Hepatic Fibrosis in Schistosomiasis

Schistosomiasis, a disease affecting over 200,000,000 human beings, Is caused by Infection with one of sev­ eral species of the Schistosoma trematodes. The In­ fectious form for mammals Is the cercaria developed by passage through snails. The major cause of death In those Infected results from distortion_ of the hepatic circulation caused by a unique kind of fibrosis In the liver. The fibrosis occurs In relation to the formation of nu�erous highly cellular and collagenous granu­ lomata as part of a cell-mediated immune response to eggs deposited by worms In the portal tract. After a period of tlme,·the granulomata disappear as new for­ mation of broad bands of collagen appear In the liver. Because of the nature of those bands the condition Is called pipestem fibrosis. The fibrosis distorts liver ar­ chitecture and with that the circulation of blood In the liver. Prevention of the disease by ecological controls directed largely against the snail vector, would seem to be most Important. Falling that, the disease Itself Is treated largely by use of a number of chemothera­ peutic agents directed against the Schistosoma. The present article reviews the modes of treatment now In use, and describes possible means of preventing or reversing the deposition of collagen that constitutes the fibrosis. Research on analogs of proline and lysine to Inhibit collagen biosynthesis or stimulate collagen degradation Is described. Possible new approaches for prevention of maturation and mating of worms lodged In ·portal tracts is considered as a means of preventing egg formation and the consequent host­ Immune response that causes fibrosis. Schistosomiasis, bilharziasis, is a worldwide problem of immense proportions affecting an estimated 200 million persons (Warren, 1980). It is a tropical disease concen­ trated among nations of northern and equatorial Africa, South America, Southeast Asia and Japan (Martinez-Baiz, 1953). However, a significant number of cases are ap­ pearing in temperate climates of industrialized nations as a result 9f immigration and foreign travel from endemic areas (Warren et al., 1974). Three species of Schistosoma cause significant human disease: S. japonicum, S. mansoni and S. hematobium. Among the many signs and symptoms associated with schistosomiasis, hepatosplenic manifestations are largely responsible for the morbidity and mortality of the disease. Approximately 100 million people suffer from liver disease as a complication of S. mansoni and S. japonicum infec­ tions. It is no wonder that schistosomiasis ranks as a major cause of liver disease worldwide.