Risk factors associated with the presence of Mycobacterium bovis in macroscopic lesions suspected as being caused by bovine tuberculosis detected in slaughterhouses

Mycobacterium bovis is a bacterium belonging to the Mycobacterium tuberculosis complex that causes tuberculosis in cattle and in other domestic and wild animals, as well as in humans. Disease control measures are carried out by slaughtering animals tested positive in the intradermal tuberculinization test and sanitation of their original living spaces, in addition to epidemiological surveillance carried out through the sanitary inspection of bovine carcasses in slaughterhouses. In the latter, official inspection services collect samples from macroscopic lesions suspected of bovine tuberculosis, which are then sent for laboratory analysis. Knowledge concerning the variables associated with the occurrence of M. bovis can aid in decision-making regarding control and disease eradication efforts. In this context, the aim of this study was to identify the risk factors for a positive M. bovis diagnosis in suspected bovine tuberculosis lesions obtained during epidemiological surveillance activities in the state of Mato Grosso, Brazil. A total of 105 suspicious lesions were analyzed using the Nested Polymerase Chain Reaction (nested q-PCR) method, of which 14 (13.33%) tested positive for M. bovis. Univariate and bivariate statistical analyses indicated that the variable “animal slaughter” was the only risk factor presenting statistical significance associated with the diagnosis of M. bovis (p < 0.05), demonstrating that macroscopic lesions suspected as being caused by bovine tuberculosis from animals with an in vivo diagnosis were 2.82 - fold more likely to result in a positive M. bovis diagnosis by molecular tests.

The Bovine Tuberculoid Granuloma

The bovine tuberculoid granuloma is the hallmark lesion of bovine tuberculosis (bTB) due to Mycobacterium bovis infection. The pathogenesis of bTB, and thereby the process of bovine tuberculoid granuloma development, involves the recruitment, activation, and maintenance of cells under the influence of antigen, cytokines and chemokines in affected lungs and regional lymph nodes. The granuloma is key to successful control of bTB by preventing pathogen dissemination through containment by cellular and fibrotic layers. Paradoxically, however, it may also provide a niche for bacterial replication. The morphologic and cellular characteristics of granulomas have been used to gauge disease severity in bTB pathogenesis and vaccine efficacy studies. As such, it is critical to understand the complex mechanisms behind granuloma initiation, development, and maintenance.

Transcriptional Profiling of Early and Late Phases of Bovine Tuberculosis.

Bovine tuberculosis, caused by Mycobacterium tuberculosis var. bovis ( M. bovis ), is an important enzootic disease affecting mainly cattle, worldwide. Despite the implementation of national campaigns to eliminate the disease, bovine tuberculosis remains recalcitrant to eradication in several countries. Characterizing the host response to M. bovis infection is crucial for understanding the immunopathogenesis of the disease and for developing better control strategies. To profile the host responses to M. bovis infection, we analyzed the transcriptome of whole blood cells collected from experimentally infected calves with a virulent strain of M. bovis using RNA transcriptome sequencing (RNAseq). Comparative analysis of calf transcriptomes at early (8 weeks) vs. late (20 weeks) aerosol infection with M. bovis revealed divergent and unique profile for each stage of infection. Notably, at the early time point, transcriptional upregulation was observed among several of the top-ranking canonical pathways involved in T-cell chemotaxis. At the late time point, enrichment in the cell mediated cytotoxicity (e.g. Granzyme B) was the predominant host response. These results showed significant change in bovine transcriptional profiles and identified networks of chemokine receptors and monocyte chemoattractant protein (CCL) co-regulated genes that underline the host-mycobacterial interactions during progression of bovine tuberculosis in cattle. Further analysis of the transcriptomic profiles identified potential biomarker targets for early and late phases of tuberculosis in cattle. Overall, the identified profiles better characterized identified novel immunomodulatory mechanisms and provided a list of targets for further development of potential diagnostics for tuberculosis in cattle.

Inferring Mycobacterium bovis transmission between cattle and badgers using isolates from the Randomised Badger Culling Trial

Mycobacterium bovis (M. bovis) is a causative agent of bovine tuberculosis, a significant source of morbidity and mortality in the global cattle industry. The Randomised Badger Culling Trial was a field experiment carried out between 1998 and 2005 in the South West of England. As part of this trial, M. bovis isolates were collected from contemporaneous and overlapping populations of badgers and cattle within ten defined trial areas. We combined whole genome sequences from 1,442 isolates with location and cattle movement data, identifying transmission clusters and inferred rates and routes of transmission of M. bovis. Most trial areas contained a single transmission cluster that had been established shortly before sampling, often contemporaneous with the expansion of bovine tuberculosis in the 1980s. The estimated rate of transmission from badger to cattle was approximately two times higher than from cattle to badger, and the rate of within-species transmission considerably exceeded these for both species. We identified long distance transmission events linked to cattle movement, recurrence of herd breakdown by infection within the same transmission clusters and superspreader events driven by cattle but not badgers. Overall, our data suggests that the transmission clusters in different parts of South West England that are still evident today were established by long-distance seeding events involving cattle movement, not by recrudescence from a long-established wildlife reservoir. Clusters are maintained primarily by within-species transmission, with less frequent spill-over both from badger to cattle and cattle to badger.

More on search for causes of sensitization to tuberculin PPD for mammals in cattle

Despite the large number of papers dealing with the description of proposed methods for bovine tuberculosis diagnosis and mechanisms of non-specific reaction development in diseased and healthy animals, various aspects require further study. Many specialists are still of the view, formulated when studying causes of pseudoallergic reactions, that the agents of actinomycosis, trematode infections etc. can cause sensitization of the animal body to tuberculin PPD for mammals. The possibility of sensitization of cattle body to Аctinomyces bovis tuberculin was studied in 240 animals identified as actinomycosis diseased among 3,473 tested animals. Only 11 (4.6%) of the total number of diseased animals were reactors to tuberculin PPD for mammals. During bacteriological tests of material from animals euthanized for diagnostic purposes (tuberculin reactors and nonreactors with a confirmed postmortem diagnosis of actinomycosis), acid-tolerant nontuberculous mycobacterium (NTM) cultures were isolated. The results of the experiment conducted in 628 cows of a dairy holding confirmed that Actinomyces bovis lacks tuberculin-associated allergenicity: actinomycosis was detected only in one of 96 (15.2%) tuberculin reactors. The conducted clinical tests with high significance level (Р < 0.005) showed that there is no association between allergic reaction to tuberculin PPD for mammals and actinomycosis infection. The obtained results are indicative of imperfections in differential diagnosis, and further studies in this field should significantly contribute to gaining a better insight into non-specific sensitization of cattle body to tuberculin.