Antemortem detection of Mycobacterium bovis in nasal swabs from African rhinoceros

Mycobacterium bovis ( M. bovis ) infection has been identified in black ( Diceros bicornis ) and white ( Ceratotherium simum ) rhinoceros populations in Kruger National Park, South Africa. However, it is unknown whether M. bovis infected rhinoceros, like humans and cattle, can shed mycobacteria in respiratory secretions. Limited studies have suggested that rhinoceros with subclinical M. bovis infection may present minimal risk for transmission. However, recent advances that have improved detection of Mycobacterium tuberculosis complex (MTBC) members in paucibacillary samples warranted further investigation of rhinoceros secretions. In this pilot study, nasal swab samples from 75 rhinoceros with defined infection status based on M. bovis antigen-specific interferon gamma release assay (IGRA) results were analysed by GeneXpert MTB/RIF Ultra, BACTEC™ MGIT™ and TiKa – MGIT culture. Following culture, speciation was done using targeted PCRs followed by Sanger sequencing for mycobacterial species identification, and a region of difference (RD) 4 PCR. Using these techniques, MTBC was detected in secretions from 14/64 IGRA positive rhinoceros, with viable M. bovis having been isolated in 11 cases, but in any IGRA negative rhinoceros (n = 11). This finding suggests the possibility that MTBC/ M. bovis -infected rhinoceros may be a source of infection for other susceptible animals sharing the environment.