Does Mycobacterium tuberculosis var. bovis Survival in the Environment Confound Bovine Tuberculosis Control and Eradication? A Literature Review

Abstract

Bovine tuberculosis (bTB) is one of the globe’s most common, multihost zoonoses and results in substantial socioeconomic costs for governments, farming industries, and tax payers. Despite decades of surveillance and research, surprisingly, little is known about the exact mechanisms of transmission. In particular, as a facultative intracellular pathogen, to what extent does survival of the causative agent, Mycobacterium tuberculosis var. bovis (M. bovis), in the environment constitute an epidemiological risk for livestock and wildlife? Due largely to the classical pathology of cattle cases, the received wisdom was that bTB was spread by direct inhalation and exchange of bioaerosols containing droplets laden with bacteria. Other members of the Mycobacterium tuberculosis complex (MTBC) exhibit differing host ranges, an apparent capacity to persist in environmental fomites, and they favour a range of different transmission routes. It is possible, therefore, that infection from environmental sources of M. bovis could be a disease transmission risk. Recent evidence from GPS-collared cattle and badgers in Britain and Ireland suggests that direct transmission by infectious droplets or aerosols may not be the main mechanism for interspecies transmission, raising the possibility of indirect transmission involving a contaminated, shared environment. The possibility that classical pulmonary TB can be simulated and recapitulated in laboratory animal models by ingestion of contaminated feed is a further intriguing indication of potential environmental risk. Livestock and wildlife are known to shed M. bovis onto pasture, soil, feedstuffs, water, and other fomites; field and laboratory studies have indicated that persistence is possible, but variable, under differing environmental conditions. Given the potential infection risk, it is timely to review the available evidence, experimental approaches, and methodologies that could be deployed to address this potential blind spot and control point. Although we focus on evidence from Western Europe, the concepts are widely applicable to other multihost bTB episystems.

Nontuberculous Mycobacteria as Sapronoses: A Review

“…The ecology of TB and NTM species has received increased attention over the last two decades due primarily to the spread of human and animal TB which still has not been significantly reduced in developing countries [ 44 , 45 ]. Furthermore, all though incidence of mycobacterial infection is generally lower in developed countries, mycobacterial infections are not reducing either [ 46 , 47 ].…”

“…Most of the representatives listed in Risk Group 3 ( Table 6 ) have been identified in various components of the environment, including soil and, as such, are classified in this group. The survival of the significant pathogen M. bovis, in soil, water, and other matrices was demonstrated by Allen et al [ 44 ].…”

Understanding Mycobacterium tuberculosis complex in elephants through a One Health approach: a systematic review

“…Hence, it signifies the need for a One Health approach to combat TB due to probable transmission pathways between humans, elephants, and other animals. These pathways could be partly mediated by environmental matrices such as shared water or feed [ 46 ].…”

Molecular surveillance of tuberculosis-causing mycobacteria in wastewater

“…TB primarily spreads person-to-person by aerosolized infective tubercle particles ( Shiloh, 2016 ). However, there are observations that TB could be transmitted through other means, such as through faecal-oral transmission ( Santos et al., 2015 ; Lombard, 2011 ; Allen et al., 2021 ). Despite the potential role of the environment in TB transmission, there is limited information on the occurrence of the causative organisms in the environment.…”