Mycobacterium caprae infection in humans

Abstract

Mycobacterium caprae, a member of the Mycobacterium tuberculosis complex, causes tuberculosis (TB) in man and animals. Some features distinguish M. caprae from its epidemiological twin, Mycobacterium bovis: M. caprae is evolutionarily older, accounts for a smaller burden of zoonotic TB and is not globally distributed, but primarily restricted to European countries. M. caprae occurs only in a low proportion of human TB cases and this proportion may even decrease, if progress toward eradication of animal TB in Europe continues. So why bother, if M. caprae is not an enigma for diagnostic TB tests and if resistance against first-line drugs is a rarity with M. caprae? This ‘European’ pathogen of zoonotic TB asks interesting questions regarding the definition of a species. The latter, seemingly only an academic question, particularly requires and challenges the collaboration between human and veterinary medicine.

Keywords::

• Mycobacterium caprae
• epidemiology
• human
• Mycobacterium tuberculosis
• zoonosis

Acknowledgements

The authors would like to thank B Brodhun and W Haas (Robert Koch Institute, Berlin), N Ackermann (Landesgesundheitsamt Bayern, Munich) and G Pfyffer von Altishofen (Lucerne, Switzerland) for providing and discussing information on Mycobacterium caprae cases, W Glawischnig and K Schöpf (Austrian Agency for Health and Food Safety, Innsbruck) for explaining the intricate veterinarian aspects of M. caprae, C Lechleitner and K-I Freilach for excellent lab assistance and S Niemann (Forschungszentrum Borstel) and F Allerberger (Austrian Agency for Health and Food Safety, Vienna) for their long-standing collaboration and support.

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Diagnostic procedures for human tuberculosis (TB) or TB notification requirements are no different for Mycobacterium caprae than for other Mycobacterium tuberculosis complex members.

• The incidence of zoonotic tuberculosis disease in humans due to M. caprae is very low worldwide, but plays a role in Central and Southern European countries and Turkey. The proportion of human TB due to M. caprae in these countries does not exceed 0.3% of all TB cases.

• Human M. caprae TB cases share characteristics with Mycobacterium bovis infections, for example, a higher proportion of extrapulmonary disease and the predominance of reactivated disease in older patients.

• Among risk factors for M. caprae infection are occupational exposure of patients in agriculture, consumption of unpasteurized dairy products and residence in rural, not urban areas.

• In contrast to M. bovis, M. caprae cases typically arise in native European patients and are rarely due to strain importation.

• M. caprae is susceptible to pyrazinamide and also resistance to other first-line drugs remains a rarity. Treatment regimens should therefore be chosen as for fully-susceptible M. tuberculosis isolates.

• Probably, the most significant problem associated with M. caprae remains with the notification systems: particularly in the veterinarian sectors in European countries, these are heterogeneous regarding the recording of M. bovis versus M. caprae.

Notes