Summary
In
the European Union, RB51 vaccine can be used only under strictly
controlled conditions for the immunisation of cattle at risk of
infection with Brucella abortus. A test is therefore necessary to
distinguish vaccinated from unvaccinated animals. The complement
fixation test with RB51 antigen (RB51-CFT), dot-blot and gamma-interferon
used to identify vaccinated animals have been described, but sensitivity
of the tests has been poor and positivity transient after calfhood
vaccination. To avail of a rapid and accurate diagnostic tool, the
authors produced, controlled and evaluated an experimental brucellin
prepared from strain RB51 (RB51 brucellin). The potency of this
brucellin was evaluated in guinea-pigs sensitised with RB51 and
compared with a commercially available brucellin. Both allergens
produced similar biological activity in guinea-pigs. The RB51 brucellin
skin test was performed in 10 cattle 414 days after calfhood vaccination
with RB51 when they were negative to the RB51-CFT. The skin test
revealed 60% sensitivity (with a confidence interval of 95%, CI
30.8%-83.3%) and 100% specificity (CI 60.7%-100%). These findings
limit the use of the skin test only for screening to detect RB51
vaccinated herds, not individual animals. Nevertheless, following
intradermal inoculation of RB51 brucellin, a transient antibody
increase to the RB51-CFT was observed, from day 9 to day 20 post
inoculation with RB51 brucellin. This transient antibody increase,
when evaluated in parallel with the RB51 brucellin skin test results,
enables detection of individual vaccinated animals (sensitivity
100%; CI 76.2%-100%).
Keywords
Brucella,
Brucellosis, Brucellin, Cows, Complement fixation test, Diagnosis,
Hypersensitivity, RB51. |