Cotylurus lutzi sp. n. (Trematoda: Strigeidae) and Its Life Cycle

Abstract

Snails Biomphalaria glabrata (Say), collected in Bahia, Brazil released furcocercariae that developed into tetracotyles in uninfected snails of the same species or as hyperparasites in rediae or sporocysts of other trematodes. Tetracotyles fed to canaries or finches become adults that usually survive 3 to 4 weeks, and are distinguished principally by numerous vitelline follicles in the holdfast lobes, size of pharynx, and size of eggs. Eggs appear in bird feces 1 week after feeding of tetracotyles, and usually hatch in 3 to 4 weeks at 28 C. In laboratory-infected albino B. glabrata, mother sporocysts may attain 28 mm in length and survive for more than 6 months. Daughter sporocysts are filiform and motile. Cercariae are released from 25 days postinfection. All stages, particularly the tetracotyle, are described in detail. This paper is one of a series describing the life cycles and biology of trematodes whose larval stages are passed in snails of the genus Biomphalaria that transmit schistosomiasis in the New World. The sporocyst stage of the strigeid described here produces furcocercariae that can easily be confused with those of Schistosoma mansoni Sambon. Several hundred Biomphalaria glabrata (Say), collected in the vicinity of Caetite, Bahia State, Brazil, by Dr. W. Lobato Paraense and co-workers in April 1967, were sent by air to our laboratory in California. All snails in the shipment harbored tetracotyle metacercariae, and two were shedding furcocercariae of the Cotylurus type. These two naturally infected snails provided the starting point for the cycle described here. MATERIALS AND METHODS The hyperparasitic habit of the metacercarial (or tetracotyle) stage was utilized for routine maintenance of the Cotylurus life cycle. Biomphalaria glabrata with advanced infections of the echinostome Paryphostomum segregatum Dietz were placed in aquaria with snails shedding cercariae of the Cotylurus type. After exposure, usually for about 24 hr, the Paryphostomum-infected snails were separated and maintained 3 weeks or more to ensure complete development of the tetracotyle Received for publication 25 October 1968. * This work was supported by Research Grant AI07054 from the NIAID, and by the University of California International Center for Medical Research and Training (UC ICMRT, Hooper Foundation, University of California San Francisco Medical Center) with Research Grant TW 00144 from the Office of International Research, both from the NIH, U. S. Public Health Service. larvae within the echinostome rediae. Hyperparasitized snails were crushed and rediae containing tetracotyles were fed to avian hosts to obtain adult worms. Other kinds of larval trematodes developing within Biomphalaria also serve equally well for incubation of tetracotyle stages. Sporocysts of S. mansoni have been used, and yield viable tetracotyles that develop into adult worms, but the handling of snails shedding S. mansoni entails unnecessary risks. Various other echinostomes being maintained in our laboratory, such as Echinostoma paraensei Lie and Basch, E. lindoense Sandground and Bonne, and E. barbosai Lie and Basch, have also been used, but cercariae of these species will encyst within the pericardial sacs of other B. glabrata, including those infected with Cotylurus sporocysts. Hence, the snails shedding Cotylurus cercariae, if exposed to echinostome cercariae over long periods, will accumulate many echinostome metacercariae in their pericardial sacs and may be adversely affected. Cercariae of P. segregatum, on the other hand, encyst only in fish and tadpoles. Snails shedding Cotylurus cercariae may be used repeatedly for several months to produce many thousands of tetracotyles within rediae of Paryphostomum without apparent ill effects to themselves. Avian hosts used in this study included young domestic ducks, pigeons, and chicks, and several types of smaller cage birds: canaries and finchesTaeniopygia castanotus (Gould), Estrilda troglodytes (Lichtenstein), and Uroloncha striata (Brisson). Four ducklings and 2 pigeons remained uninfected after ingesting large numbers of tetracotyles. Chicks became infected only when 500 or more tetracotyles were fed, but were generally not good hosts. The smaller cage birds, particularly the finches, proved to be excellent hosts highly suitable for use in the laboratory, producing many eggs of Cotylurus. The small birds were maintained in rectangular glass aquaria 14 by 24 by 17 cm high, each aquarium provided with a perch, seed cup, and cover of plastic insect screening held in place by a stout rubber band. About 1 cm of water was maintained in the aquaria at all times.