[Demonstration of a transmissible gastroenteritis virus by contrast immunofluorescence]. / Dokazvane na virusa na transmisivniia gastroenterit chrez kontrastniia imunofluorestsenten metod.

Tested were a number of procedures to employ the immunofluorescence method for diagnosing transmissive gastroenteritis in pigs--impression preparations, frozen cross-sectioned material, and infected cell cultures of the established cell line SPEV. It was found that immunofluorescence microscopy was a dependable method for the express diagnosis of transmissive gastroenteritis. It could be employed in its three variants. The use of impression preparations, however, did not prove as dependable as the remaining ways of applying the method, and this drawback had to be compensated for with the study of a greater number of impression preparations taken from more pigs that had contracted the disease. It was also established that most promising and effective was to apply the method with the use of cell cultures infected with suspensions of organs. Cell cultures of the established SPEV cell line infected with material that contained the virus could produce dependable positive results in immunofluorescence investigations at the 24th hour following inoculation. This method could be employed for the express diagnosis of transmissive gastroenteritis.

[Cultivation of various avian viruses in pheasant trachea organ cultures and chick embryos]. / Kultivirane na niakoi ptichi virusi v trakhealni organni kulturi ot fazani i kokoshi zarodishi.

Stationary tracheal organ cultures of pheasants and chick embryos, treated with a mucolytic agent were used to study the ciliostatic effect of the following viruses: fowl pest (FPV), Newcastle disease (NDV), infections laryngotracheitis (ILV), and infections bronchitis (IBV) - strain Beaudette. In chick embryo tracheal cultures ciliostasis was found to set in as follows: for FPV - at the 24th hour; for NDV - at the 72nd-120th hour; for ILV - at the 168-192nd hour; and for IBV-at the 72nd-96th hour. The ciliostatic effect produced by NDV and IBV coincided in terms of time and dynamics. In pheasant tracheal organ cultures ciliostasis set in as follows: for FPV - at the 24th hour; for NDV - at the 72nd-120th hour; and for ILV - at the 168-192nd hour. This system was shown to be unsusceptible to IBV which produced no effect whatever. In mixed organic cultures, containing several tracheal segments of pheasants and chick embryos each per petri dish IBV did bring about ciliostasis in the chick embryo segments only, within the period after inoculation as cited above. It is stated that pheasant tracheal organ cultures could be employed in the case of an express initial differentiation of FPV, NDV, and ILV, recording the time period for the setting in of full ciliostasis following the inoculation of the respective viruses. Discussed is the possibility of identifying IBV, using mixed tracheal organ cultures of pheasants and chick embryos.

[Comparative study of tracheal organ cultures obtained from different bird donors]. / Sravnitelno prouchvane na trakhealni organni kulturi, polucheni ot razlichni ptichi donori.

Comparative studies were carried out on the quality (duration, intensity, and extent) of the cliliary activity in tracheal cultures from chick embryos, chickens, and pheasants. It was found that all cultures had long life, however, they were shown to differ essentially by the function of the tracheal epithelium. In tracheal cultures from pheasants the ciliary activity remained unchanged at the initial level for 70 days. In those from-day-old chicks it remained for 15 days, and cultures from 20-day-old chick embryos showed activity for 25 days. In the second and third type of tracheal cultures the ciliary activity gradually dropped by intensity and scope down to nil within the periods of time mentioned. The ciliary activity of tracheal segments cultured in tubes of a roller apparatus persisted for a considerably longer period than that of segments stationary cultured in petri dishes. The same result was obtained when the explanted trachea was treated with a mycolytic agent (bromhexinehydrochloride), although cultivation was carried out in petri dishes. The high quality (intensity and scope) and duration (70 days) of the ciliary activity of tracheal cultures from pheasants provides an excellent system for the study of the ciliostatic effect on different viruses.

[Differentiation of immunoglobulin classes in the chicken]. / Vurkhu klasovoto diferentsirane na imunoglobulinite pri kokoshkite.

Investigations were carried out to establish and differentiate the humoral immunoglobulins in SPF-chickens, following an antigenic stimulus with Salmonella pullorum. As many as five components were found in the blood sera of the test birds, which were shown to have immunoglobulin properties. They were differentiated as IgM, IgA, IgG1, IgG2, and IgG3. Those of the IgA-type were found in exudate material from the abdominal cavity of birds infected with Salmonella pullorum. In the course of the infectious process initiated by Salmonella pullorum in SPF-birds and followed up for 16 days only immunoglobulins sensitive to 2-mercaptoethanol were produced.

[Precipitinogen activity of Newcastle disease virus and humoral immunity in birds]. / Vurkhu pretsipitinogennata aktivnost na psevdochumniia virus i khumoralniia imunitet u ptitsite.

Studies was the precipitinogenic activity of the strains La Sota, 'H', and 'II' of the Newcastle disease virus, using chick embryos. It was found that all three of the strains produce precipitinogens. An antigen was obtained for the precipitation reaction in agar gel and the demonstration of precipitins that were specific for the ND virus in the blood serum of birds. Contrary to the hemagglutinins and precipitinogens proved heatresistant. There was a correlation between the antihemagglutinins and the precipitinogens in the blood serum of the immune birds. The low percent of birds (up to 12%) having precipitins in their serum spoke of the development of solid immunity against Newcastle disease within the flock. On the other hand, the high percent of birds having precipitins (over 50%) indicated that the infection persisted, and because of the immunity present it fairly often assumed atypical course or was manifested with low mortality rate.

[Serological response and resistance to Newcastle disease in vaccinated poultry]. / Prouchvane serologichniia otgovor i ustoichivostta sreshtu psevdochuma na vaksinirani ptitsi.

Studies was the titer of antihemagglutinins of a total of 3263 serum samples taken from birds routinely vaccinated against Newcastle disease, originating from various poultry farms of the country. Chosen were 139 birds in which a weak serologic response was established through spray, aerosol, and injectable live vaccines (strain La Sota, Komarov). These birds were challenged by intramuscular application of 10(6) ELD50/bird of a velogenic viscerotropic virus of ND. High specific resistance was established in the various groups of birds regardless of the low level of serum antihemagglutinins. In all such cases individual birds of the flock responded after vaccination with a high titer of serum antibodies, so the application of an active vaccine was indicated.

[In vivo persistence of plaque mutants of viscerotropic Newcastle disease virus]. / Perzistirane na plakovi mutanti in vivo na velogenen vistserotropen virus na psevdochumata.

Studied was the persistance of 3 plaque clones of a velogenic viscerotropic Newcastle disease virus in nonimmune birds. It was found that the first plaque clone (4 mm dia of plaques) possessed higher virulence than that of the parental virus and killed all inoculated birds for 2 to 5 days. Plaque clone II (2.5 mm dia of the plaques) caused up to 30 per cent mortality, and plaque clone III (1.5 mm dia of the plaques) did not bring about death but a transient disease only. Birds inoculated with II and III plaque clones, at identical serologic response, were investigated virologically on the 40th and 60th day post infection. By means of the tracheal organ cultures the Newcastle disease virus was isolated only from birds that were inoculated with plaque clone II. No virus was demonstrated via the same method in birds inoculated with plaque clone III. It is believed that the long-term persistance of the Newcastle disease virus reported on a previous occasion was due to a subpopulation identical with plaque clone II.

[Plaque cloning of the velogenic viscerotropic Newcastle disease virus]. / Plakovo klonirane na velogenen vistserotropen virus na psevdochumata.

A plaque clone was successfully produced and the plaque characteristic was studied of a velogenic viscerotropic Newcastle disease virus (strain II). The isolated 3 plaque mutants were found to form bright plaques in chick embryo fibroblast cultures, having a different size: those of clone I had a 4 mm dia, those of clone II - 2.5 mm dia, and those of clone III - 1.5 mm dia. The clones were differing in their virulence to day-old and six-week-old susceptible birds both from one another and from the parent virus. With regard to chick embryos, however, the difference in their virulence was negligible so far as the average time of perishing was concerned. Two methods of obtaining clones of the virus were comparatively tested: (1) infecting the cells as a monolayer (method of Dulbecco) and (2) infecting the cells set as a suspension. More advantageous proved the suspension method.

[Obtaining a specific antigen for the comparative testing of immunological methods in the diagnosis of Marek's disease]. / Poluchavane na spetsifichen antigen za sravnitelno izpitvane na niakoi imunologichni metodi za diagnostika na bolestta na Marek.

Comparative studies were carried out on the diagnostic possibilities of immunological methods--precipitation in agar gel, immunofluorescence and indirect hemagglutination, as well as isolation of the virus through primary cellular cultures for the diagnosis of Marek's disease. For the purpose were obtained 9 series of specific antigens. The comparative studies were carried out on fowl and blood serums from different poultry yards, as well as from SPF chickens, experimentally infected with HPRS-16 strain. The results obtained justify a precipitation in agar gels as the most convenient for mass diagnosis of Marek's disease.

[Establishing the immune status of poultry flocks against Newcastle disease in commercial poultry raising]. / Ustanoviavane imunnoto sustoianie na ptichi stada sreshtu psevdochuma v promishlenoto ptitsevudstvo.

An experiment was carried on 133 grown up fowls and broilers from 4 industrial farms, vaccinated with spray lento and mesogenic vaccines for straining the immunity against pseodopest through RIHA and provoking pseudoplague with a pathogenic virus. A high degree of resistance was proved (94.8%), in spite of the fact that about 30% of the fowls investigated, showed low titres with regard to RIHA. Negative results with regard to RIHA were proved in 18% out of the mass counts of 3.572 blood serums of the vaccinated fowls. Attention is called to the fowls vaccinated against pseudoplague, serologically negative through RIHA, which hinder the assessment of the immune state of the fowl flock or the possibility to be potential virus-carriers during the infection with a pathogenic virus of pseudo-pest. The possibilities of the precipitation reaction in agar gel are also pointed out, both for the assessment of immunity against pseudo-pest and for the detection of a latent pseudo-pest infection in vaccinated fowl flocks.

[Comparative studies of the virulence of some Aujeszky's disease viral strains]. / Sravnitelni prouchvaniia na virulentnostta na niakoi shtamove na virusa na bolestta na Aueski.

Clinical, virological, morphological, and immunofluorescence investigations were carried out on 22 pigs experimentally infected with two strains--a virulent one (V) of a 10(-3) titer, and a slightly virulent one (K) of a 10(-7) titer--of the virus of Aujeszky's disease as well as on contact pigs. Results revealed variations in the clinical and morphological manifestation of the disease in the individual groups. They were shown to be due to the strains of the virus that varied in virulence and tissue tropism. In the strain B-infected animals there were clinical symptoms characteristic of the disease, and the morphological changes in the central nervous system were of the nonsuppurative encephalitis type. The pigs infected with the K strain of the virus showed no clinical symptoms, while the contact animals manifested only respiratory troubles as well as interstitial pneumonia. It was demonstrated that the strains of slight virulence had weak nervotropic and pronounced pneumotropic characters. Complex virologic, morphologic and immunofluorescence investigations can be used for the diagnosis of the atypical forms of Aujeszky's disease and for the differentiation of the virulent from the slightly virulent strains of the virus.

[Cytopathic effect of the Newcastle disease virus on the BHK-21 cell line]. / Izsledvane tsitopatichniia efekt na virusa na psevdochumata vurkhu kletuchna liniia BHK-21.

The cytopathic effect (CPE) of the Newcastle disease virus (NDV) in the BNK-21 permenant cell line is studied in a series of experiments. The CPE is assessed as a percentage of hemadsorption and polykaryocytosis, and the dynamics of the viral replication is followed up with the aid of the immunofluorescent method. The effect of the cyclohexamide protein inhibitor of the replication of various NDV strains, on the CPE, respectively, is likewise studied. Five vellogenic, one mesogenic and one lentogenic strains are used in the experiments. It is found that through the immunofluorescent method the viral replication is delayed some three hrs in the case of the La Sota lentogenic strain in comparison with the other strains used. The direct relationship, already established, between the virulence of the NDV and the percentage of haemadsorption and polykaryocytosis is confirmed also in the BNC-21 heterologous cellular tissue. On the basis of this relationship, a rapid typing method of virulent from avirulent field NDV strains is suggested. The blocking effect of the cyclohexamide protein inhibitor on the CPE in NDV is demonstrated in the BNK-21 line, as a result of the blocking of the viral specific protein synthesis.

[Demonstration of the Bovid herpesvirus 2 in cell cultures with the aid of fluorescent antibodies]. / Dokazvane na Bovid herpesvirus 2 v kletuchni kulturi s pomoshta na fluorestsirashti antitela

Used was the immunofluorescence method employing fluorescinisothiocyanate-labeled antibodies against Bovid herpesvirus 2. The localisation and the dynamics of the virus antigen were followed up in cell cultures of calf kidney epithelium. Results showed that there was a specific cytoplastic-nuclear fluorescence in the infected cells. The dynamics of the virus multiplication revealed the presence of a specific antigen by about the 6th hour following the infection of the cells. Discussed is the problem of using the immunofluorescence technique in the differentiation of herpes mammillitis from the rest vesicular diseases of the cow's udder that are similar to one another by clinical picture.