THE ROLE OF FIBRINOLYSIS IN THE PATHOGENESIS OF THE HEMORRHAGIC SYNDROME PRODUCED BY VIRULENT ISOLATES OF AFRICAN SWINE FEVER VIRUS

The activity of several proteins involved in fibrinolysis and the morp hological changes in the blood vessel walls of pigs infected with high ly virulent (Malawi'83) and moderately virulent (Dominican Republic '7 8-DR'78) ASF virus isolates were determined. Pigs infected with the Ma lawi'83 virus developed an increased fibrinolytic activity due to high plasma levels of tissue-plasminogen activator (t-PA) of 71.3 +/- 22.8 IU/ml (mean +/- SD), which correlated well with an increased activati on of interstitial capillary endothelial cells and high levels of 1150 +/- 73.6 nM of fibrin monomer in the circulation. Animals infected wi th DR'78 virus, in contrast, showed an inhibition of fibrinolysis in t he late stages of disease with almost a 5-fold increase of plasminogen activator inhibitor (PAI) activity of 196.0 AU/ml. These results sugg est that activation of the fibrinolytic system in pigs infected with t he Malawi'83 virus is probably due to increased formation and depositi on of fibrin in the circulation, contributing to an increased bleeding tendency and higher mortality. On the contrary, animals infected with DR'78 virus developed an inhibition of fibrinolysis and thus a reduct ion in bleeding.