The infectious bronchitis vaccine strain virus is more pathogenic in chicken embryos than the wild virus strain 2575/98

An avian infectious bronchitis virus (IBV) strain 2575/98 was attenuated using serial chicken embryo passage to become a vaccine in Taiwan. The aim of this study was to investigate the replication ability, pathogenicity, and tissue tropism of the wild and vaccine strains in chicken embryos. The embryos were inoculated with different titers of wild and vaccine strains. Quantification of virus in allantoic fluid was evaluated using real time RT-PCR. The results showed that the vaccine strain replicated in higher titers than the wild strain, and caused embryo death so quickly that only a few dwarfisms occurred. The embryos inoculated with wild and vaccine strains had similar lesions that were confined primarily to the chorionallantoic membrane (CAM), liver, and kidneys. The immunohistochemical data showed that IBV was present predominantly in the lungs, kidneys, and CAM. Although both strains caused hepatic damage, very few virus antigens were detected in the hepatic tissue. The pathogenicity of the vaccine becomes higher in embryos although it is lower in chickens than its wild strain. The vaccine strain could be used as a possible new vaccine candidate for IBV control. Key words: immunohistochemistry, infectious bronchitis, pathogenicity, vaccine Virus zaraznog bronhitisa peradi soj 2575/98 bio je oslabljen uzastopnim pasazama u pilecim zametcima da bi posluzio kao cijepni soj u Tajvanu. Cilj je ovog rada bio istraziti mogucnost umnozavanja, patogenost i tropizam terenskog i cijepnog soja u pilecim zametcima. Zametci su bili inokulirani cijepnim sojem razlicitog titra. Kolicina virusa u alantoisnoj tekucini bila je odredena RT-PCR-om u stvarnom vremenu. Rezultati su pokazali da se cijepni soj umnazao u visem titru od divljeg soja i prouzrocio uginuce zametaka tako brzo da se uspjelo razviti svega nekoliko krzljavih. U inokuliranih zametaka, bez obzira na divlji ili cijepni soj, razvile su se slicne promjene pretezito na korioalantoisnoj opni, jetrima i bubrezima. Imunohistokemijski je dokazano da se virus zaraznog bronhitisa prvenstveno nalazio u plucima, bubrezima i korioalantoisnoj opni. Iako su oba soja prouzrocila ostecenja jetara, neznatna kolicina virusnog antigena bila je dokazana u jetrenom tkivu. Patogenost cijepnog soja bila je u zametcima jaca, a u pilicima slabija od divljeg soja. Cijepni soj bi se mogao rabiti kao moguci kandidat za proizvodnju novog cjepiva protiv zaraznog bronhitisa. kjucne rijeci: imunohistokemija, zarazni bronhitis, patogen