Identification and analysis of structural protein genes and serotype of an infectious bronchitis virus in ducks

Abstract:

[Objective] It is to identify and explore the genetic variation of an infectious bronchitis virus isolated from 11-day-old cherry valley ducks that developed suspected respiratory infection in Guangxi province. [Methods] The virus was identified by hemagglutinin test, chicken embryo inoculation and gene sequence analysis of the 3ʹ untranslated region (UTR). The S1, E, M, and N genes of the virus were amplified by reverse transcriptase polymerase chain reaction (RT-PCR), cloned, sequenced, similarity comparison, phylogenetic tree and serotype analyais was conducted. [Results] The hemagglutination test was negative and dwarf embryo appeared after 5 passages of inoculation of chicken embryos. The sequencing result of 3ʹUTR gene indicated the virus was IBV. The sequence of cleavage site within S protein of the virus was RRSRR. The nucleotide similarities of S1, E, M, and N genes with those of H120, 4/91 and LTD3 reference strains were 78.6%-99.7%, 85.4%-100.0%, 91.6%-93.2% and 86.7%-91.7%, respectively. Compared with the reference strains, there is no insertion or deletion in N gene of the virus except mutations. However, substitutions, insertions and (or) deletions were found in S1, E, M genes of the isolated strain. According to the phylogenetic tree analysis, it was clustered into 4/91-type based on S1 gene and LDT3-type based on E, M and N genes. The serotype analysis showed that the serotype of the isolated strain was different from vaccine strains H120 and 4/91. [Conclusion] The strain isolated from ducks was IBV and the isolated strain existed variation both in structural genes and serotype. The present study suggests that the prevention and control of IB in poultry is facing more severe challenges.