The migration of juvenile forms of Fasciola hepatica L. through the wall of the intestines in the mouse, with some observations on food and feeding

Abstract

An attempt has been made to study the movements and feeding habits of juvenile forms of Fasciola hepatica as they pass through the wall of the host's intestines during the first 24 hr. of experimental infections in the mouse. Metacercarial cysts were fed to mice in large numbers (100–500) and the flukes were examined by means of sections during excystment and as free flukes and flukes making their way through various tissues. Excystment is regarded as essentially a feeding operation, the young fluke breaking through the fibrous inner cyst by the physical action of the ventral sucker in weakening the wall and the oral sucker in the actual breakthrough. Free forms were found in sections of infected intestines both in the lumen and lying between the villi, and penetrating forms were located inside the villi, in the submucosa and passing through the muscular layers and the serosa. A great deal of evidence was accumulated which indicates that the young fluke is able to break down epithelia, connective tissue and unstriped muscle fibrils and to feed upon the resultant products, thus proving itself to be a tissue feeder in the broadest sense of the term. The fluke's passage through the intestinal wall is by a devious route, tangential to the mucosa for some distance and then usually diagonally through the muscular layers, following the direction in which the circular muscle cells are oriented but cutting across the longitudinal muscle cells. This is probably due to the angle which the rim of the oral sucker makes with the longitudinal axis of the body, and it is a modification of the browsing habit which is seen when the feeding fluke lies on a plane surface. The tissue feeding proclivities of young flukes were also displayed in instances of penetration into lymph nodes and adipose tissue. These evidences support the opinion previously expressed by the writer that flukes migrating through the hepatic parenchyma, which are merely forms a little older and larger than the forms studied in the present researches, cannot be regarded as blood-feeders in the strict sense of the term but must also be regarded as tissue feeders. Attention is directed to the fact that very few digenetic trematodes have caecal outgrowths and that Fasciola and Fascioloides stand apart from all other genera in having dendritic outgrowths of the intestines. It is remarked also that the development of the ramifications of the intestines in Fasciola hepatica occurs during the first month, and largely during the second week, of juvenile life when the young flukes are eating their way through the hepatic parenchyma. During a few days the ramifications of the caeca develop to a greater extent than occurs during the entire lifespan of all other digenetic trematodes, with the exception of Fascioloides magna.