Consequence of prior exposure to environmental mycobacteria on BCG vaccination and diagnosis of tuberculosis infection

M. Thom, C.J. Howard, B. Villarreal-Ramos, E. Mead, M. Vordermeier, J. Hope

Research output: Contribution to journalArticlepeer-review

Abstract

The protective efficacy of Mycobacterium bovis-bacille Calmette Guerin (BCG) against tuberculosis (TB) is variable in both humans and cattle. Exposure to environmental mycobacteria is thought to result in inappropriate priming of host immune responses. To investigate the impact of environmental mycobacteria on BCG efficacy, cattle were infected with M. avium, vaccinated with BCG, challenged with M. bovis and skin tested prior to necropsy. Elevated levels of IFN gamma were evident in M. avium-exposed animals before and after BCG vaccination with a bias towards avian purified protein derivative (PPD-A), suggesting that M. avium primed host immune responses. Exposure to M. avium also resulted in a higher frequency of circulatory IFN gamma-producing cells in response to PPD antigens at the time of M. bovis challenge. After M. bovis inoculation, the IFN gamma response to bovine PPD (PPD-B) increased compared to pre-challenge levels, indicating that all animals had been exposed to M. bovis. Skin test responses indicated 2/6 M. avium-BCG-M. bovis animals as reactors and 2/6 as inconclusive compared with 6/6 BCG-M. bovis animals as reactors. M. avium-exposed animals also had fewer lesions and the number of tissues containing viable M. bovis at post-mortem was significantly lower (P
Original languageUndefined/Unknown
Pages (from-to)324-334
Number of pages11
JournalTuberculosis
Volume88
Issue number4
DOIs
Publication statusPublished - 2008

Cite this