Development Of An Inactivated Bivalent Riemerella Anatipestife Vaccine (Serotype 2 And 11)

Riemerella anatipestifer disease is an important infectious disease in the duck industry.The disease often occurs in ducklings from 1 to 8 weeks of age.Infected ducks often present with septic symptoms,and the heart,liver,and air cells have fibrinous exudates.Twenty-one serotypes have been reported and are not cross-protective with each other.Vaccination is an important means of preventing the disease.In this study,227 strains of Riemerella anatipestifer isolated from 2013 to 2018 were first identified,and the main epidemic serotypes have changed to serotype 2 and serotype11.At the same time,a new serotype was discovered,which is currently in a small epidemic.Subsequently,23 strains that were selected from the serotype 2 prevalence area,and 24 strains that were selected from the serotype 11 endemic areas were rejuvenated,and then isolated and identified by bacteria and stored for subsequent research.Three virulent strains were selected to evaluate their virulence.The results showed that the median lethal doses of serotype 2 strains RCAD0383,RCAD0385 and RCAD0570 were 3.34×10⁴CFU,1.40×10⁷ CFU,1.74×10⁶ CFU,respectively.The median lethal doses of serotype 11 strains RCAD0191,RCAD0306 and RCAD0436 were 4.89×10⁵ CFU,3.29 x 10⁴ CFU,4.37 x 10⁴CFU,respectively.Therefore,RCAD0383,RCAD0570,RCAD0306,and RCAD0436were selected as the challenge strains for the later experiments,and the doses were100×LD₅₀.Seven strains of serotype 2 and nine strains of serotype 11 of Riemerella anatipestifer were selected as inactivated oil emulsion vaccines,which were inoculated into 7-day-old ducklings and challenged at 21 days of age.Ducklings were weighed at 7,14,21 days old and serum was collected and tested for antibody levels using indirect ELISA.The results showed that both serotype 2 and serotype 11 vaccines produced higher antibody levels after immunization and had higher protection rates.At the same time,the injection of the vaccine had no effect on the normal growth of the duck.The vaccine strains RCAD0570?serotype 2?and RCAD0352?serotype 11?with the highest protection rate were screened.Subsequently,the optimal immunization dose was determined.The optimal immunization dose for serotype 2 RCAD0570 was 10¹00 CFU/0.5 ml,and the optimal immunization dose for serotype 11 RCAD0352 was 5×10⁹CFU/0.5 ml.Finally,the protective effects of inactivated vaccines prepared from white oil adjuvant,water adjuvant and aluminum adjuvant were evaluated.The results showed that the white oil adjuvant vaccine had the highest antibody level and protection rate was 8/10,9/10.This vaccine is suitable for actual production.In summary,this study found that Riemerella anatipestifer serotype 2 and serotype 11became new epidemic serotypes.At the same time,according to the vaccine immune protection effect,the strains RCAD0570 and RCAD0352 for the vaccine of the serotype 2and serotype 11 inactivated vaccine of Riemerella anatipestifer were successfully screened.Finally,a bivalent inactivated vaccine with different adjuvants of Riemerella anatipestifer was developed,and the protection rate of Riemerella anatipestifer bivalent inactivated oil emulsion vaccine was 80%,90%.