Sequence analysis of cDNA for the VP6 protein of group A avian rotavirus: a comparison with group A mammalian rotaviruses

Avian rotavirus enteritis - an updated review

Rotaviruses (RVs) are among the leading causes of enteritis and diarrhea in a number of mammalian and avian species, and impose colossal loss to livestock and poultry industry globally. Subsequent to detection of rotavirus in mammalian hosts in 1973, avian rotavirus (AvRV) was first reported in turkey poults in USA during 1977 and since then RVs of group A (RVA), D (RVD), F (RVF) and G (RVG) have been identified around the globe. Besides RVA, other AvRV groups (RVD, RVF and RVG) may also contribute to disease. However, their significance has yet to be unraveled. Under field conditions, co-infection of AvRVs occurs with other infectious agents such as astroviruses, enteroviruses, reoviruses, paramyxovirus, adenovirus, Salmonella, Escherichia coli, cryptosporidium and Eimeria species prospering severity of disease outcome. Birds surviving to RV disease predominantly succumb to secondary bacterial infections, mostly E. coli and Salmonella spp. Recent developments in molecular tools including state-of-the-art diagnostics and vaccine development have led to advances in our understanding towards AvRVs. Development of new generation vaccines using immunogenic antigens of AvRV has to be explored and given due importance. Till now, no effective vaccines are available. Although specific as well as sensitive approaches are available to identify and characterize AvRVs, there is still need to have point-of-care detection assays to review disease burden, contemplate new directions for adopting vaccination and follow improvements in public health measures. This review discusses AvRVs, their epidemiology, pathology and pathogenesis, immunity, recent trends in diagnostics, vaccines, therapeutics as well as appropriate prevention and control strategies.

Molecular survey of enteric viruses in commercial chicken farms in Korea with a history of enteritis

Several enteric viruses have increasingly received attention as potential causative agents of runting-stunting syndrome (RSS) in chickens. A molecular survey was performed to determine the presence of a broad range of enteric viruses, namely chicken astrovirus (CAstV), avian nephritis virus (ANV), chicken parvovirus (ChPV), infectious bronchitis virus (IBV), avian rotavirus (AvRV), avian reovirus (ARV), and fowl adenovirus (FAdV), in intestinal samples derived from 34 commercial chicken flocks that experienced enteritis outbreaks between 2010 and 2012. Using techniques such as PCR and reverse-transcription PCR, enteric viruses were identified in a total of 85.3% of investigated commercial chicken flocks in Korea. Furthermore, diverse combinations of 2 or more enteric viruses were simultaneously identified in 51.7% of chicken farms positive for enteric viruses. The rank order of positivity for enteric viruses was as follows: ANV (44.1%), CAstV (38.2%), ChPV (26.5%), IBV (20.6%), ARV (8.8%), AvRV (5.9%), and FAdV (2.9%). Additionally, other pathogens such as Escherichia coli, Salmonella spp., Eimeria spp., and FAdV were detected in 79% of chicken flocks positive for enteric viruses using PCR, bacterial isolation, and microscopic examination. The results of our study indicate the presence of several enteric viruses with various combinations in commercial chicken farms that experienced enteritis outbreaks. Experimental studies are required to further understand the roles of enteric viruses in RSS in commercial chickens.

An unusual case of concomitant infection with chicken astrovirus and group A avian rotavirus in broilers with a history of severe clinical signs

A molecular study of intestinal samples from 21 broiler flocks with a history of enteritis revealed that 23.8% and 14.3% were positive for chicken astrovirus (CAstV) and avian rotavirus (ARV), respectively. CAstV and group A ARV were simultaneously detected in only one broiler flock. Birds in this group developed the significant intestinal lesions characterized by frothy contents, paleness, and thin intestinal walls. In this report we present an unusual case of runting stunting syndrome (RSS) with a history of high mortality and growth retardation in broiler chickens. We also make the first identification of CAstV and group A ARV in broiler chickens in Korea.

Isolation, identification and characterization of group A rotavirus from a chicken: the inner capsid protein sequence shows only a distant phylogenetic relationship to most other avian group A rotaviruses

Rotavirus particles were identified in the intestinal content of a 35-day-old stunted chicken. The virus was isolated, RNA pattern was analysed and the viral genome segment 6 was sequenced. In particular, the sequence data showed a very close similarity to the chicken rotavirus isolate Ch-1 (99.2% amino acid homology), this is distantly related to all known avian rotaviruses and supports the existence of different VP6 types amongst avian group A rotaviruses.

Molecular characterization of the major capsid protein VP6 of bovine group B rotavirus and its use in seroepidemiology

The major inner capsid protein (VP6) gene of the bovine group B rotavirus (GBR) Nemuro strain is 1269 nt in length and contains one open reading frame encoding 391 aa. Nucleotide and amino acid sequence identities of the Nemuro VP6 gene compared with the published corresponding human and rodent GBR genes were respectively 66–67 and 70–72 %, which are notably lower than those between human and rodent viruses (72–73 and 83–84 %, respectively). Overall identities of VP6 genes among GBRs were substantially lower than those among both group A rotaviruses (GARs) and group C rotaviruses (GCRs) derived from different species of mammals. These results demonstrate that bovine GBR is remarkably distinct from other GBRs and that GBRs from different species may have had a longer period of divergence than GARs and GCRs. Recombinant VP6 was generated with a baculovirus expression system and used for an ELISA to detect GBR antibodies. All 13 paired sera from adult cows with GBR-induced diarrhoea in the field showed antibody responses in the ELISA. In serological surveys of GBR infection using the ELISA, 47 % of cattle sera were positive for GBR antibodies, with a higher antibody prevalence in adults than in young cattle. In pigs, a high prevalence of GBR antibodies (97 %) was detected in sera from sows. These results suggest that GBR infection is common in cattle and pigs, notwithstanding the scarcity of reports of GBR detection in these species to date.

Attachment and infection to MA104 cells of avian rotaviruses require the presence of sialic acid on the cell surface

To determine the characters of receptors on target cells for avian rotaviruses, the receptors on MA104 cells for the pigeon rotavirus PO-13, the turkey rotaviruses Ty-1 and Ty-3, and the chicken rotavirus Ch-1 were analyzed. Pretreatment of MA104 cells with neuraminidase greatly reduced the infection by all of the four avian rotavirus strains. Binding of the cell-attachment protein, purified VP8 expressed in bacteria, of strain PO-13 to MA104 cells was also inhibited by pretreatment of cells with neuraminidase. These findings suggest that avian rotaviruses primarily utilize sialic acid-containing molecules as receptors on MA 104 cells.

Roles of outer capsid proteins as determinants of pathogenicity and host range restriction of avian rotaviruses in a suckling mouse model

We previously demonstrated that a pigeon rotavirus, PO-13, but not turkey strains Ty-3 and Ty-1 and a chicken strain, Ch-1, induced diarrhea in heterologous suckling mice. In this study, it was suggested that these avirulent strains, but not PO-13, were inactivated immediately in gastrointestinal tracts of suckling mice when they were orally inoculated. To determine which viral proteins contribute to the differences between the pathogenicitiy and the inactivation of PO-13 and Ty-3 in suckling mice, six PO-13 x Ty-3 reassortant strains that had the genes of the outer capsid proteins, VP4 and VP7, derived from the opposite strain were prepared and were orally inoculated to suckling mice. A single strain that had both PO-13 VP4 and VP7 with the genetic background of Ty-3 had an intermediate virulence for suckling mice. Three strains with Ty-3 VP7, regardless of the origin of VP4, rapidly disappeared from gastrointestinal tracts of suckling mice. These results indicated that the difference between the pathogenicity of PO-13 and that of Ty-3 was mainly dependent on both their VP4 and VP7. In particular, VP7 was found to be related to the inactivation of Ty-3 in gastrointestinal tracts of suckling mice.

Sequential analysis of nonstructural protein NSP4s derived from Group A avian rotaviruses

We determined the NSP4 sequences of turkey rotavirus strains Ty-1 and Ty-3 and a chicken rotavirus, strain Ch-1, and compared these sequences with those of a pigeon rotavirus, strain PO-13, and mammalian rotaviruses. The turkey strains and PO-13 were found to be closely related (90-97% homologies). Ch-1 NSP4 was distinctly different from other avian rotavirus NSP4s, with 78-79% homologies. The NSP4 sequences of avian rotaviruses were found to be 6-7 amino acids shorter than those of all mammalian strains and to have considerably low identities (31-37%) with them. Therefore, it seems highly likely that the NSP4 genes of avian rotaviruses are classified into two NSP4 genotypes distinct from those of mammalian rotaviruses. The enterotoxin domain in NSP4 is conserved in terms of its sequential and structural properties despite extremely low homologies in the full lengths of NSP4s in avian and mammalian rotaviruses.

Diarrhea-inducing activity of avian rotavirus NSP4 glycoproteins, which differ greatly from mammalian rotavirus NSP4 glycoproteins in deduced amino acid sequence in suckling mice

Avian rotavirus NSP4 glycoproteins expressed in Escherichia coli acted as enterotoxins in suckling mice, as did mammalian rotavirus NSP4 glycoproteins, despite great differences in the amino acid sequences. The enterotoxin domain of PO-13 NSP4 exists in amino acid residues 109 to 135, a region similar to that reported in SA11 NSP4.

Avian-to-mammal transmission of an avian rotavirus: analysis of its pathogenicity in a heterologous mouse model

It has been suggested that group A avian rotaviruses can be transmitted to mammals, but there is no direct evidence that such viruses induce disease in mammals. Suckling mice were orally inoculated with two avian rotaviruses. A pigeon rotavirus, PO-13, was found to induce diarrhea, but a turkey rotavirus, Ty-3, did not. The diarrhea induced by PO-13 was dependent on the age of the mouse. In histopathological examinations, antigens of PO-13 were sporadically detected in absorptive cells in the ileum, and lesions were observed as ballooning degenerations of absorptive cells in a region from the duodenum to the ileum. However, the rotavirus antigen was not detected in the majority of these degenerative cells. These results indicated that PO-13 could infect and induce diarrhea in suckling mice. This is the first evidence of an avian rotavirus being experimentally transmissible to a mammal.

Complete nucleotide sequence of a group A avian rotavirus genome and a comparison with its counterparts of mammalian rotaviruses

The nucleotide sequences encoding four structural proteins (VP1-4) and six nonstructural proteins (NSP1-6) of avian rotavirus PO-13 were determined. Based on the results of earlier sequencing studies [Ito et al., 1995, Sequence analysis of cDNA for the VP6 protein of group A avian rota viruses. Arch. Vriol. 140, 605-612; Rohwedder et al., 1997, Chicken rotavirus Ch-1 shows a second type of avian VP6 gene, Virus Genes 15, 65-71; Rohwedder et al., 1997, Bovine rotavirus 993/83 shows a third subtype of avian VP7 protein, Virus Genes 14, 147-151], determination of PO-13 genome sequence has been completed. The PO-13 genome is 18845 nucleotides in length. It is 290 nucleotides longer than the genome of SA11. The amino acid sequence homology between PO-13 and mammalian rotaviruses ranged from 76-77% (VP1) to 16-18% (NSP1). The features of gene and amino acid sequence were compared with those of the corresponding protein of mammalian rotaviruses. Based on results of the phylogenetic analyses of NSP1, we speculate that an ancestral rotavirus could have separated into groups A, B and C rotaviruses at an early evolutionary stage and that group A rotavirus separated into mammalian and avian rotaviruses with host evolution.

Comparison of the rotavirus gene 6 from different species by sequence analysis and localization of subgroup-specific epitopes using site-directed mutagenesis

The nucleotide sequence of gene 6 encoding the rotavirus major capsid protein VP6 of EDIM strain (EW) was determined and compared to that of 20 previously reported strains with known subgroup specificities. Multiple alignments of amino acid sequences exhibited a high level of sequence conservation (87 to 99.2%). Site-specific mutagenesis experiments were undertaken to localize regions involved in subgroup specificity. Amino acid positions 305, 315, and a region 296-299 (or 301 for equine strain H-2) were identified as contributing to subgroup epitopes. A single amino acid mutation at position 305 or 315 was sufficient to change the subgroup specificity of EW VP6 protein from non I/II to subgroup I- or subgroup II-like, respectively. Mutation at these sites may be another important mechanism for subgroup variation, along with gene reassortment.

Sequence analysis of the VP6 gene in group A turkey and chicken rotaviruses

cDNAs corresponding to the VP6 gene of the turkey rotavirus strains Ty-1 and Ty-3, and the chicken rotavirus strain Ch-1, were cloned and sequenced. The nucleotide and deduced amino acid sequence homology in the coding region of the VP6 gene in avian rotaviruses ranged from 78.1 to 93.9% and 86.1 to 98.7%, respectively. Both sequences of VP6 from avian rotaviruses exhibited a low degree of sequence homology (67.8-70.7% and 69.8-74.6%, respectively) compared with mammalian rotaviruses. Phylogenetic tree analysis showed that all avian rotaviruses were included in a single cluster and have separated early or from mammalian rotaviruses during evolution. The chicken rotavirus strain Ch-1 was a distant relative of other avian rotaviruses.

Mapping of antigenic sites on the major inner capsid protein of avian rotavirus using an Escherichia coli expression system

The cDNA encoding the VP6 gene of avian rotavirus PO-13 strain was inserted into the bacterial expression vector pET-3a. Upon isopropyl-1-thio-beta-D-galactoside induction, the E. coli BL21 (DE3) harboring the vector containing cDNA of the VP6 gene produced an approximately 45-kDa polypeptide, which reacted with rabbit serum against PO-13 strain in Western blotting. To study the antigenic sites on VP6, various deletion mutants were constructed, expressed in E. coli and the reactivity with antigenic site I- and II-specific MAbs analyzed by Western blotting. Site I, which is shared with all group A mammalian and avian rotaviruses except for chicken rotavirus, was found to be located at amino acid positions 45 to 65, and site II, which probably contributes to an authentic group A antigen common to both mammalian and avian rotaviruses, at amino acid positions 134 to 142.

Expression of the major inner capsid protein, VP6, of avian rotavirus in mammalian cells

A gene encoding the major inner capsid protein, VP6, of avian rotavirus was inserted into the eukaryotic expression vector pAX-91 under the control of the SR alpha promoter and was expressed at a high level in simian COS7 cells. The expressed VP6 was indistinguishable in terms of electrophoretic mobility from the corresponding protein synthesized in simian MA104 cells infected with avian rotavirus. Binding assays with a series of monoclonal antibodies (mAbs) that corresponded to four antigenic sites on VP6 of avian rotavirus showed that the antigenic characteristics of the expressed product were identical to those of the native VP6 of avian rotavirus virions. Fiber-like structures that reacted strongly with antiserum against rotavirus were observed in VP6-expressing COS7 cells. Furthermore, an analysis of the tertiary structure of the expressed VP6 protein indicated that it adopts a trimeric configuration, similar to that of the major inner capsid protein of PO-13 virus. From these results, it appears that recombinant VP6 will facilitate studies of the structure and function of authentic VP6, an important protein in avian rotavirus.