Haplorchis yokogawai (Katsuta, 1932) Chen, 1936

(Figure 2-22)

ETYMOLOGY:Haplorchis = single testis and yokogawai = for Dr. Yokogawa

SYNONYMS:Monorchotrema yokogawai Katsuta, 1932; Monorchotrema taihokui Nishigori, 1924; Monorchotrema taihokui Africa and Garcia, 1935; Haplorchis vagabundi Baugh, 1963).

HISTORY: This fluke was originally described from specimens collected from dogs, cats, and human beings that were experimentally infected (Katsuta, 1932).

GEOGRAPHIC DISTRIBUTION: This trematode has a wide distribution throughout Asia and the Mediterranean. It has been reported from cats in Taiwan, China, Java, Egypt, and Hawaii, from avian hosts in India, and from the cat, a water rat (Hydromys chorogaster) and a whistling eagle (Haliastur sphenurus) in Australia (Pearson, 1964).

LOCATION IN HOST: Small intestine, within the first half.

PARASITE IDENTIFICATION:Haplorchis yokogawai differs from the other species of Haplorchis found in the cat in that the ventral sucker is covered with a small number of very small spines rather than with hooks as in Haplorchis pumilio or a few large spines as in Haplorchis taihokui.

The species Haplorchis yokogawi is a small fluke that is rather wide, 0.23 to 0.34 mm long by 0.2 to 0.28 mm wide. The eggs measure 29 to 30 µm by 13 to 17 µm.

LIFE CYCLE: The life cycle has elucidated by the feeding of infected brackish-water mullet to human beings (Katsuta, 1932). The metacercariae are encysted in the scales, gills, and fins of mullet, but not in the muscles. The snail host in Hawaii is Stenomelania newcombi where two generations of rediae develop in the digestive gland of the snail (Martin, 1958). The cercariae have a very long flagellum and lateral fins near the body. When experimentally infected fish were fed to cats, the adult worms were found to contain eggs within 10 days after infection (Martin, 1958)

CLINICAL PRESENTATION AND PATHOGENESIS: Not reported. The fact that the eggs are carried to ectopic locations in humans (see "Hazards to Humans”) would suggest that similar events could occur in other hosts including the cat.

TREATMENT: Probably praziquantel, but not reported.

EPIZOOTIOLOGY: Cats become infected by eating raw fish. Other hosts that ingest infected raw fish are also likely to become infected. The normal natural hosts are probably piscivorous birds.

HAZARD TO OTHER ANIMALS: None known; 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 have been infected, by the ingestion of the infected fish intermediate hosts. Eggs of Haplorchis yokogawai have been found in cardiac lesions of persons with cardiac failure and in the epicardiac layer of the heart (Africa et al., 1936).

CONTROL/PREVENTION: The prevention of the ingestion of raw fish.


Africa JE, de Leon W,. Garcia EY. 1937. Heterophyidiasis. VI. Two more case of heart failure associated with the presence of eggs in sclerosed veins. J Philip Is Med Assoc 17:605-609.

Katsuta I. 1931. Studies on trematodes whose second intermediate hosts are fishes from the brackish waters of Formosa. III. On a new trematode Monorchotremayokogawai of which the mullet is the second intermediate host. J med Assoc Formosa 31:25-26.

Martin WE. 1958. The life histories of some Hawaiian Heterophyid trematodes. J Parasitol 44:305-323.

Pearson JC. 1964. A revision of the subfamily Haplorchiinae Looss, 1899 (Trematoda: Heterophyidae). Parasitology 54:601-676.

Figure 2-22.Haplorchisyokogawai recovered from the intestine of a cat in Cairo, Egypt.