Comparative Study of Mycobacterium avium subsp. avium and Mycobacterium avium subsp. hominissuis in Pigs

In experimentally infected pigs, both subspecies were able to cause infections, according to researchers in Oslo, Norway. They proposed that the more extensive shedding of the hominissuis type might cause pig–to–pig transmission and contribute to the higher incidence of infection caused by this subspecies.

7 March 2012

3 minute read

By: Jackie Linden

Mycobacterium avium subsp. avium (Maa) and Mycobacterium avium subsp. hominissuis (Mah) are opportunistic pathogens that may infect several species, including humans and pigs, according to Angelika Agdestein of the Norwegian Veterinary Institute and co-authors there and at the Norwegian Pig Health Service.

In a paper published in BMC Veterinary Research, they explain that Mah is more frequently isolated from pigs than Maa, and it is unclear if this is due to difference in virulence or in exposure to the two organisms.

Clinical isolates of each subspecies were administered perorally to 10 domestic pigs. The animals were sacrificed at six and 12 weeks after inoculation. At necropsy, macroscopic lesions were recorded, and tissue samples were collected for mycobacterial culture, IS1245 real–time PCR and histopathological examination. Culturing was also performed on faecal samples collected at necropsy.

Macroscopic and histopathological lesions were detected in pigs infected with each subspecies, and bacterial growth and histopathological changes were demonstrated, also in samples from organs without gross pathological lesions. Six weeks after inoculation, live Mah was detected in faeces but not live Maa.

The presence of live mycobacteria was also more pronounced in Mah–infected tonsils. In comparison, the Maa isolate appeared to have a higher ability for intracellular replication in porcine macrophages than the Mah isolate.

The study shows that both subspecies were able to infect pigs, concluded Agdestein and co-authors. They added that the more extensive shedding of Mah might cause pig–to–pig transmission and contribute to the higher incidence of infection caused by this subspecies.

Reference

Agdestein A., T.B. Johansen, Ø. Kolbjørnsen, A. Jørgensen, B. Djønne and I. Olsen. 2012. A comparative study of Mycobacterium avium subsp. avium and Mycobacterium avium subsp. hominissuis in experimentally infected pigs. BMC Veterinary Research. 8:11. doi:10.1186/1746-6148-8-11