Chapter 150 - Pathogenesis of trematode infections (blood, liver and lung flukes)

Abstract

This chapter reviews the pathogenesis and pathology of human trematode infections caused by blood, lung, and liver flukes, but not intestinal, throat, and pancreatic flukes. The main target parasites include intestinal and hepatosplenic blood flukes (Schistosoma japonicum, S. mekongi, S. malayensis, S. mansoni, and S. intercalatum), urinary blood fluke (Schistosoma haematobium), lung flukes (Paragonimus westermani, P. heterotremus, P. skrjabini, P. skrjabini miyazakii, P. kellicoti, P. mexicanus, P. africanus, and P. uterobilateralis), small liver flukes (Clonorchis sinensis, Opisthorchis viverrini, O. felineus, Metorchis conjunctus, M. bilis, M. orientalis, Amphimerus spp., Dicrocoelium dendricitum, and D. hospes), and large liver flukes (Fasciola hepatica and F. gigantica). The pathogenicity of each parasite relates primarily to its route of migration and its predilection site in the host as well as host responses against the parasite. Mechanical irritation of host tissues and excretion/secretion of various proteases, antioxidants, toxic metabolites, and immunogenic substances by the parasites are the principal factors that underscore their pathogenicity and evasion from the host immunity. Potential neurotropic flukes with occasional cerebrospinal involvement are S. japonicum, S. mansoni, S. haematobium, P. westermani, P. skrjabini, P. skrjabini miyazakii, P. mexicanus, F. hepatica, and F. gigantica. Potential carcinogenic flukes with high clinicopathological significance are S. japonicum (hepatocellular and colorectal cancer), S. haematobium (bladder cancer), and C. sinensis, O. viverrini, and O. felineus (cholangiocarcinoma).