Study of the practicability of various diagnostic methods in the demonstration of swine fever virus of high and low virulence in organs of experimentally infected pigs.

Inoculation experiments were performed with two German strains of swine fever virus. In Experiment I, ten pigs of Danish Landrace were inoculated with a strongly virulent strain, while in Experiment II ten pigs were inoculated with weakly virulent virus. The animals were killed at varying times after inoculation and organs taken out for examination by means of fluorescent antibodies (FA), by the complement fixation test (CFT), and by the agar gel diffusion test (AGT). Cryostat sections of tonsils, spleen and lymph nodes were examined by FA staining. Tissue suspensions from the same organs were inoculated into primary pig kidney tissue cultures, which were also stained with FA. Antigen produced from spleen tissue was used in the CFT and pieces of pancreas tissue in the AGT. The strongly virulent virus could be demonstrated easily by FA in all the inoculated pigs, both by direct staining of cryostat sections and by staining of inoculated tissue cultures. The CFT and AGT were positive when the tested organs originated from animals killed at a more advanced stage of the disease. While the weakly virulent virus could be demonstrated by FA staining of tissues from eight of the ten pigs in Experiment II, virus was found in none of these animals by the FA tissue culture method. The CFT was positive in one case and the AGT in three cases. In both experiments it was found that FA staining of cryostat sections of tonsils was a particularly suitable method for the demonstration of virus. The results are discussed and compared with recent German and American studies.