Emergence of novel strains of avian infectious bronchitis virus in Sweden.

Department of Biomedical Sciences and Veterinary Public Health, Section of Virology, The Swedish University of Agricultural Sciences, Ulls Väg 2B, SE-751 89 Uppsala, Sweden.
Veterinary Microbiology (Impact Factor: 3.13). 03/2012; 155(2-4):237-46. DOI: 10.1016/j.vetmic.2011.09.022
Source: PubMed

ABSTRACT Infectious bronchitis virus (IBV) causes avian infectious bronchitis, an important disease that produces severe economic losses in the poultry industry worldwide. Recent IBV infections in Sweden have been associated with poor growth in broilers, drop in egg production and thin egg shells in layers. The complete spike gene of selected isolates from IBV cases was amplified and sequenced using conventional RT-PCR. Nucleotide and amino acid sequence comparisons have shown that the recent isolates bear 98.97% genetic similarity with strains of the QX-like genotype. The phylogenetic analysis revealed that strains predominant in the nineties, which were of the Massachusetts type, have been replaced by D388/QX-like strains, however the evolutionary link could not be established. The homology between the two genotypes was 79 and 81%. Remarkably, a strong positive selection pressure was determined, mostly involving the S1 subunit of the S gene. This strong selective pressure resulted in recombination events, insertions and deletions in the S gene. Two new isolates generated from recombination were found with nucleotide sequence diverging 1.7-2.4% from the D388/QX-like branch, indicating the emergence of a new lineage. The study demonstrates a constant evolution of IBV that might be in relation to increased poultry farming, trade and vaccine pressure. The findings underscore the importance of continuous monitoring to control spread of infections, as well as to timely adjust diagnostic methods, molecular epidemiological studies, development and use of vaccines that are adapted to the changing disease scenario.

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    ABSTRACT: Infectious bronchitis is a highly contagious viral disease of poultry caused by infectious bronchitis virus (IBV) and is considered one of the most economically important viral diseases of chickens. Control of IBV has been attempted using live attenuated and inactivated vaccines. Live attenuated vaccines of the Massachusetts (Mass.) serotype are the most commonly used for this purpose. Due to the continuous emergence of new variants of the infectious bronchitis virus, the identification of the type of IBV causing an outbreak in commercial poultry is important in the selection of the appropriate vaccine(s) capable of inducing a protective immune response. The present work was aimed at developing and evaluating a duplex SYBR Green I-based real-time RT-PCR (rRT-PCR) assay for the simultaneous detection and differentiation of Mass. and non-Mass. serotypes of IBV. The duplex rRT-PCR yielded curves of amplification with two specific melting curves (Tm1=83°C ±0.5°C and Tm2=87°C ±0.5°C) and only one specific melting peak (Tm=87°C ±0.5°C) when the IBV Mass. serotype and IBV non-Mass. serotype strains were evaluated, respectively. The detection limit of the assay was 8.2 gene copies/μL based on in vitro transcribed RNA and 0.1 EID50/mL. The assay was able to detect all the IBV strains assessed and discriminated well among the IBV Mass. and the IBV non-Mass. serotypes strains. In addition, amplification curves were not obtained with any of the other viruses tested. From the 300 field samples tested, the duplex rRT-PCR yielded a total of 80 samples that were positive for IBV (26.67%), 73 samples identified as the IBV Mass. serotype and seven samples as identified as the IBV non-Mass. serotype. A comparison of the performance of test as assessed with field samples revealed that the duplex rRT-PCR detected a higher number of IBV-positive samples than when conventional RT-PCR or virus isolation tests were used. The duplex rRT-PCR presented here is a useful tool for the rapid identification of outbreaks and for surveillance programmes during IB-suspected cases, particularly in countries with a vaccination control programme.
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    ABSTRACT: Infectious bronchitis virus (IBV) is a coronavirus of the chicken. It is a highly contagious pathogen and in addition to causing respiratory and kidney diseases, it can affect the reproductive organs, resulting loss of production and poor egg quality. Despite the global distribution of IBV, Finland has been free of clinical cases for almost three decades. Since April 2011, outbreaks involving genotypes QX, D274-like and 4/91-like, have occurred in southern Finland. The clinical samples studied were submitted to the Finnish Food Safety Authority Evira from different regions of Finland during 2011-2013 and originated from a voluntary health monitoring programme, a national survey for avian influenza and from diagnostic specimens from both commercial poultry production and hobby flocks. The sources of the infections are not known, but strains D274 and 4/91 are widely used in vaccines elsewhere.
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Sep 10, 2014