Experimental Infection with Mycobacterium Avium,Serotype 2, in Pigs: 4. Contact Infection from Orally Inoculated Pigs*

In 3 experiments, 13 pigs were inoculated orally with 0.5 mg Mycobacterium avium daily for 5 days (1 mg = 32–68×10⁶ viable units). Five to 8 days after inoculation, 16 non-inoculated pigs were added to the inoculated pigs.Cultures from faeces showed excretion of M. avium from all the inoculated pigs for some time within the period 16 to 65 days after the last inoculation; the greatest numbers of organisms (62000 per 100 g faeces) were found at about the middle of the excretion period (Table 2). Two of the contact pigs were found to excrete M. avium in small numbers, 1 at 15, the other at 37 and 44 days after contact.All the inoculated pigs and 13 of the contact pigs showed positive intradermal tuberculin reactions. Post-mortem examination showed tuberculous lesions in all the inoculated pigs (Table 3). M. avium was transmitted to 15 of 16 pigs by contact. Five of these pigs showed gross lesions, 10 of them microscopic lesions only; in 9 of them the infection was proved by culture.