COMPARATIVE VIRULENCE OF PORCINE HEMOPHILUS BACTERIA

  • 1 January 1985
    • journal article
    • research article
    • Vol. 49  (1) , 68-74
Abstract
The virulence of strains of H. pleuropneumoniae serotype 1, 2, 3, 7 and strains of the minor-group and H. parasuis were compared by inoculating specific pathogen-free pigs into the lower airways with specified doses of bacteria. H. pleuropneumoniae, strain W. serotype 1, given in 1 x 10 colony-forming units [cfu], produced a lethal acute pleuropneumonia in 4 pigs. Nonlethal localized pulmonary necrosis was induced in 4 groups of 2 pigs given 1 x 107, 1 x 106, 1 x 105 and 1 x 104, respectively, of the same strain. Two groups of 4 pigs developed chronic lesions when inoculated with 1 x 107 cfu of H. pleuropneumoniae, strain Shope 4074, serotype 1 and 1 x 107 cfu of H. pleuropneumoniae, strain WF83, serotype 7, respectively. Of 20 pigs given 1 x 108 cfu of strain 1536, serotype 2, 2 died of acute pleuropneumonia and 18 had lesions of pulmonary necrosis or abscessation and pleuritis. A dose of 4 x 109 cfu of strain BC181, serotype 3, induced pulmonary necrosis similar to the lesions in pigs given .ltoreq. 107 cfu of strain W, serotype 1, suggesting that the serotype 3 strain is less virulent. No clinical signs, but focal areas of pulmonary fibrosis and pleural adhesions were induced in 4 pigs inoculated with 4 x 109 cfu of the minor-group strain 7ATS. Four pigs inoculated with minor-group strain 33PN did not show clinical signs, but had focal necrotic and fibrotic pulmonary lesions and pleural adhesions. The virulence of minor-group strains is therefore probably low. Strain E751 of H. parasuis induced septicemia and Glasser''s disease without evidence of meningitis in 2 pigs. Except for spleen and pericardial fluid of 1 pig, none of the pigs exposed to H. pleuropneumoniae strains were positive for these bacteria outside the respiratory tract when cultured at necropsy. Results of this study suggest that differences in virulence between serotype 1, the strains of serotype 3, and the minor-group are of potential importance in comparative studies on microbial virulence factors.