Detection of natural infection with Mycobacterium intracellulare in healthy wild-caught Chacma baboons (Papio ursinus) by ESAT-6 and CFP-10 IFN-gamma ELISPOT tests following a tuberculosis outbreak.

Gerald K Chege,Robert J Wilkinson,Anna-Lise Williamson,Nico C Gey van Pittius,Enid G Shephard,Robin M Warren,Wendy A Burgers

doi:10.1186/1471-2180-8-27

Abstract

BackgroundBoth tuberculous and non-tuberculous mycobacteria can cause infection in nonhuman primates (NHP), indicating the existence of potential zoonotic transmission between these animals and visitors to zoos or animal handlers in primate facilities. Screening of mycobacterial infections in NHP is traditionally done by tuberculin skin test (TST), which is unable to distinguish between pathogenic and non-pathogenic mycobacterial infections. In this study, we investigated the use of ESAT-6 and CFP-10 for detection of mycobacterial infections in a wild-caught baboon colony after one baboon died of tuberculosis (TB).MethodsPeripheral blood lymphocytes for interferon-gamma enzyme-linked immunospot assay (IFN-γ ELISPOT) assay were obtained from TST positive baboons and those in contact with tuberculous baboons before being euthanased, autopsied and lung tissues taken for histology and mycobacterial culture.ResultsBoth ESAT-6 and CFP-10 IFN-γ ELISPOT assays were able to detect early M. tuberculosis but also M. intracellulare infection. Although this indicates potential cross-reactivity with M. intracellulare antigens, the method was able to distinguish M. bovis BCG vaccination from M. tuberculosis infection. This assay performed better than the TST, which failed to detect one M. tuberculosis and two early M. intracellulare infections.ConclusionThese results suggest that the IFN-γ ELISPOT assay could improve the detection of M tuberculosis infections when screening NHP. There is some doubt, however, concerning specificity, as the assay scored positive three animals infected with M. intracellulare.

Highlights

Both tuberculous and non-tuberculous mycobacteria can cause infection in nonhuman primates (NHP), indicating the existence of potential zoonotic transmission between these animals and visitors to zoos or animal handlers in primate facilities
Tuberculin Skin test Following the death of one baboon (B662) due to pulmonary TB diagnosed at necropsy, the remaining 89 baboons in the colony were screened for mycobacterial infection using bovine PPD tuberculin
Limited by the small sample size and an assumed exposure in the in-contact baboons, the findings in this study indicate that the ESAT-6 and culture filtrate protein 10 (CFP-10) enzyme-linked immunospot assay (ELISPOT) assays were highly effective in detecting M. tuberculosis and M. intracellulare infections

Summary

Introduction

Both tuberculous and non-tuberculous mycobacteria can cause infection in nonhuman primates (NHP), indicating the existence of potential zoonotic transmission between these animals and visitors to zoos or animal handlers in primate facilities. The majority of the disease-causing species of the genus Mycobacterium belong to two groups, the M. tuberculosis complex (MTC) and the M. avium-intracellulare complex (MAC). With the exception of BCG, these species are pathogenic and can cause tuberculosis (TB) in humans and animals [1,2,3]. Disease caused by MTC pathogens is characterised by tubercle formation in the infected tissues These bacteria are considered obligate intracellular pathogens and the most efficient mode of transmission is via respiratory route [4]. MAC comprises of two species, M. avium and M. intracellulare, and these species are considered opportunistic pathogens, their role in human and animal diseases and their pathogenic potential have become increasingly recognised, especially in immunocompromised persons with HIV-1 infection [7,8]

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