[Cultivation and demonstration of the classic swine fever virus]. / Kultivirane i indikatsiia na virusa na klasicheskata chuma po svinete.

Experiments were carried out for the cultivation and indication of the swine pestivirus in several continuous and in primary cell lines, using lapinized and field strains of the virus. It was demonstrated that in the various cell cultures the strains used showed varying rates of growth. In PK-15 and pig embryonic kidney cell lines, the field strains and the virulent Vratsa strain replicated with no preliminary adaptation, forming numerous large fluorescent plaques at the 16th to 18th hour. In the same cultures the lapinized strains K and Hudson had more delayed growth, forming double plaques not until the 36th hour. In rabbit kidney primary cultures the virulent K strain only exhibited growth, and up to the 4th hour at that. All results obtained were in agreement with the results from biologic experiments with pigs and rabbits. Experiments were also carried out for the indication of the swine pestivirus in infected lamellae of the cell cultures used, which were subject to additional treatment for 5 min following primary handling with the specific marked serum with the 1:40,000 solution of Evans blue. The infected cells treated by this method showed light green fluorescence of the protoplasm, with a dark nucleus, while the intact cells had tile-red cytoplasm.

[Cultivation of cells in a medium with blood hydrolysate]. / Kultivirane na kletki v sreda s kruven khidrolizat.

Use was made of fresh blood of swine, diluted with an equal amount of distilled water to produce a protein hydrolysate. Enzyme hydrolysis was effected through extracellular alkaline protease produced by stain DI of Bacillus subtilis. The cell lines BHK-21, PK-15 and spzv were cultured in a nutrient medium containing 0.180-0.200 mg/cm3 alpha-amine nitrogen and relevant growth factors of nonprotein character. It was found that the cells cultured in this medium showed no differences with regard both to morphology and karyology as against the control cells which were treated with the classic medium of Eagle. It was also found that the medium could successfully be used instead of the imported nutrient media.

[Experiments to produce an attenuated strain of the transmissible gastroenteritis virus and its use as a live vaccine]. / Opiti za polchavane na atenuiran shtam na virusa na transmisivniia gastroenterit i izpolzuvaneto mu kato zhiva vaksina.

Serial passages have been performed of a field virus of the transmissive gastroenteritis to obtain an attenuated strain adapted to a permanent cell line of pig kidney, "SPEV". The strain is innocuous for test animals, for pigs of all ages, and for swine during the entire period of pregnancy. It has proved genetically stable. The strain is immunogenic for swine and pigs both under laboratory and under field conditions (in new foci and on stationary farms) and can be used as a live vaccine against transmissive gastroenteritis, either untreated or in a freeze-dried state.