[The interferon reaction of the leukocytes in newborn infants and their mothers]. / Interferonna reaktsiia na levkotsitite pri novorodeni i tekhnite maiki.

The interferon reaction of leucocytes (IRL) in the newborns and their mothers were examined in vitro. The ability of leucocytes, obtained from the blood of the umbilical cord of newborns, to synthesize interferon was established in 48.78% of the investigated newborns while in their mothers the relative part was 70.73%. The mean geometrical titre of the leucocytic interferon was lower than that of the parturients (30.90-1.02 against 41.69-1.70).

[Typing of Newcastle virus isolates by mean death time of chickens in the cloacal test]. / Tipizirane na izolati na Niukiasulskiia virus po srednoto vreme za umirane na pileta v kloachen test.

The mean death time in a cloacal test (MDT/CT) was employed to define the pathogenic type of isolates of the Newcastle Disease virus (NDV) with 5-week-old birds. The results were compared with the use of standard methods for typing--the mean death time with 10-day-old chick embryos as defined by the minimal lethal dose (MDT/MLD), the intracerebral pathogenic index for day-old chicks (ICPI), the intravenous pathogenic index for 6-8-weak-old birds (IVPI). Sixteen local isolates and 6 reference strains of NDV were used in the experiments. Using the author's modified technique to determine MDT/CT the velogenic strains of NDV were strictly differentiated from the local meso- and lentogenic NDV isolates and reference strains. At the same time differentiation was made of the velogenic-viscerotropic and of the velogenic-neurotropic isolates (strains). The values of MDT/CT in the experiments with isolates of the velogenic pathotype (14 in number) varied from 4.0 to 7.8 (mean = 5.32 +/- 0.26), and by them the isolates were graded for virulence within the respective (viscero- and neurotropic) group. For the lentogenic (5) and the mesogenic (3) isolates and strains these values were approx. 10. With 6 local NDV isolates of the velogenic-viscerotropic pathotype the test birds showed edema of the head and neck, with swelling of the eyelids, and post mortem the accumulation of semi-liquid fibrinous mass under the skin in these parts of the body and conjunctivitis were found. MDT/CT in the modification employed proved simple and readily applicable, and superior to IVPI in reliability, and is, therefore, suggested for use in typing and differentiating NDV isolates.

[Comparative study of strains of Newcastle disease virus in cell cultures of chick embryo fibroblast]. / Sravnitelni prouchvaniia na psevdochumni virusni shtamove v kletuchni kulturi ot fibroblasti na kokoshi embrioni.

Comparative investigations were carried out with local velogenic strains (2 viscerotropic--Haskovo and Bregovo, and neurotropic--Rosa and Toutrakan) and 6 standard strains of the Newcastle disease virus, belonging to various pathogenic groups, in tissue cultures of chick embryo fibroblasts. The four local strains as well as the velogenic one (The. GB) and the mesogenic standard strains (Komarov, Roakin, and Hertfordshire) were reproduced in such cultures, producing a clear cytopathic effect without preliminary adaptation passages. The two strains studied parallel to the others, that were of velogenic pathogenic type (La Sota and Hitchner B1) did not produce cytopathogenic effect, and the cultural liquids did not poses agglutination activity with regard to chicken erythrocytes. The average infection titers in tissue cultures of chick embryo fibroblasts (TCID50) for the particular strains in an experiment varied in a wide range and proved higher with the velogenic (regardless of the fact that they belonged to the viscero- and neurotropic pathogenic type) that with the mesogenic strains. The TCID50/cm3 titer ratio of the strains with regard to their corresponding infection titers in chick embryos (EID50/cm3) also varied in a wide range, but invariably in favour of EID50. The latter was more strongly expressed for the mesogenic strain than for the velogenic pathotype strain of the Newcastle disease in experimental conditions.

[Plaque formation by strains of Newcastle disease virus in monolayers of chick embryo fibroblasts]. / Plakoobrazuvane na psevdochumni virusni shtamove v monosloi ot fibroblasti ot kokoshi embrioni.

Comparative studies were carried out with 4 local velogenic strains (2 viscerotropic and 2 neutropic) and 6 standard strains of the Newcastle disease virus of the various pathogenic groups with regard to their plaque-forming capacity in a monolayer of tissue cultures (TC) of chick embryo fibroblasts (CEF) under agar cover, after a routinely employed method. It was found that the velogenic strains produce a heterogenic (in terms of plaque size) population of bright, mat-white plaques regardless of their belonging to the viscero-, resp, neurotropic pathogenic type. The mesogenic produced only small, bright plaques, while the lentogenic strains produced no plaques. The plaque-forming unit titers per cm3 in TC of CEF of the strains as well as their ratio to the respective infectious titers for chick embryos (EID50) and for TC of CEF overlaid with liquid nutrient medium by microscopic record of the cytopathic effect (TCID50) varied within a wide range. It was in favour of EID50, and in most of the strains - in favour of TCID50 no matter to which type of strains belonged. The results obtained with the use of the plaque method in TC of CEF confirmed the concept of a number of authors abroad that they could be used successfully as an index in typing also for the differentiation of the Newcastle disease virus strains.

[Properties of local velogenic strains of Newcastle disease virus in poultry]. / Prouchvaniia vurkhu niakoi svoistva na mestni velogenni shtamove na virusa na psevdochumata po ptitsite.

Studies were carried out on four strains of the Newcastle disease virus, isolated in Bulgaria and referred, as typed by the routinely used methods, to the velogenic group. The strains proved to be hemagglutinin - thermostable. Two of the local virus strains (Rosa and Toutrakan) belonged to the velogenic-neurotropic pathogenic type, and two (Bregovo and Haskovo) - to the velogenic - viscerotropic pathogenic one. All four strains were slowly eluated from chicken erythrocytes. Full immunologic similarity was established between these strains by means of the live vaccines used in this country for the specific prevention of Newcastle disease, produced with the lentogenic strains Hitchner B1 and La Sota and the mesogenic Komarov.

[Vaccination schemes against Newcastle disease in poultry]. / Prouchvaniia vurkhu niakoi skhemi za vaksinatsiia sreshtu psevdochuma pri ptitsite.

Two schemes of vaccination against pseudo-pest (A and B) were tested on broiler-chickens and two schemes (C and D)--on parent form birds. Vaccine of the La Sota strain was used for the broilers and was administered twice at differing age after the spray method. For the parent birds La Sota strain vaccine was used also--twice after the spray method, plus a vaccine of the strain Komarov--twice intramuscularly and as aerosol (scheme C) and the vaccine strain La Sota spray and aerosol alone (scheme D). Immunity induced in birds after immunization was followed serologically by the titre of serum antihaemaglutinins and by provocation with a highly virulent pseudo-pest virus strain. The 4 schemes of immunization tested comparatively ensure solid immunity of birds to pseudo-pest. Better production index results were obtained from broiler chickens vaccinated after scheme B and parental form birds vaccinated after scheme C.

[Immunogenic properties of 3 local lentogenic strains of the Newcastle disease virus used in the spray method of vaccination]. / Prouchvane imunogennite svoistva na tri mestni lentogenni shtama na psevdochumniia virus, prilozheni po spray-metod na vaksinatsiia.

Three local lentogenic strains of the Newcastle disease virus, GT, D and R, were made use of to produce live liquid vaccines. These proved harmless and immunogenic when applied through the spray-method to broiler chicks, aged 5 days, at three successive revaccinations (on the 25th, 60th and 140th day of age) carried out by the same method. The strain D vaccine induced serum antihemagglutinins that had higher titers than those induced by vaccines of the other local strains and the standard strains Hitchner-B1 and La Sota.

[Attempts at specific immunoprophylaxis against herpes mammillitis]. / Opiti za spetsifichna imunoprofilaktika protiv kherpesniia mamilit.

A live cell culture adsorbate vaccine was produced against herpes mammillitis in cattle. Comparative investigations were carried out on the immunogenic properties of four vaccines having different adjuvants--aluminum hydroxide, saponin, arlacell, and Freund's adjuvant. All tested vaccines proved harmless and immunogenic for sensitive cattle, the highest immunogenic effect being produced by the vaccine that contained aluminum hydroxide and Freund's adjuvant. The vaccinated animals reacted to immunization with the formation of specific antibodies that showed a highest titre between the 21st and 28th day following treatment. Immunity was checked through challenge on the 45th day, all immunized heifers being fully protected against Bovid herpesvirus infection 2 infection. When necessary the vaccine can be used successfully in a dose of 3-6 cm3, subcutaneously, in the region of the dewlap.

[Experimental infection with bovid herpesvirus 2]. / Eksperimentalna infektsiia s Bovid Herpesvirus 2

An experimental infection with strain KOS/Haskovo of the Bovid Herpesvirus 2, isolated in Bulgaria, was induced in susceptible heifers through intradermal, intranasal, and intravenous application. Regardless of the route of infection clinically the disease manifested itself as an eczema of an urticarial type, accompanied by a febrile reaction, leukopenia, erythropenia, and oligochromemia. Highest titers of virus-neutralizing antibodies were established on the 30th day following infection in the i/v injected animals. All experimentally infected animals remained resistant to a challenge with a homologous virus on the 80th day after they were infected.

[Study of an immunization plan for broilers via the spray method against Newcastle disease using vaccines from the Bl and La Sota strains]. / Prouchvane na skhema za imunizatsiia na broileri chrez spray metod sreshtu psevodchuma po ptitsite s vaksini ot shtamove Bl i La Sota

Studied was the immunization pattern against Newcastle disease in birds with the use of a spray method on broilers obtained congenitally from their mothers, having antihemagglutinins. All birds on one of the premises ( a total of 14, 000) were vaccinated when 5 days old with a liquid vaccine of strain B1 (one fourth dose per bird) using the Dutch pulverizing apparatus Flox-10 -- group I. Other 14,000 birds of another of the premises of the same batch were treated at the same age with the same dose via the same route of application of a liquid vaccine of the La Sota strain --group II. All birds of the two groups were revaccinated in the same way at the age of 25 days with a vaccine of the La Sota strain at the rate of a whole dose per bird. The birds were kept under equal conditons of feeding and management. It was found that they built immunity which protected them fully from Newcastle disease up to the end of the fattening period (2 months). This was demonstrated by the test for establishing resistance to a control infection with a highly virulent strain of the Newcastle disease virus (challenge) as well as serologically by the hemagglutination inhibition reaction. At the slaughter by the end of the fattening period all period all birds of the two groups sshowed almost equal average body weight, however, those of group I manifested 0.97 per cent lower mortality rate and lower forage intake per kg weight (by 23 g on an average).

[Study of the immunogenic properties of 3 lentogenic strains of the Newcastle disease virus isolated in Bulgaria]. / Prouchvane immunogennite svoistva na tri lentogenni shtama na virusa na psevdochumata, izolirani u nas

Three local strains of lentogenic type of the Newcastle disease were used to produce live liquid vaccines. These were given per os to broiler chickens in order to test their immunogenicity (first vaccination at the age of 25 days and vaccination when 70 days old). The immunity thus acquired was followed serologically by the titer of the antihemagglutinins and the resistance manifested by the birds at the control infection with a proven lethal dose of a highly virulent velogenic strain of the Newcastle disease virus. The results obtained were compared with those observed with the use of liquid vaccines of the strains Hitchner-B1 and La Soto. It was concluded that the vaccines of the local Newcastle disease strains are completely harmless and immunogenic. The vaccinal strains are excreted by the immunized birds and serve to immunize the contact control chickens.