Heterophyopsis continua (Onji & Nishi, 1916) Tubangui & Africa, 1938
ETYMOLOGY:Hetero = different and phyopsis = late form (referring to the position of the testes being behind each other) along with continua = continuous referring to the expanded nature of the uterus.
SYNONYMS:Heterophyes continua Onji & Nishi, 1916; Heterophyesexpectans Africa & Garcia, 1935, Pseudoheterophyescontinuamajor in a new genus created by Yamaguti (1939).
HISTORY: This species was originally described from a naturally infected tern, Colymbus arcticus pacificus in Japan. It was also collected from a cat that was experimentally infected by the feeding of the infected tissue of a fish, Mugil cephalus.
GEOGRAPHIC DISTRIBUTION: Cats in Japan and Korea (Eom et al., 1985) and in the Philippines (Tubangui and Africa, 1938).
LOCATION IN HOST: Small intestine.
PARASITE IDENTIFICATION: Specimens of Heterophyopsis continua differ from species of Heterophyes in that the testis of Heterophyopsis spp. are tandem, i.e., one in front of the other, rather than being beside each other as in Heterophyes. The flukes collected from Korean cats measure 1.8 to 2.3 mm in length and 0.26 to 0.28 mm in width. The eggs are 25 x 15 µm.
LIFE CYCLE: The life cycle involves metacercariae encysted in the brackish-water fish, Mugil, Lateolabrax, Acanthogobius, and Clupanodon. Cats become infected by the ingestion of these fish where the metacercariae are encysted within the musculature.
CLINICAL PRESENTATION AND PATHOGENESIS: Signs in cats have not been reported. Signs have been reported with humans infected with these trematodes, but they were also hosts to other parasitic helminths which confuses the assignment of signs specifically to this parasite.
TREATMENT: Probably praziquantel. Praziquantel (15 mg/kg followed by the administration of a purgative 30 g of magnesium sulfate in order to collect the worms) has been used successfully in the treatment of humans infected with this trematode (Seo et al., 1984).
EPIZOOTIOLOGY: Cats become infected by eating raw fish. Other hosts that ingest infected raw fish are also likely to become infected, although it would appear that the rat is not a susceptible host.
HAZARD TO OTHER ANIMALS: Dogs and other animals have been infected; however, due to the requirements for two intermediate hosts, it is unlikely that an infected cat would pose a direct threat to other animals.
HAZARD TO HUMANS: Humans in Japan and along the southern coast of Korea have been infected with this parasite by the ingestion of metacercariae in brackish water fish (Seo et al., 1984).
CONTROL/PREVENTION: The prevention of the ingestion of raw fish.
Eom ES, Son SY, Lee JS, Rim HJ. 1985. Heterophyid trematodes (Heterophyopsiscontinua, Pygidiopsissumma, and Heterophyesheterophyesnocens) from domestic cats in Korea. Korean J Parasitol 23:197-202.
Tubangui MA, Africa CM. 1938. The systematic position of some trematodes reported from the Philippines. Philip J Sci:117-127.
Seo BY, Lee SH, Chai JY, Hong SJ. 1984. Studies on intestinal trematodes in Korea. XIII. Two cases of natural human infection by Heterophyopsiscontinua and the status of metacercarial infection in brackish water fishes. Korean J Parasitol 22:51-60.