[Oral immunization of suckling piglets against classic swine fever].

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.

[2 strains of swine parvoviruses isolated from aborted fetuses].

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.

[Cultivation of cells in a medium with blood hydrolysate].

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.

[Cultivation and demonstration of the classic swine fever virus].

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.

[Sensitivity of various cell cultures to the swine parvovirus].

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.

[Newcastle disease virus in tissue cultures studied by an immunofluorescence method].

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.

[Stability of Aujezky's disease virus strain MK25 in an aerosol].

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.

[Safety of foot-and-mouth disease vaccines in cell cultures].

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.

[Inactivated vaccines against rhinopneumonitis in horses].

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).

[Creation of an avirulent mutant of Aujeszky's disease virus by exposure to 5-bromodeoxyuridine].

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.

[Immunoprophylaxis of infectious bovine rhinotracheitis].

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.

[Pathogenesis of Aujeszky's disease].

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.

[Study of the immunity in swine vaccinated with type C anti-foot-and-mouth disease vaccine].

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.

[Comparative testing of methods for the control of foot-and-mouth disease vaccines on guinea pigs].

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.