Abstract

Schistosomiasis japonica, caused by the trematode Schistosoma japonicum, is a zoonotic disease with significant impact on public health in endemic regions in China, the Philippines and Indonesia. The pig is important in transmission of the infection, and is also used as an experimental animal in schistosomiasis research. The main objective of this thesis was to explore the pig as an animal model for pathological and pathogenetic aspects of human schistosomiasis japonica. Gross and histopathological changes in pigs after experimental infections of different intensity and duration were evaluated and related to parasitological variables. The hepatic egg granuloma was investigated with immunohistochemical methods. Naturally acquired infections in pigs were examined and compared to experimental infections. Lesions were essentially confined to the large intestine and liver. In the experimentally infected pigs, liver lesions were proportional in degree to the intensity of infection. Gross lesions in the intestine included multifocal areas of hyperaemia and haemorrhages, resembling those of acute human schistosomiasis japonica. Gross liver lesions were white nodules and fibrosis. Microscopically, several characteristic features of schistosomal hepatic fibrosis, including granulomatous obstruction of portal venules and periportal fibrosis, were present. Hepatic fibrosis was marked in early patency in the experimentally infected pigs with high intensity infections, and then regressed spontaneously. The degree of hepatic fibrosis was correlated with liver egg and granuloma density in both acute and chronic stages of infection, and liver egg density was correlated with faecal egg excretion in the acute stage. Faecal egg excretion could thus be used as an indicator of hepatic pathology in acute infections. The egg granuloma showed expression of MHC class II antigen and involved CD4+ T cells, as well as CD8+ T cells, B cells and IgG. Signs of a modulated granuloma formation were apparent in the liver, but not in the intestine of the naturally infected pigs, and other organ-related differences in granuloma composition were also found. Self cure was observed in the experimentally infected pigs with high intensity infections, but not in the naturally infected pigs. Natural infection, in contrast to experimental infection, was associated with clinical disease and reduced weight gain in young pigs. The results indicate that the pig would be a useful animal model for studies of acute intestinal disease, early hepatic fibrogenesis, spontaneous resolution of hepatic fibrosis, and granuloma development and regulation. In addition, the pig could be used for examining the effect of a schistosome infection on the nutritional status of the host.

Keywords

Schistosoma japonicum; pig; pathology; granuloma; MHC class II; CD4; modulation; hepatic fibrosis; self cure; weight gain

Published in

Acta Universitatis Agriculturae Sueciae. Veterinaria
2000, number: 87
ISBN: 91-576-5944-3
Publisher: Swedish University of Agricultural Sciences

Authors' information