14 mm, and the width ranges from 1.2 to 3.5 mm. There is no internal body cavity (the so-called parenchymatous type of structure), and the helminth is reliably protected on the outside by a dense tegumentary-muscular sac.

The organ systems of the cat liver fluke have a number of specific features important for microscopic identification:

• Digestive system: begins with the oral opening, passing into the pharynx and esophagus. The intestine is divided into two unbranched channels. They extend along the body and end blindly without reaching the very posterior end.
• Excretory system: built on the protonephridial type. The main diagnostic feature of the species is the central excretory canal, which has a characteristic S-shaped bend in the posterior part of the body.
• Nervous system: represented by an orthogone (ladder-type system).
• Respiration and circulation: the parasite completely lacks specialized circulatory and respiratory systems.

Reproductive system is built on the hermaphroditic type, which ensures high reproductive capacity. Two large lobed testes are located in the posterior part of the body. The middle part of the body is occupied by the branched uterus. Directly behind the uterus is a rounded ovary, next to which a small bean-shaped seminal receptacle is adjacent. Vitellaria are symmetrically distributed along the lateral parts of the body.

Life cycle and hosts

The development of the cat liver fluke is a complex process requiring an obligatory change of three hosts. The absence of even a single link interrupts the parasite's life cycle.

1. First intermediate host: freshwater mollusks belonging to the genus Codiella.
2. Second (supplementary) intermediate host: fish of the family Cyprinidae. Crucian carp, roach, ide, and wild carp are most frequently infected.
3. Definitive host: humans, as well as various domestic and wild carnivorous animals (cats, dogs, foxes, arctic foxes).

Mechanism of infection of the definitive host, including humans, is alimentary. The transmission factor is infected fish. The disease develops if a person consumes raw, sun-dried, lightly salted, or thermally undercooked cyprinid fish whose muscle tissue contains live metacercariae.

Pathogenesis, diagnosis, and prevention

Upon entering the bile ducts and pancreas, the cat liver fluke causes a complex of severe pathological changes. The metabolic products of the helminth provoke systemic toxic-allergic reactions in the body. Accumulating in the ducts, the worms create a mechanical obstruction, which causes a persistent delay in the outflow of bile and pancreatic juice. With a prolonged, chronic course of the invasion, these processes can lead to the development of liver cirrhosis.

Laboratory diagnostics of opisthorchiasis is based on the detection of the parasite's eggs. The biological material for examination is the patient's feces (stool) or duodenal contents obtained by probing.

The basis of prevention of opisthorchiasis is strict compliance with culinary processing rules. It is necessary to completely exclude raw, sun-dried, lightly salted, and insufficiently boiled or fried fish of the family Cyprinidae from the diet.

Epidemiology and taxonomic position

The disease caused by the cat liver fluke is called opisthorchiasis. The source of infection in nature and populated areas is infected humans, as well as domestic and wild carnivorous mammals. The infective stage for humans is always the metacercaria.

The geographical distribution of opisthorchiasis is uneven. The largest and most significant epidemiological focus is located in the basins of the Ob and Irtysh rivers. Much less frequently, foci of the disease are registered in the basins of rivers such as the Volga, Kama, Ural, Don, and Dnieper.

In zoological taxonomy, the cat liver fluke belongs to the order Heterophyida, family Opisthorchidae. This same family includes a related species — the Chinese liver fluke (Clonorchis sinensis). This parasite is the causative agent of clonorchiasis, a natural-focal anthropozoonotic disease with a similar pathogenesis.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Features of the structure of cat liver fluke eggs for laboratory diagnostics
• Comparative characteristics of Opisthorchis felineus and Clonorchis sinensis
• Mechanisms of development of liver cirrhosis in chronic opisthorchiasis
• Sanitary and epidemiological requirements for thermal processing of fish

Other topics in the "Medical Helminthology" section

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