Apophallus venustus (Ransom, 1921) Cameron, 1936
(Figure 2-15)
ETYMOLOGY:Apo (away from) + phallus (phallus) [the genital opening is anterior to the ventral sucker] and venustus (=handsome, comely in appearance)
SYNONYMS:Cotylophallus venustus Ransom, 1920; Tocotrema donicum (Skrjabin and Lindtrop, 1919) Witenberg, 1929; Apophallus donicus (Skrjabin and Lindtrop, 1919) Price, 1931; Rossicotrema venustus (Ransom, 1921) Ciurea, 1933.
HISTORY: Cameron (1936) considered Apophallus venustus a species distinct from its European counterpart Apophallus donicus. The morphological distinctions that he noted were anterior extent of the vitellaria (to the esophageal bifurcation in Apophallus venustus, to the ventral sucker in Apophallus donicus), Apophallusvenustus being slightly longer and having eggs that are slightly larger.
GEOGRAPHIC DISTRIBUTION: North America, mainly eastern North America. The Alaskan fox from which it was originally described was from the National Park Zoo in Washington DC. The original description also included specimens collected from a cat in the Washington D.C. area (Ransom, 1920.
LOCATION IN HOST: Small intestine.
PARASITE IDENTIFICATION: This worm is small, less than 1.44 mm in length, but typically slightly larger than Apophallus donicus. The ventral sucker is small, the large, globular testes are located obliquely in the posterior of the body, and the vitellaria extend anterior to the ventral sucker, often to the level of the esophageal bifurcation.
The eggs are 26 to 32 µm long by 18 to 22 µm in width.
LIFE CYCLE: The life cycle was examined by Cameron (1937). The snail, Goniobasis livescens, becomes infected by ingesting the embryonated egg from which the miracidium then hatches. From the stages in the snail, cercariae are produced that have long, unbranched tails, with flanges, and pigmented eyespots. These cercariae penetrate the skin of fish, and then produce metacercariae in the musculature. Cats become infected by ingesting the infected fresh-water fish, e.g., catfish and sunfish. The prepatent period appears to be one to three weeks, and the adult flukes appear to live only a few months.
CLINICAL PRESENTATION AND PATHOGENESIS: Thought to be asymptomatic even though the parasite becomes embedded in the mucosa of the ilium.
TREATMENT: Probably praziquantel, but not reported.
EPIZOOTIOLOGY: Cats become infected by eating raw fish. Animals other than the cat that have been shown to serve as hosts of the adult fluke include the dog, raccoon (Procyon lotor), Alaskan fox (Vulpes lagopus), harbor seal (Phoca vitulin), and the great blue heron (Ardea herodias).
HAZARD TO OTHER ANIMALS: None. Although other hosts are infected, the major means of infection is through the ingestion of the fish intermediate host which requires that the appropriate snail also be available. Thus, infection of these other hosts will typically only occur in the wild.
HAZARD TO HUMANS: None. Humans theoretically could become infected if they ingested an infected piscine host.
CONTROL/PREVENTION: Prevention of the ingestion of raw fish.
REFERENCES:
Cameron TWM. 1936. Studies on the heterophyid trematode, Apophallusvenustus (Ransom, 1920) in Canada. Part I. Morphology and taxonomy. Can J Res 14:59-69.
Cameron TWM. 1937. Studies on the heterophyid trematode Apophallusvenustus (Ransom, 1920) in Canada. Part II. Life history and bionomics. Can J Res 15:38-51.
Ransom BH. 1920. Synopsis of the trematode family Heterophyidae with descriptions of a new genus and five new species. Proc U.S. Nat Mus 57:527-573.