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Modelling the variation in skin‐test tuberculin reactions, post‐mortem lesion counts and case pathology in tuberculosis‐exposed cattle: Effects of animal characteristics, histories and co‐infection
Author(s) -
Byrne A. W.,
Graham J.,
Brown C.,
Donaghy A.,
GuelbenzuGonzalo M.,
McNair J.,
Skuce R. A.,
Allen A.,
McDowell S. W.
Publication year - 2018
Publication title -
transboundary and emerging diseases
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.392
H-Index - 63
eISSN - 1865-1682
pISSN - 1865-1674
DOI - 10.1111/tbed.12814
Subject(s) - tuberculin , breed , lesion , herd , tuberculosis , pathology , veterinary medicine , mycobacterium bovis , biology , physiology , medicine , immunology , zoology , mycobacterium tuberculosis
Summary Correctly identifying bovine tuberculosis ( bTB ) in cattle remains a significant problem in endemic countries. We hypothesized that animal characteristics (sex, age, breed), histories (herd effects, testing, movement) and potential exposure to other pathogens (co‐infection; BVDV , liver fluke and Mycobacterium avium reactors) could significantly impact the immune responsiveness detected at skin testing and the variation in post‐mortem pathology (confirmation) in bTB ‐exposed cattle. Three model suites were developed using a retrospective observational data set of 5,698 cattle culled during herd breakdowns in Northern Ireland. A linear regression model suggested that antemortem tuberculin reaction size (difference in purified protein derivative avium [ PPD a ] and bovine [ PPD b ] reactions) was significantly positively associated with post‐mortem maximum lesion size and the number of lesions found. This indicated that reaction size could be considered a predictor of both the extent (number of lesions/tissues) and the pathological progression of infection (maximum lesion size). Tuberculin reaction size was related to age class, and younger animals (<2.85 years) displayed larger reaction sizes than older animals. Tuberculin reaction size was also associated with breed and animal movement and increased with the time between the penultimate and disclosing tests. A negative binomial random‐effects model indicated a significant increase in lesion counts for animals with M. avium reactions ( PPD b− PPD a < 0) relative to non‐reactors ( PPD b− PPD a = 0). Lesion counts were significantly increased in animals with previous positive severe interpretation skin‐test results. Animals with increased movement histories, young animals and non‐dairy breed animals also had significantly increased lesion counts. Animals from herds that had BVDV ‐positive cattle had significantly lower lesion counts than animals from herds without evidence of BVDV infection. Restricting the data set to only animals with a bTB visible lesion at slaughter ( n = 2471), an ordinal regression model indicated that liver fluke ‐ infected animals disclosed smaller lesions, relative to liver fluke‐negative animals, and larger lesions were disclosed in animals with increased movement histories.