African swine fever: morphopathology of a viral haemorrhagic disease

Twelve miniature pigs were infected experimentally with the moderately-virulent Spanish isolate of African swine fever virus E75. The disease was reproduced acutely and subacutely, and six days after infection the animals showed severe clinical and pathological signs characterised by diffuse haemorrhages in lymphoid and non-lymphoid organs. An immunohistopathological study, using two different methods, and a monoclonal antibody (mAb) (18BG3) were used to analyse the distribution of the virus protein 73 (VP73) and IgM and IgG. VP73 was observed primarily in cells of the mononuclear phagocyte system, and in many megakaryocytes, some tubular epithelial cells of the kidneys, tonsillar epithelium, some hepatocytes, and in a few endothelial cells and neutrophils in the later stages of the infection. The histological findings and the distribution of VP73 and IgM and IgG indicated that the virus caused haemorrhagic lesions through its effect on various haemostatic mechanisms.