Mycobacterium orygis: a zoonosis, zooanthroponosis, or both?
Authors: Sven David Charles Parsons
Journal: The Lancet Microbe (2020)

Shannon Duffy and colleagues propose that the operational definition of zoonotic tuberculosis should be broadened to include disease caused by Mycobacterium orygis and that human M orygis infection should be regarded as evidence of zoonotic transmission.1Duffy SC Srinivasan S Schilling MA et al.Reconsidering Mycobacterium bovis as a proxy for zoonotic tuberculosis: a molecular epidemiological surveillance study.Lancet Microbe. 2020; 1: e66-e73Summary Full Text Full Text PDF PubMed Scopus (22) Google Scholar However, although human infection has often been assumed to be of animal origin there is no direct evidence of this.2van Ingen J Rahim Z Mulder A et al.Characterization of Mycobacterium orygis as M. tuberculosis complex subspecies.Emerg Infect Dis. 2012; 18: 653-655Crossref PubMed Scopus (130) Google Scholar The detection of M orygis in both humans and animals presents three possible scenarios: 1) the infection is endemic in animals, which are a source of transmission to humans; 2) humans are the principal maintenance host of M orygis and spill over occurs to other species during close contact; or 3) the infection is endemic in both humans and animals. The absence of clarity in this regard has been highlighted by others.2van Ingen J Rahim Z Mulder A et al.Characterization of Mycobacterium orygis as M. tuberculosis complex subspecies.Emerg Infect Dis. 2012; 18: 653-655Crossref PubMed Scopus (130) Google Scholar, 3Parsons SDC Miller MA van Helden PD The Mycobacterium tuberculosis complex in Africa.in: Dibaba AB Kriek NPJ Thoen CO Tuberculosis in animals: an African perspective. Springer International Publishing, Cham2019: 73-86Crossref Google Scholar Duffy and colleagues present data in support of their assumption that M orygis infection in humans is zoonotic (ie, that the patients in their study presented with extra-pulmonary tuberculosis and that infecting strains were genetically similar to isolates from cattle).1Duffy SC Srinivasan S Schilling MA et al.Reconsidering Mycobacterium bovis as a proxy for zoonotic tuberculosis: a molecular epidemiological surveillance study.Lancet Microbe. 2020; 1: e66-e73Summary Full Text Full Text PDF PubMed Scopus (22) Google Scholar However, numerous cases of human pulmonary tuberculosis caused by M orygis have been reported and genetic markers cannot be used to definitively assign directionality of transmission.2van Ingen J Rahim Z Mulder A et al.Characterization of Mycobacterium orygis as M. tuberculosis complex subspecies.Emerg Infect Dis. 2012; 18: 653-655Crossref PubMed Scopus (130) Google Scholar Moreover, in most animal cases, M orygis has been isolated from domesticated animals and animals held in captivity or semi-captivity.2van Ingen J Rahim Z Mulder A et al.Characterization of Mycobacterium orygis as M. tuberculosis complex subspecies.Emerg Infect Dis. 2012; 18: 653-655Crossref PubMed Scopus (130) Google Scholar, 3Parsons SDC Miller MA van Helden PD The Mycobacterium tuberculosis complex in Africa.in: Dibaba AB Kriek NPJ Thoen CO Tuberculosis in animals: an African perspective. Springer International Publishing, Cham2019: 73-86Crossref Google Scholar, 4Rahim Z Thapa J Fukushima Y et al.Tuberculosis caused by Mycobacterium orygis in dairy cattle and captured monkeys in Bangladesh: a new scenario of tuberculosis in South Asia.Transbound Emerg Dis. 2017; 64: 1965-1969Crossref PubMed Scopus (24) Google Scholar This suggests that animal infection might be strongly associated with human contact. Notably, the only study to have documented interspecies transmission of M orygis showed transmission from a human to a cow.5Dawson KL Bell A Kawakami RP Coley K Yates G Collins DM Transmission of Mycobacterium orygis (M. tuberculosis complex species) from a tuberculosis patient to a dairy cow in New Zealand.J Clin Microbiol. 2012; 50: 3136-3138Crossref PubMed Scopus (36) Google Scholar Given the current ambiguity surrounding the epidemiology of M orygis it is premature to consider this infection as definitive evidence of zoonotic transmission. I declare no competing interests. Reconsidering Mycobacterium bovis as a proxy for zoonotic tuberculosis: a molecular epidemiological surveillance studyM bovis prevalence in humans is an inadequate proxy of zoonotic tuberculosis. The recovery of M orygis from humans highlights the need to use a broadened definition, including MTBC subspecies such as M orygis, to investigate zoonotic tuberculosis. The identification of M tuberculosis in cattle also reinforces the need for One Health investigations in countries with endemic bovine tuberculosis. Full-Text PDF Open AccessMycobacterium orygis: a zoonosis, zooanthroponosis, or both? – Authors' replyWe thank Sven David Charles Parsons for highlighting the many unknowns concerning zoonotic tuberculosis and Mycobacterium orygis. We concur with the assessment that the evidence from the literature, including our Article,1 precludes a definitive understanding of whether M orygis is a marker of zoonosis, zooanthoponosis, or both. Whether cattle or humans (or other species, such as oryxes) serve as reservoir hosts for M orygis is unknown, highlighting the need for genomic epidemiological investigations to refine our understanding of the transmission dynamics of this pathogen. Full-Text PDF Open Access