Mycobacterium avium infections in cattle and pigs in Great Britain

Abstract

During the 16 years, 1953 to 1968, specimens from 14,439 cattle in Great Britain were examined for tubercle bacilli. From the total of 2,917 strains recovered, 371 (12-7 percent) were typed as Mycobacterium avium. Except for 13 isolates of M. tuberculosis, the remaining infections, comprising 87 per cent of the total, were all M. bovis. In 24 cattle active excretion of M. avium during the life of the animal was established. The percentage of avian type isolations during the second period of eight years was more than double that during the first, so that at present approximately one in six isolates of tubercle bacilli from cattle is M. avium. During the 18 years, 1951 to 1968, 81 per cent of 353 routine isolations of tubercle bacilli from pigs in Great Britain were M. avium and 19 per cent M. bovis. During this period there was a relative increase in avian type infections compared with bovine type, the proportion of avian type isolations changing from 43 per cent in the first six years to 91 per cent in the final six years. Bovine type infection in pigs has declined concurrently with the eradication of tuberculosis in cattle, so that more than nine out of ten tuberculous pigs in Great Britain today are affected with the avian type infection. Since the number of recorded cases of tuberculosis in man caused by M. avium is steadily growing, cattle and pigs should be considered as possible sources of avian type infections in human beings.