The infectious bronchitis virus (IBV) is continuously evolving through point mutation and recombination of their genome, subsequently the emergence of IBV variants complicates disease control. The objective of this study was to investigate genetic characterization of new IBV variants isolated from commercial chicken flocks in Korea collected between 2005 and 2010. Phylogenetic analysis revealed that all new IBV isolates belonged to Korean group II (K-II), which included the nephropathogenic IBV strains. However, the isolates formed a new gene cluster that was distinguished from the two distinct K-II subgroups (KM91-like and QX-like). Recombination events were identified in the S1 gene, with their putative parental strains being the KM91-like or QX-like subgroup. In addition, two crossover sites were observed in the S1 gene of IBV isolates. These results suggest that natural genetic recombination between heterologous strains classified into different genetic groups has occurred and may have caused the emergence of new IBV strains. This finding provides important information on IBV evolution and is essential for the effective control of IB in Korea.

The complete DNA sequence of bovine adenovirus type 3 is reported here. The size of the genome is 34,446 bp in length with a G+C content of 54%. All the genes of the early and late regions are present in the expected locations of the genome. However, the late-region genes are organized into seven families, instead of five as they are in human adenovirus type 2. The deduced amino acid sequences of open reading frames (ORFs) in the late regions and early region 2 (E2) and for IVa2 show higher degrees of homology, whereas the predicted amino acid sequences of ORFs in the E1, E3, and E4 regions and the pIX, fiber, and 33,000-molecular-weight nonstructural proteins show little or no homology with the corresponding proteins of other adenoviruses. In addition, the penton base protein lacks the integrin binding motif, RGD, but has an LDV motif instead of an MDV motif. Interestingly, as in other animal adenoviruses, the virus-associated RNA genes appear to be absent from their usual location. Sequence analysis of cDNA clones representing the early- and late-region genes identified splice acceptor and splice donor sites, polyadenylation signals and polyadenylation sites, and tripartite leader sequences.

A nephropathogenic K2/01 strain of infectious bronchitis virus (IBV) was attenuated by 170 serial passages in embryonated chicken eggs for possible use as a future IBV vaccine strain. High-growth properties and narrow tissue tropisms (limited replication in respiratory tracts) were achieved by the adaptation process. Unlike the parent strain, the attenuated strain (K2p170) was safe in day-old specific-pathogen-free chicks since replication of the virus did not induce mortality and nephritis, and rarely induced histological changes in the trachea and kidney after intraocular administration. In day-old broilers, even though coarse spray administration of K2p170 induced clinical signs, ciliostasis, and histopathological lesions in the trachea and the kidney, they were all comparable to birds vaccinated with commercial H120 vaccine. Despite restriction of viral replication in the respiratory tract, K2p170 elicited the production of antiserum with a neutralization index of 4.5. K2p170 provided almost complete protection against both two distinct subgroups of Korean nephropathogenic strain (KM91-like and QX-like subgroup). Furthermore, K2p170 provided significantly greater cross-protection against two heterologous strains (Massachusetts and Korean respiratory strain) than those conferred by the commercial H120 vaccine. K2p170 also had no virulence reversion after five back passages in chickens. In conclusion, K2p170 exhibits a fine balance between attenuation and immunogenicity, possesses cross-protective efficacy, and merits further investigation as a potential live vaccine as an alternative means of protection against the recently emergent nephropathogenic IBV infection in many Eurasian countries.

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These results demonstrate that orally administered L. rhamnosus M21 activates humoral as well as cellular immune responses, conferring increased resistance to the host against influenza virus infection.