Melioidosis in animals in north Queensland. 1. Incidence and pathology, with special reference to central nervous system lesions

Abstract

Between June 1956 and July 1961, 194 strains of Pseudomonas pseudomallei were recovered from 116 animals in North Queensland, comprising 75 pigs, 23 sheep, 14 goats, 3 cattle and a horse. Most of the material was obtained near Townsville and most of the isolations were from that area. The infected animals were from 21 different properties.
One hundred and four of the animals showed no symptoms, and the majority of isolations were made from abscesses detected during routine meat inspection. Abscesses were most commonly found in the mandibular lymph node, spleen and lung with associated lymph nodes in pigs, lung and mediastinal lymph node in sheep and lung, mediastinal lymph node and spleen of goats. Ps. pseudomallei was the most common organism recovered from abscesses in pigs, and was recovered from 30 per cent. of the abscesses examined. In sheep, this organism was recovered from only 11 per cent. of abscesses, while Corynebacterium ovis was recovered from 47 per cent.
Melioidosis abscesses were not characteristic, and varied from a barely visible caseous lesion to a quite extensive suppurating mass. The abscesses were quite poorly or quite well encapsulated. Abscesses caused by Ps. pseudomallei were often indistinguishable macroscopically from abscesses from which Streptococcus spp., Corynebacterium spp. Salmonella spp., Brucella suis, Erysipelothrix insidiosa, Chromobacterium violaceum or Pasteurella septica were isolated.
Only 12 of the 116 naturally infected animals showed clinical evidence of disease. These were 3 pigs, 3 sheep, 3 cattle, 2 goats and a horse. Four of these, 2 cows, 1 goat and the horse, had infection of the central nervous system. Involvement of the C.N.S. was also seen in 6 out of 10 experimentally infected sheep. The lesions in the C.N.S. were usually not seen macroscopically. Microscopically they were a mixed purulent and non-purulent lesion involving the leptomeninges and grey and white matter of one or several areas of the C.N.S.