Should they stay, or should they go? Relative future risk of bovine tuberculosis for interferon-gamma test-positive cattle left on farms.
Bovine tuberculosis (bTB), caused by Mycobacterium bovis, is a serious infectious disease that remains an ongoing concern for cattle farming worldwide. Tuberculin skin-tests are often used to identify infected animals (reactors) during test-and-cull programs, however, due to relatively poor sensitivity, additional tests can be implemented in parallel. For example, in Northern Ireland interferon-gamma (IFN-g) testing is used in high-risk herds. However, skin-test negative animals which are positive to the IFN-g test are not required by law to be slaughtered - therefore the final choice for these animals' fate is left with the owner. During this study we investigated whether these animals represented a greater risk of becoming a skin reactor, relative to IFN-g test negative animals from the same herds. Our study population included 1107 IFN-g positive animals from 239 herds. A Cox-proportional hazard model indicated that animals which tested IFN-g positive were 2.31 times (95% CI: 1.92-2.79; P < 0.001) more likely to become a reactor compared with IFN-g negative animals. Animals from dairy herds, and from herds in the south-east, were of higher risk than animals from beef herds and other regions, respectively. Our findings suggest that IFN-g positive animals represent a higher risk of failing a skin-test in the future, indicating the value of IFN-g testing for identifying early-stage infected animals. These IFN-g positive animals are not under any disease restriction, and may move freely (trade), which may put recipient herds at increased risk. Our findings provide important evidence for stakeholders engaged in bTB eradication programs.
Veterinary Science Division, Department of Bacteriology, Agri-food and Biosciences Institute, Stormont, Belfast, BT4 3SD, UK. angela.lahuerta-marin@afbini.gov.uk.
Angela
A
Lahuerta-Marin
Veterinary Science Division, Department of Bacteriology, Agri-food and Biosciences Institute, Stormont, Belfast, BT4 3SD, UK. mjg695@gmail.com.
Martin
M
Gallagher
Veterinary Science Division, Department of Bacteriology, Agri-food and Biosciences Institute, Stormont, Belfast, BT4 3SD, UK. stewart.mcbride@afbini.gov.uk.
Stewart
S
McBride
Veterinary Science Division, Department of Bacteriology, Agri-food and Biosciences Institute, Stormont, Belfast, BT4 3SD, UK. robin.skuce@afbini.gov.uk.|School of Biological Sciences, Queen's University Belfast, Belfast, BT7 1NN, UK. robin.skuce@afbini.gov.uk.
Robin
R
Skuce
Veterinary Epidemiology Unit, Department of Agriculture and Rural Development, Dundonald House, Stormont, Belfast, UK. fraser.menzies@dardni.gov.uk.
Fraser
F
Menzies
Veterinary Science Division, Department of Bacteriology, Agri-food and Biosciences Institute, Stormont, Belfast, BT4 3SD, UK. jim.mcnair@afbini.gov.uk.
Jim
J
McNair
Veterinary Science Division, Department of Bacteriology, Agri-food and Biosciences Institute, Stormont, Belfast, BT4 3SD, UK. stanley.mcdowell@afbini.gov.uk.
Stanley W J
SW
McDowell
Veterinary Science Division, Department of Bacteriology, Agri-food and Biosciences Institute, Stormont, Belfast, BT4 3SD, UK. andrew.byrne@afbini.gov.uk.
Andrew W
AW
Byrne
D000818:Animals; D002417:Cattle; D005260:Female; D007371:Interferon-gamma; D008297:Male; D009163:Mycobacterium bovis / Q000502:physiology*; D009660:Northern Ireland / Q000453:epidemiology; D012307:Risk Factors; D014374:Tuberculin Test / Q000662:veterinary*; D014380:Tuberculosis, Bovine / Q000453:epidemiology* / Q000382:microbiology
D007371:Interferon-gamma