Heterophyes heterophyes (von Siebold, 1852) Stiles and Hassal, 1900
(Figure 2-25)
ETYMOLOGY:Hetero = different and phyes = form (named early in the study of trematodes to distinguish it from another fluke Paragonimus by Cobbold in 1866).
SYNONYMS:Heterophyes aegyptiaca Cobbold, 1866; Mesogonimus heterophyes Railliet, 1890; Coenogonimus heterophyes Looss, 1900; and Cotylogonimus heterophyes Lühe, 1900. In the orient, Heterophyes nocens Onji and Nishio, 1915 was described, but it is now considered a subspecies of Heterophyes heterophyes.
HISTORY: This species was originally collected in 1851 by Bilharz from a human being in Egypt; the fluke was named Distoma heterophyes by von Siebold. The first report in cats is that of Looss (1902).
GEOGRAPHIC DISTRIBUTION: This trematode has been reported from Egypt, Israel, Kuwait, Greece, Turkey, and Spain (probably throughout the Mediterranean); as the subspecies Heterophyes heterophyes nocens, it has been reported from cats in Japan (Miyazaki, 1991). It has also been reported on rare occasions from west Africa and India (Malek, 1980).
LOCATION IN HOST: Middle and upper portion, jejunum and duodenum of the small intestine (Tarachewski, 1987).
PARASITE IDENTIFICATION: Specimens of the genus Heterophyes have a large genital sucker. The adult trematodes are found embedded in the villi, and measure about 1 mm by 0.5 mm. The spines on the genital sucker of Heterophyes heterophyes number 50 to 80 and are digitate, looking like small leafless trees. The eggs are yellow brown in color, contain a miracidium, and have an average size of 27 µm by 16 µm.
LIFE CYCLE: The life cycle in Egypt involves the snail Pironella conica and the brackish-water fish host Mugil cephalus. In Asia, the life cycle involves snails, Certhideopsilla cingulata, that live in the mouths of rivers and various brackish-water fish hosts, including Mugil cephalus, Liza haematocheila, Acanthogobius flavimanus, Glossogobiusgiuris, and Tridentiger obscurus. The metacercariae are found within the muscle of the fish hosts.
CLINICAL PRESENTATION AND PATHOGENESIS: An examination of the histopathology of the intestine of infected cats revealed that the parasites were closely associated with the villi (Hamdy and Nicola, 1980). At the sites of infection, the villi were swollen, the columnar epithelium was destroyed, and there was swelling of the underlying submucosa. There was a local cellular reaction and the Peyer's patches were hyperplastic. Immature flukes were found in lymphoid follicles and in Peyer's patches. Mature flukes were also found within mesenteric lymph nodes. However, no clinical signs were described.
TREATMENT: Probably praziquantel, but not reported.
EPIZOOTIOLOGY: Cats become infected by eating raw fish as do other piscivorous animals.
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: Numerous humans have been infected with this parasite. In 1933, Khalil found 53 of 60 school children infected in an area close to the Suez Canal; in 1983, it was found in 14 of 65 cats in Egypt (Abo-Shady et al., 1983). Infection rates in Japan have also reached levels as high as 30%; however, more recently, infection levels in humans in Japan are less than 1%.
CONTROL/PREVENTION: The prevention of the ingestion of raw fish.
REFERENCES:
Abo-Shady AF, Ali MM, Abdel-Magied S. 1983. Helminth parasites of cats in Dakahlia, egypt. J Egypt Soc PArasitol 13:129-133,
Hamdy EI, Nicola E. 1980. On the histopathology of the small intestine in animals experimentally infected with H. heterophyes. J Egypt Med Assoc 63:179-184.
Looss A. 1902. Notizen zur Helminthologie egyptens. V. Eine Revision der Fasciolidengattung Heterophyes Cobb. Centralblatt bakt. Orig. I. 32:886-891.
Malek E.A. 1980. Snail-Transmitted Parasitic Diseases. Volumes I and II. 334 & 324 pages. CRC Press, Boca Raton, FL. USA.
Miyazaki I. 1991. Helminthic Zoonoses. 494 pages. International Medical Foundation of Japan. Fukuoka, Japan.
Tarachewski H. 1987. Experiments on habitat selection of Heterophyes species in different definitive hosts. J Helminthol 61:33-42.
Figure 2-25. Heterophyesheterophyes recovered from the from the intestine of a cat in Egypt. In this figure, it is difficult to appreciate the genital sucker except as a darkened area to the right and slightly posteriad to the ventral sucker.