Abstract
The brucellin skin test and the lymphocyte transformation test were compared in heifers infected with virulent Brucella abortus strain 544, heifers vaccinated against brucellosis and unexposed cattle. Results of the in vitro lymphocyte transformation test were consistently positive for all 9 Brucella-infected heifers while the skin test was consistently positive for 6 of the 9 heifers. In 7 heifers repeatedly vaccinated with B. abortus strain-19 vaccine the in vitro test classified 3 animals as positive whereas the skin test identified all the animals as infected during most of the experimental period. Four heifers injected with a single dose of B. abortus strain 19 were consistently negative to the lymphocyte transformation test while the skin test classified all the animals as infected during most of the experimental period. The skin test gave strong reactions indicative of Brucella infection in heifers vaccinated with 'Duphavac' and 'Abortox' vaccines whereas the lymphocyte transformation test was consistently negative with these vaccines. The two tests were negative in unexposed cattle. It was concluded that the in vitro test correlated better with Brucella isolation than the in vivo test did and that the lack of agreement between the results of the two tests is likely to be due to the different antigens used in the assays.