Comparison of virulence of different Actinobacillus pleuropneumoniae serotypes and biotypes using an aerosol infection model.

An aerosol infection model for inoculation of pigs with Actinobacillus pleuropneumoniae is described. With this model the virulence of three A. pleuropneumoniae biotype 1 strains representing serotypes 2, 5b and 6, and one Danish biotype 2 were compared using 13-week-old pigs for inoculation. The pigs were sacrificed 24 h after aerosol exposure and lung lesions were evaluated. In pigs exposed to aerosols of suspensions containing 10(4) CFU/ml of serotypes 2, 5b and 6, a number of 5-10 lesions of haemorrhagic necrotizing pneumonia were induced. For the biotype 2 strain the dose creating similar lesions was 10(9) CFU/ml. Repeated experiments confirmed these results showing similar virulence of serotypes 2, 5b and 6 whereas the biotype 2 strain proved less virulent. The aerosol infection model allowed a comparison of the number of A. pleuropneumoniae CFU/liter air which were necessary to induce lung lesions in susceptible pigs. This indicates that the model will be well suited for virulence studies of A. pleuropneumoniae serotypes in pigs.