A comparative study of Mycobacterium avium subsp. avium and Mycobacterium avium subsp. hominissuis in experimentally infected pigs

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.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.The genus Mycobacterium covers a broad spectrum of acid-fast staining species, ranging from harmless saprophytes to significant pathogens [1]. M. avium subsp. avium (Maa) and M. avium subsp. hominissuis (Mah) are two subspecies of M. avium, subordinated the Mycobacterium avium complex (MAC) [2]. Mah can cause serious systemic infection in immunocompromised patients, such as humans infected with HIV [3]. Additionally, this opportunistic pathogen can cause cervical lymphadenitis in children and lung infections in patients with underlying lung disease [1]. In pigs, Mah is frequently responsible for lesions in lymph nodes of the digestive tract, and can also lead to systemic infection with affection of parenchymatous organs. Since Mah usually does not cause clinical signs in pigs, the lesions are mainly detected at slaughter [4]. Maa is the causative agent of tuberculosis in birds, in which it acts as an obligate pathogen, causing contagious, chronic disease [5,6]. Maa has also been isolated from humans and pigs with mycobacteriosis [7,8].Before molecular typing enabled differentiation of Maa and Mah isolates, birds were believed to be an important source of mycobacteriosis in pigs [9]. However, various molecular invest