The trematodes are a group of organisms that are related to the planarian of biology class. The planarian belongs to the free-living form of platyhelminth called the turbellarian. The trematodes differ from their free-living turbellarian relatives in that trematodes are all parasitic and lack the cilia that cover the body surface of the adult turbellarian.

There are two kinds of trematodes: monogenetic and digenetic. This terminology refers to whether or not there is development through morphologically dissimilar stages in some type of intermediate host, i.e., whether or not there is an "alternation of generations." The digenetic trematodes undergo a form of development wherein a larval stage develops in a mollusk and the adult develops in a different host. This dissimilar nature of the larval and adult forms caused the larvae and adults to be considered separate entities until the work of Steenstrup in 1842 showed them to be the same animals. This problem of stage identification did not exist for the monogenetic trematodes that look like adults when they hatch from the egg. The monogenetic trematodes are parasites of amphibians, fish, and other hosts, and are only important if their eggs are found in the feces of a cat that has eaten an infected host. A wide variety of digenetic trematodes, on the other hand, commonly infect cats.

The digenetic trematodes undergo their first larval development in a mollusk, typically a snail. The snail is infected with a ciliated stage, the miracidium, that hatches from the egg produced by the adult trematode. In most cases, after the larva develops through one to several stages within the snail, a proliferative stage is reached that produces the cercaria, the stage that ultimately leaves the snail. After leaving the snail, the cercaria may take one of several routes, it may encyst on vegetation, it may encyst in the tissues of a second intermediate host that will ultimately be eaten by the final host, or it may (in the case of schistosomes only) penetrate directly into the final host. Cats typically become infected by either eating an infected host or via the penetration of the skin. Feline feeding habits are such that cats seldom fall prey to the trematodes that utilize vegetation.

Digenetic trematodes can be classified in several ways. The "Natural" classification used by taxonomists takes into account many characteristics of biology and morphology to place similar organisms into similar groups. Due to the very large numbers of trematodes, this system unfortunately is often considered cumbersome by practitioners. Another means of classification is the mode of infection for the final host. Thus, the adult trematodes could be listed as those from fish, those from crabs, those from lizards, direct penetration, etc. Again, although useful for epizootiology and prevention, this is not of great use to the practitioner. Thus, the trematodes presented herein are given as to where they are typically found within the body of the final host. At the end of the chapter, a table lists how cats become infected and the geographical distribution of the species discussed in this chapter.

Trematodes of the buccal cavity


Clinostomumfalsatum Ortlepp, 1963

Clinostomumkalappahi Bhalerao, 1947

Clinostomum abdoni Tubangui and Garcia, 1939\

Trematodes of the intestine


Mesostephanusmilvi Yamaguti, 1939

Prohemistomum vivax (Sonsino, 1893) Azim, 1933


Alariamarcianae (LaRue, 1917) Walton, 1949

Cynodiplostomumazimi (Gohar, 1933) Dubois, 1936

Fibricolaminor Dubois, 1936

Pharyngostomumcordatum (Diesing, 1850) Ciurea, 1922



Echinochasmusperfoliatus (Ratz, 1908) Dietz, 1909

Echinochasmus breviviteilus Fahmy, Khalifa, Sakla, 1981

Echinochasmusliliputanus (Looss, 1896) Odhner, 1911

Episthmiumcaninum (Verma, 1935) Chatterji, 1954

Stephanoproradenticulatoides Isaichikoff, 1925


Artyfechinostomumsufrartyfex (Schrank, 1788) Lühe, 1909

Isthmiophoramelis (Schrank, 1788) Lühe, 1909

Echinoparyphium Dietz, 1909



Apophallus donicus (Skrjabin & Lindtrop, 1919) Cameron, 1936

Apophallusvenustus (Ransom, 1920) Cameron, 1936

Apophallusmuehlingi (Jägerskiöld, 1899) Lühe, 1909


Ascocotyleascolonga (Witenberg, 1929) Travassos, 1930

Ascocotylelongicollis (Kuntz and Chandler, 1956) Sogandares-Bernal and Lumsden, 1963

Ascocotyleminuta Looss, 1899

Ascocotyleangrense Travassos, 1916

Ascocotylelonga Ransom, 1921

Ascocotyle pachycystis Schroeder and Leigh, 1965

Ascocotylearnoldoi (Travassos, 1928) Soganderes-Bernal and Lumsden, 1963


Centrocestuscaninus Leiper, 1913

Pygidiopsisgenata Looss, 1907

Pygidiopsissumma Onji and Nishio, 1916

Pygidiopsoidesspindalis Martin, 1951


Cryptocotylelingua (Creplin, 1825) Fischoeder, 1903

Cryptocotyleconcavum (Creplin, 1825) Lühe, 1899

Cryptocotylequinqueangularis (Skrjabin, 1923)


Euryhelmissquamula (Rudolphi, 1819) Poche, 1926

Euryhelmismonorchis Ameel, 1938

Euryhelmispacifica Senger and Macy, 1952


Galactosomumfregatae Prudhoe, 1949


Haplorchispumilio (Looss, 1896) Looss, 1899

Haplorchisyokogawai (Katsuta, 1932) Chen, 1936

Haplorchistaichui (Nishigori, 1924) Witenberg, 1930

Haplorchissprenti Pearson, 1964

Haplorchisparataichui Pearson, 1964

Procerovumvarium Onji and Nishio, 1916

Procerovumcalderoni (Africa and Garcia, 1935) Price, 1940

Stellantchasmusfalcatus Onji and Nishio, 1916


Heterophyesheterophyes (Siebold, 1852) Stiles and Hassal, 1900

Heterophyesaequalis Looss, 1902

Heterophyopsis continua (Onji & Nishi, 1916) Tubangui & Africa, 1938


Metagonimusyokogawai (Katsurada, 1912) Katsurada, 1912

Metagonimustakahashii Suzuki, 1930

Dexiogonimusciureanus Witenberg, 1929


Stictodorasawakinensis Looss, 1899

Stictodora thapari Witenberg, 1953


Microphalloides vajrasthirae Waikagul, 1983


Plagiorchis massino Petrov & Tikhonov, 1927


Nanophyetus salmincola Chapin, 1928

Trematodes of the pancreas


Eurytrema procyonis Denton, 1942

Trematodes of the gallbladder and bile ducts


Euparadistomum pearsoni Talbot, 1970

Euparadistomumbuckleyi Singh, 1958

Euparadistomumheiwschi Buckley and Yeh, 1958

Platynosomumconcinnum (Braun, 1901) Purvis, 1933


Amphimeruspseudofelineus (Ward, 1901) Barker, 1911

Clonorchissinensis (Cobbold, 1875) Looss, 1907

Opisthorchisfelineus (Rivolta, 1884) Blanchard, 1895

Opisthorchisviverrini (Poirier, 1886) Stiles and Hassall, 1896

Opisthorchischabaudi Bourgat and Kulo, 1977

Paropisthorchiscaninus Stephens, 1912

Metorchisconjunctus (Cobbold, 1860) Looss, 1899

Metorchisalbidus (Braun, 1893) Looss, 1899

Metorchisorientalis Tanabe, 1919

Parametorchiscomplexum (Stiles and Hassal, 1894) Skrjabin, 1913

Pseudamphistomumtruncatum (Rudolphi, 1819) Lühe, 1909

Trematodes of the nasal fossae


Orchipedumisostoma (Rudolphi, 1819)


Troglotrema mustelae Wallace, 1932

Trematodes of the lungs


Paragonimuswestermani (Kerbert, 1878) Braun, 1899

Paragonimuspulmonalis (Baelz, 1880) Miyazaki, 1978

Paragonimusmiyazakii Kamo, Nishida, Hatsushika, and Tomimura, 1961

Paragonimusheterotremus Chen and Hsia, 1964

Paragonimussiamensis Miyazaki and Wykoff, 1965

Paragonimusskrjabini Chen, 1964

Paragonimusohirai Miyazaki, 1939

Paragonimuskellicotti Ward, 1908

Paragonimusmexicanus Miyazaki and Ishii, 1968

Paragonimusinca Miyazaki, Mazabel, Grados, and Uyema, 1975

Paragonimusafricanus Voelker and Vogel, 1965

Paragonimusuterobilateralis Volker and Vogel, 1965

Trematodes of the blood vessels


Heterobilharziaamericana Price, 1929

Ornithobilharziaturkestanica (Skrjabin, 1913)

Schistosomajaponicum (Katsurada, 1904) Stiles, 1905



Intermediate hosts and geographic distribution of the trematode parasites of the domestic cat.



Intermediate Host

Geographical Distribution

Clinostomum falsatum Fresh-water fish South Africa
Clinostomum kalappahi Fresh-water fish India
Clinostomum abdoni Fresh-water fish Philippines
Mesostephanus milvi Brackish-water fish (?) Japan, India, Africa
Prohemistomum vivax Brackish & fresh-water fish Middle East
Alaria marcianae Frogs, paratenic mammals N America
Cynodiplostomum azimi Frogs (?) Middle east
Fibricola minor Frogs Australia
Pharyngostomum cordatum Toads, Reptiles, shrews Europe, Africa, China
Echinochasmus perfoliatus Fresh-water fish Europe, Middle & Far East
Echinochasmus breviviteilus Fresh-water fish (?) Middle east
Echinochasmus liliputanus Fresh-water fish (?) Middle east
Episthmium caninum Fresh-water fish (?) India
Stephanoprora denticulatoides Fresh-water fish (?) Europe
Artyfechinostomum sufrartyfex Snail, frogs India
Isthmiophora melis Frogs N America
Echinoparyphium Frogs Tasmania
Apophallus donicus Fresh-water fish Europe
Apophallus venustus Fresh-water fish N America
Apophallus muehlingi Brackish-water fish (?) Europe
Ascocotyle ascolonga Brackish-water fish Middle East
Ascocotyle longicollis Brackish-Water fish Middle East
Ascocotyle minuta Brackish-water fish (?) Middle East
Ascocotyle angrense Fresh-water fish Brazil
Ascocotyle longa Brackish-water fish Americas
Ascocotyle pachycystis Brackish-water fish N America
Ascocotyle arnoldoi Brackish-water fish S America
Centrocestus caninus Fresh-water fish Taiwan
Pygidiopsis genata Brackish-water fish Europe, Middle East, Asia
Pygidiopsis summa Brackish-water fish (?) Asia
Pygidiopsoides spindalis Brackish-water fish N America
Cryptocotyle lingua Salt-water fish N America
Cryptocotyle concavum Brackish-water fish (?) Russia
Cryptocotyle quinqueangularis Brackish-water fish Europe, N Africa, N America
Euryhelmis squamula Newt, Toads Europe, N America
Euryhelmis monorchis Frogs N America
Euryhelmis pacifica Salamanders N America
Galactosomum fregatae Brackish-water fish W Indies, India
Haplorchis pumilio Fresh-water fish Middle East, Asia, Australia
Haplorchis yokogawai Brackish-water fish Middle East, Asia
Haplorchis taichui Brackish-water fish Middle East, Asia
Haplorchis sprenti Brackish-water fish Australia
Haplorchis parataichui Fresh-water fish Australia
Procerovum varium Brackish-water fish Australia
Procerovum calderoni Brackish-water fish Philippines
Stellantchasmus falcatus Brackish & fresh-water fish M East, Asia, Australia, Hawaii
Heterophyes heterophyes Brackish-water fish Mediterranean, India, Japan
Heterophyes aequalis Salt, brackish, & fresh-water fish Middle East
Heterophyopsis continua Brackish-water fish Japan, Korea
Metagonimus yokogawai Fresh-water fish Asia, Spain, Balkans
Metagonimus takahashii Fresh-water fish Asia
Dexiogonimus ciureanus Brackish-water fish (?) Middle East
Stictodora sawakinensis Brackish-water fish (?) Middle East
Stictodora thapari Brackish-water fish (?) Middle East
Microphalloides vajrasthirae Crab Thailand
Plagiorchis massino Snail (?) Eurasia, Canada
Nanophyetus salmincola Fresh-water fish Northern Pacific coast
Eurytrema procyonis Arthropod (?) N America
Euparadistomum pearsoni Arthropod (?) New Guinea
Euparadistomum buckleyi Arthropod (?) Siberia, Europe
Euparadistomum heiwschi Arthropod (?) Africa
Platynosomum concinnum Lizards, frogs, toads S. Pacific, W. Africa, Caribbean
Amphimerus pseudofelineus Fresh-water fish Americas
Clonorchis sinensis Fresh-water fish Asia
Opisthorchis felineus Fresh-water fish Siberia, Europe
Opisthorchis viverrini Fresh-water fish Thailand
Opisthorchis chabaudi Frogs Africa
Paropisthorchis caninus Fresh-water fish (?) India
Metorchis conjunctus Fresh-water fish N America
Metorchis albidus Fresh-water fish Europe
Metorchis orientalis Fresh-water fish Asia
Parametorchis complexum Fresh-water fish N America
Pseudamphistomum truncatum Fresh-water fish (?) Europe, India
Orchipedum isostoma Crabs Africa

Troglotrema mustelaeFresh-water fishN America Paragonimus westermaniFresh-water crabsAsia Paragonimus pulmonalisFresh-water crabs & crayfishJapan, Korea, Taiwan Paragonimus miyazakiiFresh-water crabsJapan Paragonimus heterotremusFresh-water crabsChina Paragonimus siamensisFresh-water crabsThailand Paragonimus skrjabiniFresh-water crabsChina Paragonimus ohiraiBrackish-water crabsAsia Paragonimus kellicottiFresh-water crayfishN America Paragonimus mexicanusFresh-water crabsMexico, C & S America Paragonimus incaFresh-water crabsPeru Paragonimus africanusFresh-water crabsAfrica Paragonimus uterobilateralisFresh-water crabsAfricaSchistosomatidae  Heterobilharzia americanaSkin penetrationN America Ornithobilharzia turkestanicaSkin penetrationEurasia Schistosoma japonicumSkin penetrationAsia