Final answer:
The Single Intradermal Comparative Cervical Tuberculin (SICCT) test uses two injection sites to diagnose tuberculosis (TB) in animals. It relies on delayed hypersensitivity, an immune response that is measured and compared between two different tuberculin injections after 72 hours.
Step-by-step explanation:
The Single Intradermal Comparative Cervical Tuberculin (SICCT) test, also known as the tuberculin skin test, is used to diagnose tuberculosis (TB) in animals, notably cattle. In the SICCT test, two injection sites are selected on the neck of the animal. One site is injected with avian tuberculin and the other with bovine tuberculin. The test measures the immune response to the tuberculin injected, and the size of the reaction is compared between the two sites after 72 hours to determine if the animal has been exposed to TB.
Delayed hypersensitivity, as in the case of the tuberculin reaction, is a cell-mediated immune response that involves the T-cell cytokine-mediated inflammatory response, resulting in local inflammation or tissue damage due to activated macrophages. Identifying exposure to Mycobacterium tuberculosis is crucial because a positive tuberculin test indicates that the subject has been exposed to the bacteria and exhibits a cellular immune response to it.