Abstract
In both humans and animals, controversy exists concerning the duration of protection induced by BCG vaccine against tuberculosis (TB) and whether revaccination enhances protection. A long-term study was undertaken to determine whether BCG-vaccinated calves would be protected against challenge with Mycobacterium bovis 2½ years after vaccination and to determine the effect of revaccination after 2 years. Seventy–nine calves were divided into five groups (n = 15–17 calves/group) with four of the groups vaccinated subcutaneously with 105 CFU of BCG Danish at 2–4 weeks of age and the fifth group serving as non-vaccinated controls. Three of the four BCG-vaccinated groups were revaccinated 2 years after the initial vaccination. One BCG-vaccinated group was revaccinated with BCG. A second group was vaccinated subcutaneously with a TB protein vaccine consisting of biopolyester particles (Biobeads) displaying two mycobacterial proteins, ESAT-6 and Antigen 85A, mixed with an adjuvant. A third group was vaccinated with TB proteins from M. bovis culture filtrate, mixed with an adjuvant. Twenty-three weeks after the BCG revaccination, all animals were challenged endotracheally with virulent M. bovis and a further 13 weeks later, animals were killed and necropsied to determine protection against TB. The BCG-vaccinated animals produced positive tuberculin caudal fold intradermal (15 of 62 animals) and IFN-γ TB test responses (six of 62 animals) at 6 months after vaccination, but not at subsequent time-points compared to the non-vaccinated animals. Calves receiving a single vaccination with BCG vaccine 2½ years prior to challenge were not protected against TB, while those revaccinated with BCG 2 years after the initial vaccination displayed significant reductions in lung and pulmonary lymph node lesion scores compared to the non-vaccinated animals. In contrast, no reduction in lesion scores was observed in the animals revaccinated with the TB protein vaccines with their immune responses biased towards induction of antibody.
Highlights
Bovine tuberculosis (TB) caused by Mycobacterium bovis constitutes a major animal health problem in many countries and improved control strategies are urgently required
The aims of the current study were to establish how long BCG vaccination interfered with the interpretation of the tuberculin intradermal caudal fold test (CFT) and the whole blood interferon-c (IFN-c) test, whether BCG-vaccinated calves were protected against a TB challenge after 2K years and if protection was enhanced by revaccination with BCG or with TB protein vaccines
Vaccination with BCG resulted in higher proportions of animals reacting positively in the tuberculin intradermal CFT and purified protein derivative (PPD) IFN-c tests, but not in the DIVA test, ESAT-6/CFP10 IFN-c test, at 6 months after vaccination compared to those for the nonvaccinated animals, the differences were not significant (Table 1)
Summary
Bovine tuberculosis (TB) caused by Mycobacterium bovis constitutes a major animal health problem in many countries and improved control strategies are urgently required. Further studies are required to determine whether a similar decline in tuberculin intradermal test sensitivity is observed in cattle which are tuberculin-tested using the intradermal caudal fold test (CFT) This test is undertaken in countries in the Southern hemisphere and North America as it is more cost-effective and practical for the yarding conditions which exist in these regions. For this test, bovine tuberculin is inoculated intradermally into the caudal fold of the tail, in contrast to the SICCT where responses to bovine and avian tuberculin are compared following intradermal inoculations in the neck
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