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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.

In March 1978 an outbreak of African swine fever (ASF) occurred in Malta. The disease spread rapidly and by April 13, ASF had been found on 304 premises involving 25,100 pigs. A census carried out on April 15/16 showed that there were at least 1440 premises containing 70,700 pigs on the island. A slaughter policy was implemented and depopulation of known infected premises started on April 15. Pigs which appeared normal on these premises were stored in freezers for subsequent processing for human consumption and by the end of June more than 4500 carcases were in cold store. The most consistent clinical signs were fever, anorexia and reluctance to move. Haemorrhagic lymph nodes and petechial haemorrhages in the kidneys were the predominant macroscopic lesions. A serum survey, using the immunoelectroosmophoresis technique, was carried out on 2409 sera from 200 farms collected at the Government abattoir during a four-week period. Of these sera, 308 (12.8 per cent) from 65 (32.5 per cent) of the farms contained antibodies to ASF virus. By August the original pig population had been reduced to one-third and a second census taken on August 15/16 showed that a total of 501 owners and 13,975 pigs remained. The decision was taken to slaughter all the remaining pigs and by the end of January 1979 there were no pigs in Malta. The outbreak cost an estimated 5 million pounds and provided the first occasion when any country had slaughtered all members of a species of domestic animal in order to eliminate a disease.