Cross-immunity study of two experimentally oil-emulsion inactivated Infectious bronchitis vaccines in SPF chickens

A study has been carried out for determining of cross-immunity between Massachusetts (Mass) M41 and Iranian IR/773/2001 (793/B) strains of infectious bronchitis virus. Two groups of 20 three weeks old SPF chickens vaccinated subcutaneously with two oil-emulsions inactivated Infectious Bronchitis Vaccines (Mass M41 and Iranian IR/773/2001 strains) that had been manufactured in Razi institute in the laboratory scale. A further group of 20 SPF chickens were kept as non-vaccinated control. Four weeks post vaccination half part of the birds of the each vaccinated groups were challenged by eye drop with 103EID50 of M-41 strain of Mass serotype and another part of the birds of the each vaccinated groups were challenged with 103EID50 of Iranian IR/773/2001 793/B strain. The birds of the control group were also divided in two parts and challenged with the viruses (M-41 and IR/773/2001) like the birds of the vaccinated groups. Each of the birds of the vaccinated groups manifested a very strong resistance to homologous virus strains and only 10% of them showed ciliostasis in tracheal section examination. Whereas after challenge with heterologous virus strains, the vaccinated birds with IR/773/2001 killed vaccine revealed 50% resistance against M41 and the birds vaccinated with M41 killed vaccine only showed 30% immunity against IR/773/2001 based on the degree of 50% and 70% ciliostasis in tracheal section examination respectively. All of the control birds showed complete ciliostasis without any protection against the challenge of the both viruses. Upon the results, it is suggested that the distribution of 793/B serotype should be carefully studied in different parts of Iran for appropriate vaccination programmes against infectious bronchitis.