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) M۴۱ and Iranian IR/۷۷۳/۲۰۰۱ (۷۹۳/B) strains of infectious bronchitis virus. Two groups of ۲۰ three weeks old SPF chickens vaccinated subcutaneously with two oil-emulsions inactivated Infectious Bronchitis Vaccines (Mass M۴۱ and Iranian IR/۷۷۳/۲۰۰۱ strains) that had been manufactured in Razi institute in the laboratory scale. A further group of ۲۰ 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 ۱۰۳EID۵۰ of M-۴۱ strain of Mass serotype and another part of the birds of the each vaccinated groups were challenged with ۱۰۳EID۵۰ of Iranian IR/۷۷۳/۲۰۰۱ ۷۹۳/B strain. The birds of the control group were also divided in two parts and challenged with the viruses (M-۴۱ and IR/۷۷۳/۲۰۰۱) 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 ۱۰% of them showed ciliostasis in tracheal section examination. Whereas after challenge with heterologous virus strains, the vaccinated birds with IR/۷۷۳/۲۰۰۱ killed vaccine revealed ۵۰% resistance against M۴۱ and the birds vaccinated with M۴۱ killed vaccine only showed ۳۰% immunity against IR/۷۷۳/۲۰۰۱ based on the degree of ۵۰% and ۷۰% 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 ۷۹۳/B serotype should be carefully studied in different parts of Iran for appropriate vaccination programmes against infectious bronchitis.