Mycobacterium orygis: a zoonosis, zooanthroponosis, or both? – Authors' reply
Authors: Shannon C Duffy, Sreenidhi Srinivasan, Joy S Michael, Marcel A Behr, Vivek Kapur
Journal: The Lancet Microbe (2020)

We 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,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 (25) Google Scholar 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. This is not only the case for M orygis, definitive knowledge of reservoir host and host-range remain unknown for most of the animal-associated lineages within the Mycobacterium tuberculosis complex, including those that have been reported to infect and cause tuberculosis in humans.2Rodríguez S Bezos J Romero B et al.Mycobacterium caprae infection in livestock and wildlife, Spain.Emerg Infect Dis. 2011; 17: 532-535Crossref PubMed Scopus (82) Google Scholar, 3Jurczynski K Lyashchenko KP Gomis D Moser I Greenwald R Moisson P Pinniped tuberculosis in Malayan tapirs (Tapirus indicus) and its transmission to other terrestrial mammals.J Zoo Wildl Med. 2011; 42: 222-227Crossref PubMed Scopus (22) Google Scholar Parsons notes there is no published evidence of direct animal to human transmission of M orygis. We add that there are no reports of human to human transmission of M orygis either. Accumulating evidence suggests that M orygis, like many other members of the M tuberculosis complex, is a multispecies pathogen.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 (26) Google Scholar Parsons cites that most M orygis cases are reported from humans and a variety of animals in captivity; but it remains unclear whether this reflects a sampling bias because free-living animals are also reported to be infected.5Thapa J Paudel S Sadaula A et al.Mycobacterium orygis–associated tuberculosis in free-ranging rhinoceros, Nepal, 2015.Emerg Infect Dis. 2016; 22: 570-572Crossref PubMed Scopus (19) Google Scholar Therefore, the host range of M orygis is not fully defined. This highlights a need for comprehensive genomic epidemiology investigations to establish the host range of M orygis and other animal-lineage members of the M tuberculosis complex and determine their potential for zoonotic and or zooanthroponotic infection in regions where they are endemic. As reflected by the title, the central message of our Article was to broaden the operational definition of zoonotic tuberculosis to include any animal lineage M tuberculosis complex subspecies capable of causing human disease.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 (25) Google Scholar This recommendation was based on the observation of M orygis circulating in both humans and cattle, and the inability to recover M bovis from humans in a region where bovine tuberculosis is endemic with considerable opportunities for zoonotic transmission. This broader definition should sensitise medical and veterinary practitioners and laboratories to the M tuberculosis species that might be associated with zoonotic or zooanthroponotic infections and enable future definitive studies of the important questions raised by Parsons and in our Article. MAB reports grants from the Canadian Institutes for Health Research, during the conduct of this study. VK reports grants from the Bill & Melinda Gates Foundation, during the conduct of this study. All other authors 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?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.1 However, although human infection has often been assumed to be of animal origin there is no direct evidence of this.2 Full-Text PDF Open Access