Long-term efficacy of BCG vaccination in goat herds with a high prevalence of tuberculosis

Claudia Arrieta-Villegas,Maite Martín,Alberto Allepuz,Miriam Grasa,Irene Mercader,Mariano Domingo,Zoraida Cervera,Bernat Pérez De Val,Sergio López-Soria

doi:10.1038/s41598-020-77334-1

Abstract

Vaccination of goats against tuberculosis (TB) has been promoted as an ancillary tool for controlling the disease in infected livestock herds. A three-year trial to assess the efficacy of BCG vaccine was carried out in five goat herds. At the beginning of the trial (month 0), all animals were tested for TB using thee different diagnostic tests. Animals negative to all tests were vaccinated with BCG and all replacement goat kids were also systematically vaccinated throughout the trial. All animals were tested by Interferon-gamma release assay (IGRA) using vaccine compatible reagents at months 6, 12, 24, and 36. The risk factors for TB infection were also evaluated. At the end of the study, four out of five farms showed variable reductions of the initial prevalence (93.5%, 28.5%, 23.2%, and 14.3% respectively), and an overall incidence reduction of 50% was observed in BCG vaccinated goats, although adult vaccinated goats showed higher incidences than vaccinated goat kids. The unvaccinated positive animals remaining in herds and adult BCG vaccinated goats significantly enhanced the risk of infection in vaccinated animals. A systematic vaccination of goats with BCG, together with the removal of positive unvaccinated animals, may contribute to reducing the TB prevalence in goat herds.

Highlights

Caprine tuberculosis (TB) is an infectious disease caused by different members of the Mycobacterium tuberculosis complex (MTBC), mainly by Mycobacterium caprae and Mycobacterium bovis[1,2,3]
One of the major challenges for bacillus Calmette-Guérin (BCG) vaccination in livestock is its interference with TB current diagnostic tests, namely the single intradermal test (SIT) or the single intradermal cervical comparative tuberculin test (SICCT) and the Interferon-gamma (IFN-γ) release assay (IGRA)
The vaccine efficacy was determined as the reduction of prevalence, the attributable fraction (AF), and the reduction of incidence of each herd during three years, by using IGRA responses against differentiate infected from vaccinated animals (DIVA) antigens

Summary

Introduction

Caprine tuberculosis (TB) is an infectious disease caused by different members of the Mycobacterium tuberculosis complex (MTBC), mainly by Mycobacterium caprae and Mycobacterium bovis[1,2,3]. In underdeveloped countries or high TB prevalent settings (such as Spain), eradication programs based only on test and slaughter are not always the best cost-effective strategy. In this regard, vaccination of goats against TB has been promoted as an ancillary tool for reducing TB p revalence[13]. Identifying factors that increase or reduce the persistence of TB in infected herds become crucial for eradicating and controlling strategies. Even though previous experimental studies demonstrated that BCG vaccination of goats confers protection against T B30–32, the factors influencing TB persistence should be disclosed to assess the efficacy of vaccination strategies at a herd level

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Results

Conclusion