Life History of Heterobilharzia americana Price 1929, a Schistosome of the Raccoon and Other Mammals in Southeastern United States

Abstract

The life cycle of Heterobilharzia americana, a bloodfluke of the raccoon, nutria, dog, and rabbit in southern Louisiana, was completed in the laboratory. The cercariae were found in naturally infected Lymnaea cubensis at Pass a Loutre in the Mississippi River delta. Although infected Pseudosuccinea columella was not found in nature, in laboratory experiments it was as susceptible as L. cubensis. Cercariae were liberated from the infected snails about 4 weeks after exposure. The eggs, oval with a smooth shell, contain miracidia which resemble those of other known species of mammalian schistosomes, except that the number of ciliated epidermal plates is 22 instead of 21. The furcocercous, apharyngeate cercaria has six pairs of flame cells and five pairs of penetration glands; it has eyespots and furcal fin-folds. It swims towards the light close to the water surface. In mice the migrating schistosomula caused pulmonary hemorrhages of two sizes, the earlier ones being the larger. The developing worms became sexually mature in the liver on the 40th day, but eggs containing mature miracidia were not observed until the 68th day following infection. Two species of schistosomes, Schistosomatium douthitti (Cort 1914) and Heterobilharzia americana Price 1929, are known to occur in mammals in the United States. The life cycle stages of S. douthitti have been studied by H. Price (1931) and others (Kagan et al., 1954). The original description of H. americana was based on two male specimens from a bobcat (Lynx rufus floridanus) taken in Florida. Later, Price (1943) described the female and redescribed the male from specimens found in a raccoon (Procyon lotor) in Texas. More recently this species was reported in raccoons in North Carolina (Miller and Harkema, 1960) and Florida (W. H. Leigh, pers. comm., 1960). In the coastal swamplands of Louisiana and the mud flats of the Mississippi River delta, it has been found in the raccoon, nutria (Myocastor coypus), and dog (Malek et al., 1961). Brief notes on the life cycle were published by Lee Received for publication 9 July 1962. *A portion from a thesis submitted to the Graduate School of Tulane University in partial fulfillment of the requirements for the degree of Doctor of Philosophy. The study was supported in part by research grants 2E-2 and E-2898 from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Public Health Service. t Present address: Department of Parasitology, Faculty of Medicine, University of Singapore, Singapore. in 1960 and by Greene in 1962. In the present repor the stages in the life cycle are described more fully. MATERIALS AND METHODS Eggs were obtained by gravity sedimentation in 0.85% saline from feces of infected raccoons captured locally and maintained in the laboratory. The miracidia were hatched and concentrated from washed feces in Erlenmeyer flasks filled to the brim with aged tap water, the miracidia being pipetted from the water surface. The side-armflask method described by McMullen and Beaver (1945) for concentrating miracidia of bird schistosomes was found unsuitable for H. americana. Lymnaea cubensis (Pfeiffer) and Pseudosuccinea columella (Say), collected in the vicinity of New Orleans, were used as laboratory intermediate hosts. As the former species adapted poorly to laboratory conditions, snails from field collections, negative on repeated checking for cercariae, were used for experimental infections. P. columella used in the experiments were laboratory bred and maintained in aerated aquaria. L. cubensis was maintained in aquaterraria. Both species were fed fresh lettuce. Some snails were exposed en masse by placing them together with many miracidia in a stender dish 50 mm in diameter. Others were exposed to five miracidia each in a shell vial, 45 mm high and 15 mm in diameter, containing a small quantity of water. To prevent the snails' escape from the water, a piece of nylon net, about 4 cm square, was pushed down to the level of the water surface. The snails were examined for cercariae daily beginning at 20 days after exposure and continuing for at least 3 weeks. Swiss white mice were infected by placing them