Tonsils of the Soft Palate Do Not Mediate the Response of Pigs to Oral Vaccination with Heat-Inactivated Mycobacterium bovis

Abstract

f Mycobacterium bovis causes animal tuberculosis (TB) in cattle, humans, and other mammalian species, including pigs. The goal of this study was to experimentally assess the responses of pigs with and without a history of tonsillectomy to oral vaccination with heat-inactivated M. bovis and challenge with a virulent M. bovis field strain, to compare pig and wild boar responses using the same vaccination model as previously used in the Eurasian wild boar (Sus scrofa), to evaluate the use of several enzymelinked immunosorbent assays (ELISAs) and lateral flow tests for in vivo TB diagnosis in pigs, and to verify if these tests are influenced by oral vaccination with inactivated M. bovis. At necropsy, the lesion and culture scores were 20% to 43% higher in the controls than those in the vaccinated pigs. Massive M. bovis growth from thoracic tissue samples was observed in 4 out of 9 controls but in none of the 10 vaccinated pigs. No effect of the presence or absence of tonsils was observed on these scores, suggesting that tonsils are not involved in the protective response to this vaccine in pigs. The serum antibody levels increased significantly only after challenge. At necropsy, the estimated sensitivities of the ELISAs and dual path platform (DPP) assays ranged from 89% to 94%. In the oral mucosa, no differences in gene expression were observed in the control group between the pigs with and without tonsils. In the vaccinated group, the mRNA levels for chemokine (C-C motif) receptor 7 (CCR7), interferon beta (IFN-␤), and methylmalonyl coenzyme A mutase (MUT) were higher in pigs with tonsils. Complement component 3 mRNA levels in peripheral blood mononuclear cells (PBMC) increased with vaccination and decreased after M. bovis challenge. This information is relevant for pig production in regions that are endemic for M. bovis and for TB vaccine research.

Testing Eurasian wild boar piglets for serum antibodies against Mycobacterium bovis

“…In general, ELISA test sensitivity in piglets was lower than those reported in previous studies on wild boar of all ages (>70%; Lyashchenko et al, 2008) and in pigs (94%; Beltrán-Beck et al, 2014). In human TB, diagnosis in pediatric patients is also difficult by any available method and serology is not an exception.…”

Oral Vaccination with Heat-Inactivated Mycobacterium bovis Does Not Interfere with the Antemortem Diagnostic Techniques for Tuberculosis in Goats

“…This study demonstrates that the use of oral HI vaccine does not produce interference in diagnostic techniques used in TB eradication programs, as previously was observed in wild boar ( 20 ), pig ( 23 ), red deer ( 25 ), and cattle ( 26 ). The mechanism for this absence of interference has not been elucidated although it may be related to the different absorption routes or to the adjuvants used.…”

“…This limited sampling time schedule was due to these animals entering a second experimental phase where they were subsequently exposed to a group of TB-infected animals in order to continue with an efficacy study. Third, the age of vaccination with the HI vaccine differed among previous studies: red deer (adults), cattle (5–7 months), wild boar (3–4 months), and pigs (3–4 months); sampling schedule after vaccination was also different in these studies: red deer (months 7 and 12), cattle (weekly up to 8 weeks after vaccination), wild boar (day 60), and pigs (day 57) ( 20 , 23 – 26 ). Few studies in humans have focused on the role of vaccine administration-related parameters on vaccine efficacy, since factors as the number and interval between immunizations could trigger different immunological responses ( 40 ).…”

“…Both parenteral and oral vaccinations with IV have shown a significant reduction in TB-compatible lesions in wild boar ( 20 , 22 ). The efficacy of the HI vaccine against a virulent M. bovis field strain has been also demonstrated in domestic pigs, reducing significantly the lesion and culture scores ( 23 ). In these previous studies, the absence of a sensitization effect was suggested, showing neither IGRA nor ELISA positivity in orally immunized wild boar.…”

Detection of Antibodies against Mycobacterium bovis in Oral Fluid from Eurasian Wild Boar

“…Therefore, we could not perform a bacterial culture of target tissues. The "Serum ELISA" used in our pilot study as a reference test has previously shown a sensitivity ranging from 86.4% (in natural wild boar infections) to 94.4% (in experimental wild boar infections, [44]), and a specificity of 100% [45]. Diagnostic accuracy may be underestimated when a reference standard with reduced sensitivity is used.…”