The routes of migration and dispersion of Schistosoma Mansoni and Schistosoma Haematobium Schistosomula in the mouse

The routes of migration and dispersion of Schistosoma mansoni and Schistosoma haematobium schistosomula in the mouse were investigated. Factors such as larval growth, the host's response to the larvae and the changing dimensions of the larvae, which may affect dispersion, were also studied. Host exposure was percutaneous, in order to reproduce the natural mode of infection. The distribution of parasites was traced throughout the first 16 days after infection, between the point of vascular entry in the skin and the site of maturation, the liver. The results of the investigation were obtained by histological, histochemical and autoradiographic techniques. It was shown that after penetration of the skin the schistosomula take pathways in a random fashion. Larval use of the blood vascular route was demonstrated by the presence of schistosomula in the vessels of various organs and tissues. Passive transportation within the systemic circulation to all regions seems likely, including multiple circulation in the absence of larval growth. The patterns of lymphatic drainage were determined in order to be able to ascertain whether the lymphatic system facilitates schistosomular migration. Schistosomula were seen to utilize lymphatic pathways; lymph nodes did not act as barriers. Infection via the tail or hind limb resulted in schistosomula being found in the lung as early as days 2 or 3, which indicates that the route was entirely through the blood vascular system. On subsequent days the lung contained a mixed larval population comprising those which arrived solely by the venous system and those which entered the venous system through the thoracic and right lymphatic ducts. Extravascular routes may be possible when larvae abnormally retain the enzymatic mechanism used for penetration and which is usually lost during the initial phase of migration through the skin. However, few larvae adopt an extravascular route and it is doubtful whether any are able to reach the liver in this way. The author discusses her findings in detail and compares them with those of other workers. Further problems arising from the present work are outlined and discussed.