The Laboratory Propagation of Spirometra mansonoides as an Experimental Tool. I. Collecting, Incubation and Hatching of the Eggs

Abstract

Although parasitic helminths in general are increasingly the subject of biochemical, physiologic, and immunologic investigation, comparatively few species are employed in such studies due to the difficulty of propagating the worms in the laboratory. The only tapeworms which have received extensive experimental attention are the small cyclophyllideans Hymenolepis nana, H. diminuta and, to a lesser extent, Taenia crassicollis, Echinococcus granulosus, and E. multilocularis. The plerocercoids of certain pseudophyllidean cestodes (Ligula, Schistocephalus, Dibothriocephalus latus, and Diphyllobothrium sp.) have been used for similar investigations, but require access to particular lakes where naturally infected fishes occur. Cyclical propagation of these forms under artificial conditions is difficult or impossible, because of the wild hosts involved. Since pseudophyllidean cestodes are more primitive than their cyclophyllidean relatives, have a more expanded life history, and show important differences of vitamin B12 content, it would appear that a pseudophyllidean which can easily be propagated in the laboratory should offer a fertile field for comparative studies. A variety of forms are included in the genus Spirometra. Some of these require wild hosts, and most of them are so intergrading and poorly characterized that species definition is an unsolved problem (Iwata, 1933). S. mansonoides (Mueller 1935) is unique in having constant, well-defined characters (Mueller, 1936), and thrives in hosts that are easily maintained under artificial conditions. In the spring of 1956, the author reactivated work on S. mansonoides with the primary purpose of attempting to culture the plerocercoid, and possibly other stages, in vitro. Since it required an abundant supply of all life history stages, practical methods had to be developed for the massive propagation of the worm. These methods have now been perfected and simplified to a point that could not have been anticipated. The Syracuse focus of natural infection in domestic cats with S. mansonoides, originally reported by Mueller (1935), still exists, as does also enzootic infection in local water snakes (Mueller, 1938). Since incidence of natural infection in cats is low (2 or 3 percent), spargana were collected from water snakes. A collection of 7 Natrix, from Big Bay Creek, at the western end of Oneida Lake, taken on May 25, 1956, yielded 2 small spargana lying under the skin of a single snake. These spargana were fed to 2 worm-free cats on May 29. Both cats showed ova in the feces 12 to 13 days later. These 2 cats were the source of our present experimental