Liquid scintillation counting of polycarbonates: a sensitive technique for measurement of activity concentration of some radioactive noble gases.

This work explores the application of the liquid scintillation counting of polycarbonates for measurement of the activity concentration of radioactive noble gases. Results from experimental studies of the method are presented. Potential applications in the monitoring of radioactive noble gases are discussed.

Replication of the pseudorabies virus in cultured pancreatic islet cells: further evidence of their paraneuronal nature.

Pancreatic B cells are known to be damaged by a wide range of viruses, causing diabetes. Though these viruses belong to different taxonomic groups, their single shared characteristic is neurotropism. In the present study, pseudorabies viral infection was modelled on fetal porcine islets cultivated in vitro. It was demonstrated that the endocrine cells of the pancreas, especially B cells, were infected in vitro and so served as a medium for the replication of the virus. All stages of the morphogenesis of the virus were observed ultrastructurally within the cells. The exocrine cells located close to the endocrine ones were free from attachment and invasion of the virus. The potential of the pseudorabies virus to develop within pancreatic endocrine cells is regarded as evidence of the paraneuronal nature of these cells.

[Characteristics of Newcastle virus isolated from live vaccine-immunized chickens--the unusual biological properties]. / Kharakteristika na Niukiasulskiia virus, izoliran ot imunizirani s zhiva vaksina pileta--neobiknoveni biologichni svoistva.

A strain of the Newcastle disease virus, denoted GF, was isolated from birds vaccinated twice with a live vaccine. In some flocks of the farm this strain has caused oligosymptomatic disease, and in others the infection has run a latent course. It was shown that the GF strain possessed unusual biologic properties--an extremely high virulence in vitro combined with a total lack of pathogenicity in vivo. With regard to the tests mean death time with 10-day-old chick embryos (44.6 h) and plaque morphology (a heterogeneous plaque population of clear plaques, sizing 0.5 to 3.5 mm) it was referred to the velogenic group. With regard to the intracerebral pathogenic index (1.21) it belonged to the mesogenic group. In terms of the intravenous pathogenic index (0) it had to be classified with the lentogenic group of of strains of the Newcastle disease virus. All these properties of the strain were shown to be stable. Besides the difficulties with its differentiation the behaviours of this strain pose a number of problems with regard to its origin and the variability of the Newcastle disease virus in nature, which are subject to discussion.

[Demonstration of a reovirus in helicopter disease of broilers]. / Dokazvane na reovirus na "khelikoptera bolest" pri broileri.

A reovirus was isolated from 5-13-day-old broiler birds with signs of the so-called helicopter disease--one of the forms of the malabsorption syndrome. A number of organs were investigated (trachea, liver, spleen, bursa of Fabricius, proventricular stomach, and tendon sheath of musculus gastrocnemius). The virus was isolated from the proventricular stomach and the tendon sheath in cell cultures of chick embryo kidney as well as in 5-7-day-old chick embryos inoculated in the yolk sac. The remaining organs proved virologically negative. All organs, including the primarily positive ones, were shown to be virologically negative upon the inoculation of chick embryo fibroblast cultures and of chorioallantoic membranes of 10-11-day-old chick embryos. The isolate was identified as an avian reovirus, and was denoted with the initials R-85--on the grounds of its biologic and physico-chemical properties, of its morphology (negative-contrast electron microscopy), and of its morphogenesis (ultrathin electron-microscopic cross sections). Investigated were the histopathologic changes in chick embryos inoculated with the R-85 reovirus and the pathologic changes in the liver of spontaneously affected birds.

[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.

[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.

[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.

[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.

[Serological response and the viral carrier state in chickens infected with the pathogenic Newcastle disease virus]. / Izsledvane vurkhu serologichniia otgovor i virusonositelstvoto pri pileta, infektirani s patogenen virus na psevdochuma.

Three groups of susceptible chickens were treated with Newcastle Disease vaccine, as follows: group I--orally, strain La Sota; group II--aerosole treatment, strain La Sota and group III--intramusculary, Komarov's vaccine. Varying HI antibody levels were observed following vaccine application. The average antibody titer of group I and II experimental chickens (40 in number for each group) was 25 days post vaccination respectively log2 = 3.47 and log2 = 6.2 while of group III (50 chickens) it was 14 days post vaccination log2 = 8.4. Aerosole challenge with velogenic viscerothropic strain of Newcastle Disease virus caused a sharp change in serum antibody titer. The low antibody titer in group I rose quickly post challenge while in groups II and III, on the contrary, it fell sharply. This characteristic dynamics is proposed for use as an indicator showing the presence of pathogenic virus in vaccinated birds. It was proven that pathogenic Newcastle Disease virus persisted in birds from group I for 40 days and 10% of them were in a state of latent infection (clinically healthy). The virus was isolated after method of organ cultures of tracheal explantates. It was established that the HI antibody level in the blood serum of virus carriers was higher as compared with that of the remaining birds in the group. The use of this fact as an indicator for beginning virusological investigations aiming to reveal latent Newcastle Disease infection is proposed.

[Pathogenic Newcastle virus carrier state in congenitally immune chickens]. / Virusonositelstvo na patogenen virus na psevdochumata ot kongenitalno immuni pileta.

Five-day-old chickens decendants of hens vaccinated several times under conditions existing in the practice were ophtalmo-nasally inoculated with 10(5),5ELD50 velogenic viscerothropic Newcastle Disease virus NDV. Thirty two per cent of them were stricken by the disease and died, but the remaining 68% resisted the provocation and showed no clinical symptoms 80 days post inoculation. The virulogical investigation of the chickens resistant to inoculation proved they are spreading the virus for 45 days and remained virus-carriers for 54 days post inoculation. NDV did not change its pathogenic properties even after persisting for long periods of time. Two virulogical methods for virus isolation were used -- tissue homogenates and cloaca washings inoculated on hen embryos and tracheal organ culture. The advantages and the great possibilities for discovering latent NDV infection of the organ culture are pointed out. Latent fowl pest infection in birds is discussed.

[Variability and the virulence of the Newcastle disease virus]. / Izmenchivost i virulentnost na psevdochumniia virus.

Six isolates of the Newcastle Disease virus (NDV), taken at different periods of time after provocation of immune birds with velogenous viscerotrophic strain, are used. It is shown that the virulence of the initial NDV challenge strain remains unchanges up the 46th day of persistence. The isolate, taken after 70 days of carriage, manifests a considerably decreased virulence. It is established that the reduced virulence is not genetically stable and reverts towards the initial one following passage through appropriate host organism. The latent infection with NDV is examined from ecological and practical aspects.

[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.

[Retention of the Newcastle disease virus in immunized poultry]. / Zadurzhane na virusa na psevdochumata v imunizirani ptitsi.

The period of virus harbouring was followed up in a total of 50 experimentally infected (Newcastle disease) birds. Two methodes were used to isolate the challenging virus: the ordinary virologic procedures and the method of tissue cultures. Studied was also the effect of the humoral immunity on the persistence of the virus. Investigations by the tissue culture method revealed a persisting latent infection in the course of 70 day, which in certain cases could assume an acute course and become apparent. The Newcastle disease virus was isolated from birds having either low or very high levels of serum agglutinins. The currently employed virologic methods failed to demonstrate the virus after the 16th day of infection.

[Role of the housefly in the epizootology of pseudoplague in birds]. / Znachenie na domashnata mukha v epizootologiiata na psevodochumata po ptitisite.

It has been demonstrated that Musca domestica L. could harbour the Newcastle disease virus. It has been isolated from the surface of the flies body 96 hours after these had been in contact with it, and from their digestive tract--after 240 hours. It has also been found that virus excretion in infected flies continues for 96 hours. It is believed that Musca domestica L. flies can participate in the spreading of the ND virus.