Expression and structural analysis of infectious bronchitis virus nucleoprotein

Genetics, antigenicity and virulence properties of three infectious bronchitis viruses isolated from a single tracheal sample in a chicken with respiratory problems

Three different IBV genotypes/serotypes, designated ck/CH/LDL/150434–I (LDL/150434–I), ck/CH/LDL/150434–II (LDL/150434–II) and ck/CH/LDL/150434–III (LDL/150434–III), were detected in a single tracheal sample from a chicken showing signs of respiratory disease. The viruses were isolated using a cross-neutralization test and limiting dilution in embryonated specific-pathogen-free (SPF) eggs. Isolate LDL/150434–I was a re-isolation of H120 vaccine strain that was introduced into the chicken flock by vaccination, transmitted between chickens, and later accumulated several genomic mutations. Isolate LDL/150434–II was a novel variant that originated from recombination events between H120 and ck/CH/LDT3/03-like viruses. The widespread use of H120 vaccine, which offered incomplete protection against heterotypic IBVs in the fields, may play important roles in the emergence of such a novel genetic variant. Based on the analysis of S1 and complete genomic sequence, isolate LDL/150434–III was related genetically but distinct from the established strains of nrTW I type viruses of GI-7 lineage circulating in Mainland China since 2009. The three IBV isolates were avirulent when they infected SPF chickens. Furthermore, synergistic effects on pathogenicity were not observed when the different types co-infected the SPF chickens. However, the isolates persisted in the respiratory tracts longer in combined infected birds than those in individual infected birds. The results provide insights into the evolution of the viruses and co-infection of chickens with different virus serotypes.

Comparison of SYBR green I real-time RT-PCR with conventional agarose gel-based RT-PCR for the diagnosis of infectious bronchitis virus infection in chickens in Morocco

BACKGROUND

A rapid, sensitive, and specific molecular method for the diagnosis of infectious bronchitis virus (IBV) infection is important in curbing infectious bronchitis outbreaks in Morocco and other countries.

METHODS

In this study, an easy-to-perform SYBR green I real-time reverse transcriptase polymerase chain reaction (RT-PCR) targeting the nucleocapsid gene of IBV was developed and compared with conventional agarose gel-based RT-PCR for the detection of IBV infection.

RESULTS

We found that the SYBR green I real-time RT-PCR was at least 10 times more sensitive than the agarose gel electrophoresis detection method. The assay exhibited high specificity for IBV infection. All negative controls, such as Newcastle disease virus, infectious bursal disease virus, and avian influenza virus, were not detected.

CONCLUSION

The SYBR green I real-time RT-PCR test described herein can be used to rapidly distinguish IBV from other respiratory pathogens, which is important for diagnosis and control of infectious bronchitis outbreaks in Morocco. The test is a valuable and useful method as a routine assay for diagnosis of clinical IBV infection in commercial chickens.

Development of a real-time TaqMan RT-PCR assay for the detection of infectious bronchitis virus in chickens, and comparison of RT-PCR and virus isolation

A sensitive and specific method for the diagnosis of infectious bronchitis virus (IBV) is of great importance. In this study the development of a real-time TaqMan RT-PCR targeting the highly conserved nucleocapsid (N) gene of IBV and including an internal PCR control is described. The assay was specific for IBV and did not detect other avian pathogens, including turkey coronaviruses. A comparative limit of detection was determined for M41, an embryo-adapted strain, and IS/885/00, a poorly embryo-adapted variant. For M41 real-time RT-PCR and virus isolation were one or two times more sensitive than RT-PCR targeting the N or spike glycoprotein (S1) genes, respectively. For IS/885/00, real-time RT-PCR was more sensitive by tenfold than virus isolation and 30- or 40-fold than by N gene or S1 gene RT-PCR, respectively. Real-time RT-PCR and virus isolation were 17-75% more sensitive than RT-PCR targeting the S1 gene for testing tracheal swabs directly from experimentally infected chicks. When tracheal and cloacal swabs from clinical specimens were tested directly, 50% more samples were positive by real-time RT-PCR than by the S1 gene RT-PCR. Real-time RT-PCR targeting the N gene is more sensitive than common diagnostic assays, allowing rapid and accurate IBV detection directly from clinical specimens, facilitating differential diagnosis.

Role of phosphorylation clusters in the biology of the coronavirus infectious bronchitis virus nucleocapsid protein

The coronavirus infectious bronchitis virus (IBV) nucleocapsid (N) protein is an RNA binding protein which is phosphorylated at two conserved clusters. Kinetic analysis of RNA binding indicated that the C-terminal phosphorylation cluster was involved in the recognition of viral RNA from non-viral RNA. The IBV N protein has been found to be essential for the successful recovery of IBV using reverse genetics systems. Rescue experiments indicated that phosphorylated N protein recovered infectious IBV more efficiently when compared to modified N proteins either partially or non-phosphorylated. Our data indicate that the phosphorylated form of the IBV N protein plays a role in virus biology.