Schistosoma mansoni Eggs

Abstract

An electron microscope study of the shell of living schistosome eggs was made in an effort to elucidate further the mechanism of their nutrition and excretion. Stenger et al. (1) studied the fine structure of murine he-patosplenic Schistosomiasis mansoni and also studied the fine structure of the schistosome egg. These authors described a fenestrated shell and also observed microspicules. Extracellular degradation of these shells in host tissues was observed. They also credit J. H. Smith and F. Von Lichtenberg for observing the fenestra and microspicules independently. The published photographs by Stenger et al. show their fenestrations to be irregular in size, of random distribution, and to be unlined by a plasma or unit membrane. They suggested that these fenestrations might facilitate diffusion of antigenic material from S. mansoni eggs, since Andrade et al. (2) and Lichtenberg (3) demonstrated schistosomal antigens in granuloma tissue.

In our study, living eggs grown in vitro by the method of Lee and Michaels (4) were isolated, fixed in collidine buffered paraformaldehyde, and embedded in epon according to the method of Lynn et al. (5). Thin sections were made on an ultramicrotome, stained with lead citrate (Reynolds, 6) and uranyl acetate (Watson, 7), and viewed with an RCA EMU 3. A shell with microbarbs was observed (Fig. 1). The shell also had discrete pores that traversed the shell in a direct manner. These pores were located principally in the anterior portion of the eggs. No pores could be demonstrated in the spurs, suggesting that the function of the spur is essentially mechanical. Each pore was lined by a trilaminar unit membrane, in contradistinction to the unlined, randomly oriented, fenestrated spaces described in the presumed degenerating eggs of other studies.