Division 1

Direct immuno fluorescent test (DIFT)

The principle of the test is the microscopic detection of viral antigens on impression smears or thin cryosections of organ material from pigs suspected of being infected with the ASF virus. Intracellular antigens are detected using FIT-conjugated^f1 specific antibodies. Fluorescent inclusion bodies or granules appear in the cytoplasm of infected cells.

Suitable organs are kidney, spleen, and various lymph nodes. A smear of bone marrow cells might also be used for feral pigs, if their organs are not available or are autolysed.

The test can be performed within two hours. As organ samples can only be obtained from dead animals its use for screening purposes is limited.

This is a highly sensitive test for cases of acute ASF. For subacute or chronic forms, the DIFT presents only a sensitivity of approximately 40 %, probably due to the presence of antigen-antibody complexes, which block the reaction with the ASF-conjugated antibody. Confidence in the test result may be limited by doubtful staining, particularly where considerable experience in performing the test has not been acquired or if the organs tested are autolysed.