RESUMO
African swine fever (ASF) virus strains cause haemorrhage by producing a variety of defects, which vary in severity from strain to strain. To distinguish the main haemostatic defects leading to haemorrhage, two groups of pigs were infected with moderately virulent (Dominican Republic '78) and less virulent (Malta '78) ASF virus strains. Mortality rate and severity of clinical observations were greater in pigs infected with DR '78 virus compared with pigs infected with Malta '78 virus. The animals became febrile from day 3 to 4 onwards at a time when the viraemia was high (10(7) to 10(8) HAD50/ml). No difference was found during the period observed in their pattern of viraemia or pyrexia. Thrombocytopenia developed in both groups but with different kinetics, suggesting two different mechanisms of sequestration of platelets. When coagulation tests were performed, significant abnormalities were found, including evidence for disseminated intravascular coagulation. These abnormalities were much less pronounced in the group infected with Malta '78. Antithrombin III activity did not change significantly in either group. Decreased plasminogen activity was found in the early phase of disease in DR '78 infected pigs. These results indicate that when haemorrhage does occur in DR '78 infected pigs, it is a consequence of more pronounced degrees of haemostatic impairment probably due to a marked endothelial injury and/or generation of procoagulant activity.