Morphological characterization of chicken anaemia agent (CAA)

Genetic diversity, distribution, and evolution of chicken anemia virus: A comparative genomic and phylogenetic analysis

Chicken infectious anemia (CIA) is an immunosuppressive poultry disease that causes aplastic anemia, immunosuppression, growth retardation and lymphoid tissue atrophy in young chickens and is responsible for huge economic losses to the poultry industry worldwide. The disease is caused by the chicken anemia virus (CAV), which belongs to the genus Gyrovirus, family Anelloviridae. Herein, we analyzed the full-length genomes of 243 available CAV strains isolated during 1991–2020 and classified them into two major clades, GI and GII, divided into three and four sub-clades, GI a-c, and GII a-d, respectively. Moreover, the phylogeographic analysis revealed that the CAVs spread from Japan to China, China to Egypt and subsequently to other countries, following multiple mutational steps. In addition, we identified eleven recombination events within the coding and non-coding regions of CAV genomes, where the strains isolated in China were the most active and involved in ten of these events. Furthermore, the amino acids variability analysis indicated that the variability coefficient exceeded the estimation limit of 1.00 in VP1, VP2, and VP3 proteins coding regions, demonstrating substantial amino acid drift with the rise of new strains. The current study offers robust insights into the phylogenetic, phylogeographic and genetic diversity characteristics of CAV genomes that may provide valuable data to map the evolutionary history and facilitate preventive measures of CAVs.

Occurrence of Chicken Infectious Anemia Virus in Industrial and Backyard Tunisian Broilers: Preliminary Results

Chicken infectious anemia virus (CIAV) is an economically important and widely distributed immunosuppressive agent in chickens. This study performed an epidemiological investigation on CIAV circulation in 195 Tunisian broilers, belonging to 13 lots from five industrial farms and in one rural farm. Fifteen animals were detected positive by a VP1 nested PCR. The amplicons were molecularly characterised by complete genome sequencing. All positive samples obtained in this study were from the rural farm, whereas the industrial farms sampled were negative. Nucleotide and amino acid sequence analyses showed a high degree of similarity among the sequences obtained, suggesting the circulation of a single CIAV strain in the positive lot. Phylogenetic analysis based on the CIAV VP1 nucleotide sequence and/or the complete genome showed that the sequences obtained in this study clustered with CIAV strains previously detected in Tunisia, Italy and Egypt, belonging to genogroup II. Our results highlight the need for constant CIAV surveillance in backyard chicken production.

Newcastle Disease Virus Vectored Chicken Infectious Anaemia Vaccine Induces Robust Immune Response in Chickens

Newcastle disease virus (NDV) strain R2B, with an altered fusion protein cleavage site, was used as a viral vector to deliver the immunogenic genes VP2 and VP1 of chicken infectious anaemia virus (CIAV) to generate a bivalent vaccine candidate against these diseases in chickens. The immunogenic genes of CIAV were expressed as a single transcriptional unit from the NDV backbone and the two CIA viral proteins were obtained as separate entities using a self-cleaving foot-and-mouth disease virus 2A protease sequence between them. The recombinant virus (rR2B-FPCS-CAV) had similar growth kinetics as that of the parent recombinant virus (rR2B-FPCS) in vitro with similar pathogenicity characteristics. The bivalent vaccine candidate when given in specific pathogen-free chickens as primary and booster doses was able to elicit robust humoral and cell-mediated immune (CMI) responses obtained in a vaccination study that was conducted over a period of 15 weeks. In an NDV and CIAV ELISA trial, there was a significant difference in the titres of antibody between vaccinated and control groups which showed slight reduction in antibody titre by 56 days of age. Hence, a second booster was administered and the antibody titres were maintained until 84 days of age. Similar trends were noticed in CMI response carried out by lymphocyte transformation test, CD4⁺ and CD8⁺ response by flow cytometry analysis and response of real time PCR analysis of cytokine genes. Birds were challenged with virulent NDV and CIAV at 84 days and there was significant reduction in the NDV shed on the 2nd and 4th days post challenge in vaccinated birds as compared to unvaccinated controls. Haematological parameters comprising PCV, TLC, PLC and PHC were estimated in birds that were challenged with CIAV that indicated a significant reduction in the blood parameters of controls. Our findings support the development and assessment of a bivalent vaccine candidate against NDV and CIAV in chickens.

Isolation and Molecular Characteristics of a CIAV Isolate From Pigeons, China

Chicken infectious anemia virus (CIAV) mainly infects chickens and causes immunosuppression. In this study, a CIAV isolate, designated as Pigeon-CIAV-1906, was efficiently isolated from two sick pigeons by inoculating the samples into MSB1 cells. The genome of Pigeon-CIAV-1906 was amplified by PCR and analyzed. The genome size of Pigeon-CIAV-1906 was 2,298 bp with the highest homology (99.5%) to Jilin strain (JL14023) and the lowest homology (91.5%) to Brazil strain (KY024579), which phylogenetically clustered into Group A. Notably, several amino acids such as 139K and 394Q related with high virulence were found in the VP1 of Pigeon-CIAV-1906. The isolation of Pigeon-CIAV-1906 and its molecular characteristics provide evidence for the cross-transmission of CIAV from chicken to pigeon and give novel insights into the molecular epidemiology of CIAV.

The Role of Apoptin in Chicken Anemia Virus Replication

Apoptin is the Vp3 protein of chicken anemia virus (CAV), which infects the thymocytes and erythroblasts in young chickens, causing chicken infectious anemia and immunosuppression. Apoptin is highly studied for its ability to selectively induce apoptosis in human tumor cells and, thus, is a protein of interest in anti-tumor therapy. CAV apoptin is known to localize to different subcellular compartments in transformed and non-transformed cells, depending on the DNA damage response, and the phosphorylation of several identified threonine residues. In addition, apoptin interacts with molecular machinery such as the anaphase promoting complex/cyclosome (APC/C) to inhibit the cell cycle and induce arrest in G2/M phase. While these functions of apoptin contribute to the tumor-selective effect of the protein, they also provide an important fundamental framework to apoptin’s role in viral infection, pathogenesis, and propagation. Here, we reviewed how the regulation, localization, and functions of apoptin contribute to the viral life cycle and postulated its importance in efficient replication of CAV. A model of the molecular biology of infection is critical to informing our understanding of CAV and other related animal viruses that threaten the agricultural industry.

Preparation of Chicken Anemia Virus (CAV) Virus-Like Particles and Chicken Interleukin-12 for Vaccine Development Using a Baculovirus Expression System

Chicken infectious anemia (CIA) is a poultry disease that causes huge economic losses in the poultry industry worldwide. Commercially available CIA vaccines are derived from wild-type chicken anemia viruses (CAVs) by serial passage in cells or chicken embryos. However, these vaccinal viruses are not completely attenuated; therefore, they can be transmitted vertically and horizontally, and may induce clinical symptoms in young birds. In this study, we sought to eliminate these issues by developing a subunit vaccine exploiting the CAV structural proteins, engineering recombinant baculovirus-infected Spodoptera frugiperda (Sf9) cells that contained both the viral protein 1 (VP1) and VP2 of CAV. Moreover, we produced single-chain chicken interleukin-12 (chIL-12) in the same system, to serve as an adjuvant. The recombinant VP1 was recognized by chicken anti-CAV polyclonal antibodies in Western blotting and immunofluorescence assays, and the bioactivity of the recombinant chIL-12 was confirmed by stimulating interferon-γ (IFN-γ) secretion in chicken splenocytes. Furthermore, the ability of the recombinant VP1 to generate self-assembling virus-like particles (VLPs) was confirmed by transmission electron microscopy. Specific pathogen-free (SPF) chickens inoculated with VLPs and co-administered the recombinant chIL-12 induced high CAV-specific antibodies and cell-mediated immunity. Taken together, the VLPs produced by the baculovirus expression system have the potential to be a safe and effective CIA vaccine. Finally, we demonstrated the utility of recombinant chIL-12 as an adjuvant for poultry vaccine development.

Epidemiology and molecular characterization of chicken anaemia virus from commercial and native chickens in Taiwan

Chicken infectious anaemia (CIA) is a disease with a highly economic impact in the poultry industry. The infected chickens are characterized by aplastic anaemia and extreme immunosuppression, followed by the increased susceptibility to secondary infectious pathogens and suboptimal immune responses for vaccination. Commercially available CIA vaccines are routinely used in the breeders in Taiwan to protect their progeny with maternal-derived antibodies. However, CIA cases still occur in the field and little is known about the genetic characteristics of Taiwanese chicken anaemia viruses (CAVs). In this study, CAV DNA was detected in 72 of 137 flocks collected during 2010-2015. Among the PCR-positive samples, the coding regions of 51 CAVs were sequenced. Phylogenetic analysis of the VP1 gene revealed that, although most of Taiwanese CAVs belonged to genotypes II and III, some isolates were clustered into a novel genotype (genotype IV). Moreover, a Taiwanese isolate in this novel genotype IV appeared to be derived from a recombination event between genotypes II and III viruses. Five Taiwanese CAV isolates were highly similar to the vaccine strains, 26P4 or Del-Ros. Taken together, these results indicate that the sequences of CAVs in Taiwan are variable, and inter-genotypic recombination had occurred between viruses of different genotypes. Moreover, vaccine-like strains might induce clinical signs of CIA in chickens. Our findings could be useful for understanding the evolution of CAVs and development of a better control strategy for CIA.

T-cell reprogramming through targeted CD4-coreceptor and T-cell receptor expression on maturing thymocytes by latent Circoviridae family member porcine circovirus type 2 cell infections in the thymus

Although porcine circovirus type 2 (PCV2)-associated diseases have been evaluated for known immune evasion strategies, the pathogenicity of these viruses remained concealed for decades. Surprisingly, the same viruses that cause panzootics in livestock are widespread in young, unaffected animals. Recently, evidence has emerged that circovirus-like viruses are also linked to complex diseases in humans, including children. We detected PCV2 genome-carrying cells in fetal pig thymi. To elucidate virus pathogenicity, we developed a new pig infection model by in vivo transfection of recombinant PCV2 and the immunosuppressant cofactor cyclosporine A. Using flow cytometry, immunofluorescence and fluorescence in situ hybridization, we found evidence that PCV2 dictates positive and negative selection of maturing T cells in the thymus. We show for the first time that PCV2-infected cells reside at the corticomedullary junction of the thymus. In diseased animals, we found polyclonal deletion of single positive cells (SPs) that may result from a loss of major histocompatibility complex class-II expression at the corticomedullary junction. The percentage of PCV2 antigen-presenting cells correlated with the degree of viremia and, in turn, the severity of the defect in thymocyte maturation. Moreover, the reversed T-cell receptor/CD4-coreceptor expression dichotomy on thymocytes at the CD4⁺CD8^interm and CD4SP cell stage is viremia-dependent, resulting in a specific hypo-responsiveness of T-helper cells. We compare our results with the only other better-studied member of Circoviridae, chicken anemia virus. Our data show that PCV2 infection leads to thymocyte selection dysregulation, adding a valuable dimension to our understanding of virus pathogenicity.

Circoviruses: immunosuppressive threats to avian species: a review

Circoviruses are small, non-enveloped, icosahedral viruses that are unique among animal viruses in having circular, single-stranded DNA genomes. Their genomes are also the smallest possessed by animal viruses. The circovirus family currently comprises three members, chicken anaemia virus, porcine circovirus, and psittacine beak and feather disease virus, with pigeon circovirus being classified as a tentative member. Infections with each of the four circoviruses are associated with potentially fatal diseases in which virus-induced damage to lymphoid tissue and immunosuppression are common features. Experience with other animal virus families suggests that additional animal species will be infected by, as yet undiscovered, circoviruses and that these may display similar tissue tropism and disease-causing potential. Recent reports describing the association of circovirus-like viruses with immunodeficiency-related diseases of geese and southern black-backed gulls suggest that circovirus infections of avian species may be more common than previously recognized, and prompt the question of whether novel circoviruses infect poultry to cause clinical and/or subclinical diseases that may be economically important. This review has three purposes. First, it is designed to summarize the currently available information about the classified circoviruses and viruses that are regarded as circovirus-like. Second, it aims to alert the readership to the possibility that other avian species, including commercial poultry, may be infected with novel circoviruses. Finally, possible methods for discovering novel circoviruses and for controlling infections by such viruses are suggested.

Quantification of chicken anaemia virus by competitive polymerase chain reaction

A quantitative method for chicken anaemia virus (CAV) was developed using competitive polymerase chain reaction (PCR). Competitive template was constructed by deletion of 33 nucleotides from a wildtype DNA clone of CAV. Quantification of CAV DNA molecules by the competitive PCR was rapid and highly reproducible when compared with conventional infectivity titration methods. The ratios of the viral DNA molecules and infectivity titres in MDCC-MSB1 cells varied between 1.3 and 3.55 log(10) among several isolates, suggesting the existence of different infection efficiencies to MDCC-MSB1 cells by isolates. The competitive PCR will be useful for studying CAV infection in vivo and/or in vitro.

Duplex PCR assay for the detection of avian adeno virus and chicken anemia virus prevalent in Pakistan

Avian Adeno viruses and Chicken Anemia Viruses cause serious economic losses to the poultry industry of Pakistan each year. Timely and efficient diagnosis of the viruses is needed in order to practice prevention and control strategies. In the first part of this study, we investigated broilers, breeder and Layer stocks for morbidity and mortality rates due to AAV and CAV infections and any co-infections by examining signs and symptoms typical of their infestation or post mortem examination. In the second part of the study, we developed a duplex PCR assay for the detection of AAV and CAV which is capable to simultaneously detect both the viral types prevalent in Pakistan with high sensitivity and 100% specificity.

Porcine circovirus type 2 and porcine circovirus-associated disease

Porcine circovirus type 2 (PCV2) belongs to the viral family Circoviridae and to the genus Circovirus. Circoviruses are small, single-stranded nonenveloped DNA viruses that have an unsegmented circular genome. PCV2 is the primary causative agent of several syndromes collectively known as porcine circovirus-associated disease (PCVAD). Many of the syndromes associated with PCVAD are a result of coinfection with PCV2 virus and other agents such as Mycoplasma and porcine reproductive and respiratory syndrome virus. PCV2 infection is present in every major swine-producing country in the world, and the number of identified cases of PCVAD is rapidly increasing. In the United States, the disease has cost producers an average of 3-4 dollars per pig with peak losses ranging up to 20 dollars per pig. The importance of this disease has stimulated investigations aimed at identifying risk factors associated with infection and minimizing these risks through modified management practices and development of vaccination strategies. This paper provides an overview of current knowledge relating to PCV2 and PCVAD with an emphasis on information relevant to the swine veterinarian.

Chicken anemia virus

Chicken anemia virus (CAV), the only member of the genus Gyrovirus of the Circoviridae, is a ubiquitous pathogen of chickens and has a worldwide distribution. CAV shares some similarities with Torque teno virus (TTV) and Torque teno mini virus (TTMV) such as coding for a protein inducing apoptosis and a protein with a dual-specificity phosphatase. In contrast to TTV, the genome of CAV is highly conserved. Another important difference is that CAV can be isolated in cell culture. CAV produces a single polycistronic messenger RNA (mRNA), which is translated into three proteins. The promoter-enhancer region has four direct repeats resembling estrogen response elements. Transcription is enhanced by estrogen and repressed by at least two other transcription factors, one of which is COUP-TF1. A remarkable feature of CAV is that the virus can remain latent in gonadal tissues in the presence or absence of virus-neutralizing antibodies. In contrast to TTV, CAV can cause clinical disease and subclinical immunosuppression especially affecting CD8+ T lymphocytes. Clinical disease is associated with infection in newly hatched chicks lacking maternal antibodies or older chickens with a compromised humoral immune response.

Complete nucleotide sequence of a novel porcine circovirus-like agent and its infectivity in vitro

A novel agent (hence termed as P2) was isolated from pig sera in China, which contained covalently bound circular genomic DNAs of 993 nucleotides. Sequence analyses indicated that the agent was closely related to the porcine circovirus (PCV). The molecular clone of P2 was constructed subsequently and used for the following studies. Intracytoplasmic inclusions and intranuclear inclusions were only found in PK-15 cells transfected with the tandem dimer of P2 molecular DNA clone. Intracytoplasmic inclusions were round or irregular in shape and 0.1-0.4 microm in diameter, and intranuclear inclusions were electronically denser than intracytoplasmic inclusions and had two general shapes: round/small (0.1 microm in diameter) and hexagonal/large (0.5-1.4 microm in diameter). The inclusions were not membranously bound. The cells transfected with the tandem dimer of P2 molecular DNA clone were tested positive for P2 DNA at passages 5. The P2 antigen could be detected in both transfected and passaged PK-15 cells. This is the first report regarding the complete nucleotide sequence of a small DNA genome in a circovirus-like infectious agent in vitro.

Detection of chicken anaemia virus by DNA hybridization and polymerase chain reaction

A clone containing the complete genome of chicken anaemia virus (CAV) was used in hybridizations with DNA from various field isolates of CAV. CAV DNA from all field isolates was detected in a polymerase chain reaction with oligonucleotides derived from the sequence of the cloned CAV DNA as primers. By way of Southern blot analysis with (32)P-labelled DNA probes derived from cloned CAV DNA, all field isolates were shown to contain DNA molecules of about 2.3 kb, i.e. the size of cloned CAV DNA. In a dot-blot assay it was demonstrated that non-radioactively-labelled cloned CAV DNA hybridized specifically to DNA from field isolates. The cloned CAV DNA is highly similar to the DNA of field isolates, as borne out by restriction-enzyme mapping. We conclude that our cloned CAV genome is representative for CAV in the field. The described PCR and hybridization techniques, may, therefore, be used for research and diagnosis of CAV infections.

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 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.

A VP3/VP1 gene polymerase chain reaction assay for detection of chicken anemia virus in broiler samples

A PCR assay was designed for amplification of the highly conserved VP3 gene and a 5' region of the VP1 gene, for the diagnosis of CAV in organ samples of broiler flocks suspected of chicken infectious anemia. A comparison of the VP3/VP1 PCR with in vivo virus isolation revealed 100% agreement of the results, with 13 positive and 3 negative samples in both assays, indicating that the VP3/VP1 PCR is a specific diagnostic method. Tissues from additional 24 broiler chicken flocks, with CAV-like lesions and clinical history were then tested only by the VP3/VP1 PCR and a reference PCR with published primers for the VP1 gene. Nineteen samples resulted positive and one negative in both PCR, while another 4 samples were positive only in the VP3/VP1 PCR. These results indicate that the VP3/VP1 PCR is a sensitive, specific diagnostic test, suitable as an alternative to the expensive and time consuming in vivo virus isolation method, specially considering the difficult diagnosis of CAV strains not readily adaptable to MSB-1 cell culture.

Isolation and Preliminary Characterization of Chicken Anemia Virus from Chickens in Nigeria

Chicken anemia virus (CAV) was isolated for the first time from the Nigerian chicken population. The virus was recovered from necropsied birds from broiler and pullet flocks that suffered disease outbreaks tentatively diagnosed as infectious bursal disease. A sensitive polymerase chain reaction (PCR) assay detected CAV DNA in tissues of necropsied birds. Restriction endonuclease analysis performed with the 733-bp PCR product and the Cfo I enzyme indicated at least two different CAVs were circulating among the Nigerian chicken population. Four isolates were obtained from pooled liver and thymus tissues using the MDCC-MSB1 cell line. These isolates were found to be antigenically closely related to the Cuxhaven-1 (Cux-1) reference strain of CAV when reacted with four monoclonal antibodies prepared against the Cux-1 virus. One of the isolates (isolate A) induced thymus atrophy, bone marrow aplasia, and low hematocrit values when inoculated into 1-day-old specific-pathogen-free chickens. These findings not only demonstrate that CAV is present in Nigeria, but they also likely represent the first cell culture isolation of the virus in Africa.

Detection of chicken anemia virus in the gonads and in the progeny of broiler breeder hens with high neutralizing antibody titers

Previous evidence for the presence of chicken anemia virus (CAV) in the gonads of immune specific-pathogen-free chickens raised the question whether this occurs also in commercial breeders. The presence of CAV was investigated by nested PCR in the gonads and spleens of hens from two 55- and 59-week-old, CAV-vaccinated (flocks 2 and 3), and two 48- and 31-week-old non-vaccinated broiler breeder flocks (flocks 1 and 4). In addition, lymphoid tissues of 20-day-old embryos from these hens were also investigated for the presence of CAV. CAV was detected in the gonads and of 5/6 and 11/22 of the vaccinated hens and in some hens also in the spleen alone. Embryos from 7/8 and 5/18 of these hens were positive. In the non-vaccinated flocks, CAV was detected in the gonads of 11/34 and 10/10 hens in flocks 1 and 4, respectively. In addition, 11 birds in flock 1 had positive spleens. CAV DNA was detected in 3/11 and 2/10 of their embryos. CAV-positive gonads and embryos were detected in samples from hens with moderate as well as high VN antibody titers. Vaccinated chickens positive for CAV in the gonads and in their embryos had VN titers ranging from >1:512 to <1:2048. In non-vaccinated chickens, the VN titers of CAV positive chickens ranged from 1:128 to 1:4096. These results demonstrate that CAV genome can remain present in the gonads of hens in commercial broiler breeder flocks even in the presence of high neutralizing antibody titers that have been associated with protection against CAV vertical transmission. It also suggests that transmission to the progeny may occur irrespectively of the level of the humoral immune response in the hens.

Chicken Infectious Anemia Virus: An Example of the Ultimate Host–Parasite Relationship

Chicken infectious anemia virus (CIAV) is a resistant and ubiquitous virus of chickens causing disease in young chickens and immunosuppression in all birds. This paper reviews the current knowledge of CIAV with a focus on new findings indicating that immunosuppressive effects have not been fully appreciated, especially as they relate to the development of antigen-specific cytotoxic T cells. A more complete understanding of the immunosuppressive effects of CIAV emphasizes the need for better vaccines, especially for the broiler industry. In addition, a new model is proposed for the control of viral replication in the reproductive tract of specific-pathogen-free chickens, which may be latently infected. This model suggests that virus transcription is controlled by viral enhancer and repressor elements, which are regulated by different hormones. As a consequence, CIAV has a well-adapted relationship with its host, avoiding immune detection, ensuring passage of virus to the next generation, and eliciting limited pathology to the host.

Comparison of the structures of three circoviruses: chicken anemia virus, porcine circovirus type 2, and beak and feather disease virus

Circoviruses are small, nonenveloped icosahedral animal viruses characterized by circular single-stranded DNA genomes. Their genomes are the smallest possessed by animal viruses. Infections with circoviruses, which can lead to economically important diseases, frequently result in virus-induced damage to lymphoid tissue and immunosuppression. Within the family Circoviridae, different genera are distinguished by differences in genomic organization. Thus, Chicken anemia virus is in the genus Gyrovirus, while porcine circoviruses and Beak and feather disease virus belong to the genus CIRCOVIRUS: Little is known about the structures of circoviruses. Accordingly, we investigated the structures of these three viruses with a view to determining whether they are related. Three-dimensional maps computed from electron micrographs showed that all three viruses have a T=1 organization with capsids formed from 60 subunits. Porcine circovirus type 2 and beak and feather disease virus show similar capsid structures with flat pentameric morphological units, whereas chicken anemia virus has stikingly different protruding pentagonal trumpet-shaped units. It thus appears that the structures of viruses in the same genus are related but that those of viruses in different genera are unrelated.

A tumor-specific kinase activity regulates the viral death protein Apoptin

Apoptin, a chicken anemia virus-encoded protein, is thought to be activated by a general tumor-specific pathway, because it induces apoptosis in a large number of human tumor or transformed cells but not in their normal, healthy counterparts. Here, we show that Apoptin is phosphorylated robustly both in vitro and in vivo in tumor cells but negligibly in normal cells, and we map the site to threonine 108. A gain-of-function point mutation (T108E) conferred upon Apoptin the ability to accumulate in the nucleus and kill normal cells, implying that phosphorylation is a key regulator of the tumor-specific properties of Apoptin. An activity that could phosphorylate Apoptin on threonine 108 was found specifically in tumor and transformed cells from a variety of tissue origins, suggesting that activation of this kinase is generally associated with the cancerous or pre-cancerous state. Moreover, analyses of human tissue samples confirm that Apoptin kinase activity is detectable in primary malignancies but not in tissue derived from healthy individuals. Taken together, our results support a model whereby the dysregulation of the cellular pathway leading to the phosphorylation of Apoptin contributes to human tumorigenesis.

Comparison of a putative second serotype of chicken infectious anemia virus with a prototypical isolate II. Antigenic and physicochemical characteristics

A putative new serotype of chicken infectious anemia virus (CIAV) isolated from 17-wk-old broiler breeder pullets was compared with a known, previously characterized CIAV isolate, the Del-Ros strain. Physicochemical characteristics evaluated induded thermal stability, size, pH, and chloroform sensitivity. Physicochemically, CIAV-7 was identical to CIAV. The virus isolates were compared antigenically by enzyme-linked immunosorbent assay, virus neutralization, immunofluorescence assay, and western blot. All four serologic assays demonstrated that CIAV-7 is antigenically distinct from the Del-Ros strain of CIAV. Additionally, polymerase chain reaction (PCR) and Southern blot were used to determine if there were similarities in genome sequence between the two viruses. CIAV-7 could not be detected with CIAV-specific PCR primers or a with CIAV-specific probe by Southern hybridization.

Changes in CD4(+), CD8(+), CD4(+) CD8(+), and immunoglobulin M-positive peripheral blood mononuclear cells of postweaning multisystemic wasting syndrome-affected pigs and age-matched uninfected wasted and healthy pigs correlate with lesions and porcine circovirus type 2 load in lymphoid tissues

Forty-one 8- to 12-week-old wasted pigs were selected from several conventional farms with histories of postweaning multisystemic wasting syndrome (PMWS) and classified into two groups according to their porcine circovirus type 2 (PCV2) infection status, as determined by in situ hybridization (ISH). Twenty-four pigs tested positive for PCV2 (PCV2-positive group), while 17 pigs tested negative for PCV2 (PCV2-negative group). In addition, eight uninfected healthy pigs from an experimental farm were used as controls. Heparinized blood samples were taken to obtain peripheral blood mononuclear cells. The CD4(+), CD8(+), CD4(+) CD8(+) (double-positive [DP]), and immunoglobulin M-positive (IgM(+)) cell subsets were analyzed by flow cytometry with appropriate monoclonal antibodies. Histopathological studies were done to evaluate the apparent degrees of lymphocyte depletion in different lymphoid organs (superficial inguinal and mesenteric lymph nodes, Peyer's patches, tonsils, and spleen) and to determine the viral load of the PCV2 genome by using an ISH technique. Animals of the PCV2-positive group showed a significant downshift of the CD8(+) and DP cell subsets compared to the other groups (P < 0.05). Moreover, in PCV2-positive pigs, the amount of PCV2 genome in lymphoid tissues was related to the degree of cell depletion in those tissues (P < 0.05) as well as to the relative decrease in IgM(+) and CD8(+) cells in peripheral blood. These data support the notion that PCV2-positive pigs might have an impaired immune response.

Molecular properties, biology, and clinical implications of TT virus, a recently identified widespread infectious agent of humans

TT virus (TTV) was first described in 1997 by representational difference analysis of sera from non-A to non-G posttransfusion hepatitis patients and hence intensively investigated as a possible addition to the list of hepatitis-inducing viruses. The TTV genome is a covalently closed single-stranded DNA of approximately 3.8 kb with a number of characteristics typical of animal circoviruses, especially the chicken anemia virus. TTV is genetically highly heterogeneous, which has led investigators to group isolates into numerous genotypes and subtypes and has limited the sensitivity of many PCR assays used for virus detection. The most remarkable feature of TTV is the extraordinarily high prevalence of chronic viremia in apparently healthy people, up to nearly 100% in some countries. The original hypothesis that it might be an important cause of cryptogenic hepatitis has not been borne out, although the possibility that it may produce liver damage under specific circumstances has not been excluded. The virus has not yet been etiologically linked to any other human disease. Thus, TTV should be considered an orphan virus.

Chicken anemia virus strains with a mutated enhancer/promoter region share reduced virus spread and cytopathogenicity

Plasmid pCAV/E contains an infectious cloned double-stranded CAV (chicken anemia virus) DNA genome (Noteborn et al., J. Virol. 65 (1991) 3131-3139). We have constructed mutated CAV genomes by introducing mutations into the CAV promoter/enhancer region of pCAV/E. Various mutated CAV strains were functional and had a smaller cytopathogenic effect in chicken T cells than wild-type CAV. In particular, mutations within the '12-bp insert' of the promoter/enhancer region had this effect. PCR and sequence analysis showed that the CAV mutants were stable under cell-culture conditions. Southern-blot analysis showed that all replication DNA intermediates were normally formed by the CAV mutants. All viable mutant CAV strains were able to produce a neutralizing conformational epitope, which implies that they can trigger the required protective immune response. These features make these mutant CAV strains potential candidates for the development of an attenuated CAV vaccine.

Detection of chicken anaemia virus DNA from formalin-fixed tissues by polymerase chain reaction

Chicken anaemia virus (CAV) DNA was detectable from various samples such as cell-free virus, infected MDCC-MSB1 cells, unfixed liver homogenates, formalin-fixed liver homogenate or formalin-fixed paraffin-embedded (FFPE) tissues from experimental or field infected chicks using PCR assay. The detection limit of the first PCR assay was 1 infected cell or 10(-1.5) TCID50 of cell-free virus (strain A2). The nested PCR assay increased the sensitivity 10- or 100-fold. CAV DNA was detectable in the other 14 Japanese strains isolated from 1976 to 1994 by the PCR assay. All the amplified products were digested with BglII, HindIII, PstI and SacI. These results suggest that the region amplified was highly conserved among the strains. The nested PCR assay was very sensitive. However, CAV DNA was detectable in most field samples using the first PCR assay. Therefore, the nested PCR assay may not always be necessary. In contrast, the nested PCR assay was necessary to detect CAV DNA in FFPE tissues or formalin-fixed material. Use of the PCR assay in CAV DNA detection from FFPE tissues may be most valuable in diagnosis of diseases caused by or associated with CAV, because it allows detection of both microscopic lesions and CAV DNA.

In situ hybridization for detection of chicken anaemia virus in peripheral blood smears

Blood smears, obtained from chickens known to be infected with or free from chicken anaemia virus (CAV), were tested to detect CAV DNA by in situ hybridization (ISH). A double-stranded, 1485 base-pair (bp) DNA probe was prepared employing polymerase chain reaction (PCR). The probe was labelled with digoxigenin or biotin by nick translation. In situ hybridization employing simple specimen preparation, using both digoxigenin- and biotin-labelled probes, provided a rapid and inexpensive method for diagnosis of CAV infection. Infection with CAV was detected by ISH prior to seroconversion by indirect immunofluorescence assay.

Serological survey on the prevalence of chicken anaemia virus infection in Hungarian chicken flocks

A serological survey on the prevalence of chicken anaemia virus (CAV) infection was performed by using the indirect immunofluorescence (IF) and the virus neutralization (VN) tests in commercial Hungarian chicken populations. By the indirect IF test, a total of 846 serum samples from 13 meat-type parent flocks of two breeds were investigated between 10 and 62 weeks of age. All flocks were found to be positive for anti-CAV antibodies, and the rates of antibody-positive birds among flocks ranged from 40 to 93.3% and with an average of 73.3%. From nine 1-day- to 9-week-old progeny broiler flocks, 96 serum samples were tested. In the 3 flocks, sampled at the hatchery, 75 to 100% (average 86.4%) of the 22 tested birds were antibody positive. From the 6 flocks, tested between 4 to 9 weeks of age, 3 were antibody negative at 4 and 5 weeks of age, whereas in the 3 remaining 6- to 9-week-old flocks 10 to 20% (average 13.5%) of the birds were antibody positive. In egg-laying parent flocks of 14 and 35 weeks old, 54.4 and 71.7% of the tested 79 and 46 birds had antibodies to CAV, respectively. By the VN test, a total of 670 serum samples from 9 meat-type parent flocks aged between 11 and 37 weeks were investigated. The rate of antibody positivity in flocks was always over 80% and averaged 90.9%. From 7 progeny broiler flocks, 261 serum samples were tested between one day and 7 weeks of age, and the rates of seropositivity in flocks were between 93.3 to 100% and averaged 96.9%. In an egg-laying parent flock, 89.2% of the tested 102 birds had neutralizing antibodies to CAV at 35 weeks old. It was concluded that CAV is widespread in Hungarian commercial chicken populations. Though, according to simultaneous examination of 195 flock sera, the VN test revealed 11.3% more antibody-positive birds, the indirect IF test was found suitable for serological surveys at flock(s) level, provided that sufficient numbers of individual chicks were tested.

Identification of the promoter region of chicken anemia virus (CAV) containing a novel enhancer-like element

The single promoter region in the cloned genome [Noteborn et al., J. Virol. 65 (1991) 3131-3139] of chicken anemia virus (CAV) in chicken T-cells was analysed via CAT assays. A unique region containing four or five near-perfect direct repeats (DR) of 21 bp with one 12-bp insert was proven to be the main transcription-activation element, with enhancer-like characteristics. PCR studies revealed that CAV isolates from across the world all contained this promoter sequence. Electrophoretic mobility-shift assays (EMSA) showed that individual DR units, as well as the 12-bp insert, can bind to nuclear factors of chicken T-cells. Competition assays revealed that the DR units bound to factors other than the 12-bp insert. A synthetic oligodeoxyribonucleotide containing an SP1-box (5'-GGGCGG) could compete with factors binding to the 12-bp insert. Purified human SP1 was shown to have very strong affinity for the 12-bp insert.

Some biological and physico-chemical properties of porcine circovirus

Some important biological and physico-chemical characteristics of porcine circovirus are reported. These include a study on the host distribution in nature, levels of colostrum-derived antibodies in piglets from sero-positive sows and the susceptibility of a range of cell cultures to infection with this virus. The results of haemagglutination studies, resistance to pH 3, chloroform and heat are also reported as are comparative buoyant densities and sedimentation coefficients of porcine circovirus and chicken anaemia virus.

Cloning and sequencing of the chicken anaemia virus (CAV) ORF-3 gene, and the development of an ELISA for the detection of serum antibody to CAV

Chicken anaemia virus (CAV) is a small, unclassified virus involved in anaemia and suspected of causing immunosuppression in young chickens. We have developed an ELISA for the detection of serum antibody to CAV based on cloned antigen. The gene for ORF-3 (the putative capsid protein) was cloned, sequenced and expressed in a bacterial expression system, pGEX. An ORF-3 fusion protein was used to produce an indirect ELISA.

Chicken anaemia virus influences the pathogenesis of Marek's disease in experimental infections, depending on the dose of Marek's disease virus

Eight groups of 1-day-old chickens were inoculated with 0, 250, 5000, or 100,000 white blood cells of chickens infected with Marek's disease virus strain K (MDV-WBC). Four of these groups were additionally infected with 10(5) TCID50 chicken anaemia virus (CAV). At day 14 after inoculation, chickens infected with CAV had reduced haematocrit levels, reduced body weights, and depletion of the thymic cortex and bone marrow. Semi-quantitative immunohistochemical examination of nerves and visceral organs was performed at day 28 by immunoperoxidase staining in which a monoclonal antibody specific for leucocytes was used. CAV significantly enhanced the number of lymphoproliferative lesions induced by 5000 MDV-WBC. In contrast, CAV significantly reduced the number of lymphoproliferative lesions induced by 100,000 MDV-WBC. Comparable results were found at day 61 after macroscopic examination of nerves and visceral organs. These findings show that the pathogenesis of MD in experimental infections appears to be enhanced or inhibited by CAV, depending on the dose of MDV.

Chicken anemia virus causes apoptosis of thymocytes after in vivo infection and of cell lines after in vitro infection

After infection of 1-day-old chickens, chicken anemia virus (CAV) causes a complete depletion of the thymic cortex by day 14. Since cell death can be caused either by necrosis or by apoptosis, we investigated which type of cell death occurs after in vivo and in vitro infections with CAV. Using electron microscopy and biochemical methods, we demonstrated that CAV induces apoptosis of cortical thymocytes after in vivo infection and of lymphoblastoid cell lines after in vitro infection. At day 13 after in vivo infection, virus-like particles were detected in apoptotic bodies that were absorbed by epithelial cells. These results show that apoptosis, a phenomenon that has been observed for a few other viruses, is also an important phenomenon during the pathogenesis of CAV.

Immune dysfunction following infection with chicken anemia agent and infectious bursal disease virus. I. Kinetic alterations of avian lymphocyte subpopulations

The potential effect of chicken anemia agent (CAA) alone or in combination with infectious bursal disease virus (IBDV) on the immune system of young chickens was determined by measuring alterations in hematocrit values, lymphoid organ-to-body weight ratios and lymphoid cell concentrations at 4, 7, 10, 14, 17, 21, 28 and 42 days post-inoculation (PI). Lymphocyte subpopulations were identified and counted by flow cytometry using cell suspensions stained with monoclonal antibodies (Mabs) for panlymphocytes (K55), cytotoxic T-cells (CTLA3), T-helper cells (CT3), Ia-expressing cells (P2M11) and macrophages (P7). Chicken anemia agent induced a substantial but transient decrease in hematocrit value, thymus-to-body weight ratio and bursa-to-body weight ratio between 7 and 21 days PI corresponding to a generalized lymphocytopenia in the thymus, bursa and spleen. However, cytotoxic T-cell, T-helper cell and Ia-expressing cell concentrations increased in the bone marrow of birds inoculated with CAA alone or in combination with IBDV during the same time period. T-helper-to-cytotoxic T-cell ratios increased in the thymus and spleen during severe lymphocytopenia, indicating a selective decrease in cytotoxic T-cells. T-helper-to-cytotoxic T-cells ratios increased in the bone marrow, indicating a selective increase in T-helper cell concentrations. The increase in Ia-expressing cells in the bone marrow may be a reflection of increased number of activated T-cells which express Ia antigen. Infectious bursal disease virus alone induced a persistent depression of Ia-expressing cells in the bursa and the spleen and no measurable change in the bone marrow lymphocyte subpopulations. Chickens inoculated simultaneously with CAA and IBDV experienced clinical signs observed in chickens inoculated with each virus separately with a prolonged acute phase prior to recovery or mortality.

Transcription of the chicken anemia virus (CAV) genome and synthesis of its 52-kDa protein

This paper describes the expression of the chicken anemia virus (CAV) genome, a recently characterized single-stranded circular-DNA virus of a new type [Noteborn et al., J. Virol. 65 (1991) 3131-3139]. The major transcript from the CAV genome is an unspliced mRNA of about 2100 nucleotides (nt). Its transcription start point and poly(A)-addition site are located at nt 354 and 2317 of the CAV sequence, respectively. In vitro translation experiments provide evidence that the major CAV open reading frame encodes a 52-kDa protein by using the fifth AUG as a start codon of the unspliced CAV mRNA.

Characterization of viral DNAs from cells infected with chicken anaemia agent: sequence analysis of the cloned replicative form and transfection capabilities of cloned genome fragments

The viral DNAs induced by the unclassified animal virus, chicken anaemia agent (CAA), during replication in MDCC-MSB 1 cells have been investigated. Analyses after S1 nuclease, restriction endonuclease and denaturation treatments indicated that infected cell extracts contained genome-size, single-stranded DNA (M(r) 2.3 kb), closed and open circular, double-stranded replicative form (RF) DNAs (M(r) 2.3 kbp) and a population of smaller double-stranded DNAs (M(r) 0.8 kbp). Recombinant plasmids containing 2.3 kbp CAA RF fragments cloned at the PstI, BamHI and EcoRI sites failed to transfect MDCC-MSB 1 cells. However, one plasmid, which contained two 2.3 kbp CAA RF fragments ligated in tandem at the PstI site, and cloned 2.3 kbp PstI, BamHI and EcoRI fragments, excised from their respective plasmids by restriction endonuclease digestion, were capable of transfection. The nucleotide sequence of the circular genome (2298 bp) of the Cux-1 isolate of CAA has indicated the presence of three overlapping open reading frames (ORFs) of 52 kDa, 24 kDa and 13 kDa on one strand. The existence of these ORFs was corroborated by analyses of partial sequences from three other isolates. The non-coding region of the CAA genome contained sequences with putative regulatory function. These results are discussed in relation to the "rolling circle" model of DNA replication.

Detection and differentiation of chicken anemia virus isolates by using the polymerase chain reaction

Complementary oligonucleotide primers which flank a 675-bp DNA fragment encompassing part of the putative gene for the capsid protein of chicken anemia virus (CAV) were used for the enzymatic amplification of CAV DNA by the polymerase chain reaction (PCR). Application of a dot blot hybridization assay by using a 32P-labeled cloned CAV DNA probe allowed PCR product amplified from as little as 0.1 fg of the target DNA sequence to be detected. When it was used for PCR amplification, DNA extracted from thymus tissue by a guanidine isothiocyanate-based method proved to be more efficient than that extracted by methods involving phenol or boiling. DNAs specified by 14 CAV isolates originating in the United Kingdom, Ireland, Germany, Sweden, the United States, Japan, and Australia were amplified. Restriction endonuclease analysis of the PCR-amplified DNAs with the enzymes HaeIII, HinfI, and HpaII indicated that the 14 CAV isolates can be assigned to seven groups, with isolates from different countries usually exhibiting the greatest number of restriction site differences.

Recent advances in avian virology

Selected, recent research on the following avian diseases, and their causative viruses, has been reviewed: chicken anaemia, infectious bursal disease, turkey rhinotracheitis, avian nephritis, fowlpox, influenza, infectious bronchitis and turkey enteritis.

Detection of chicken anaemia agent DNA sequences by the polymerase chain reaction

A polymerase chain reaction (PCR) assay was developed for detection of chicken anaemia agent (CAA) DNA. The assay used a single set of 20-base primers complementary to sequences located in the coding regions of the CAA replicative form (RF) DNA genome at positions 485 to 504 and 1048 to 1067. The observed amplification product had the expected size of 583 bp and was confirmed to derive from CAA RF DNA by a unique Hind III restriction enzyme cleavage pattern. The amplified fragment was shown to be specific for CAA RF DNA after chemiluminescence dot blot hybridisation with a digoxigenin-labelled 25-base internal probe. The optimised PCR assay was specific for CAA and highly sensitive, being able to detect a single CAA-infected MDCC-MSB1 cell and at least 100 fg of CAA RF DNA. Preliminary results also showed that the PCR assay can detect CAA DNA in clinical specimens from chicks experimentally infected with CAA.

Chicken anemia agent

Chicken anemia agent (CAA) is a small, spherical, non-enveloped virus containing a circular single-stranded DNA genome. CAA remains unclassified and probably should be classified in a new virus family. The chicken is the only recognized natural host for CAA. CAA was initially isolated in Japan and the associated disease chicken infectious anemia described in 1979. The virus has a world-wide distribution and is common in intensive poultry raising areas. Chicken infectious anemia is not a new disease but a newly recognized disease. CAA is now thought to play a key role in several multiple etiology disease syndromes; hemorrhagic syndrome; aplastic anemia, gangrenous dermatitis, hemorrhagic anemia syndrome, hemorrhagic aplastic anemia syndrome, anemia dermatitis and blue wing disease. The pathogenesis of chicken infectious anemia is described. Vertical transmission appears to be more important than horizontal spread. A yellow fatty bone marrow is the most characteristic lesion and thymic atrophy is the most consistent finding in CAA infection. Thymic and bone marrow intranuclear inclusion bodies occur with infection but are of limited value diagnostically and are very transient and rarely seen. Five different disease-producing scenarios that lead to clinical CAA infection in young chickens are presented.

Characterization of cloned chicken anemia virus DNA that contains all elements for the infectious replication cycle

Circular double-stranded replication intermediates were identified in low-molecular-weight DNA of cells of the avian leukemia virus-induced lymphoblastoid cell line 1104-X-5 infected with chicken anemia virus (CAV). To characterize the genome of CAV, we cloned linearized CAV DNA into the vector pIC20H. Transfection of the circularized cloned insert into chicken cell lines caused a cytopathogenic effect, which was arrested when a chicken serum with neutralizing antibodies directed against CAV was added. Chickens inoculated at 1 day of age with CAV collected from cell lines transfected with cloned CAV DNA developed clinical signs of CAV. The 2,319-bp cloned CAV DNA contained all the genetic information needed for the complete replication cycle of CAV. The CAV DNA sequence has three partially overlapping major reading frames coding for putative peptides of 51.6, 24.0, and 13.6 kDa. The CAV genome probably contains only one promoter region and only one poly(A) addition signal. Southern blot analysis using oligomers derived from the CAV DNA sequence showed that infected cells contained double- and single-stranded CAV DNAs, whereas purified virus contained only the minus strand. It is the first time that the genome of one of the three known single-stranded circular DNA viruses has been completely analyzed.