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BioMed Research International
Volume 2014 (2014), Article ID 313252, 7 pages
Identification of a Chicken Anemia Virus Variant-Related Gyrovirus in Stray Cats in China, 2012
1College of Animal Science, South China Agricultural University, Wushan Road, Tianhe District, Guangzhou, Guangdong 510642, China
2College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China
3State Key Laboratory of Biocontrol, College of Life Sciences, Sun Yat-Sen University, Guangzhou 510006, China
4Key Laboratory of Chicken Genetics, Breeding and Reproduction, Ministry of Agriculture, Guangzhou 510642, China
Received 14 October 2013; Revised 25 December 2013; Accepted 27 December 2013; Published 13 February 2014
Academic Editor: Marcelo A. Soares
Copyright © 2014 Xinheng Zhang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The chicken anemia virus (CAV), is a known member of the genus Gyrovirus and was first isolated from chickens in Japan in 1979. Some reports have also demonstrated that CAV can be identified in human stool specimens. In this study, a variant of CAV was detected using PCR with CAV-based primers in fecal samples of stray cats. The genome of CAV variant was sequenced and the results suggest that it could be a recombinant viral strain from parental CAV strains JQ690762 and AF311900. Recombination is an important evolutionary mechanism that contributes to genetic diversification. These findings indicate that CAV variant might have originated from CAV-infected chickens. The epidemiology and pathogenesis of this novel virus remains to be elucidated. This study underscores the importance of CAV surveillance and it presents the first evidence suggesting the possibility of CAV homologous recombination in cat.
The chicken anemia virus (CAV) is a transmissible pathogen that infects young chickens, resulting in aplastic anemia, hemorrhages in the muscle and subcutaneous tissues, thymus atrophy, and severe immune suppression . The infection can be propagated within the flock both vertically and horizontally. CAV is a member of the Gyrovirus genus, belonging to the family Circoviridae . The CAV genome is comprised of single-stranded, circular DNA approximately 2.3 kb in length, with three partially overlapping open reading frames (ORFs), coding for the VP1, VP2, and VP3 proteins . VP3, also named apoptin, is a proapoptotic protein. Infection with this virus, which is mainly transmitted through contaminated feathers, has been shown to trigger apoptosis in thymocytes and myeloid progenitor cells in young chickens . Viral surveillance programs have isolated more than 50 CAV samples from different provinces in China during 2009–2012, and the epidemiological analysis suggested that CAVs were prevalent in China. We also analyzed the characteristic of one strain (GD-1-12), which was isolated in Southern China in 2012; the GD-1-12 isolate’s genome at position 183 has a 21 nt deletion (TCCGTACAGGGGGGTACGTCA) in comparison with the genome (accession no. JQ690762) of the CAV isolate from human fecal samples. It is unclear if the 21 nt deletion is related to host specificity or pathogenicity . In 2010, the CAV genome has been detected in breeder and commercial chicken flocks in South Korea . The CAV (JQ690762) was also detected in pediatric fecal samples in Beijing, China (http://www.ncbi.nlm.nih.gov/nuccore/JQ690762/) . In 2011, a novel human virus was identified on the surface of human skin and was designated human gyrovirus (HGyV), due to its homology with the chicken anemia virus . In 2012, another gyrovirus species named GyV3 was detected in diarrhoea and normal faeces from Chilean children in the USA, which may reflect consumption of CAV-infected/vaccinated chickens due to the low sequence similarity with other gyroviruses . Another gyrovirus (GyV4) was identified in human stool samples and in chicken meat sold for human consumption in Hong Kong in 2012 . In the same year, four HGyV DNA samples were detected, three were from kidney transplant recipients and one was from an HIV-infected patient in Italy . Human gyrovirus apoptin protein (VP3) has a similar subcellular distribution pattern and apoptotic function as its CAV homolog . However, whether or not the first gyrovirus-carrying human was infected by eating CAV-infected/vaccinated chickens and the molecular mechanism of HGyV infection are still unclear and require further study. Cases of CAV recombination have been reported in chickens in China and the only recombination region is located in the coding region of VP1 [13, 14]. In this study, the first evidence of CAV homologous recombination in cats is explored in an attempt to elucidate the mechanism through which CAV infects various species.
2. Materials and Methods
2.1. Clinical Specimens
In order to identify circulating CAV viruses in cats in Southern China, 102 fecal samples were selected from two humane shelters located in Baiyun district () and Conghua () district of Guangzhou in 2012, where stray cats were most widespread in the south central area of Guangdong Province.
2.2. Extraction of Viral DNA
Viral DNA was extracted from 102 fecal samples using a commercial DNA extraction kit (QIAamp DNA Stool Mini Kit, QIAgen, Hilden, Germany) according to the manufacturer’s instructions. The DNA was then quantitated and stored at −20°C until PCR was performed.
2.3. Virus Detection by PCR
The extracted DNA was screened by PCR. The primers were as sollows: JCP1: 5′CATCAACGGTGTTCAGGC3′ and JCP2: 5′CCTTGGAAGCGGATAGTCAT3′. Primers were designed by Primer Premier 5.0 to amplify 535 bp from the partial coding regions of CAV. The PCR amplification was performed in a total volume of 25 uL, including 12.5 uL of buffer I, 4 uL dNTPs, 0.5 uL of each primer, 6 uL distilled water, 1 uL DNA, and 0.5 uL LA Taq polymerase (TaKaRa, Biotechnology, Dalian, China). Amplification reactions were performed using the automated thermal cycler (Gene Amp PCR System 9700, Applied Biosystems, Foster City, CA, USA) with the following cycling profile: initial denaturation at 94°C for 4 min followed by 30 cycles of denaturation, annealing, and extension at 94°C for 30 s, 57°C for 30 s, and 72°C for 2 min, respectively, and a final extension step was carried out at 72°C for 10 min. The 535 bp reaction product was analyzed on 1% agarose gels. Negative controls were included in every three PCR reactions and one positive control was included in each set of reactions performed. The standardized PCR amplification yielded a distinct band of 535 bp in size as expected.
2.4. Amplification, Cloning, and Sequencing of the CAV Variant Genome
The DNA from the PCR-positive sample of CAV variant was further analyzed by two primers pairs to amplify the complete CAV variant genome. Primers KQ1F, 5′-CAATCACTCTATCGCTGTGT-3′ and KQ1R: 5′-TTCGTCCATCTTGACTTTCT-3′ and primers KQ2F: 5′-GGCTACTATTCCATC(A/T)CCATTCT-3′, and KQ2R: 5′-GCTCGTCTTGCCATCTTACA-3′, were designed to amplify 1778 bp and 831 bp fragments, respectively, covering the entire genome. The PCR amplification was carried out in 50 uL volume containing 25 uL buffer I, 16 uL dNTP, 0.5 uL of each primer, 13.5 uL distilled water, 1 uL of the DNA, and 0.5 uL LA Taq polymerase (TaKaRa, Biotechnology, Dalian, China). Amplification of the 831 bp region was carried out using the following PCR conditions: initial denaturation of 94°C for 4 min followed by 30 cycles of denaturation, annealing, and extension at 94°C for 30 s, 59°C for 30 s, and 72°C for 2 min, respectively, and a final extension step was carried out at 72°C for 10 min. Amplification of the 1778 bp region proceeded for 35 cycles as follows: 5 min at 94°C, 30 s at 94°C, 30 s at 58°C, 2 min 30 s at 72°C, and a final extension step was carried out at 72°C for 10 min. PCR amplification products were analyzed on 1% agarose gels stained with ethidium bromide. PCR products were purified using the Gel Band Purification Kit (Omega Bio-Tek, USA) and cloned into the pMD19-T vector (TaKaRa Bio Inc, Japan) followed by sequencing in triplicate using an ABI 3730 Sanger-based genetic analyzer (Carlsbad, CA, USA).
2.5. Sequence Alignment
The complete nucleotide sequence of CAV variant and reference sequences from different hosts from various countries were available from GenBank (Table 1). The DNA sequences and amino acid sequences were assembled using DNAStar (version 7; Madison, WI, USA) and Multiple sequence alignment was performed with the Clustal X (BioEdit version 7) program. Phylogenetic trees were constructed for genome sequences using the MEGA 5.1 program .
2.6. Sequence Recombination Analysis
Detection of potential recombinant sequences, identification of potential parental sequences, and localization of possible recombination break points were performed with the Recombination Detection Program (RDP4) v.4.1.3 . Five different methods (RDP, Chimaera, MaxChi, Bootscan, and 3Seq) were used to detect recombination events in Cat-GyV. Meanwhile, in order to confirm the results, putative recombinant sequences and their parental strains were further analyzed with Simplot version 3.5.1 . Evidence for networked relationships in CAV variant was examined using MEGA 5.1.
3.1. Prevalence of CAV Variant
The survey data showed that the percentage of CAV positive samples was nearly 10% (10 of 102 fecal samples).
3.2. Molecular Characteristics and Phylogenetic Analysis of CAV Variant
The complete genome sequence of CAV variant was submitted to GenBank, under the accession number KC414026. The CAV variant genome was 2,295 nt long, very close to the genome size (2,316 nt) of the CAV isolated from human fecal samples (accession no. JQ690762). Comparative analyses showed that CAV variant shared the greatest sequence identity (98.1%) with the CAV isolate from Japan (AH9410) and the least identity (38%) with the GyV3 isolate from the USA. The VP1, VP2, and VP3 genes of the CAV variant showed nucleotide variations of 1–63.1%, 0.5–51.9%, and 0.5–50.5%, respectively, among the 36 relevant sequences from GenBank. Previous studies have confirmed that the VP1 protein has the highest variability with a hypervariable region located from residues 139 to 151, while the amino acids 139 and 144 play vital roles in virus growth and spread, as VP1 residues Q139 and/or Q144 are associated with a decreased rate of spread of CIA-1 isolate . In the CAV variant, VP1 residues 139 and 144 are lysine and glutamic acid, respectively, while in the two CAV isolates JQ690762 and AF311900, they are both glutamines. There were four unique amino acid mutations (L/M/F113P, K/S/V341R, V357A, and A371V) in VP1 of CAV variant, which were not previously reported (Figure 1). The VP1 residue 394 is a major genetic determinant of virulence, with glutamine (Q) and histidine (H) representing high and low pathogenicity, respectively [19, 20]. In the CAV variant, residue 394 was glutamine (Q) and was, therefore, highly pathogenic. There were two mutations (E20G, T/S116A) in VP2 and one mutation (D79N) in VP3 of CAV variant, which had not been previously observed (Figure 1). Phylogenetic analysis of the complete genome of CAV variant showed that CAV variant clustered to a clade with the CAV strains in chickens (Figure 4(a)).
3.3. Recombination Analysis
The above results suggested that CAV variant (accession no: KC414026) was a potential recombinant isolate between two CAV strains, namely, CAV strain AF311900 as the minor parent and CAV strain JQ690762 as the major parent (Figure 2) with the recombination breakpoints mapping to position 2,100 (beginning breakpoint) and 158 (ending breakpoint). The recombination region of CAV variant was located in the partial VP1 coding region, the entire 3′ untranslated region (UTR), and a portion of the 5′UTR (Figure 3). In order to identify if the two breakpoints are precise, we divided the CAV variant genome into two segments: the recombinant region from genomic nucleotide position 2,100-158 and the nonrecombinant region from genomic nucleotide positions 159-2,099. The phylogenetic tree revealed that the breakpoints delimit sequence regions with distinct phylogenies (Figures 4(b) and 4(c)). There was a recombination event in the nucleotide position from 2,100 to 158 of the CAV variant genome, which suggests that recombination could speed up the evolution of CAV.
A CAV variant was isolated from stray cat fecal samples in China, and its genome was sequenced. The variant virus was found in 10% of samples. The CAV variant was highly pathogenic and had a very high sequence similarity with CAV. Davidson et al. reported that feathers contribute to the horizontal transmission of CAV, by carrying CAV either on their surface or within their feather pulp . Although horizontal transmission is considered the most significant mode of CAV dissemination, the process is not well understood. Further analysis showed that CAV variant was a recombinant virus strain descended from CAV strain JQ690762 and CAV strain AF311900. Homologous recombination is considered rare in single-stranded circular DNA viruses and has not been reported for CAV in cats. Homologous recombination might result in the potential change in viral epidemiology. The results of this study indicate that CAV variant might have originated from CAV-infected chickens. It seems plausible that the stray cats were in contact with and/or ingested CAV-infected/vaccinated chickens. Similarly, humans could be similarly infected by contact with infected cats at the animal shelters. However, the pathogenesis of CAV variant in cats or chickens remains to be elucidated. So far, CAV has been identified in three different species including cats, chickens, and humans. This virus, first reported by Yuasa et al. (1978)  from contaminated vaccines in Japan, has a worldwide distribution. Phan et al. confirmed a high prevalence of CAV DNA in diarrhoea and normal faeces from Chilean children . Chu et al. reported that the high rate of codetection of the three gyroviruses (CAV, AGV2/HGV and GyV3) in human specimens may indicate common dietary exposure to foods that contain all three viruses (e.g., chicken skin and meat) or it may imply some undefined dependency or codependency for successful proliferation . As an immune suppression agent, CAV is often associated with secondary bacterial and viral infections. Whether human infection results in reduced immunity to other foreign agents and morbidity requires further study. It is important to understand the extent of sequence variability in CAV, in order to improve the management strategies to prevent CAV infections in chickens and to prevent the transmission from chickens to humans or cats. The epidemiology and pathogenesis of this virus in chickens and in cats require further investigation. Our reports also underscore the need to study and monitor circulating CAVs in China.
Conflict of Interests
All authors declare that they have no conflict of interests related to the research presented in this paper.
The authors thank Prof. Li of the Veterinary College of South China Agricultural University for helping in collecting the fecal samples from stray cats in Guangdong province. This work was supported by grants from Guangdong Momentously Scientific and Technological Project (no. 2009B020201008) and the Strategic Cooperation Project of Guangdong Province & Chinese Academy (no. 2010B090301019).
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