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Juste RA. Bovine TB serological diagnosis: blindness rather than conundrum. Vet Res Commun 2024; 48:1309-1310. [PMID: 38263502 DOI: 10.1007/s11259-023-10288-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Accepted: 12/21/2023] [Indexed: 01/25/2024]
Affiliation(s)
- Ramon A Juste
- NEIKER-BRTA, Berreaga, 1, Derio (Bizkaia), 48160, Spain.
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Madden JM, O'Donovan J, Casey-Bryars M, Sweeney J, Messam LL, McAloon CG, More SJ, Kenny K, Ryan E, Gormley E. The impact of changing the cut-off threshold of the interferon-gamma (IFN-γ) assay for diagnosing bovine tuberculosis in Ireland. Prev Vet Med 2024; 224:106129. [PMID: 38325115 DOI: 10.1016/j.prevetmed.2024.106129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2023] [Revised: 01/02/2024] [Accepted: 01/15/2024] [Indexed: 02/09/2024]
Abstract
In Ireland, the interferon-gamma (IFN-γ) assay is routinely used as an ancillary test interpreted in parallel with the single intradermal comparative tuberculin test (SICTT) to maximize the detection of bovine tuberculosis (bTB) infected animals. Up until 2018, a positive test result was recorded in the IFN-γ ELISA assay following whole blood stimulation with purified protein derivative (PPD)-bovine (B), PPD-avian (A) and nil sample (N), using the interpretation criteria, B-N > 50 optical density units (OD), B > 100 and B-A > 0. Following a review of available data, the threshold of the B-A component changed to B-A > 80. As predicting the impact of changing the cut-off thresholds for the IFN-γ test de novo is challenging, the aims of this study were to follow animals that initially tested negative using the new IFN-γ assay interpretation criteria and investigate their future risk of disclosure with bTB, with a focus on animals that otherwise would have been removed when using the older interpretation criteria (0 < B-A ≤ 80). Enrolled animals (n = 28,669 cattle from 527 herds) were followed up for two years (2019-2021), or to point of bTB detection or death. At the end of follow-up, 1151 (4.0%) of enrolled animals were bTB cases. The majority of these cases were diagnosed using SICTT (80.5%). The cumulative number of positive animals that would have been removed if the old cut-off (0 < B-A ≤ 80) was used amounted to 1680 cattle (5.9% of the enrolled cohort). Of these, 127 (7.5%) were diagnosed with bTB during follow-up. In contrast, 1024 of the 1151 cattle which subsequently tested positive during the study period following a negative IFN-γ test would not have been identified with the old or new IFN-γ cut-off criteria. Survival analysis showed that animals that would have been removed under the old interpretation criteria were at increased risk of a positive diagnosis with bTB during follow-up compared to other test negative animals. A newly developed risk prediction model (using a Cox proportional hazard model) showed that age, animal number of SICTT tests, number of inconclusive SICTT tests, B-A (IFN-γ assay), B-N (IFN-γ assay), animals from store herds and the percentage of the rest of the herd that were positive during the breakdown were statistically significantly associated with bTB detection. However, inclusion of the IFN-γ OD variables did not show added value in terms of prediction performance of the model.
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Affiliation(s)
- Jamie M Madden
- Centre for Veterinary Epidemiology and Risk Analysis (CVERA), University College Dublin (UCD), Dublin, Ireland.
| | - Jim O'Donovan
- Department of Agriculture, Food and the Marine, Regional Veterinary Laboratory, Cork, Ireland
| | - Miriam Casey-Bryars
- Centre for Veterinary Epidemiology and Risk Analysis (CVERA), University College Dublin (UCD), Dublin, Ireland
| | - James Sweeney
- Department of Mathematics and Statistics, University of Limerick, Limerick, Ireland
| | - Locksley L Messam
- Section: Herd Health and Animal Husbandry, School of Veterinary Medicine, University College Dublin (UCD), Dublin, Ireland
| | - Conor G McAloon
- Section: Herd Health and Animal Husbandry, School of Veterinary Medicine, University College Dublin (UCD), Dublin, Ireland
| | - Simon J More
- Centre for Veterinary Epidemiology and Risk Analysis (CVERA), University College Dublin (UCD), Dublin, Ireland
| | - Kevin Kenny
- Department of Agriculture, Food and the Marine, Central Veterinary Research Laboratory, Backweston Co., Kildare, Ireland
| | - Eoin Ryan
- Department of Agriculture, Food and the Marine, Ruminant Animal Health Division, Backweston, Co., Kildare, Ireland
| | - Eamonn Gormley
- Tuberculosis Diagnostics and Immunology Research Laboratory, School of Veterinary Medicine, University College Dublin (UCD), Dublin, Ireland
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Juste RA, Fernández-Veiga L, Fuertes M, Fernández-Ortiz de Murua I, Cardona G, Geijo MV, Garrido JM, Sevilla IA. A humoral diagnostic test outperforms cellular tests in a farm with a latent tuberculosis outbreak caused by a new Mycobacterium tuberculosis complex spoligotype that affected sheep but not goats. Front Vet Sci 2024; 10:1310205. [PMID: 38317788 PMCID: PMC10839146 DOI: 10.3389/fvets.2023.1310205] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Accepted: 12/26/2023] [Indexed: 02/07/2024] Open
Abstract
Tuberculosis (TB) is a disease caused by members of the M. tuberculosis complex (MTC) that affects numerous species. M. caprae, a member of the complex which is close to M. bovis, is emerging and affects several different hosts that include goats, cattle, sheep, pigs, rabbits, wild boar, red deer, foxes and also humans. A new M. caprae spoligotype (SB2737) was isolated from an outbreak of sheep tuberculosis affecting a mixed sheep (323)-goat (29) farm in 2021. The index case was detected by the La Rioja slaughterhouse veterinary inspection. Tracing back to the farm of origin, both species were submitted to Comparative Intradermal Tuberculin Test (CITT) and M. bovis-specific antibody ELISA tests. A subsample was also examined by IFN-γ release assay (IGRA) and all positives were slaughtered and pathologically and microbiologically investigated. Only 1.2% of sheep and no goat were positive in the CITT, and 11.4% in the IGRA sheep subsample, while up to 36.8% were positive in two consecutive M. bovis-specific antibody ELISA tests. Goats had always tested negative in annual intradermal follow-up since 2013. Upon confirmation of the immunologically positive sheep at slaughter, all the remaining negative animals were killed and 29.2% of sheep were still found infected. This raised the final overall prevalence to 37.5%. Antibody ELISA was the most sensitive (81.4%) in vivo detection method still showing a 85.0% specificity relative to pathological and microbiological tuberculosis status. It was nearly 10 times more sensitive than skin test and had an 86.8% positive predictive value. Notwithstanding a possible singular pathogenesis of the new spoligotype, this outbreak adds up to previous reports suggesting that sheep tuberculosis could be huge reservoir of infection worldwide overlooked by skin test low sensitivity or simply lack of investigation. This makes it urgent to extend the use antibody tests to address the Trojan horse of hidden M. tuberculosis complex infections on bovine TB control programs.
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Affiliation(s)
- Ramon A. Juste
- Animal Health Department, NEIKER – Basque Institute for Agricultural Research and Development, Basque Research and Technology Alliance (BRTA), Derio, Spain
| | - Leire Fernández-Veiga
- Animal Health Department, NEIKER – Basque Institute for Agricultural Research and Development, Basque Research and Technology Alliance (BRTA), Derio, Spain
| | - Miguel Fuertes
- Animal Health Department, NEIKER – Basque Institute for Agricultural Research and Development, Basque Research and Technology Alliance (BRTA), Derio, Spain
| | | | - Guillermo Cardona
- Servicio de Ganadería, Diputacion Foral de Alava, Vitoria-Gasteiz, Spain
| | - Maria V. Geijo
- Animal Health Department, NEIKER – Basque Institute for Agricultural Research and Development, Basque Research and Technology Alliance (BRTA), Derio, Spain
| | - Joseba M. Garrido
- Animal Health Department, NEIKER – Basque Institute for Agricultural Research and Development, Basque Research and Technology Alliance (BRTA), Derio, Spain
| | - Iker A. Sevilla
- Animal Health Department, NEIKER – Basque Institute for Agricultural Research and Development, Basque Research and Technology Alliance (BRTA), Derio, Spain
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