Abstract
Vaccination against tuberculosis (TB) is prohibited in cattle or other species subjected to specific TB eradication campaigns, due to the interference that it may cause with the official diagnostic tests. However, immunization with a heat-inactivated (HI) Mycobacterium bovis vaccine via the oral route has been suggested to overcome this issue. In this study, the main goal was to assess the interference of the HI vaccine by different routes of administration using a previous vaccination and re-vaccination (boosting) protocol. TB-free kid goats were divided into three groups: oral (n = 16), intramuscular (IM; n = 16), and control (n = 16). Results showed that there was a significant difference in the percentage of animals positive to the single intradermal test (SIT) and blood based interferon-gamma release assay (IGRA) caused by vaccination when performed in the IM group compared to the oral group (p < 0.001). Nevertheless, no positivity to the SIT or IGRA test was observed in orally vaccinated goats regardless of the different interpretation criteria applied. None of the groups presented positive antibody titers using an in-house ELISA and samples collected 2 months after the boost. These results suggest the potential usefulness of the HI vaccine by the oral route in goats to minimize the interference on diagnostic tests (skin and IGRA tests) and reducing the necessity of defined antigens to replace the traditional purified protein derivatives for diagnosis. Finally, the results pave the way to future efficacy studies in goats using different routes of HI vaccination.
Highlights
Tuberculosis (TB) in goats is mostly caused by Mycobacterium bovis and Mycobacterium caprae, both of which have been isolated in Spain from other domestic and wildlife species [1,2,3]
The application of non-sensitizing vaccines could be a suitable choice, in species not subjected to eradication programs or in regions/countries where the investment in distinguish vaccinated from infected animals (DIVA) antigens is not affordable, since the implementation of DIVA tests at a large scale entails high logistical demands and costs
To the best of our knowledge, this is the first study evaluating the interference on TB cell and antibody-based diagnosis caused by the vaccination with a M. bovis HI vaccine in goats, as well as the effect of booster re-vaccination protocols
Summary
Tuberculosis (TB) in goats is mostly caused by Mycobacterium bovis and Mycobacterium caprae, both of which have been isolated in Spain from other domestic and wildlife species [1,2,3]. Some regions with a high density of caprine flocks have implemented specific TB control programs for goats [4] These programs are mainly based on the application of skin tests [single intradermal tuberculin test and comparative intradermal tuberculin test, single intradermal test (SIT) and SCIT tests, respectively], while using the blood-based interferongamma release assay (IGRA) as an ancillary test under specific circumstances [2]. The development of immunization schemes against TB to reduce the diagnostic interferences and the use of DIVA antigens would be of paramount importance, since they could accelerate the control/ eradication process. Such schemes may be more cost-effective, which is important for other species than cattle
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