[Replication of a local strain of swine parvovirus in swine kidney cell cultures]. / Replikatsiia na mesten shtam parvovirus po svinite v kletuchni kulturi ot svinski bubrek.

The kinetics of replication of strain of parvovirus in swine was investigated in the primary cell cultures of swine kidney. The morphologic changes were traced in inoculated cultures by microscopic observation and the replication of the virus in the cells by immune-fluorescent examinations. The quality of the virus in the cell monolayer and in the nutritive medium, in the different periods after the infection, was determined by hemagglutination test. By the immune-fluorescent examinations, the virus was proved still in the first hours, while the first morphologic changes of the monolayer were determined 72 hours after the infection. The nuclear fluorescent appears at the 12-th hour and increases its intensity 24 hours after the infection. At the 72-nd hour and later predominates the cytoplasmatic fluorescent. The cell monolayer produces virus up to the 96-th hour, and the virus titer reaches its maximum 120 hours after the inoculation, which is the most appropriate moment for the yield of virus.

[Demonstration of the swine fever virus by the infection of cell cultures of lymphocytes and lysed red blood cells]. / Dokazvane na virusa na chumata po svinete chrez zaraziavane na kletuchni kulturi s limfotsiti i lizirani cherveni kruvni kletki.

A method was worked out for the diagnosing of swine fever by means of infecting sensitive cell cultures on lamellae with lyzed red blood cells and lymphocytes, the demonstration being performed through immunofluorescence. The new method made it possible to avoid killing of suspected animals for diagnostic purposes (in order to prepare suspensions of parenchymal organs and isolate the virus) while the characteristic morphologic changes were still not well manifested.

[2 strains of swine parvoviruses isolated from aborted fetuses]. / Prouchvane na dva shtama parvovirus po svinete, izolirani ot abortirani fetusi.

Two hemagglutinating virus strains were isolated (in primary cell cultures of pig kidneys) from viscera of aborted swine fetuses. A number of serologic, cytologic, physico-chemical, and laboratory investigations with the strains revealed that they belonged to the group of porcine parvovirus (PPV). The isolation of SPV from aborted fetuses pointed to the fact that the disease had been widespread among the swine population and plays a part in reproduction disturbances that have come to be known recently. The isolated strains did not produce a clear and distinguishable cytopathic effect in inoculated cell cultures. They, however, could be demonstrated in the cultures indirectly through cytologic investigation (the demonstration of intranuclear inclusion bodies, type B after Cowdry, through hemagglutination tests, and via immunofluorescent microscopy.

[Sensitivity of various cell cultures to the swine parvovirus]. / Chuvstvitelnost na razlichni kletuchni kulturi kum parvovirusa po svinete.

Attempts were made to culture the swine parvovirus under laboratory conditions. A reference strain and a field isolate were used along with steady cell lines of pig kidney PK-15, IBAS-2, and SPEV as well as primary and secondary cell cultures of pig kidney. It was found that the steady cell lines were slightly sensitive or totally unsusceptible to the swine parvovirus. The could serve for its isolation from pathologic material and culturing in laboratory conditions. Both the primary and the secondary cell cultures proved strongly susceptible to the virus, and they could be used for the isolation of filed strains as well as for the laboratory maintenance of the virus. The strains used produced no clearly distinguishable cytopathic effects in the inoculated cell cultures. The morphologic changes that set in following inoculation with higher amounts of the virus could be seen under the light microscope and could be evaluated through cytologic investigations (the presence of intranuclear inclusion bodies). The virus could be most readily demonstrated in the infected cell cultures via the hemagglutination test.

[Isolation of Escherichia coli O 157 from pigs with diarrhea]. / Izolirane na Escherchia coli O 157 ot praseta s diariia.

Biochemical and serologic studies were carried out with Escherichia coli strains isolated from pigs affected with diarrhea. A total of 161 were investigated, 13 (8.01 per cent) of which were found to belong to serogroup O 157. Almost all strains proved beta-hemolytic, enterotoxigenic, and K 88-positive. The strains of this serogroup were found for the first time in this country in swine colibacteriosis.

[Oral immunization of suckling piglets against classic swine fever]. / Oralna imunizatsiia na bozaeshti praseta protiv klasichna chuma pri svinete.

Attempts were made to immunize suckling pigs against classic swine fever. The pigs were treated orally, originating from sows which were immunized on the 30th-40th and the 90th-100th day of pregnancy, as well as from sows which were vaccinated one month prior to impregnation. A Bulgarian lapinized K vaccine and a Soviet LK-VNIIVViM cell culture were used (immunization being carried out 1-2 hours before the newborns were allowed to suck) at the rate of 150 doses for both vaccines. It was demonstrated that the application of a live vaccine, which was patterned as cited above, eliminated the inhibiting action of colostral antibodies and induced stable postvaccinal immunity. However, the effectiveness of the immunity conferred depended on the vaccine used in each specific case. The Soviet vaccine, in which the amount of the virus per vaccinal dose was five times as much, was shown to be more appropriate to the needs for oral immunization of suckling pigs of sows that were immune to classic swine fever than the lapinized K vaccine.

[Isolation of conjugated sera for the immunofluorescence demonstration of swine parvovirus]. / Poluchavane na koniugirani serumi za imunofluorestsentno dokazavane na parvovirusa po svinete.

High-titer, specific serum against porcine parvovirus was obtained via hyperimmunization of rabbits, with the use of a Bulgarian isolate that had been partially purified after a known, modified technique. A specific, high-titer conjugate was produced for the immunofluorescence diagnosis of porcine parvoviruses. The microscopic observation of the lamellae of cell cultures, treated with the conjugate, revealed the presence of a specific, typically granulated perinuclear (mostly unilaterally) and, in some cases nuclear fluorescence--at negative reaction in the control preparations. Immunofluorescent light was also established in cell cultures infected with the virus at highest dilution. It showed that immunofluorescence microscopy could be employed to demonstrate even the lowest amounts of the virus.

[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.