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Tuberculosis in African lions

Tuberculosis in African lions
Miriam Maas

2013

Faculty of Veterinary Medicine, Utrecht University, 3584 CG Utrecht, THE NEDERLANDS.

ABSTRACT

Lions (Panthera leo) are susceptible to Mycobacterium bovis (M. bovis) infection, resulting in bovine tuberculosis (BTB). This chronic, debilitating disease can affect multiple organs, particularly the lungs, and may ultimately lead to death of the infected animal. Cases of lion BTB have been described in zoological collections as well as in free-ranging lion populations, where M. bovis prevalence may be as high as 79%. Practical limitations complicate current BTB testing of free-ranging lions. Therefore, a lion-specific interferon-gamma assay was developed, by producing recombinant lion IFN-γ (rLIFN-γ) and subsequently monoclonal antibodies. The lion IFN-γ-specific capture ELISA detected rLIFN-γ to the level of 160 pg/ml. Recognition of native lion IFN-γ was shown in an initial assessment of supernatants of mitogen stimulated whole blood cultures of 11 known BTB-negative lions. No false-positive reactions were found after antigen-stimulation of blood samples of these BTB-free lions. This ELISA shows potential as a diagnostic assay for bovine tuberculosis in lions. Preliminary results also indicate the possible use of the test for other (feline) species. Knowledge of immune responsiveness after Mycobacterium bovis infection may facilitate development of vaccines and diagnostic assays for lions. Since in several species immune responses in course of infection with Mycobacterium bovis were characterized by differential cytokine expression, reverse transcriptase real-time PCR’s for lion cytokines IFN-γ, TNF-α, IL-4 and IL-10 were developed. These assays were tested in a pilot study consisting of 26 lions with either tuberculin skin test positive (n=19) or negative (n=7) statuses. Cytokine profiles in blood tended to differ between skin test positive lions and skin test negative lions and need to be confirmed and extended in larger study groups and longitudinal follow up. Feline immunodeficiency virus (FIVple) is endemic in many lion populations, including the Kruger National Park lions. In humans, co-infection between M. tuberculosis and human immunodeficiency virus increases disease burden. If BTB were to reach high levels of prevalence in lions, and if similar worsening effects would exist between FIVple and BTB as for their human equivalents, this could pose a lion conservation problem. We collected data on lions in KNP from 1993-2008 for spatio-temporal analysis of both FIVple and BTB, and to assess whether a similar relation between the two diseases exists in lions. We found that both infections affected haematology and blood chemistry values, FIVple in a more pronounced way than BTB. The effect of co-infection on these values, however, was always less than additive. Though a large proportion (31%) of the lions was co-infected with FIVple and Mycobacterium bovis, there was no evidence for a synergistic relation as in their human counterparts. Whether this results from different immunopathogeneses remains to be determined. We also found a steep increase in time of M. bovis prevalence in lions in the northern part of the KNP. Although major effects of BTB on the lion population are not apparent at the moment, improvement of our knowledge about BTB in lions therefore remains important.