Cercaria and First Intermediate Host of Euryhelmis squamula

Abstract

The cercaria of Euryhelmis squamula is lophocercous and spinose. It develops in a redia in the operculate snail Bythinella hemphilli in Oregon. The metacercaria was found encysted subcutaneously in the frog Ascaphus truei. Laboratory-reared Rana aurora have been experimentally infected with cercariae. Metacercariae from wild infections of Ascaphus truei were fed to hamsters. Infections persisted in frogs for up to 44 days and for as long as 9.5 months in hamsters. The life cycle of Euryhelmis squamula (Rudolphi, 1819) Poche, 1926, has never been completely reported. This heterophyid trematode was described from the intestine of the European polecat, Mustela putorius L. It has also been reported from Mustela nivalis L., Lutreola lutreola Wagner, L. vison Schreber, and Vulpes vulpes L. in Europe (Baer, 1931). McIntosh (1936) found specimens of adults from the mink from Maryland and Minnesota in the U. S. National Museum, and also recovered adults from a cat which he experimentally infected from metacercariae found in Alexandria, Virginia. Parker (1950) found adults in a raccoon, Procyon lotor, at Durham, N. C., and in Oregon, Senger and Macy (1952) and Senger and Neiland (1955) found adults in the small intestine of the mink, Mustela vison Schreber. The metacercariae were first found (Zeller, 1867) encysted under the skin of the brown grass frog, Rana temporaria L., and were later reported also from R. esculenta L., and Triturus cristatus Laurenti, and toads (Baer, 1931). In the United States E. squamula metacercariae have been found in R. pipiens Schreber in Virginia (McIntosh, 1936), and in R. aurora Baird and Girard, and R. cascadae Received for publication 10 August 1964. * Supported in part by Research Grant AI-00867 from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Public Health Service. Published with the approval of the Oregon State University Monographs Committee. Research Paper No. 468, Department of Zoology, School of Science. Baird and Girard in Oregon (Senger and Macy, 1952). We have recovered metacercariae of E. squamula from under the skin of the tailed frog, Ascaphus truei Stejneger, collected in mountain streams in western Oregon. The first intermediate host of E. squamula in Oregon is a tiny, operculate snail, Bythinella hemphilli Pilsbry (family Hydrobiidae). Approximately 4,000 snails were collected and observed during the course of a year. Cercariae were recovered after emerging from the snails. The incidence of infection in 200 snails, which were examined by removing the shells, was 2%. From 6 to 14 rediae were found in each of the infected snails. The cercariae penetrate the skin of frogs exposed to them and encyst in the subcutaneous connective tissue. These cysts are most abundant on the hind legs, but are found on all parts of the body in heavily infected frogs. Thirty-eight of 43 Ascaphus examined (88.4%) harbored an average of 23.6 metacercarial cysts of Euryhelmis. Cercariae were placed in dishes with young laboratory-reared Rana aurora and the resulting metacercarial cysts were removed and examined. All measurements are given in microns unless otherwise indicated. Three cysts removed from R. aurora 44 days after infection measured 412 (363 to 461) in diameter (the mean is followed by the extremes). One of these metacercariae (Fig. 4) studied under slight cover slip pressure measured: body, 588 long by 599 wide; oral sucker, 51; pharynx, 26; and ventral sucker 44 in diameter. This specimen had well-developed gonads, seminal receptacle, and uterus.