Summary
The activity of several proteins involved in fibrinolysis and the morphological changes
in the blood vessel walls of pigs infected with highly virulent (Malawi’83) and moderately
virulent (Dominican Republic ‘78-DR’78) ASF virus isolates were determined. Pigs infected
with the Malawi’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 activation of interstitial capillary
endothelial cells and high levels of 1150 ± 73.6 nM of fibrin monomer in the circulation.
Animals infected with DR’78 virus, in contrast, showed an inhibition of fibrinolysis
in the late stages of disease with almost a 5-fold increase of plasminogen activator
inhibitor (PAI) activity of 196.0 AU/ml. These results suggest that activation of
the fibrinolytic system in pigs infected with the Malawi’83 virus is probably due
to increased formation and deposition 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 reduction in bleeding.
