The migration of Cercaria X Baylis (Strigeida) within the fish intermediate host

Publisher Website
Google Scholar
Abstract
1. Studies, using serial sections and a method of numerical assessment of the, numbers of cercariae in the various tissues, have shown that cercarial entry occurs through the skin at any point along the length of the fish and also through the gills and pharynx in the head region. The distribution of penetration along the length of the body is not uniform but exhibits a marked concentration in the head region.2. As the time after infection increases, this initial unimodal distribution is maintained and becomes even more restricted.3. Nearly all the cercariae have localized in the eye 12–24 hr. after infection. The few that remain outside the eye after this period appear to be moribund and undergoing phagocytosis.4. The majority of migrating cercariae are present in connective tissue and muscle. Very few occur in the blood system and even fewer in the other organs of the body. The numbers in the blood system show a local anterior concentration in the blood vessels anterior to the heart and in the region of the gills. It seems probable that the blood system does not form the major route of migration.5. Entry into the eye may occur at any point.6. Cercarial migration causes extensive tissue damage, but this is fatal only when major blood vessels are perforated and severe internal haemorrhage results. Interference with the nervous system and lateral line system may be the cause of the orientation disturbances which are sometimes noted within 12 hr. after infection.7. It is suggested that migration through the tissues is achieved mainly by the action of the anterior spination and that the function of the penetration gland cells may be lubricatory and/or adhesive rather than lytic.8. The restricted tissue distribution during migration and the retention of an essentially unimodal distribution of cercariae along the length of the body through-out the whole period of migration suggest that localization in the lens is not achieved by chance migration.