Schistosoma manonsi: cercarial penetration of host epidermis at the ultrastructural level

Invasion of the outer layers of the epidermis of mouse ear skin by cercariae of Schistosoma mansoni within 7 min of their application to it has been studied with the optical and the scanning and transmission electron microscopes.Entrance of cercariae was under the edges of the dead flattened keratinized cells of the horny layer (squames), and penetration through this layer was by disarticulation of the stacks of squames at their interdigitations. Mucus from the postacetabular glands was recognized with the light and electron microscopes on the skin surface, especially at squame edges and between layers of squames and along the keratogenous zone. The findings suggested that disarticulation of the squames was not effected solely by the muscular probing and pushing of the parasite, but that it might be aided by swelling of the mucus secretion deposited in the area from the postacetabular glands. Loosening of the interlocked edges of the squames by enzymatic action is also a possibility, but was not evaluated for this report.The migration path along the keratongenous zone was marked by extensive damage to the transitional cells of the granular layer subjacent to the squames. Packets of secretion from the cercarial preacetabular glands were identified below the horny layer in the cytoplasm of these cells. It was considered that the host tissue damage in this area was the result not only of tearing of the tissues by passage of the spiny schistosomules, but also of enzymatic activity, the enzyme source being the granules in the packets of preacetabular gland secretion.