Experimental Infection of the Planorbid Snail Menetus dilatatus buchanensis (Lea) with Spirorchis sp. (Trematoda)

Abstract

Twenty per cent of nearly 500 laboratory-reared Menetus dilatatus buchanensis (Lea) exposed individually to mature eggs or miracidia of Spirorchis sp. from painted turtles became infected. Infected snails when grouped in finger-bowl cultures lived longer, had shorter prepatent periods (15 to 20 days), and had greater cercarial output per snail than did individuals kept separately in small cultures. Snails lived an average of 82 days after infection and shed as many as 1,500 cercariae per snail. Maximum survival, with persistent infection, was 201 days. Nocturnal cercarial shedding was reversed by a 12-hr alteration of day-night with artificial light. Goodchild and Kirk (1960) described the life cycle of Spirorchis elegans Stunkard, 1923 from painted turtles, Chrysemys picta picta (Schneider), captured at the Decatur reservoir, DeKalb County, Georgia. Eggs obtained from these turtles were used to establish infections in laboratory-raised Helisoma anceps Menke and Menetus dilatatus buchanensis (Lea). Cercariae identical to those emitted from the laboratory-infected snails were later found in Menetus collected at the reservoir. Attempts to reactivate spirorchiid studies were delayed in the summer of 1961 because Menetus from the reservoir were negative for spirorchiid cercariae and no Chrysemys picta picta could be collected. In the event that a spirorchiid egg source became available, a breeding population of M. d. buchanensis was established in the laboratory (Fried and Goodchild, 1963). In the fall of 1961 wild painted turtles, Chrysemys picta bellei Gray, obtained from a commercial dealer in Minnesota (J. R. Schettle Frog Farm, Inc., Route 1, Stillwater) revealed Spirorchis scripta Stunkard, 1923 in the head and heart washings and Spirorchis elegans in the esophageal wall. Schroeder and Ulmer (1959) reported these two species, and in addition Spirorchis artericola (Ward, 1921) and Received for publication 12 March 1963. * This investigation was supported (in part) by a training grant (2-TI-AI-37) from the Institute of Allergy and Infectious Diseases, National Institutes of Health. U. S. Public Health Service. Spirorchis pseudemyae Byrd, 1939 from Chrysemys picta bellei captured in Iowa. They stated that all specimens positively identified as S. elegans were taken from the sub-mucosa of the esophagus. Turtles from Minnesota yielded single or mixed infections of adults identified as S. elegans or S. scripta. Other turtles revealed no adult worms, but had eggs in the tissues. Eggs from all these types of turtles were used as a source of miracidia to challenge laboratoryraised Menetus. All cercariae subsequently emitted from these snails appeared identical, but differed from the cercaria of S. elegans described by Goodchild and Kirk (1960). Because all cercariae derived from infected Minnesota turtles were morphologically alike, the possibility exists that S. elegans and S. scripta are identical in C. p. bellei from Minnesota and Iowa. Laboratory studies using parasite-free Chrysemys picta hatchlings are in progress. Preliminary findings indicate that members of a species in the genus Spirorchis show intraspecific variation depending upon their age and location in the host, and that the number of valid species may be reduced. Since an ample and dependable source of cercariae was prerequisite for infection studies, reliable and convenient methods for obtaining spirorchiid eggs and miracidia and for exposing laboratory-reared Menetus were needed. Moreover, cercariae from these infections should be obtainable at convenient times to expose tur-