Porcine mycobacteriosis caused by Mycobacterium avium subspecies hominissuis

Abstract

More than 150 species of mycobacteria are described, most being opportunistic pathogens and all representing a risk for human and animal health. Human infections derived from environmental mycobacteria are increasing in both industrialized and developing countries. The most susceptible groups are children, the elderly and those, including animals, with immunocompressive conditions. Drug therapy for mycobacteriosis is difficult and not always successful. Infections caused by drug-resistant mycobacteria can be life threatening also for healthy adults and thus represent a real risk for humans. Environmental mycobacterial infections of pigs are usually without clinical signs and the lesions are mainly detected at slaughter. Mycobacterium-infected pork can pass for human consumption due to the poor sensitivity of visual meat control at slaughterhouses, and mycobacteria in pigs also cause economic losses due to condemnation of carcasses. The main challenge is represented by evaluation of the hygiene risk associated with using mycobacteria-contaminated pork. Most environmental mycobacteria species have been isolated from sources such as water, swimming pools, soil, plants and bedding material. In our study mycobacterial growth in piggeries was identified in all bedding materials, sawdust, straw, peat and wood chips in most cases, and water and food samples in many cases, and only occasionally in dust and on wall surfaces. The maximum number of mycobacteria was almost 1 billion (109) per gram of bedding, which is close to the maximum concentration in any growth media. Mycobacteria can multiply in piggeries and contaminate feed and water. Isolation of mycobacteria from pig faeces can be considered an indicator for risk of human infection. Environmental mycobacteriosis in humans and pigs is mainly caused by M. avium subsp. hominissuis. There is little evidence of direct transmission from animals to humans, but particular strains can be recovered from both humans and pigs. In our studies, identical mycobacteria RFLP and MIRU-VNTR fingerprints of porcine and human origins were evident. Interspecies clusters were more common than intraspecies clusters using both methods. Therefore, we concluded that pigs act as a reservoir for virulent M. avium strains and the vector for transmission of infections in humans to pigs, and vice versa, may have an identical source of infection. Culturing mycobacteria is the gold standard for diagnosis, but detection of environmental mycobacteria based on cultivation and biochemical methods can take several weeks. Culture-independent, rapid and accurate techniques for detecting mycobacteria in food and feed chains are urgently needed. In this work we developed a rapid and accurate real-time quantitative PCR for detecting environmental mycobacteria in bedding materials and pig organs. Conclusion: Mycobacteria can multiply in bedding materials and the consequent heavy contamination can cause simultaneous infections in pigs. Mycobacterial DNA was found in pig organ samples, including those without lesions, and similar strains were found from humans and pig organ samples, which suggests that mycobacteria can be transmitted between humans and pigs