[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.

[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.

[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.

[Newcastle disease virus in tissue cultures studied by an immunofluorescence method]. / Prouchvane na Niukiasulskiia virus v tukanni kulturi s imunofluorestsentniia metod.

Studied was the opportunity to demonstrate the Newcastle Disease Virus in tissue cultures with the employment of an immunofluorescence method. The development was followed up of four strains--the vaccinal ones Hitchner B1, La Sota, and Komarov and the velogenic one, Texas GB, using chick fibroblasts. It was found that the velogenic strain cumulated earlier and more intensely than the vaccinal ones, where the virus was seen to explicitly locate perivascularly. The most dependable demonstration of the virus proved possible with the velogenic strain at the 4th hour, and with the vaccinal strains--from the 6 th to the 10 th hour following the infection of the cultures. The virus antigen cumulated progressively, and with the velogenic strain it was accompanied with the production of a cytopathic effect which destroyed the cells by the 20th hour; with the vaccinal strains the cells remained intact up to the 48th hour following infection.

[Stability of Aujezky's disease virus strain MK25 in an aerosol]. / Stabilnost na virusa na bolestta na Aueski--shtam MK25 v aerozol.

Twenty-two tests were carried out to evaluate the stability of the virus of Aujeszky's disease in aerosol. Use was made of a aerosol chamber of a flow dynamic type, 450 l, of 60 l/min of passing air, 5 min. exposure, 80-100 per cent relative humidity, and temperature range of 14-21.2 degrees C. The size of aerosol particles surpassed 5 micron, and changed according to the composition of the dilution medium of the vaccine. The aerosol was sampled via impinger at the rate of air flow of 5.2 l/min. Tested were the stabilizing properties of 2% glycerin, 10% pepton, 0.8-2.0% saccharose, 2% gelatin, and 5% skimmed milk added to the extender consisting of a 0.2 M phosphate buffer saline, pH 7, specifically for the MK25 strain of the Aujeszky's disease virus in a dispersed status. Highest stability, reaching 11.2% survival rate of the virus in aerosol was recorded at the dispersion of the vaccine in a 0.2 M buffer saline with the addition of 10% pepton and 0.8% saccharose at pH 7.

[Safety of foot-and-mouth disease vaccines in cell cultures]. / Bezvrednost na protivoshapnite vaksini vurkhu kletuchni kulturi.

Experiments were carried out to test imported and home-produced production and experimental series of foot- and-mouth vaccines in cell cultures. It was found that the primary cell cultures of swine kidney were most appropriate to study the innocuity of the F. M. D. vaccines, which, in terms of sensitivity proved of superior quality as compared to the primary cell cultures of calf kidney and the BHK 21 cells. Comparative investigations have revealed that the most promising method for testing the innocuity of the F. M. D. vaccines is the elution of the antigen from the aluminium hydroxide after Dannacher and coll. The problem is discussed of using cell cultures to check the innocuity of F. M. D. vaccines prior to their release.

[Creation of an avirulent mutant of Aujeszky's disease virus by exposure to 5-bromodeoxyuridine]. / Suzdavane na avirulenten mutant ot virusa na Aueski pod vuzdeistvieto na 5-bromdoezoksiuridin.

A mutant with new biologic properties has been obtained at the cultivation of a virulent strain of the Aujeszky's disease virus in chick embryo fibroblast cultures, following a definite number of passages. It has proved resistant when culturing at the present of 5-brom-desoxyuridine and 5-iod-2-desoxyuridine, retaining its infections titer. It produces small plaques and destroys cell cultures of a tiny granular structure, the plaque-forming titer being 5. 6X10-7. The mutant has been shown to be avirulent for sheep, suckling pigs, and rabbits. In confers solid and lasting immunity in vaccinated animals which are virus-free and show no virus excretion. The newly obtained MK-35 mutant has proved to be stable in terms of its new biologic properties.

[Inactivated vaccines against rhinopneumonitis in horses]. / Inaktivirani vaksini sreshtu rinopnevmonita po konete.

Attempts were made to produce inactivated vaccines against horse Herpes virus 1, using various inactivating agents and adjuvants, Best results were obtained with vaccine No 3 (glutaraldehide inactivator and "CTC" adjuvant). Used were two strains of the virus (St. Karaja and Varna). isolated in this country in cell cultures of a sucking pig kidney. Vaccine No 3 showed good immunogenic properties. Its application resulted in the full cease of abortions and respiratory diseases on the base of infection with the horse Herpes virus 1. The vaccination protects newborn colts from rhinopneumonitis if reimmunization of mares is carried out in the 6th-7th month of pregnancy.

[Immunoprophylaxis of infectious bovine rhinotracheitis]. / Vurkhu imunoprofilaktikata na zarazniia rinotrakheit po govedata.

The live attenuated vaccine against infectious rhinotracheitis (LAV), the live trivaccine against infectious rhinotracheitis (LT), the concentrated etanolsaponin vaccine against infectious rhinotracheitis (CESV) and the ethanol-saponin vaccine against infectious rhinotracheitis (ESV) can all be used as immunoprophylactic means in the control of infectious rhinotracheitis in cattle. The first two live vaccines are applied to calves in infection foci, and the two inactivated vaccines are used with cows. The comparative testing of CESV and ESV in experimental conditions on calves has shown that the first possesses higher immunogenicity--used in a twice lower dose it produces several times higher level of the neutralizing antibodies against the infectious rhinotracheitis virus. The use of LAV and LT in the practice under the conditions of established infections of infectious rhinotracheitis in calves has given good results. The immunization of calves at the immediate menace of this infection has lowered the morbidity rate, and death cases were no longer observed. The use of CESV and ESV with pregnant cows on a prophylactic basis against infectious rhinotracheitis has also given good results manifested in the full suppression of abortions.

[Pathogenesis of Aujeszky's disease]. / Vurkhu patogenezata na bolestta na Aueski.

Results are presented of studies on the various localization of the virus of Aujeszky's disease (the avirulent mutant strain MK and the virulent strain 2) in the organism of experimentally infected pigs. At the oral infection of pigs with strain MK the virus has been isolated from the submandibular lymph nodes of the animals only, the pigs being killed on the second and fifth day following infection with a low plaque-forming titer. However, from pigs that have been infected subcutaneously no virus was isolated. In experiments with the virulent strain 2, 15 out of 20 pigs have died up to the seventh day following infection. The examination has revealed that a virus of a high plaque-forming titer was present in almost all organs. Histologic investigations in the experiments with the virulent strain 2 have revealed the presence of a strongly manifested nonsuppurative encephalitis, interstitial pneumonia, necroses, and nuclear inclusion bodies. In the experiments with strain MK these changes have been much more slightly expressed, and after the tenth day of infection they tended to disappear. In the authors' opinion the changes are due to the 'interaction' between the viral particles of the vaccinal virus and the competent cells, being the cytologic manifestation of the enhanced immunobiologic status of the host organism. This is an expression of the cell manifestation of immunogenesis and not of the toxic injury of cells which has been observed in experiments with the virulent strain.

[Study of the immunity in swine vaccinated with type C anti-foot-and-mouth disease vaccine]. / Prouchvane na imuniteta u svine, vaksinirani s protivoshapna vaksina tip C

Experiments were carried out to adapt a cell culture strain of the foot-and-mouth disease virus, type C, to the organism of susceptible pigs. It was established that 4 to 5 passages are needed to adapt the virus, all treated animals showing the symptoms of the disease from the 24 hour following infection which assumed a generalized course. In determining the index of protection (P) of a given F.M.D. vaccine through challenging immunized pigs its value proves to be 4.5. It is stressed that this is a suitable and economic method to evaluate the immunogenic properties of F.M.D. vaccines for pigs.

[Comparative testing of methods for the control of foot-and-mouth disease vaccines on guinea pigs]. / Sravnitelno izpitvane metodite za kontrol na protivoshapnite vaksini v'rkhu morski svincheta

It was found that the so-called direct methods for the control of vaccines give better idea about the immunogenic properties of the F. M. D. vaccines. The direct method for the determination of the value for guinea pigs is to be preferred to the method determining the protection index C, and is convenient, fast and readily applicable in terms of economy and preciseness. Discussed is the problem of employing the method in the research and production activities under laboratory conditions.