Research article

Bovine tuberculosis in African buffaloes: observations regarding Mycobacterium bovis shedding into water and exposure to environmental mycobacteria

Anita L Michel¹ , Lin-Mari de Klerk² , Nico C Gey van Pittius³ , Rob M Warren³ and Paul D van Helden³

¹  Tuberculosis Laboratory, ARC-Onderstepoort Veterinary Institute, Private Bag x05, Onderstepoort 0110, South Africa

²  Game Capture Unit, South African National Parks, Private Bag x402, Skukuza 1350, South Africa

³  DST/NRF Centre of Excellence in Biomedical Tuberculosis Research, US/MRC Centre for Molecular and Cellular Biology, Department of Biomedical Science, Faculty of Health Sciences – Stellenbosch University, PO Box 19063, Tygerberg 7505, South Africa

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BMC Veterinary Research 2007, 3:23doi:10.1186/1746-6148-3-23

Published:	27 September 2007

Abstract

Background

African buffaloes are the maintenance host for Mycobacterium bovis in the endemically infected Kruger National Park (KNP). The infection is primarily spread between buffaloes via the respiratory route, but it is not known whether shedding of M. bovis in nasal and oral excretions may lead to contamination of ground and surface water and facilitate the transmission to other animal species. A study to investigate the possibility of water contamination with M. bovis was conducted in association with a BCG vaccination trial in African buffalo. Groups of vaccinated and nonvaccinated buffaloes were kept together with known infected in-contact buffalo cows to allow natural M. bovis transmission under semi-free ranging conditions. In the absence of horizontal transmission vaccinated and control buffaloes were experimentally challenged with M. bovis. Hence, all study buffaloes in the vaccination trial could be considered potential shedders and provided a suitable setting for investigating questions relating to the tenacity of M. bovis shed in water.

Results

Serial water samples were collected from the drinking troughs of the buffaloes once per season over an eleven-month period and cultured for presence of mycobacteria. All water samples were found to be negative for M. bovis, but 16 non-tuberculous Mycobacterium spp. isolates were cultured. The non-tuberculous Mycobacterium species were further characterised using 5'-16S rDNA PCR-sequencing, resulting in the identification of M. terrae, M. vaccae (or vanbaalenii), M. engbaekii, M. thermoresistibile as well as at least two species which have not yet been classified.

Conclusion

The absence of detectable levels of Mycobacterium bovis in the trough water suggests that diseased buffalo do not commonly shed the organism in high quantities in nasal and oral discharges. Surface water may therefore not be likely to play an important role in the transmission of bovine tuberculosis from buffalo living in free-ranging ecosystems. The study buffalo were, however, frequently exposed to different species of non-tuberculous, environmental mycobacteria, with an unknown effect on the buffaloes' immune response to mycobacteria.