Zoonotic tuberculosis-a call for an open One Health debate

Buruli ulcer, tuberculosis and leprosy: Exploring the One Health dimensions of three most prevalent mycobacterial diseases: A narrative review

ΟBJECTIVES: Although Buruli ulcer, tuberculosis, and leprosy are the three most common mycobacterial diseases, One Health dimensions of these infections remain poorly understood. This narrative review aims at exploring the scientific literature with respect to the presence of animal reservoir(s) and other environmental sources for the pathogens of these infections, their role in transmission to humans and the research on/practical implementation of One Health relevant control efforts.

METHODS

The literature review was conducted using the online databases PubMed, Scopus, ProQuest and Google Scholar, reviewing articles that were written in English in the last 15 years. Grey literature, published by intergovernmental agencies, was also reviewed.

RESULTS

For the pathogen of Buruli ulcer, evidence suggests possums as a possible animal reservoir and thus having an active role in disease transmission to humans. Cattle and some wildlife species are deemed as established animal reservoirs for tuberculosis pathogens, with a non-negligible proportion of infections in humans being of zoonotic origin. Armadillos constitute an established animal reservoir for leprosy pathogens with the transmission of the disease from armadillos to humans being deemed possible. Lentic environments, soil and other aquatic sources may represent further abiotic reservoirs for viable Buruli ulcer and leprosy pathogens infecting humans. Ongoing investigation and implementation of public health measures, targeting (sapro)zoonotic transmission can be found in all three diseases.

CONCLUSION

Buruli ulcer, tuberculosis and leprosy exhibit important yet still poorly understood One Health aspects. Despite the microbiological affinity of the respective causative mycobacteria, considerable differences in their animal reservoirs, potential environmental sources and modes of zoonotic transmission are being observed. Whether these differences reflect actual variations between these diseases or rather knowledge gaps remains unclear. For improved disease control, further investigation of zoonotic aspects of all three diseases and formulation of One Health relevant interventions is urgently needed.

Vaccines to control tuberculosis in cattle

The age-old cattle disease has resisted rigorous control, but the BCG vaccine may do better.

Assessing risks for bovine and zoonotic tuberculosis through spatial analysis and a questionnaire survey in Fiji - A pilot study

Mycobacterium bovis causes tuberculosis in cattle and when transmitted to humans typically causes extra-pulmonary tuberculosis (EPTB). Bovine tuberculosis (bTB) has a global distribution and is controlled in most countries to protect animal and public health. Recent studies revealed that bTB is established on dairy farms in Fiji where EPTB cases have been reported in people. The aims of this pilot investigation were to look for putative zoonotic TB (EPTB) cases in people and to evaluate practices that might contribute to the persistence and transmission of M. bovis between cattle and to humans. Existing data sets were shared between the Fiji Ministry of Agriculture and Ministry of Health and a questionnaire-based survey was implemented using One Health principles. Statistically significant co-location and close proximity of EPTB cases and bovine TB affected farms were identified. The bTB infection status of farms was significantly associated with unfenced water sources where cattle grazed. Of 247 households, 65 % shared drinking water sources with cattle and 36 % consumed raw milk without boiling, while 62 % of participants reported backyard slaughter of cattle. Several participants reported current symptoms potentially suggestive of TB (chronic cough) but the impact of smoking and history of previous TB treatment could not be evaluated. Farmers had limited understanding of the practices required to prevent bTB at farm level. Further study is recommended and should include an assessment of lifetime EPTB diagnoses, classification of farms based on more recent bTB test data and molecular typing of mycobacterial isolates from humans, cattle and the environment. A targeted awareness and education approach is required to reduce the future risk of zoonotic TB and to help ensure uptake of recommendations and practices aimed at controlling and preventing bTB.

Systematic review and meta-analysis of tuberculosis in animals in Nigeria

Animal tuberculosis (TB) is a contagious and chronic disease caused by mycobacteria belonging to theMycobacterium tuberculosis complex (MTBC) in domestic and wild animals. MTBC strains infection has been confirmed in many animal species in Nigeria, including captive wildlife, cattle, dromedary camels, goats, and pigs. Despite widespread infection and the potential impact of the disease on public health, active surveillance and control strategies are absent in Nigeria. This study aimed to conduct the first comprehensive meta-analysis to assess the distribution of tuberculosis and analyze the potential moderators of infection in animals in Nigeria. Eligible studies (sixty-one (Cadmus et al., 2014) [61] prevalence and seven (Menzies and Neill, 2000) [7] case reports) were retrieved and included in the analysis. The analyses showed an overall pooled TB prevalence of 7.0% (95% CI: 6.0-8.0) comprising of infection distributed in cattle (8.0%, 95% CI: 7.0-8.0), goats (0.47%, 95% CI: 0-1.2), sheep (0.27%, 95% CI: 0.14-0.46), camels (13.0%, 95% CI: 0-47), and wildlife (13.0%, 95% CI: 9-16) respectively. The occurrence of infection was significantly moderated by the publication periods, geographical location, sample size, and detection methods. TB prevalence was heterogeneous across several predictors, with the year of publication exhibiting a higher rate (46%) of the detected heterogeneity. These findings should provide policy-relevant information to guide the design and establishment of prevention and control measures amenable to the local situations in Nigeria.

Neutrophils in Tuberculosis: Cell Biology, Cellular Networking and Multitasking in Host Defense

Neutrophils readily infiltrate infection foci, phagocytose and usually destroy microbes. In tuberculosis (TB), a chronic pulmonary infection caused by Mycobacterium tuberculosis (Mtb), neutrophils harbor bacilli, are abundant in tissue lesions, and their abundances in blood correlate with poor disease outcomes in patients. The biology of these innate immune cells in TB is complex. Neutrophils have been assigned host-beneficial as well as deleterious roles. The short lifespan of neutrophils purified from blood poses challenges to cell biology studies, leaving intracellular biological processes and the precise consequences of Mtb–neutrophil interactions ill-defined. The phenotypic heterogeneity of neutrophils, and their propensity to engage in cellular cross-talk and to exert various functions during homeostasis and disease, have recently been reported, and such observations are newly emerging in TB. Here, we review the interactions of neutrophils with Mtb, including subcellular events and cell fate upon infection, and summarize the cross-talks between neutrophils and lung-residing and -recruited cells. We highlight the roles of neutrophils in TB pathophysiology, discussing recent findings from distinct models of pulmonary TB, and emphasize technical advances that could facilitate the discovery of novel neutrophil-related disease mechanisms and enrich our knowledge of TB pathogenesis.

Zoonotic Tuberculosis - The Changing Landscape

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Globally, Zoonotic TB remains a poorly monitored and an important unaddressed burden.

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Zoonotic TB primarily from consumption M. bovis contaminated unpasteurized dairy products.

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Novel zoonotic TB strains (e.g. M. orygis), warrants more attention and intervention.

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Early detection and control of M. bovis in cattle remains the mainstay of reducing zoonotic TB risk.

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Reverse zoonosis to animals of treatment resistant TB strains is a threat to eliminating TB.

Despite slow reductions in the annual burden of active human tuberculosis (TB) cases, zoonotic TB (zTB) remains a poorly monitored and an important unaddressed global problem. There is a higher incidence in some regions and countries, especially where close association exists between growing numbers of cattle (the major source of Mycobacterium bovis) and people, many suffering from poverty, and where dairy products are consumed unpasteurised. More attention needs to be focused on possible increased zTB incidence resulting from growth in dairy production globally and increased demand in low income countries in particular. Evidence of new zoonotic mycobacterial strains in South Asia and Africa (e.g. M. orygis), warrants urgent assessment of prevalence, potential drivers and risk in order to develop appropriate interventions. Control of M. bovis infection in cattle through detect and cull policies remain the mainstay of reducing zTB risk, whilst in certain circumstances animal vaccination is proving beneficial. New point of care diagnostics will help to detect animal infections and human cases. Given the high burden of human tuberculosis (caused by M. tuberculosis) in endemic areas, animals are affected by reverse zoonosis, including multi-drug resistant strains. This, may create drug resistant reservoirs of infection in animals. Like COVID-19, zTB is evolving in an ever-changing global landscape.

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

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.