Pharyngostomum cordatum (Diesing, 1850) Ciurea, 1922
(Figs. 2-10 and 2-11)
ETYMOLOGY:Pharyngo (Pharynx) + stomum (mouth) and cordatum for heart-shaped
SYNONYMS:Hemistomum cordatum Diesing, 1850; Alaria cordata (Diesing, 1850) Railliet, 1919; Pharyngostomum congolense Van den Berghe, 1939; Pharyngostomum fausti (Skrjabin and Popov, 1930)
HISTORY: This worm was first described from Felis sylvestris by Diesing (1850). It was considered solely a parasite of cats until it was discovered in cheetahs and genets in Africa.
GEOGRAPHIC DISTRIBUTION: Besides cats of Europe this trematode has been reported from domestic cats in China (Faust, 1927; Chen, 1934). It has also been reported from Japan (Kifune et al., 1967; Kurimoto, 1976) and Korea (Cho & Lee, 1981). It has been found in the lower Volga of Russia and in cats from Astakhan. Skrjabin and Popov (1930) described a species Pharyngostomum fausti from the delta of the Volga; this is considered a synonym according to Baer and Dubois (1951). Pharyngostomum cordatum has been reported from a cheetah in Tanganika (Baer and Dubois, 1951) and from a genet in the Congo (Van der Berghe, 1939).
LOCATION IN HOST: Upper small intestine.
PARASITE IDENTIFICATION: These trematodes are about 2 to 3 mm long. Pharyngostomum differs from Alaria, Cynodiplostomum, and Fibricola in that it has a very large tribocytic organ that fills the hollow on the ventral surface of the forebody. The egg is 100 µm long and 70 µm wide.
The average number of eggs produced by each worm is about 1,000 per day (To et al., 1988); thus, a gram of feces from an infected cat harboring a single fluke would be between 13 to 70 eggs.
LIFE CYCLE: The life cycle of this species was examined by Wallace (1939). Eggs passed into the environment in the feces of the cat require about 3 to 4 weeks of development before miracidia bearing pigmented eyespots hatch. The miracidium penetrates a snail of the genus Segmentina wherein it produces sporocysts. The cercaria that is produced is pharyngeate and longifurcate with colorless eyespots; the body is covered with small spines. The cercaria penetrates tadpoles or adult frogs and develops to the metacercarial stage. Metacercariae can exist in various paratenic hosts including toads, snakes, turtles, and shrews. In experimentally infected cats, developing trematodes were present in the intestine two days after treatment. Eggs first appeared in the feces 31 days after infection; another report found the prepatent period to be 28 to 34 days (Kurimoto, 1976). Metacercariae recovered from the European grass snake, Rhabdophis tigrina, in Korea were shown to be capable of developing to adults in cats but not in other experimental hosts including mice, rats, hamsters, ducklings, and a dog; in the cats that were infected adult flukes were recovered 5 weeks after being fed the metacercariae (Chai et al., 1990).
CLINICAL PRESENTATION AND PATHOGENESIS: The main clinical sign of pharnygostomiasis is chronic diarrhea (Sugano, 1985) probably as a result of a loss of the epithelium at the attachment sites of the trematodes (Uchida and Itagaki, 1980; Okada et al., 1984). The trematode imbeds itself amongst the villi, and pulls bits of mucosa into the anterior spoon-shaped region of the body.
TREATMENT: Thirty-five cats were treated successfully with praziquantel (30 mg/kg subcutaneously). The treatment completely eliminated eggs from the feces and removed the symptoms of diarrhea (Fukase et al., 1987).
EPIZOOTIOLOGY: The cat appears to serve as the major host of this parasite. The metacercaria has been recovered from the thigh muscles of frogs in Japan (Kajiyama et al, 1980).
HAZARD TO OTHER ANIMALS: None. Although other hosts are infected, the major means of infection is through the ingestion of the intermediate host which requires that the appropriate snail also be available.
HAZARD TO HUMANS: None.
CONTROL/PREVENTION: This will be exceedingly difficult in cats that hunt.
Baer JG, Dubois G. 1951. Note sur le genre Pharyngostomum Ciurea, 1922 (Trematoda: Strigeida). Bull Soc neuchâtel Sci nat 74:77-82.
Chai JY, Sohn WM, Chung HL, Hong ST, Lee SH. 1990. Metacercariae of Pharyngostomum cordatum found from the European grass snake, Rhabdophistigrina, and its experimental infection to cats. Korean J Parasitol 28:175-181.
Chen HT. 1934. Helminths of cats in Fukien and Kwangtung provinces with a list of those recorded from China. Lingnan Sci J 13:261-273.
Cho SY, Lee JB. 1981. Pharyngostomumcordatum (Trematoda: Alariidae) collected from a cat in Korea. Korean J Parasitol 19:173-174.
Diesing CM. 1859. Systema Helminthus, Band I, Vienna, Austria.
Faust EC. 1927. Studies on asiatic holostomes (Class Trematoda). Rec Ind Mus 29:215-227.
Fukase T, Sugano H, Chinone S, Itagaki H. 1987. Anthelmintic effect of praziquantel on Pharyngostomumcordatum in naturally infected domestic cats. J Jap Vet Med Assoc 40:640-643.
Kajiyama M, Nakamoto M, Suzuki N. 1980. Studies on Pharyngostomumcordatum (Diesing, 1850). 3. An epidemiological survey in the vicinity of Yamaguchi City, Japan. Yamaguchi J Vet Med 7:1-6.
Kifune T, Shiraishi S, Takao Y. 1967. Discovery of Pharnygostomumcordatum (Diesing, 1850) in cats from Kyushu, Japan (Trematoda; Strigeoidea; Diplostomatidae) Jap J Parasitol 16:403-409.
Kurimoto H. 1976. Study on the life history of Pharyngostomumcordatum (Diesing, 1850) I. The second intermediate host in Japan and experimental infection to the final host. Jap J Parasitol 25: 241-246.
Okada R, Imai S, Ishii T. 1984. Scanning electron microscopic observations on the parasitism of Pharyngostomumcordatum (Diesing, 1850). Jap J Parasitol 33:333-339.
Skrjabin KI, Popov NP. 1930. Pharyngostomum fausti n. sp. Tierärztl rundschau 35:709-710.
Sugano H. 1985. Chemotherapy of Pharyngostomum infection in dogs and domestic cats. J Jap Vet Med Assoc 38:297-301.
To M, Okuma H, Ishida Y, Imai S, Ishii T. 1988. Fecundity of Pharyngostomumcordatum parasitic in domestic cats. Jap J Vet Sci 50:908-912.
Uchida A, Itagaki H. 1980. Distribution of metacercariae of Pharyngostomumcordatum in Aichi prefecture and pathological findings on cats infected. J Jap Vet Med Assoc 33:594-597.
Wallace FG. 1939. The life cycle of Pharyngostomumcordatum (Diesing) Ciurea (Trematoda: Alariidae). Trans Am Mic Soc 58:49-61.
Figures 2-10 and 2-11.Pharyngostomumcordatum collected from domestic cats in Taiwan. Note the division into fore and hind bodies, and the ability of the two body portions to telescope into each other to give the compressed appearance seen in Fig. 2-11 when it is compared to Fig. 2-10.