Detectability of bovine TB using the tuberculin skin test does not vary significantly according to pathogen genotype within Northern Ireland

• Published in: Infection, genetics and evolution genetics and evolution, 2013-10, Vol.19, p.15-22
• Main Authors: Wright, David M., Allen, Adrian R., Mallon, Thomas R., McDowell, Stanley W.J., Bishop, Stephen C., Glass, Elizabeth J., Bermingham, Mairead L., Woolliams, John A., Skuce, Robin A.
• Format: Article
• Language: English
• Subjects: Animals; Bovine tuberculosis; Cattle; community structure; data collection; delayed hypersensitivity; Detectability; disease control; disease incidence; farming systems; Female; genetic markers; Genotype; host specificity; industry; Male; minisatellite repeats; Mycobacterium avium; Mycobacterium bovis; Mycobacterium bovis - classification; Mycobacterium bovis - genetics; Mycobacterium bovis - isolation & purification; Northern Ireland - epidemiology; pathogens; slaughterhouses; tuberculin; Tuberculin test; Tuberculin Test - methods; Tuberculin Test - veterinary; Tuberculosis, Bovine - diagnosis; Tuberculosis, Bovine - epidemiology; Tuberculosis, Bovine - microbiology; virulence; watersheds
• ISSN: 1567-1348; 1567-7257
• DOI: 10.1016/j.meegid.2013.05.011

•Bovine tuberculosis in the UK is primarily detected using the tuberculin skin test.•21,000 Mycobacterium bovis isolates from cattle in Northern Ireland (2003–2010) were genotyped.•Responses to the tuberculin skin test did not vary among genotypes.•The proportion of cases detected by skin testing did not vary among genotypes.•We show that genotypes of M. bovis in NI have similar detectability to the skin test. Strains of many infectious diseases differ in parameters that influence epidemic spread, for example virulence, transmissibility, detectability and host specificity. Knowledge of inter-strain variation can be exploited to improve management and decrease disease incidence. Bovine tuberculosis (bTB) is increasingly prevalent among farmed cattle in the UK, exerting a heavy economic burden on the farming industry and government. We aimed to determine whether strains of Mycobacterium bovis (the causative agent of bTB) identified and classified using genetic markers (spoligotyping and multi-locus VNTR analysis) varied in response to the tuberculin skin test; this being the primary method of bTB detection used in the UK. Inter-strain variation in detectability of M. bovis could have important implications for disease control. The skin test is based on a differential delayed type hypersensitivity (DTH) response to intradermal injections of purified protein derivative (PPD) from M. bovis (PPD-B) and Mycobacterium avium (PPD-A). We searched for an association between skin test response (PPD-B skin rise minus PPD-A skin rise) and M. bovis genotype at the disclosing test in culture-confirmed cases using a field dataset consisting of 21,000 isolates belonging to 63 genotypes of M. bovis from cattle in Northern Ireland. We found no substantial variation among genotypes (estimated responses clustered tightly around the mean) controlling for animal sex, breed and test effects. We also estimated the ratio of skin test detected to undetected cases (i.e. cases only detected at abattoir). The skin test detection ratio varied among abattoirs with some detecting a greater proportion of cases than others but this variation was unrelated to the community composition of genotypes within each abattoir catchment. These two lines of evidence indicate that M. bovis genotypes in Northern Ireland have similar detectability using the skin test.