[Sensitivity of cell cultures to the bovine respiratory syncytial virus]. / Chuvstvitelnost na kletuchnite kulturi kum govezhdiia respiratorno sintsitialen virus.

Investigated was the individual susceptibility of individual batches of primary cell cultures of fetal and normal calf kidney as well as of individual series of cultures of fetal and normal lamb kidney to the replication of the strains Antonovo/448 and Nomi of the bovine respiratory-syncytial virus. It was found that both types of primary cultures possessed varying susceptibility to the virus, which was likely to be genetically substantiated. It was shown that beside such susceptibility of various batches of the same origin the susceptibility of cell cultures of different origin was also essential for the replication of the virus. Thus, the AUBEK stable cell line of bovine origin and the diploid cell culture of lamb thyroid proved definitely more susceptible to the virus as compared to the primary cultures of calf kidney and testis. It is stated that the addition of dimethylsulfoxide in final concentration of 0.5 per cent in the maintaining medium of the infected cell culture of calf kidney raised the infectious titer and the yield of virus by 1 log and enhanced syncytium production.

[Enhanced luminescence intensity in immunofluorescent preparations following trypsin treatment]. / Povishavane intenziteta na svetene pri imunofluorestsentni preparati sled tretirane s tripsin.

Comparative investigations were carried out on the immunofluorescent preparations of cell cultures infected with bovine viruses--rota-, corona-, respiratory-syncytial, parainfluenza-3, adeno-1, and herpes-1--to test various fixatives and the effect of trypsin in raising the sensitivity of the immunofluorescence method. The effect of trypsin was manifested in fixation with formalin, ethanol, methanol, and acetone treated immunofluorescent preparations of cell cultures infected with rota- and adeno-viruses as well as in fixation with acetone of cultures infected with respiratory syncytial virus, parainfluenza-3 virus, and corona virus. Formalin, ethanol, and partly methanol were shown to be unsuitable for the purpose of fixation of cell culture preparations infected with viruses that contained a lipoprotein envelope. It was found that the treatment of immunofluorescent preparations with trypsin following fixation and prior to their treatment with conjugated antisera enhanced considerably the number of fluorescent cells and the intensity of fluorescence itself provided 0.1 per cent trypsin was used for 5 to 10 min at 37 degrees C--for cell culture preparations, and 0.1 per cent trypsin was used for 20 to 30 min at 37 degrees C--for paraffin sections of acetone-fixed tissues.

[Immunofluorescent demonstration of respiratory syncytial virus infection in calves]. / Imunofluorestsentno dokazvane na respiratorno sintsitialnata virusna infektsiia po teletata.

Specific high-titre bovine conjugated antisera were obtained against respiratory syncytial virus. Use was made of the reference strain Nomi and the local isolate Antonovo/448. The conjugates produced were shown to have equal qualities to those of the Belgian conjugate used for comparison. The anti-Antonovo/448 conjugated serum was used in the direct immunofluorescent method to demonstrate a respiratory syncytial virus antigen in organs of animals with acute respiratory diseases as well as to control the replication of the virus in cell cultures. An infection with a respiratory syncytial virus was demonstrated with the employment of the same test in 16 per cent of a total of 119 samples taken from diseased animals. In the inoculation of the diploid cell culture of lamb thyroid gland with strains of the virus a specific antigen was established at the forty-eighth to the seventy-second hour following infection.

[Immunofluorescent diagnosis of rota-, corona- and pestivirus infections in calves]. / Immunofluorestsentna diagnostika na rota-, korona- i pestivirusni infektsii po teletata.

Bovine hyperimmune fluorescent sera were obtained for indication of the rota- and corona-virus infections in calves, which were highly specific and of immunofluorescent titers within the 1:32-64 range. Their testing was carried out via the direct immunofluorescence method, using histologic cross-sectioned material and impression preparations of the mucous membrane of calves died of enteritis as well as cell cultures of fetal calf kidney and organic cultures of calf trachea all contaminated, resp., infected with feces. The study of the intestinal membrane of a total of 100 diseased calves, employing this method, has demonstrated a rotavirus antigen in 38.0 per cent of the cases, and a coronavirus one--in 37.0 per cent. The causative agent of mucous disease (a pestivirus) was demonstrated by means of the respective conjugate in 47.3 per cent of the cases, using abomasal membrane of a total of 55 calves. Rota- and corona-virus infections were also established in the abomasal membrane of diseased calves, and pesti-virus infections--in the intestinal mucosa as well. Established were also mixed infections with the three viruses taking part at various combinations. A celloidin method was worked out for making immunofluorescent preparations of infected monolayer cell cultures. In the cell cultures infected with feces the totavirus antigen was demonstrated in 19.4 per cent of the cases, and the coronavirus one--in 25.6 per cent.

[Isolation of the respiratory syncytial virus from calves with respiratory diseases]. / Izolatsiia na respiratorno-sintsitialniia virus ot teleta s respiratorni zaboliavaniia.

Described is a respiratory enzootic in calves aged 30 to 90 days. Two cytopathic strains of the bovine respiratory syncytial virus were isolated from diseased calves in a cell culture of lamb thyroid. Clinical observations and the results of virologic and serologic investigations have revealed that mixed infections of the respiratory syncytial virus and the mucosa disease virus take part in the etiology of the respiratory enzootic described.

[Experiments to isolate cytopathic strains of bovine rotaviruses]. / Opiti za izolirane na tsitopatichni shtamove govezhdi rotavirusi.

Experiments were carried out to isolate cytopathic strains of bovine rotaviruses. Material from a total of 129 positive fecal samples, taken from calves affected with rotavirus gastroenteritis, was used to infect cell cultures. In the roller culturing of 19 of the positive samples in suspension of the MA-104 cell line in the presence of trypsin two cytopathic strains were isolated. The cell line used was more sensitive than the cells of calf kidney.

[Demonstration of respiratory syncytial virus infection in calves by the complement fixation reaction]. / Dokazvane na respiratorno-sintsitialnata virusna infektsiia po teletata chrez reaktsiia za svurzvane na komplementa.

Studied was tentatively the occurrence of a respiratory syncytial virus infection on some farms with records of the disease. Investigations were carried out on the base of the complement-fixation test (CFT) specially worked out and on the specific complement-fixing antigen obtained from a bovine respiratory syncytial virus (BRSV). Tested were several methods for the production of a complement-fixing antigen. Most appropriate proved the one obtained by the extraction of an infected cell monolayer in glycerine buffer saline. It was stated that CFT was a proper test for the rapid herd diagnosis of BRSV infection. The study of double serum samples from 240 calves involved in 40 enzootics revealed that CFT could successfully be employed in 18 per cent of the cases of respiratory infections in calves in as many as 17 enzootics. However, the etiologic part played by the virus was dominating in some of these enzootics only. In the remaining ones the participation of the virus was either partial or sporadic.

[Isolation of adenoviruses from calves with bronchopneumonia]. / Izolatsiia na adenovirusi ot bronkhopnevmonichni teleta.

The virologic investigation of clinical and pathological material from calves affected with a respiratory disease at the age of 30 days to 10 months on 16 infected stock-breeding farms led to the isolation of two virus strains (D-117 and Ch-216) on primary cell cultures of fetal calf kidney from the nasal discharge of two 8-month-old calves. By their cytopathic changes, physico-chemical properties and the presence of a group-specific antigen they were said to belong to the adenovirus family. The results of the cross virus-neutralization test pointed to the assumption that they had to be referred to the bovine adenovirus type 1. Discussed is the problem concerning the participation and the importance of individual types of adenoviruses in the acute respiratory enzootics of grown-up calves.

[Comparative studies of plaque formation by strains of the mucosal disease-viral diarrhea virus (MD-VD)]. / Sravnitelni izsledvaniia vurkhu plakoobrazuvaneto na shtamove na virusa na mukoznata bolest-virusna diareia (MB-VD).

Studied was the phenomenon of plaque forming with 2 local and 1 reference cytopathogenic strain of the MD-VD virus in cell cultures of calf kidney and testis. Studied was also the effect of trypsin in the preliminary treatment of the cell culture as well as the varying composition of the cover medium. The strains were found to form plaques that were varying in type and size. The ratio between the large and small plaques as well as the percent of plaques having unclear edges could serve as tentative strain features. It was established that at such experimental procedure the preliminary trypsin treatment of the cultures increased but slightly the plaque-forming capacity of the strains. The results obtained give grounds to the necessity of characterizing the vaccinal strains used through the type and ratio of the plaques formed.

[Isolation of the bovine herpesvirus-3 from sick calves]. / Izolirane na govezhdi kherpesvirus-3 ot bolni teleta.

Three herpes strains identified as herpes virus-3 were isolated in revolving test-tubes with cell cultures of nasal samples and lung parenchyma from diseased calves at the time of a respiratory enzooty. Large crystalloid aggregates of herpes virus virions were observed in the nucleus and in the cytoplasma by the electron-microscopic investigation performed on infected cell cultures. The experimental infection of calves with the isolated strain produced slight symptoms of respiratory disease in single calves only. The infected calves were susceptible to a following infection with cattle herpes virus-1.