Abstract
Mycobacterium bovis (M. bovis), a member of the Mycobacterium tuberculosis complex (MTBC), is the causative agent of bovine TB (bTB) in animals. Spread occurs through inhalation or ingestion of bacilli transmitted from infected individuals. Early and accurate detection of infected African buffaloes shedding M. bovis is essential for interrupting transmission. In this pilot study, we determined if MTBC DNA could be detected in M. bovis infected buffalo oronasal secretions using a molecular transport media (PrimeStore MTM) with oronasal swabs and a rapid qPCR assay (Xpert MTB/RIF Ultra). Bovine TB test-positive buffaloes were culled, then tissue samples and oronasal swabs collected post-mortem for mycobacterial culture and Ultra testing, respectively. The Ultra detected MTBC DNA in 5/12 swabs from M. bovis culture-confirmed buffaloes. Oronasal swabs from M. bovis negative buffaloes (n = 20) were negative on Ultra, indicating the high specificity of this test. This study showed that MTM can successfully preserve MTBC DNA in oronasal swabs. The proportion of MTBC positive oronasal swabs was higher than expected and suggests that the Ultra may be an additional method for identifying infected buffaloes. Further studies are needed to confirm the utility of the Ultra assay with oronasal swabs as an assay to evaluate possible MTBC shedding in buffaloes.
Highlights
Bovine tuberculosis is a debilitating chronic infectious disease in livestock and wildlife species, caused by the slow-growing aerobic bacteria of the Mycobacterium tuberculosis complex (MTBC), primarily Mycobacterium bovis[1]
12 buffaloes were confirmed M. bovis infected, based on mycobacterial culture of tissues and downstream genotyping of isolates by region of difference (RD) polymerase chain reaction (PCR)[14]; the remaining three buffaloes were negative on all bovine TB (bTB) tests (IPRA, interferon-gamma (IFN-γ) release assay (IGRA) and single comparative intradermal tuberculin test, SCITT) and mycobacterial tissue culture (Table 1)
All M. bovis infected buffaloes (n = 12) had at least one positive result among the three immunological assays, i.e., SCITT, induced protein (IP-10) assay (IPRA) and IGRA, which were used to screen these animals before culling. The aim of this pilot study was to determine whether MTBC DNA could be detected in M. bovis infected buffalo, by using oronasal swabs, stored in a commercially available nucleic acid stabilising, pathogen inactivating transport media (PrimeStore molecular transport medium (MTM)) with the rapid Xpert MTB/RIF use of a highly sensitive qPCR assay (Ultra) assay
Summary
Bovine tuberculosis (bTB) is a debilitating chronic infectious disease in livestock and wildlife species, caused by the slow-growing aerobic bacteria of the Mycobacterium tuberculosis complex (MTBC), primarily Mycobacterium bovis[1]. Mycobacterial bacilli are small, nonmotile rods with a waxy mycolic acid cell wall that allows them to survive in the environment outside the host up to several months, depending on environmental conditions[1,6]. This allows infection of hosts indirectly through ingestion or inhalation of bacilli shed from infected individuals into the environment. Diagnosis of bTB typically relies on the measurements of delayed-type hypersensitivity responses to the intradermal injection of tuberculin, known as the tuberculin skin test (TST), and in vitro antigen-specific cell-mediated immune responses These are typically based on cytokine release in plasma from whole blood. Tissue samples Tissue samples collected for mycobacterial culture L&R Retropharyngeal LN Tonsils Tonsils Tonsils & retropharyngeal LN Lung lesion Retropharyngeal LN Mediastinal LN lesions R Retropharyngeal LN lesion Abdominal serosa L&R Tracheobronchial LN lesions L&R Tracheobronchial LN lesions Tonsil lesion; retropharyngeal LN Mediastinal LN Lung Lung lesion
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