Infected birds with advanced lesions often excrete the organism in their feces; therefore, ingestion of contaminated feces is the most common route of transmission. Cadavers and offal may infect predators and cannibalistic flock mates. Rabbits, pigs, nonhuman primates, and mink are readily infected. Cattle exposed to contaminated feces may develop granulomatous lesions in lymph nodes associated with the GI tract and respond to M bovis purified protein derivative (PPD) tuberculin and to PPD of M avium. M avium serovar 1 is often isolated from tuberculous free-living wild birds and birds in captivity. Mycobacterium avium ss and M genavense have been isolated from immunocompromised people; however, these organisms only rarely cause disease in nonimmunocompromised individuals.