Full-length infectious clone of a pathogenic Australian isolate of chicken anaemia virus

Molecular characterization of chicken infectious anaemia virus (CIAV) in China during 2020-2021

Chicken infectious anaemia virus (CIAV) has been identified as the causative agent of chicken infectious anaemia (CIA), causing huge economic losses to the poultry industry globally. In this study, a total of 573 clinical samples were collected from 197 broiler farms in 17 provinces of China during 2020-2021. Among them, 375 samples (375/573, 65.4%) were positive for CIAV by real-time PCR. The positive rate of CIAV detection between different regions of China ranged from 46.67% (North China) to 81.25% (Central China). The nucleotide sequences of the VP1 gene were obtained for 91 CIAV strains, whole genome sequencing was successful for 72 out of 91 strains. Phylogenetic analysis based on the VP1 gene revealed that 91 CIAV strains currently circulating in China belong to three genotypes (II, IIIa and IIIb), and most of the CIAV strains belong to genotype IIIa. Phylogenetic analysis of the whole genome showed that 71 CIAV strains belong to genotype IIIa, and one strain belongs to genotype II. Sequence analysis showed several amino acid substitutions in both the VP1, VP2 and VP3 proteins. Our results enhance the understanding of the molecular characterization of CIAV infection in China.RESEARCH HIGHLIGHTS A molecular systematic survey of CIAV in China during 2020-2021.CIAV genotype IIIa is the predominant genotype in China.

Molecular characterization of chicken anemia virus in Guangxi Province, southern China, from 2018 to 2020

Background

Chicken anemia virus (CAV) causes chicken infectious anemia, which results in immunosuppression; the virus has spread widely in chicken flocks in China.

Objectives

The aim of this study was to understand recent CAV genetic evolution in chicken flocks in Guangxi Province, southern China.

Methods

In total, 350 liver samples were collected from eight commercial broiler chicken farms in Guangxi Province in southern China from 2018 to 2020. CAV was detected by conventional PCR, and twenty CAV complete genomes were amplified and used for the phylogenetic analysis and recombination analysis.

Results

The overall CAV-positive rate was 17.1%. The genetic analysis revealed that 84 CAVs were distributed in groups A, B, C (subgroups C1-C3) and D. In total, 30 of 47 Chinese CAV sequences from 2005-2020 belong to subgroup C3, including 15 CAVs from this study. There were some specific mutation sites among the intergenotypes in the VP1 protein. The amino acids at position 394Q in the VP1 protein of 20 CAV strains were consistent with the characteristics of a highly pathogenic strain. GX1904B was a putative recombinant.

Conclusions

Subgroup C3 was the dominant genotype in Guangxi Province from 2018–2020. The 20 CAV strains in this study might be virulent according to the amino acid residue analysis. These data help improve our understanding of the epidemiological trends of CAV in southern China.

Effects of immunosuppression on the efficacy of vaccination against Mycoplasma gallisepticum infection in chickens

Immunosuppression can increase the susceptibility of chickens to other disease-causing pathogens and interfere with the efficacy of vaccination against those pathogens. Chicken anaemia virus (CAV) and infectious bursal disease virus (IBDV) are common causes of immunosuppression in chickens. Immunosuppression was induced by experimental infection with either CAV or IBDV to assess the effect of immunosuppression on the efficacy of vaccination with Mycoplasma gallisepticum strain ts-304 against infection with virulent M. gallisepticum, a common bacterial pathogen of chickens worldwide. Birds were experimentally infected with either CAV or IBDV at 1 week of age, before vaccination and challenge with M. gallisepticum to examine the effect of immunosuppression at the time of vaccination, or at 6 weeks of age, after vaccination against M. gallisepticum but before challenge with virulent M. gallisepticum, to investigate the effect of immunosuppression at the time of challenge. All birds were vaccinated with a single dose of the ts-304 vaccine at 3 weeks of age and experimentally challenged with the virulent M. gallisepticum strain Ap3AS at 8 weeks of age. In immunosuppressed chickens there was a reduction in protection offered by the ts-304 vaccine at two weeks after challenge, as measured by tracheal mucosal thicknesses, serum antibody levels against M. gallisepticum, air sac lesion scores and virulent M. gallisepticum load in the trachea. Immunosuppressed birds with detectable serum antibodies against M. gallisepticum were less likely to have tracheal lesions. This study has shown that immunosuppression caused by infection with CAV or IBDV can interfere with vaccination against mycoplasmosis in chickens.

Genetic Heterogeneity among Chicken Infectious Anemia Viruses Detected in Italian Fowl

Chicken infectious anemia virus (CIAV) is a pathogen of chickens associated with immunosuppression and with a disease named chicken infectious anemia. The present survey reports an epidemiological study on CIAV distribution in Italian broiler, broiler breeder and backyard chicken flocks. Twenty-five strains were detected by a specifically developed nested PCR protocol, and molecularly characterized by partial VP1 gene or complete genome sequencing. Viral DNA amplification was successfully obtained from non-invasive samples such as feathers and environmental dust. Sequence and phylogenetic analysis showed the circulation of field or potentially vaccine-derived strains with heterogeneous sequences clustered into genogroups II, IIIa, and IIIb. Marker genome positions, reported to be correlated with CIAV virulence, were evaluated in field strains. In conclusion, this is the first survey focused on the molecular characteristics of Italian CIAVs, which have proved to be highly heterogeneous, implementing at the same time a distribution map of field viruses worldwide.

Full-length infectious clone of an Iranian isolate of chicken anemia virus

An Iranian field strain of chicken anemia virus (CAV), designated IR CAV, was isolated in the Marek's disease virus-transformed lymphoblastoid cell line MDCC-MSB1 (MSB1) culture for the first time. The full-length CAV DNA of this strain was cloned in the bacterial plasmid pTZ57R/T to create the molecular clone pTZ-CAV. The nucleotide and deduced amino acid sequences of viral proteins of IR CAV were compared with those of representative CAV sequences including reference and commercial vaccine strains. IR CAV was not related to vaccine strains and also found to have glutamine at positions 139 and 144 confirming previous studies in which such mutations were associated with a slow rate of virus spread in cell culture. pTZ-CAV was digested with PstI to release IR CAV DNA and then transfected into MSB1 cell by electroporation. The transfected cells showed cytopathic effect similar to virion-initiated infection. One-day old specific pathogen-free chicks were inoculated with the regenerated virus, which had been obtained from transfected MSB1 cells, and compared with the chicks inoculated with IR CAV. Gross lesions in the birds inoculated with the regenerated virus illustrated the infectious nature of the regenerated virus from the cloned IR CAV DNA.

Evidence of apoptosis induced by viral protein 2 of chicken anaemia virus

Although viral protein 3 (VP3) of chicken anaemia virus (CAV) has been well recognised as an inducer of apoptosis, viral protein 2 (VP2) of the virus has only been speculated to have apoptotic activity. This has not been verified because the open reading frame (ORF) encoding VP2 completely encompasses that encoding VP3, and thus the possibility of expression of VP3 cannot be excluded. The aim of this study was to elucidate the potential role of VP2 as an inducer of apoptosis. Site-directed mutagenesis was used to generate a point mutation that knocked out VP3 by early termination of its translation with a stop codon without imposing any change in the amino acid sequence of VP2. The mutated sequence was inserted into the pCAT plasmid preceded by a favorable Kozak's consensus sequence to create pCAT-VP2(+)VP3(-). The absence of VP3 expression in MSB1 cells transfected with this plasmid was confirmed using Western blotting, and DNA strand breaks and nuclear morphological changes were assessed to detect apoptosis. There was an increased level of apoptotic death in cells transfected with pCAT-VP2(+)VP3(-) compared to those transfected with the vector alone. This provides evidence that CAV VP2 can induce apoptosis.

Experimental pathological studies of an Indian chicken anaemia virus isolate and its detection by PCR and FAT

Chicken Infectious Anaemia Virus (CIAV) is one of the potent immunosuppressive and economically important agents affecting poultry industry worldwide. Recent reports indicate the emergence of this virus in the poultry flocks of the country. The present study aimed to investigate the pathogenic potential of a recent isolate of CIAV obtained from poultry flock of Uttaranchal State, India. Twenty first day-old age Specific Pathogen Free (SPF) chicks were inoculated intramuscularly with 10(4.5) median tissue culture infective dose (TCID50) of CIAV passaged in the Marek's disease virus transformed chicken splenic T lymphocyte (MDCC-MSB 1) cell line while 15 chicks were kept as control. The CIAV isolate produced consistent clinical signs, loss in body weight gain, anaemia, low haematocrit values, bone marrow aplasia and generalized lymphoid atrophy. Mean Packed Cell Volume (PCV) value of the infected chicks was significantly low (18.22±2.22) compared to control group (34.12±4.72) at 14 day post infection (dpi). The establishment of virus infection in chicks was confirmed both at molecular and antigenic levels by Polymerase Chain Reaction (PCR) and Indirect Immunofluorescent Test (IIFT), respectively. Characteristic apoptotic pattern was also detected in the affected organs and the virus was re-isolated successfully in MDCC-MSB1 cell cultures. The present results revealed that the virus circulating in poultry flocks of Uttaranchal state is both pathogenic and immunosuppressive in nature. Extensive epidemiological studies are suggested in the poultry flocks of the country along with adaptation of appropriate diagnostic, prevention and control strategies so as to prevent economic losses caused by this important poultry pathogen.

Unraveling the puzzle of human anellovirus infections by comparison with avian infections with the chicken anemia virus

Current clinical studies on human annelloviruses infections are directed towards finding an associated disease. In this review we have emphasized the many similarities between human anellovirus and avian circoviruses and the cell and tissue types infected by these pathogens. We have done this in order to explore whether knowledge acquired from natural and experimental avian infections could reflect and be extrapolated to the less well-characterized human annellovirus infections. The knowledge gained from the avian system may provide suggestions for decoding the enigmatic human anellovirus infections, and finding the specific disease or diseases caused by these human anellovirus infections. Each additional parallelism between chicken anemia virus (CAV) and Torque teno virus (TTV) further strengthens this premise. As we have seen information from human infections can also be used to better understand avian infections as well. Increased attention must be focused on the "hidden" or unrecognized, seemingly asymptomatic effects of circovirus and anellovirus infections. Understanding the facilitating effect of these infections on disease progression caused by other pathogens may help to explain differences in outcome of complicated poultry and human diseases. The final course of a pathogenic infection is determined by variations in the state of health of the host before, during and after contact with a pathogen, in addition to the phenotype of the pathogen and host. The health burden of circoviridae and anellovirus infections may be underestimated, due to lack of awareness of the need to search past the predominant clinical effect of identified pathogens and look for modulation of cellular-based immunity caused by co-infecting circoviruses, and by analogy, human anneloviruses.

Attenuation of chicken anemia virus by site-directed mutagenesis of VP2

Chicken anemia virus (CAV) is a significant immunosuppressive pathogen of chickens, but relatively little is known about the effect of specific mutations on its virulence. In order to study the virulence of CAV, an infection model was developed in embryos. Significant growth depression, measured as a reduction in mean body weight, was found for wild-type CAV infection. Infection with wild-type CAV resulted in a significant reduction in thymic and splenic weights and consistently produced severe lesions in the thymus, spleen and bone marrow, as well as haemorrhages. CAVs mutated in the VP2 gene were infectious for embryos, but were highly attenuated with respect to growth depression and CAV-specific pathology. Relative to wild-type infection, viruses Mut C86R, Mut R101G, Mut H103Y, Mut R129G, Mut Q131P, Mut R/K/K150/151/152G/A/A, Mut D/E161/162G/G and Mut E186G were highly attenuated, and viruses Mut L163P and Mut D169G were moderately attenuated. Attenuation of the ability to produce lesions was found consistently for the thymus, spleen and bone marrow, thymic and splenic weights, and for CAV-induced haemorrhage. There was no growth depression associated with infection by the group of highly attenuated mutant viruses and a moderate reduction in mean body weight was only found for virus Mut L163P. These findings show that mutations in the VP2 gene can reduce the virulence of CAV and these mutant viruses may have value as vaccine candidates.

Viral load in 1-day-old and 6-week-old chickens infected with chicken anaemia virus by the intraocular route

Although the effects of chicken anaemia virus (CAV) infection have frequently been investigated in young chickens, there have been few studies of the pathogenesis of CAV infection in older birds. The aim of the work reported here was to study viral loads in 6-week-old chickens and to compare these with those seen in younger birds. Specific pathogen free chickens were inoculated at 1 day or at 6 weeks of age with 10(4) median tissue culture infective doses of CAV by the intraocular route. Chicks infected when 1 day old were euthanized at day 14, 18 or 22 post inoculation (p.i.), and those infected when 6 weeks old at day 16, 18 or 20 p.i. Their body and thymus weights were determined and samples were collected from their spleen, liver and thymus. A quantitative polymerase chain reaction assay was developed and used to determine the number of viral genome copies in the tissue samples. In both age groups, viral genome concentrations increased in all organs up to day 18 p.i. and reached a peak in the spleen and liver at day 18 p.i. The peak viral concentrations in the thymus were detected at day 18 in the younger birds and at day 20 p.i. in older chickens. These studies have shown that exposure to CAV in older birds leads to similar levels of active viral replication to those seen in younger birds, and may result in subclinical infections in older birds with the potential to increase susceptibility to other infectious agents.

Genome sequencing analysis of Brazilian chicken anemia virus isolates that lack MSB-1 cell culture tropism

Specific amino acid (aa) substitutions in VP1, VP2 and VP3 genes were reported as a distinctive feature of the American CIA-1 strain, characterized as having a variable rate of growth and tropism for different MSB-1 cell sublines [Renshaw RW, Soiné C, Weinkle T, O'Connell PH, Ohashi K, Watson S, et al. A hypervariable region in VP1 of chicken anemia virus mediates rate of spread and cell tropism in tissue culture. J Virol 1996;70(12):8872-8]. DNA sequencing of 878 nucleotides from twelve Brazilian CAV, eight of which tested for in vitro isolation in three different sources of MDCC-MSB1 cell line and identified as lacking capacity to propagate in any of these cells, were compared to sequence data available for CAV strains propagated or not in cell culture. Alignment of the deduced aa resulted in a lack of singled out amino acid substitutions in the partial genomic sequences of Brazilian isolates that would entirely contrast them to viruses propagated in MSB-1 cells, indicating that the combined VP1, VP2 and VP3 substitutions observed may not entirely account as sole determinants of CAV isolation and propagation in MDCC-MSB-1 cells.

Biological and molecular characterization of chicken anaemia virus isolates of Indian origin

In the present study, four chicken anaemia virus (CAV) isolates (CAV-A, -B, -E and -P) recovered from different geographical regions of India were characterized. CAV genome of 1,766 bp nucleotide region containing the complete coding region of VP2 and VP3 proteins, and partial coding region of VP1 protein were sequenced. The nucleotide and deduced amino acid sequence of the Indian CAV isolates were aligned and compared with CAV isolates of European, Asian, American and Australian origin. Phylogenetic analysis of the Indian CAV isolates were also carried out based on the nucleotide and deduced amino acid sequences. The results indicated that Indian isolates were genetically evolved from different parts of the world. Indian isolate, CAV-A was found closely related to European Cux-1 strain, CAV-B and -P were closely related to Bangladesh BD-3 strain and CAV-E was closely related to Australian 704 strain. The pathogenicity of the four CAV isolates was studied in day-old specific pathogen free (SPF) chicks. Day-old SPF chicks (n=50) were divided into five groups comprised of 10 chicks in each group. Group 1 was kept as control and groups 2-5 were infected with each CAV isolate separately. The chicks were infected at a dose rate of 1 ml cell culture fluid (10(4.5)TCID(50)/0.1 ml) per bird intramuscularly. The clinical signs, mortality and packed cell volume (PCV) and body weight gain were recorded on 5, 10 and 15 days post-infection. At 15th day, all the birds were sacrificed and various organs, viz., thymus, bone marrow, spleen, liver and bursa were examined for gross and microscopic changes. The pathogenicity study indicated that all the CAVs except CAV-B were able to produce clinical disease and immunosuppression in young chicks whereas the isolate CAV-B produced no clinical disease but only induced immunosuppression, which was revealed by microscopic examination of the lymphoid organs. The study showed valuable information on molecular epidemiological status of CAV isolates prevalent in India for the first time.

Site-directed mutagenesis of the VP2 gene of Chicken anemia virus affects virus replication, cytopathology and host-cell MHC class I expression

Chicken anemia virus (CAV) is an immunosuppressive pathogen of chickens. To further examine the role of viral protein 2 (VP2), which possesses dual-specificity protein phosphatase (DSP) activity, in viral cytopathogenicity and its influence on viral growth and virulence, an infectious genomic clone of CAV was subjected to site-directed mutagenesis. Substitution mutations C87R, R101G, K102D and H103Y were introduced into the DSP catalytic motif and R129G, Q131P, R/K/K150/151/152G/A/A, D/E161/162G/G, L163P, D169G and E186G into a region predicted to have a high degree of secondary structure. All mutant constructs were infectious, but their growth curves differed. The growth curve for mutant virus R/K/K150/151/152G/A/A was similar to that for wild-type virus, a second cluster of mutant viruses had an extended latent period and a third cluster of mutant viruses had extended latent and eclipse periods. All mutants had a reduced cytopathogenic effect in infected cells and VP3 was restricted to the cytoplasm. Mutation of the second basic residue (K102D) in the atypical DSP signature motif resulted in a marked reduction in virus replication efficiency, whereas mutation of the first basic residue (R101G) attenuated cytopathogenicity, but did not reduce replication efficiency. Expression of major histocompatibility complex (MHC) class I was markedly downregulated in cells infected with wild-type CAV, but not in those infected with mutants. This study further demonstrates the significance of VP2 in CAV replication and shows that specific mutations introduced into the gene encoding this protein can reduce virus replication, cytopathogenicity and downregulation of MHC I in infected cells.

Biological and Molecular Characterization of Chicken Anemia Virus Isolates from Slovenia

The presence of chicken anemia virus (CAV) in Slovenia was confirmed by inoculation of 1-day-old chickens without antibodies against CAV and isolation of the virus on the Marek's disease chicken cell-MSB1 line and by polymerase chain reaction (PCR). Experimental inoculation of 1-day-old chickens resulted in lower hematocrit values, atrophy of the thymus, and atrophy of bone marrow. CAV was confirmed by PCR in the thymus, bone marrow, bursa of Fabricius, liver, spleen, ileocecal tonsils, duodenum, and proventriculus. The nucleotide sequence of the whole viral protein (VP)1 gene was determined by direct sequencing. Alignment of VP1 nucleotide sequences of Slovenian CAV isolates (CAV-69/00, CAV-469/01, and CAV-130/03) showed 99.4% to 99.9% homology. The VP1 nucleotide sequence alignment of Slovenian isolates with 19 other CAV strains demonstrated 94.4% to 99.4% homology. Slovenian isolates shared highest homology with the BD-3 isolate from Bangladesh. Alignment of the deduced VP1 amino acids showed that the Slovenian isolates shared 100% homology and had an amino acid sequence most similar to the BD-3 strain from Bangladesh (99.6%) and were 99.1% similar to the G6 strain from Japan and the L-028 strain from the United States. The Slovenian isolates were least similar (96.6%) to the 82-2 strain from Japan. A phylogeneric analysis on the basis of the alignment of the VP1 amino acids showed that CAV isolates used in the study formed three groups that indicated the possible existence of genetic groups among CAV strains. The CAV isolates were grouped together independent of their geographic origin and pathogenicity.

Mutation of chicken anemia virus VP2 differentially affects serine/threonine and tyrosine protein phosphatase activities

Novel dual-specificity protein phosphatases (DSPs), which catalyse the removal of phosphate from both phosphotyrosine and phosphoserine/phosphothreonine substrates, have recently been identified in two viruses within the familyCircoviridae. Viral protein 2 (VP2) of chicken anemia virus (CAV) and ORF2 of TT virus have been shown to possess DSP activityin vitro. CAV VP2 is unusual in possessing two vicinal cysteines within the protein phosphatase signature motif. The first cysteine residue (C95) within the motif has been identified by mutagenesis as the essential catalytic cysteine. In this study, it was shown that virus mutated at this residue displayed a marked inhibition of growth, with titres reduced 104-fold, and reduced cytopathogenic effect in cell culture, indicating that viral DSP activity may be significant during infection. As with virus mutated at the first cysteine residue, mutation of the second cysteine (C97) within the motif resulted in a marked reduction in viral growth and attenuation of cytopathogenicity in infected cell cultures. However, mutagenesis of this second cysteine only reduced phosphotyrosine phosphatase activity to 70 % of that of wild-type VP2, but increased phosphoserine/phosphothreonine phosphatase activity by as much as 700 %. The differential effect of the C97S mutation on VP2 activity does not appear to have parallels in other DSPs and suggests a unique role for the second cysteine in the function of these viral proteins, particularlyin vivo.

Pathogenesis of Chicken Anemia Virus: Comparison of the Oral and the Intramuscular Routes of Infection

The events during the pathogenesis of chicken anemia virus (CAV) infection following intramuscular (IM) and oral inoculation were further elucidated and compared by sequential clinical, pathologic, and morphometric histopathologic evaluations, and by sequential determination of CAV genome concentrations in different organs. Specific-pathogen-free chickens were inoculated by IM or oral routes with the same dose (2 x 10(6) mean tissue culture infective dose [TCID50]) of CAV isolate 03-4876 at 1 day of age. Weights and hematocrits were obtained at 7, 10, 14, 18, 21, 25, and 28 days postinoculation (DPI). Seven birds from each group were necropsied at 7, 10, 14, and 28 DPI, and samples of thymus, Harderian gland, and cecal tonsils (CT) were obtained for histopathologic examination and CAV genome quantification by real-time polymerase chain reaction. Peak CAV genome concentrations were detected in the thymus at 10 and 14 DPI in the IM and orally infected chickens, respectively. High CAV DNA concentrations were maintained throughout the experimental period until 28 DPI, despite specific seroconversion occurring by 14 DPI in the IM-inoculated chickens. CAV was isolated from both orally and IM-infected chickens 28 DPI. Peak CAV genomes in the thymuses of IM and orally infected chickens coincided with peak lymphocyte depletion in these organs. Lymphocyte repopulation of the thymus occurred by 28 DPI in spite of the presence of the virus in the organs of both infected chicken groups. CAV genomes were detected in the CT, but histopathologic changes were not observed. Compared with the IM route of infection, orally infected chickens did not show apparent signs of illness. Clinical parameters, including reduction of weight gains and hematocrits, and gross and histopathologic changes were delayed and less severe in the orally inoculated chickens. This was concurrent with a delay in accumulation of CAV genomes in the thymus of these chickens.

Chicken anemia virus VP2 is a novel dual specificity protein phosphatase

The function of viral protein 2 (VP2) of the immunosuppressive circovirus chicken anemia virus (CAV) has not yet been established. We show that the CAV VP2 amino acid sequence has some similarity to a number of eukaryotic, receptor, protein-tyrosine phosphatase (PTPase) alpha proteins as well as to a cluster of human TT viruses within the Sanban group. To investigate if CAV VP2 functions as a PTPase, purified glutathione S-transferase (GST)-VP2 fusion protein was assayed for PTPase activity using the generalized peptide substrates ENDpYINASL and DADEpYLIPQQG (where pY represents phosphotyrosine), with free phosphate detected using the malachite green colorimetric assay. CAV GST-VP2 was shown to catalyze dephosphorylation of both substrates. CAV GST-VP2 PTPase activity for the ENDpYINASL substrate had a V(max) of 14,925 units/mg.min and a K(m) of 18.88 microm. Optimal activity was observed between pH 6 and 7, and activity was specifically inhibited by 0.01 mm orthovanadate. We also show that the ORF2 sequence of the CAV-related human virus TT-like minivirus (TLMV) possessed PTPase activity and steady state kinetics equivalent to CAV GST-VP2 when expressed as a GST fusion protein. To establish whether these viral proteins were dual specificity protein phosphatases, the CAV GST-VP2 and TLMV GST-ORF2 fusion proteins were also assayed for serine/threonine phosphatase (S/T PPase) activity using the generalized peptide substrate RRApTVA, with free phosphate detected using the malachite green colorimetric assay. Both CAV GST-VP2 and TLMV GST-ORF2 fusion proteins possessed S/T PPase activity, which was specifically inhibited by 50 mm sodium fluoride. CAV GST-VP2 exhibited S/T PPase activity with a V(max) of 28,600 units/mg.min and a K(m) of 76 microm. Mutagenesis of residue Cys(95) to serine in CAV GST-VP2 abrogated both PTPase and S/T PPase activity, identifying it as the catalytic cysteine within the proposed signature motif. These studies thus show that the circoviruses CAV and TLMV encode dual specificity protein phosphatases (DSP) with an unusual signature motif that may play a role in intracellular signaling during viral replication. This is the first DSP gene to be identified in a small viral genome.

Sequence analysis of the full-length cloned DNA of a chicken anaemia virus (CAV) strain from Bangladesh: evidence for genetic grouping of CAV strains based on the deduced VP1 amino acid sequences

Chicken anaemia virus (CAV) was detected in the bursa of Fabricius of a 4-week-old chicken obtained from an outbreak of acute infectious bursal disease in Bangladesh. Repeated attempts to grow this virus in MDCC-MSB1 cells were not successful. A full-length PCR amplicon of the genome of this strain, designated as BD-3 CAV, was cloned and sequenced. The complete nucleotide sequence and the deduced amino acid sequence were compared with those of 12 other CAV strains. The genetic analysis of the amino acid sequences of VP1 indicated the possible existence of genetic groups among CAV strains, as BD-3 CAV along with four other strains (CIA-1, L-028, Isolate 704 and TR-20) formed a distinct lineage. These strains have four signatory amino acids in VP1, such as 75I/T, 97L, 139Q and 144Q, out of which the latter two are located in a small hydrophilic peak.