Pleuropneumonia in swine associated with urease-negative variant of Actinobacillus pleuropneumoniae serotype 1

A pig farm of 6000 weaning to market age pigs had a mortality rate of 2.8% in October 1989 and 1.9% in April 1990. Four pigs were examined PM. All pigs had pulmonary haemorrahage with patchy necrosis and fibrinous pleuritis which was seen, on histological examiantion, as severe haemorrhagic and necrotizing pleuropneumonia with extensive fibrin exudate into alveoli and interlobular septa. Gray stickly colonies of gram-negative pleomorphic rods were isolated from 1 or 2 sites on each pig. These were identified as urease negative variants of Actinobacillus pleuropneumoniae serotype 1