Properties of experimental samples of vaccine against avian infectious coryza

Avian infectious coryza is an infectious disease caused by bacteria Avibacterium paragallinarum occurring worldwide in the countries with well-developed poultry farming and causing significant economic losses to the poultry industry. The specific prevention is the main link in the system of measures to combat infectious rhinitis of chicken. Vaccination of birds provides the production of expressed immunity due to the presence of antihemagglutinating antibodies. The presented experimental study relates to the assessment of the safety, antigenicity and protectivity the experimental samples of vaccine against avian infectious coryza. The tested vaccine samples included the formaldehyde-inactivated antigen of the new A. paragallinarum strain No. 5111 (serogroup B). The aim of the work was to evaluate the safety, antigenic and protective properties of samples of a sorbed and emulsion vaccine against infectious rhinitis of chickens based on the A. paragallinarum strain No. 5111. A whole-cell antigen of the A. paragalli narum strain No. 5111 (serotype B-1), inactivated with formaldehyde, was used for the production of experimental samples of the vaccine. The concentration of inactivated bacterium in the immunizing dose (0,5 cm3) was 109 microbial cells. The sample of the sorbed vaccine contained 3.75 mg of aluminum hydroxide in the immunizing dose. The sample of the emulsion vaccine contained the oil adjuvant Montanide ISA 70 VG («SEPPIC», France) in an amount of 70 % by weight. The immunobiological properties of the vaccine were tested in 125 seronegative to A. paragallinarum chickens ( Gallus gallus L .) of the Haysex brown cross at the age of 1.5-2.0 months. The safety of the vaccine samples was tested by injecting chickens in a 2-fold dose (1.0 cm3). Each sample was injected subcutaneously in the middle third of the neck and intramuscularly in the chest (5 chickens per each variant). Observation of the clinical status of the birds were carried out daily for 42 days. At the end of the experiment, the chickens were slaughtered and the tissue state at the injection site was visually assessed on the incision. The protective properties of the vaccine were determined for 75 chickens (three groups per 25 birds). The birds of the I group were immunized with a sample of sorbed vaccine,the chickens of II group - with an emulsion sample, and unvaccinated chickens of group III were used as a control. The samples were injected subcutaneously into the middle third of the neck at a dose of 0.5 cm3, 2-fold with an interval of 20 days. The chickens were infected with a 1-day broth culture of the A. paragallinarum strain No. 5111 with a concentration of 5 units according to the optical turbidity standard after 15 days of revaccination. The clinical status of the chickens was observed during 7 days after infection. The post-mortem examination was performed with a bacteriological analysis of the contents of the nasal sinuses during the experiment and at the end of the experiment. The vaccine antigenicity and the duration of immunity were determined on 30 birds (three groups per 10 birds). The chickens of group I were immunized with a sorbed vaccine sample, group II - with an emulsion sample, and unvaccinated birds of group III were served as a control. The vaccine antigenicity was assessed based on humoral antibody level using the hemagglutination inhibition test (HI test). The mild to moderate tissue lesions were observed at the injection site without a obvious inflammatory reaction. Slight subcutaneous dropsy and hyperemia were observed at the injection site of the sorbed sample and the formation of connective tissue granules with the presence of vaccine residues without necrotic lesions and a obvious inflammatory reaction of the surrounding tissues were noted at the injection site of the emulsion sample. No significant differences in the condition of chicks from vaccinated groups were observed (p>0.05), but there was a significant difference between the birds of the experimental and control groups (p 0.05) after 20 days of the first vaccination with sorbed and emulsion samples of vaccine. Increased antibody titers in chicken sera were observed only at day 15 post second immunization and 60 post vaccination the antibody levels in the chicken sera reached their maximum: in poultry immunized with the adsorbed vaccine - 7.5 ± 0.8 log2, and in those immunized with the emulsion vaccine - 8.9 ± 0.7 log2 (p > 0.05). In chickens vaccinated with the aluminum hydroxide gel vaccine, a decrease in the antibody titer to 5.5 ± 0.7 log2 was observed at day 240, while in birds immunized with the emulsion vaccine the titer remained at the level of 8.7±0.8 log2 (p > 0.05).