Prevalence of Mycobacterium avium in slaughter pigs in the Netherlands andcomparison of IS1245 restriction fragment length polymorphism patterns of porcine and human isolates

A significant increase in the incidence of caseous lesions in the lymph nod es of slaughter pigs prompted a large-scale investigation in fire slaughter houses in The Netherlands. In total, 158,763 pigs from 2,899 groups underwe nt gross examination At least one pig Kith caseous lesions in the submaxill ary and/or mesenteric lymph nodes was observed in each of 154 of the 2,899 groups examined (5%). In total, 856 pigs (0.5%) Here affected. As many as f ive pigs in each of 141 of the 154 positive groups (91.5%) had lymph node l esions. Greater numbers of pigs with affected lymph nodes were found in 13 groups (8.5%). Four pigs had lesions in the kidneys, liver, or spleen. Acid -fast bacteria were detected by microscopic examination of 121 of 292 Ziehl -Neelsen-stained smears of caseous lesions (41%). In a follow-up study. Myc obacterium ar avium complex (MAC) bacteria were isolated from 219 of 402 af fected IS-mph nodes (54.2%). Ninety-one of the isolated strains sere analyz ed by restriction fragment length polymorphism (RFLP) typing with insertion sequence IS1245 as a probe. All but I of these 91 strains contained IS1245 DNA, indicating that pigs in The Netherlands carried almost esclusively M. avium bacteria and no other bacteria of MAC, Only one pig isolate exhibite d the bird-type RFLP pattern. MAC isolates from 191 human patients in The N etherlands in 1996 were also typed by RFLP analysis. Computer-assisted anal ysis showed that the RFLP patterns of 61% of the human isolates and 59% of the porcine isolates were at least 75% similar to the RFLP patterns of the other group of strains. This indicates that pigs mag. be an important vehic le for M. avium infections in humans or that pigs and humans share common s ources of infection.