Improvement of the chlamydial antigen in the composition of an associated vaccine

Infectious respiratory diseases of cattle are multifactorial; they usually have a viral or viral-bacterial etiology and can spread rapidly among productive animals. Consequently, controlling respiratory infections in cattle is a major challenge for the livestock industry worldwide. Purpose of the study is improvement the “Associated vaccine against IRT, VD-BS, PG-3 and bovine chlamydiosis, inactivated emulsion” by expanding the antigenic spectrum of the chlamydial antigen. The sterility of the vaccines was evaluated according to "OFS 1.2.4.0003.15 General Pharmacopoeia article. Sterility" (section 2.3) by direct inoculation. Safety was assessed in accordance with State Standard 31926. Tolerability was monitored for the first 10 days after immunization. The tolerance of vaccines was judged by the absence of a local and general reaction of animals to the introduction of the biological product. PG-3specific antibody titers were determined by hemagglutination inhibition test (HIT). Specific antibodies to the IRT and VD-BS viruses were determined in ELISA. Anti-chlamydial antibodies were quantified by complement fixation test (CFT). Vaccine immunogenicity was evaluated in an acute experiment with white mice. All vaccine batches proved sterile and safe for laboratory animals. Both vaccine formulations were well tolerated by rabbits. Altering the chlamydial antigen composition did not impair antiviral humoral immunity. Rabbits receiving the improved vaccine developed higher anti-chlamydial antibody titers than those vaccinated with the standard formulation. The protection index in white mice immunized with the improved vaccine was 1.3-fold higher than in mice receiving the standard vaccine. Modifying the chlamydial antigen composition in the “Associated vaccine against IRT, VD-BS, PG-3 and bovine chlamydiosis” did not adversely affect the development of antiviral humoral immunity. Inclusion of two additional chlamydial strains enhanced the humoral response to chlamydial antigen and increased overall vaccine immunogenicity by 1.3-fold.