Final answer:
Animals that test positive for Mycobacterium bovis in SICCT have been exposed to the bacteria and exhibit a cellular immune response.
Step-by-step explanation:
Animals that are positive for Mycobacterium bovis in the Single ID comparative cervical tuberculin test (SICCT) have been exposed to the bacteria and exhibit a cellular immune response to it. A positive test is indicated by a raised red area called an induration a couple of days after the test. This induration is a consequence of the accumulation of activated macrophages.