Protection against Tuberculosis in Eurasian Wild Boar Vaccinated with Heat-Inactivated Mycobacterium bovis

Abstract

Tuberculosis (TB) caused by Mycobacterium bovis and closely related members of the Mycobacterium tuberculosis complex continues to affect humans and animals worldwide and its control requires vaccination of wildlife reservoir species such as Eurasian wild boar (Sus scrofa). Vaccination efforts for TB control in wildlife have been based primarily on oral live BCG formulations. However, this is the first report of the use of oral inactivated vaccines for controlling TB in wildlife. In this study, four groups of 5 wild boar each were vaccinated with inactivated M. bovis by the oral and intramuscular routes, vaccinated with oral BCG or left unvaccinated as controls. All groups were later challenged with a field strain of M. bovis. The results of the IFN-gamma response, serum antibody levels, M. bovis culture, TB lesion scores, and the expression of C3 and MUT genes were compared between these four groups. The results suggested that vaccination with heat-inactivated M. bovis or BCG protect wild boar from TB. These results also encouraged testing combinations of BCG and inactivated M. bovis to vaccinate wild boar against TB. Vaccine formulations using heat-inactivated M. bovis for TB control in wildlife would have the advantage of being environmentally safe and more stable under field conditions when compared to live BCG vaccines. The antibody response and MUT expression levels can help differentiating between vaccinated and infected wild boar and as correlates of protective response in vaccinated animals. These results suggest that vaccine studies in free-living wild boar are now possible to reveal the full potential of protecting against TB using oral M. bovis inactivated and BCG vaccines.

Assessment of an Oral Mycobacterium bovis BCG Vaccine and an Inactivated M. bovis Preparation for Wild Boar in Terms of Adverse Reactions, Vaccine Strain Survival, and Uptake by Nontarget Species

“…BCG Danish (CCUG strain 27863) was cultured in the laboratory, and the suspension turbidity was adjusted to a 1.0 McFarland standard. The BCG CFU values were calculated by plating aliquots of 10 Ϫ1 to 10 Ϫ6 dilutions onto Coletsos medium in duplicate, as described previously (33,34). The baits contained 0.150 ml of this suspension, equaling 5.2 ϫ 10 5 to 7.6 ϫ 10 5 CFU.…”

“…Tenfold serial dilutions were plated onto OADC-enriched agar-solidified Middlebrook 7H9 broth, to assess the CFU in the suspension. The inoculum was then heat inactivated (34). Animals received the equivalent of 6 ϫ 10 6 to 10 7 CFU.…”

“…Data originated from several vaccination experiments. In total, data on possible adverse effects such as signs of fever, loss of appetite, and body condition deterioration were available for 7 wild boar vaccinated with BCG Danish by the parenteral route and 20 wild boar vaccinated by the oral route in four different experiments (33,34,36; B. Beltrán-Beck and C. Gortázar, unpublished data). For the heat-inactivated vaccine, data were available for 9 parenterally vaccinated wild boar (34; Beltrán-Beck and Gortázar, unpublished) and 12 orally vaccinated wild boar (34; Beltrán-Beck and Gortázar, unpublished).…”

“…Oropharyngeal tonsil, mandibular lymph node (LN), parotid and retropharyngeal LN, lung, tracheobronchial LN, mediastinal LN, spleen, ileocecal valve, mesenteric LN, and hepatic LN specimens from 27 BCG-vaccinated wild boar in four different experiments were collected at necropsy (days 175, 189, 258, and 300 p.v.) and cultured in solid and liquid media using the Bactec MGIT system (Becton, Dickinson, Sparks, MD), as described by Garrido et al (34). The isolates resulting from positive cultures were further characterized by spoligotyping (37), which allows identification of Mycobacterium tuberculosis complex strains based on the presence or absence of spacers in the direct repeat region.…”

“…Wild boar (Sus scrofa) is the main wild reservoir of TB in Spain (1); therefore, recent research has focused on immune responses in this species and the protection conferred after oral immunization with BCG and a prototype based on a heat-inactivated M. bovis preparation (4,33,34). Target animals for vaccination are 3-to 4-month-old piglets (28,32) (an age usually achieved by early summer).…”