A survey of mycobacteriosis of feral pigs in the Northern Territory

Abstract

Seven hundred and fifty-one feral pigs from the subcoastal plains of the Northern Territory were examined. The sample population consisted of 52.4% females and 47.6% males. They ranged in age from newborn piglets to mature animals of over 72 months. Of the pigs examined 47.7% had macroscopic abscesses and of these 80.2% were probably caused by mycobacteria. Tissues from 193 pigs were examined bacteriologically and 93 strains of mycobacteria were isolated. These were typed as M. bovis (37 strains); M. avium serotype 2 (1); M. intracellulare serotypes 6 (2), 7 (3), 9 (1) and 18 (1); M. intracellulare double serotypes 6 + 12 (1), 8 + 12 (1), and 11 + 12 (1); M. intracellulare unclassified serotype (4); M. scrofulaceum serotype 41 (1); M. scrofulaceum unclassified serotype (7); M. gordonae (2); M. Kansasii (1); M. simiae (2); M. szulgai (2); M. vaccae (1); and M. xenopi (2). Additionally, 3 strains were unidentifiable members of the M. avium-M. intracellulare-M. scrofulaceum (MAIS) complex, one strain was a Runyon's group IV and 4 strains were typed as members of the genus Rhodococcus. Five strains were non-viable on subculture and 10 did not conform to any currently recognised species of mycobacteria. Of the 93 strains, 3 were isolated from tissue that did not contain macroscopic lesions, viz. M. simiae, Runyon's group IV and an unidentifiable member of the MAIS complex. It was concluded that the feral pig is probably an end host for both M. bovis and atypical mycobacteria and not a significant source of infection for cattle. M. bovis is not a significant cause of mortality in feral pigs but mycobacterioses are a significant cause of morbidity. With increasing age, the proportion of pigs having lesions increased whereas the proportion of lesions from which mycobacteria could be isolated decreased.