Evaluation of gamma interferon and antibody tuberculosis tests in alpacas.
We describe the performance of cell-based and antibody blood tests for the antemortem diagnosis of tuberculosis (TB) in South American camelids (SAC). The sensitivity and specificity of the gamma interferon (IFN-γ) release assay, two lateral flow rapid antibody tests (Stat-Pak and Dual Path Platform [DPP]), and two enzyme-linked immunosorbent assay (ELISA)-based antibody tests (Idexx and Enferplex) were determined using diseased alpacas from Mycobacterium bovis culture-confirmed breakdown herds and TB-free alpacas from geographical areas with no history of bovine TB, respectively. Our results show that while the sensitivities of the IFN-γ and antibody tests were similar (range of 57.7% to 66.7%), the specificity of the IFN-γ test (89.1%) was lower than those of any of the antibody tests (range of 96.4% to 97.4%). This lower specificity of the IFN-γ test was at least in part due to undisclosed Mycobacterium microti infection in the TB-free cohort, which stimulates a positive purified protein derivative (PPD) response. The sensitivity of infection detection could be increased by combining two antibody tests, but even the use of all four antibody tests failed to detect all diseased alpacas. These antibody-negative alpacas were IFN-γ positive. We found that the maximum sensitivity could be achieved only by the combination of the IFN-γ test with two antibody tests in a "test package," although this resulted in decreased specificity. The data from this evaluation of tests with defined sensitivity and specificity provide potential options for antemortem screening of SAC for TB in herd breakdown situations and could also find application in movement testing and tracing investigations.
Animal Health and Veterinary Laboratories Agency-Weybridge, Addlestone, Surrey, United Kingdom. Shelley.Rhodes@ahvla.gsi.gov.uk
Shelley
S
Rhodes
Tom
T
Holder
Derek
D
Clifford
Ian
I
Dexter
Jacky
J
Brewer
Noel
N
Smith
Laura
L
Waring
Tim
T
Crawshaw
Steve
S
Gillgan
Konstantin
K
Lyashchenko
John
J
Lawrence
John
J
Clarke
Ricardo
R
de la Rua-Domenech
Martin
M
Vordermeier
D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood*; D000942:Antigens, Bacterial / Q000276:immunology; D002161:Camelids, New World; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D007371:Interferon-gamma / Q000097:blood*; D009163:Mycobacterium bovis / Q000276:immunology; D012680:Sensitivity and Specificity; D012698:Serologic Tests; D014373:Tuberculin / Q000097:blood / Q000276:immunology; D014374:Tuberculin Test / Q000379:methods / Q000662:veterinary*; D014376:Tuberculosis / Q000175:diagnosis / Q000276:immunology / Q000382:microbiology / Q000662:veterinary*
D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D014373:Tuberculin; D007371:Interferon-gamma