[Experimental infection of lambs with strains of the bovine respiratory syncytial virus]. / Eksperimentalno zaraziavane na agneta s shtamove na govezhdi respiratorno-sintsitialen virus.

Lambs were successfully infected with bovine strains of a respiratory syncytial virus. When the Nomi reference strain and the local Antonovo strain of the RSV were used i/v and via the trachea the animals reacted on the 3rd to 5th day with dizziness, dyspnea, conjunctivitis, nasal discharges, etc., more strongly manifested with the use of the Antonovo strain. The temperature reaction started on the 3rd day and receded on the 7th day, with a second peak on the 8h day. Serologically, RSV-antibodies were released on the 14th day, and that correlated in dependence on the severity of the clinical manifestations. Such observations made it possible to use lambs as a sensitive animal species to differentiate the virulence of the tested strains. Testing along these lines rendered is feasible to obtain attenuated strains and use various immunoprophylactic agents against the respiratory syncytial virus.

[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.

[Adaptation of attenuated strain of P. parainfluenzae-3 in cultured swine kidney cells and analysis of its immunogenicity]. / Adaptirane na atenuiran shcham na P. parainfluenza-3 vurkhu kletuchni kulturi ot svinski bubrek i prouchvane na imunogennostta mu.

Strain Mihailovgrad of P. parainfluenza-3 was successfully adapted to cell cultures of pig kidney at its 15th passage. Its testing for innocuity was carried out through the inoculation of test calves with high amounts of the pathogen. No pathologic, temperature, and anaphylactic reactions were established. This confirmed the harmless character of the attenuated strain. Comparative testing for immunogenicity was performed with 8-month-old calves. Full coincidence with the antibody response was obtained with strain Mihailovgrad as a vaccinal strain. The use of the adapted strain for the production of a vaccine is to be preferred as there is no possibility of contamination with other bovine viruses.