Experimental aerosol transmission of Actinobacillus pleuropneumoniae to pigs

In order to demonstrate the possible role of aerosol in the transmission of Actinobacillus pleuropneumoniae, an experiment including 18 specific patho gen-free (SPF), 10-week-old piglets, randomly distributed into 2 adjacent u nits, was carried out. In these facilities, air was forced through absolute filters to prevent any contact with infectious agents. During the first 6 d post inoculation, the 2 units were connected by a rectangular opening and the air circulation was forced by the ventilation system from unit A (inoc ulated pigs) to unit B (non-inoculated pigs). The A. pleuropneumoniae strai n (biovar 1 serovar 9) was isolated in France from an outbreak of porcine p leuropneumonia. Two different infecting doses, 10(7) cfu/animal and 10(8) c fu/animal, were inoculated by intranasal route in 6 pigs of unit A. The inf ection spread quickly from the inoculated pigs to the noninoculated pigs. C linical signs were acute during the 4 d post inoculation: hyperthermia, res piratory distress and, sometimes, death (6 pigs of the unit A and 2 pigs of the unit B). All pigs seroconverted against A. pleuropneumonine serovar 9 within 2 weeks. Lung lesions were severe: fibrinous pleurisy and lung hemor rhages in the acute stage, pleural adherences and focal pulmonary necrosis in the chronic stage. Actinobacillus pleuropneumoniae was isolated from the tonsils and/or lungs in 16 animals. It could be also isolated from the air of the experimental unit. This study showed that A. pleuropneumoniae was r eadily transmitted through aerosol over a distance of at least 2.5 m.