Field Evaluation of the Mycobacterium bovis-BCG Vaccine Against Tuberculosis in Holstein Dairy Cows

摘要

An epidemiological field study was performed on a commercial dairy herd with a 40% prevalence of tuberculosis (on their 1st year of age and 45 days after first partum), in order to evaluate in two stages the Mycobacterium bovis-Bacillus Calmette-Guerin (Mb-BCG) vaccine. For this study, a total of 130 calves (2 weeks or younger), which tested negative to tuberculosis where arranged into two groups: Group 1 included 65 vaccinated calves (with a single dose 1x10-6) and group 2 included 65 non vaccinated animals. During the first 3 days after birth both groups were given pasteurized colostrums and up to weaning time (60 days of age) were fed with pasteurized milk and concentrate. Later from the second to their 24 months of age both groups were gathered in the same pen being exposed in a natural way to animals with tuberculosis. For this study, it was considered that an animal was infected with tuberculosis when a positive reaction was the result to the next series of tests: Tuberculin, IFNγ PPD-B and IFNγ ESAT6-CFP10. The results for the first year showed that the frequency of tuberculosis between both groups was different p = 0.02 (24.5 vs. 8.9%). Also the non-vaccinated calves had a 2.7 higher risk of infection than the vaccinated ones (IC95%: 1.05-7.17). The frequency of the non-vaccinated group during the 2nd year was of 57.1% (24/42), while the vaccinated one was of 36.1% (13/36). This frequency between both groups had no statistical significance perhaps due to the sample size on which the study ended. In addition, the vaccine efficacy by PCR test was determined by nasal secretion. The difference in the elimination rates between both groups were not statistically different with a p = 0.06 (16.6% from the non-vaccinated against 7.7% vaccinated). The results in this study show a protective efficacy at 1 year of age; unfortunately, it was not possible to effectively measure the real efficacy at the 2nd year because of the limited sample size. Future studies should include a higher number of experimental units anticipating factors that compromise the sample size such as: sales or elimination to slaughter by other reasons than tuberculosis.