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1、Full Terms poultry; chicken; coronavirus; infectious bronchitis virus; Asia; review 1. Introduction Coronaviruses (CoVs) are known to be one of the major respiratory pathogens that cause a range of diseases in both human and animal communities. Some have led to concerns for a threat to Downloaded by
2、 Florida State University at 14:30 05 December 2015 global public health in the twenty-first century, such as the CoVs causing severe acute respiratory syndrome (SARS) (Zhong et al. 2003) and those responsible for the recently identified Middle East respiratory syndrome (MERS) (Zaki et al. 2012). Fo
3、r CoVs in avian species, avian coronaviruses (ACoVs) are classified into the genus Gammacoronavirus. The infectious bronchitis virus (IBV) is among the most important ACoVs affecting the poultry industry. IBV was first reported as an avian respiratory pathogen in the 1930s in Massachusetts, USA. It
4、exhibits extensive antigenic variation, and the strains present in each country are almost unique. Therefore, many genotypes of IBV have been identified worldwide, and new variants keep emerging despite vaccination (reviewed in de Wit et al. 2011; Jackwood 2012). Vaccines against IBVs are generally
5、effective, but new strains continue to emerge causing clinical diseases and production problems in vaccinated flocks, eventually having an economic impact on the global poultry industry (Gelb et al. 2005; Liu et al. 2006; Han et al. 2011). The pathogenicity of IBV is very complex as it is influenced
6、 by many factors, such as the strain of the virus, the breed of chicken, environmental conditions, and concurrent infection from other pathogens. IBV alone may not cause severe and devastating disease, but IBV-infected birds can be susceptible to superinfection by bacteria (for example, Escherichia
7、coli), mycoplasma (for example, Mycoplasma gallisepticum, M. synoviae) and co-infection with other viruses such as the infectious bursal disease virus (IBDV), Newcastle disease virus (NDV), avian influenza virus (AIV), and Mareks disease virus (MDV) (Bradbury 1984; Matthijs et al. 2003; Cavanagh and
8、 Gelb 2008; Dwars et al. 2009). IBV consists of a single-stranded positive-sense RNA genome. Its genome encodes four structural proteins: phosphorylated nucleocapsid protein (N), membrane glycoprotein (M), spike glycoprotein (S), and small envelope protein (E) (Cavanagh 2007). The spike glycoprotein
9、 S, in the form of club-shaped projections present on the surface of the virus, is post-translationally cleavable into two subunits: the S1 forming the outer spike portion of the protein; and the S2, the protein anchoring it to the viral envelope. The S1 is responsible for attachment to the host cel
10、l receptors, while the S2 subunit mediates fusion of the virus and the host cell membrane, thereby entering into the host cells. Moreover, the S1 subunit contains epitopes and determinants for serotype-specificity, hemagglutinin activity, and for neutralizing antibodies that provide protective immun
11、ity (Masters 2006; Cavanagh and Gelb 2008). All known different IBV genetic types appear to have little or no overlap to cross-protect each other, causing existing recurrent outbreaks. Currently, genotypes based on the sequence of the S1 protein gene, especially in the hypervariable 5 region (HVR),
12、are used for classification of IBVs. This genotyping is very useful in the continuous determination of the epidemic genotype of IBV field strains, and for predicting the effectiveness of vaccines against field isolates. In addition, the production of a new generation of vaccines, genetically related
13、 to the circulating IBV local strains, is economically beneficial for control of infectious bronchitis (IB) in global geographic regions. This review aims to provide an update on the dynamics of avian coronavirus, particularly focusing on the economically important IBV strains that are circulating i
14、n commercial farms in Downloaded by Florida State University at 14:30 05 December 2015 Asian countries. The review also identifies the potential risks of IBV spreading in a traditional backyard poultry farming situation, which usually has links to rural communities and contributes to local consumpti
15、on. The review goes on to discuss the IB situation occurring in species of birds other than poultry. This information draws attention to how possible diverse IBVs (and also other ACoVs) are persistently circulating around this continent. The collection of IBV isolates in different Asian geographic r
16、egions is listed in Table 1. This includes: country of origin, name and genetic types of the isolates, tissue tropism, common breeds, and age range of IBV-infected birds. GenBank accession numbers are included that can document the reference citation of each representative strain. Figure 1 illustrates the phylogenetic tree indicating the relationship between the S1 amino acid sequences of the selected strains obtained from the Asian IBV isolates listed in Table 1. 2. The contribut
