Ninetythree B type, the Predominant Circulating Type of Avian Infectious Bronchitis Viruses ۱۹۹۹ - ۲۰۰۴ in Iran: a retrospective study

In order to identify predominant circulating types of infectious bronchitis(IB) virus in the period of ۱۹۹۹-۲۰۰۴ in Iran, samples(trachea, lung, kidney) from ۱۵۰ various flocks showing respiratory signs suspected to be related to IB infection were inoculated to SPF eggs. Then allantoic fluids studied by RT-PCR and Nested PCR using group and type specific primers to probing Massachusset, ۷۹۳/B and D۲۷۴ types viruses respectively. Out of ۱۵۰ tested flocks approximately ۷۲% were IBV positive in RT PCR tests. Specific nested PCRs on RT- PCR products of tested samples revealed that ۵۷ flocks (۵۲.۷%) had been infected by ۷۹۳/B type IBV alone. Massachusetts type IBV also could be detected in ۱۸ flocks (۱۶.۶%) alone. Thirty three (۳۰.۵%) flocks had been infected by ۷۹۳/B and Massachusetts type IBV in combination. Collectively, there were ۹۰(approximately ۸۳%) flocks that were infected by ۷۹۳/B type IBV. Our results showed that the predominant circulating serotype of IBVs during the study period was ۷۹۳/B type. The ۲۷۴D type did not detected in any flocks during this study. The co-existence of Masachusset and ۷۹۳/B type’s viruses in the same times in ۳۳ flocks revealed that Masachuset type virus vaccines have not conferred a proper immunity against ۷۹۳/B type viruses.