Experimental infection of normal and immunosuppressed pigs with Pseudomonas pseudomallei

Abstract

A single dose of 5 x 108 bacilli of P. pseudomallei by intratracheal injection resulted in acute (21 cases) or chronic (19 cases) melioidosis in 40 of 48 pigs. Fifteen (10 acute and 5 chronic) had been immunosuppressed by cyclophosphamide before inoculation. The major clinical signs were initial fever, marked neutrophilia and, in the acute cases, respiratory distress. There were no signs of the nasal and ocular discharge, paresis or diarrhoea seen in acute cases in south-east Asia.
The cyclophosphamide treatment caused a significant decrease in the neutrophil count by 7 days after inoculation in all 15 immunosuppressed pigs, and all were culture positive at PM examination. Pigs overcoming the initial phase of infection had more abscess-like nodules that were bacteriologically sterile at PM examination than the pigs with acute cases of melioidosis. P. pseudomallei was isolated predominantly from the spleen, lungs and the injection site. Although only one strain was used in this study, it is likely that Australian strains of P. pseudomallei are not as virulent as the south-east Asian isolates.