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Updated: May 25, 2026
Intradermal Inoculation of Mycobacterium avium in the Mouse Ear
Published on: July 3, 2025
A comparative study of Mycobacterium avium subsp. avium and Mycobacterium avium subsp. hominissuis in experimentally
Angelika Agdestein1, Tone B Johansen, Øyvor Kolbjørnsen
1Norwegian Veterinary Institute, PO Box 750 Sentrum, N-0106 Oslo, Norway. angelika.agdestein@vetinst.no
Background:
Mycobacterium avium subsp. avium (Maa) and Mycobacterium avium subsp. hominissuis (Mah) are opportunistic pathogens that may infect several species, including humans and pigs. Mah is however 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 ten domestic pigs, respectively. 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.
Results:
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, as opposed to 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 of intracellular replication in porcine macrophages compared to the Mah isolate.
Conclusions:
The study shows that both subspecies were able to infect pigs. Additionally, the more extensive shedding of Mah might cause pig-to-pig transmission and contribute to the higher incidence of infection caused by this subspecies.
Insights
Mycobacterium avium subspecies avium (Maa) and hominissuis (Mah) both infect pigs. Mah shedding may explain its higher prevalence, while Maa replicates better within macrophages.
Area of Science:
- Veterinary Microbiology
- Infectious Diseases
- Bacteriology
Background:
- Mycobacterium avium subspecies avium (Maa) and hominissuis (Mah) are opportunistic pathogens affecting humans and pigs.
- Mah is more frequently isolated from pigs than Maa, with unclear reasons for this disparity.
- The study investigates potential differences in virulence and exposure between Maa and Mah in a porcine model.
Purpose of the Study:
- To compare the infectivity and pathogenesis of Maa and Mah in domestic pigs.
- To determine if differences in shedding or replication contribute to the higher prevalence of Mah in swine.
- To evaluate the potential for pig-to-pig transmission of these Mycobacterium avium subspecies.
Main Methods:
- Clinical isolates of Maa and Mah were administered perorally to domestic pigs.
- Pigs were necropsied at 6 and 12 weeks post-inoculation for gross pathology and tissue sampling.
- Mycobacterial culture, IS1245 real-time PCR, and histopathology were used for diagnosis; fecal cultures were also performed.
Main Results:
- Both Maa and Mah caused macroscopic and histopathological lesions in pigs.
- Live Mah was detected in feces by 6 weeks, unlike Maa, indicating greater shedding.
- Mah showed more pronounced presence in tonsils, while Maa exhibited higher intracellular replication in porcine macrophages.
Conclusions:
- Both Maa and Mah subspecies effectively infect pigs.
- Increased Mah shedding suggests a higher potential for pig-to-pig transmission, explaining its greater incidence.
- Understanding subspecies-specific pathogenesis is crucial for controlling Mycobacterium avium infections in swine.
