In Vivo Microscopy of Schistosomiasis

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Abstract
In vivo microscopy was used to examine the dynamics of Schistosoma mansoni schistosomule and egg migration in an attempt to clarify some of the controversial facets. Schistosomule migration in the organs was found to be restricted to the vascular system. The migration of the youngest schistosomules was a passive process, while the migration of schistosomules with pigment in their ceca was an active one. In the liver, schistosomules with blood in their ceca were only found in the intrahepatic branches of the portal system. In these vessels the worms fed facing the direction of blood flow. The consequences of their presence in these venules were an interference with blood flow not only in these vessels but also in the adjacent sinusoides, which caused dilatation and sacculation of the sinusoides with margination of leucocytes, deposition of blood pigment in Kupffer cells and, finally, stasis. This resulted in necrosis of the surrounding hepatocytes, whereupon leucocytes and macrophages invaded the site producing a midzonal necrosis. Eggs in the mural venules of the intestine were always found in venules with a diameter greater than 60 µm. When single eggs were present in venules with a diameter almost equal to the diameter of the egg, the vessel sacculated at this site. Such eggs transited through the wall without deformation of the egg and without hemorrhage. In contrast to single eggs, clusters of eggs compromised blood flow, resulting in necrosis of the wall and thereby liberating the eggs in the parenchyma for migration. In the parenchyma the eggs were first parallel to the lumen of the intestine, and were present throughout the various layers of the intestinal wall with the exception of the villi, in which they were never found.