Circovirus infection in European racing pigeons

Pigeon Circovirus over Three Decades of Research: Bibliometrics, Scoping Review, and Perspectives

The pigeon circovirus (PiCV), first described in the literature in the early 1990s, is considered one of the most important infectious agents affecting pigeon health. Thirty years after its discovery, the current review has employed bibliometric strategies to map the entire accessible PiCV-related research corpus with the aim of understanding its present research landscape, particularly in consideration of its historical context. Subsequently, developments, current knowledge, and important updates were provided. Additionally, this review also provides a textual analysis examining the relationship between PiCV and the young pigeon disease syndrome (YPDS), as described and propagated in the literature. Our examination revealed that usages of the term ‘YPDS’ in the literature are characterizations that are diverse in range, and neither standard nor equivalent. Guided by our understanding of the PiCV research corpus, a conceptualization of PiCV diseases was also presented in this review. Proposed definitions and diagnostic criteria for PiCV subclinical infection (PiCV-SI) and PiCV systemic disease (PiCV-SD) were also provided. Lastly, knowledge gaps and open research questions relevant to future PiCV-related studies were identified and discussed.

Genome sequence characterization of canine parvoviruses prevalent in the Sichuan province of China

Canine parvovirus 2 (CPV-2) infection is responsible for large numbers of animal deaths worldwide and is one of the most dangerous infectious diseases in young puppies. Twenty-four rectal swabs were collected from dogs with clinical signs of vomiting and haemorrhagic diarrhoea and were initially verified to be infected with CPV-2 using colloidal gold test strips. From the 24 CPV-positive samples, complete genome of 5050-5054 nucleotides was sequenced with a next-generation sequencing platform. Characteristics of the Open Reading Frames from different CPV-2 strains detected in this study were analyzed. Several VP2 point mutations were discovered, and demonstrated the co-circulation of new CPV-2a, new CPV-2b and CPV-2c in Sichuan province of China. The analysis results of the Chinese CPV-2 retrieved from the NCBI nucleotide, showed that new CPV-2a has become the predominant variant in some provinces of China. Phylogenetic analysis of global VP2 and NS1 nucleotide sequences revealed certain correlations among geographical regions, types and circulating time, which lays the foundation for further research concerning the epidemiology, genetic variation, vaccination and molecular evolutionary relationships of the CPV-2 identified at different times and from different regions.

Detection and Characterization of Circovirus in Canary Flocks

Circovirus infections have been documented in adult and nestling canaries (Fringillidae) but the distribution of the virus in the world is not yet known. In captive canary flocks, Circovirus infections have been reported based on the clinical observations. In this study, the presence of both canary circovirus (CaCV) and chicken anemia virus (CAV) in canary flocks was investigated. Virus strains were detected by PCR and direct sequencing of amplified products. Nucleotide sequences were aligned and compared with existing data in GenBank. PCR identified CaCV-positive birds, giving an overall positivity rate of 25%, but all samples were negative for CAV. According to the sequencing data, three distinct strains were identified. Our results indicated a relationship between genetic variation in the replicase gene ( rep) and the geographic regions as well as the feasibility of using the rep gene for virus detection and molecular epidemiology investigations. We are reporting detection and characterization of canary circovirus based on the rep gene. Sequencing results and sequence identity analysis revealed that the rep gene could be used for detecting and discriminating the members of family Circoviridae. This manuscript is the first report of canary circovirus in Iran and of three new strains in the world.

The epidemiology, molecular characterization and clinical pathology of circovirus infections in pigeons - current knowledge

The first cases of circovirus infections in pigeons were documented less than 25 years ago. Since then, circovirus infections have been reported on nearly all continents. The specificity of pigeon breeding defies biosecurity principles, which could be the reason for the high prevalence of PiCV infections. PiCV infections in pigeons lead to atrophy of immune system organs and lymphocyte apoptosis. Infected birds could be more susceptible to infections of the respiratory and digestive tract. PiCV has been associated with the young pigeon disease syndrome (YPDS). PiCVs are characterized by high levels of genetic diversity due to frequent point mutations, recombination processes in the PiCV genome and positive selection. Genetic recombinations and positive selection play the key role in the evolution of PiCV. A protocol for culturing PiCV under laboratory conditions has not yet been developed, and traditional vaccines against the infection are not available. Recombinant capsid proteins for detecting anti-PiCV antibodies have been obtained, and these antigens can be used in the production of diagnostic tests and subunit vaccines against PiCV infections. However, YPDS has complex etiology, and it remains unknown whether immunization against PiCV alone will contribute to effective control of YPDS.

Genome sequence characterization of pigeon circoviruses in China

Pigeon circovirus (PiCV) was detected by PCR in pigeons from China. Altogether, 48 out of 244 pigeons tested positive for PiCV (positive rate, 19.67%), suggesting that the virus was prevalent in China. From the 48 PiCV-positive samples, about 2040bp complete genome fragments were obtained by full length genome amplification and sequenced with a next-generation sequencing platform. Characteristics of the ORFs from different PiCV strains tested in this study were analyzed. Several insertion, deletion or substitutions were discovered during the analysis of the nucleotide sequence compared with sequences reported previously. In phylogenetic tree analysis, 48 sequences isolated in this study could be further divided into five clades (A, B, C, D, and F), clade E includes reference sequences only. Two major groups were found in the six clades, distinguished by ATA and ATG initiation codons. Most of the viruses isolated in the study were in the ATG group, with fewer in the ATA branch.

Circovirus-like infection in a southern black-backed gull (Larus dominicanus)

A juvenile black-backed gull (Larus dominicanus) from the Manawatu region of New Zealand was found to have chronic airsacculitis due to Aspergillus spp. Histologically, there was moderately severe inflammation in the bursa of Fabricius associated with large, basophilic, intracytoplasmic inclusions, which ultrastructurally had an appearance typical of circovirus inclusions. This finding suggests that circoviruses may be more widespread in avian species than previously recognized and may be responsible for diseases associated with immunosuppression in free-living birds.

Recurrent positive selection and heterogeneous codon usage bias events leading to coexistence of divergent pigeon circoviruses

The capsid genes from 14 pigeon circovirus (PiCV) sequences, collected from Taiwan between 2009 and 2010, were sequenced and compared with 14 PiCV capsid gene sequences from GenBank. Based on pairwise comparison, PiCV strains from Taiwan shared 73.9-100% nucleotide identity and 72-100% amino acid identity with those of the 14 reported PiCV sequences. Phylogenetic analyses revealed that Taiwanese PiCV isolates can be grouped into two clades: clade 1 comprising isolates from Belgium, Australia, USA, Italy and China, and clade 2 showing close relation to isolates from Germany and France. Recurrent positive selection was detected in clade 1 PiCV lineages, which may contribute to the diversification of predominant PiCV sequences in Taiwan. Further observations suggest that synonymous codon usage variations between PiCV clade 1 and clade 2 may reflect the adaptive divergence on translation efficiency of capsid genes in infectious hosts. Variation in selective pressures acting on the evolutionary divergence and codon usage bias of both clades explains the regional coexistence of virus sequences congeners prevented from competitive exclusion within an island such as Taiwan. Our genotyping results also provide insight into the aetiological agents of PiCV outbreak in Taiwan and we present a comparative analysis of the central coding region of PiCV genome. From the sequence comparison results of 28 PiCVs which differs in regard to the geographical origin and columbid species, we identified conserved regions within the capsid gene that are likely to be suitable for primer selection and vaccine development.

Occurrence and genetic diversity of pigeon circovirus strains in Poland

Pigeon circovirus (PiCV) is an immunosuppressive agent widespread throughout the world, which causes a disease in pigeons called Young Pigeon Disease Syndrome. The aim of the study was to evaluate the prevalence of PiCV in Poland and investigate the genetic diversity relative to other known PiCV isolates. Samples from 152 pigeon flocks (88 flocks of racing pigeons and 64 flocks of fancy pigeons) from various regions of Poland were tested by polymerase chain reaction and an approximately 326-base fragment of the capsid protein gene (Cap gene) of the virus was amplified. The average viral prevalence was found to be 70.3% (76.13% in racing pigeons and 62.5% in fancy pigeons). Among the obtained positive samples, 21 were selected for sequencing and a phylogenetic analysis was performed. It was found that the majority of Polish PiCV isolates, to varying degrees, are related to isolates occurring in Europe. It was also observed that the Cap gene is variable and mutations often occur in it, which impacts the amino acid sequences in the capsid protein (nucleotide similarity averaged 86.57%, amino acid similarity averaged 89.02%).

First detection of circovirus-like sequences in amphibians and novel putative circoviruses in fishes

The negative samples of a collection, established originally for seeking new adeno- and herpesviruses in lower vertebrates, were screened for the pres-ence of circoviruses by a consensus nested PCR targeting the gene coding for the replication-associated protein. Six fish samples representing five species, namely asp (Aspius aspius), roach (Rutilus rutilus), common bream (Abramis brama), round goby (Neogobius melanostomus) and monkey goby (Neogobius fluviatilis), as well as three frog samples were found positive for circoviral DNA. Sequence analysis of the amplicons indicated the presence of three novel putative circo-like viruses and a circovirus in Hungarian fishes and one novel circovirus in a common toad (Bufo bufo), and another one in a dead and an alive specimen of green tree frog (Litoria caerulea), respectively. In phylogeny reconstruction, the putative bream circovirus clustered together with circoviruses discovered in other cyprinid fishes recently. Three other piscine circoviral sequences appeared closest to sequences derived from different environmental samples. Surprisingly, the nucleotide sequence derived from two fish samples (a bream and a monkey goby) proved to be from porcine circovirus 2 (PCV2), almost identical to a sequence detected in Sweden previously. This is the first report on the detection of PCV2 in fish and circoviral DNA in amphibian hosts.

Epidemiological investigation of selected pigeon viral infections in Poland

Due to a lack of data in regard to the spread of viral infections in Polish pigeon populations, studies were undertaken to assess the frequency of adeno-, circo- and herpesvirus infections in flocks of pigeons across the entire country. In total, 107 flocks were examined, of which 61 per cent consisted of racing and 39 per cent of fancy pigeons. The flocks were divided into groups according to breed (racing and fancy pigeons) as well as physical condition (healthy and sick). In the studied pigeon flocks, the pigeon circovirus (PiCV) genetic material was the most frequently detected (44.5-100 per cent depending on the group), pigeon herpesvirus genetic material was second in frequency (0-30 per cent depending on the group), while genetic material of pigeon adenovirus was found only in two flocks of young birds with clinical symptoms of Young Pigeon Disease Syndrome (YPDS). The presence of fowl adenovirus (FAdV) genetic material was not detected in any of the studied flocks. Results obtained demonstrate a wide spread of circovirus in pigeon flocks in Poland, and substantiate earlier theories proposed by other authors, that immunosuppression evoked by PiCV infection is one of the main causative agents of YPDS.

Pigeon circovirus infection: pathological observations and suggested pathogenesis

Pigeon circovirus infection (PiCV) was diagnosed by light and transmission electron microscopy in 15 birds from five lofts in western France. Histopathological findings were suggestive of primary bursotropism of pigeon circovirus, followed by secondary systemic spread from the bursa of Fabricius, particularly to non-bursal lymphoid organs. The last stage of the disease was associated with various secondary (particularly bacterial) infections. In situ detection of apoptosis in the bursa of Fabricius indicated that PiCV was concomitant with an increase in bursal lymphocytic apoptotic events related to viral infection and leading to severe acquired immunosuppression.

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.

Prevalence of pigeon circovirus infections in feral pigeons in Ljubljana, Slovenia

Pigeon circovirus (PiCV) was detected by real-time PCR in cloacal swabs, pharyngeal swabs, and serum samples taken from 74 feral pigeons (Columba livia var. domestica) that were caught at various locations in the city of Ljubljana, Slovenia. PiCV infections were detected in the majority of the tested birds. The highest (74.3%) detection rate was observed in the cloacal swabs and the lowest (31.1%) in serum samples. PiCV DNA was more readily detected in the cloacal swabs, pharyngeal swabs, and serum samples of birds younger than 1 yr. Molecular analysis of partial open reading frame V1 sequences showed that PiCV strains detected in feral pigeons share high nucleotide and amino acid sequence identities with PiCV strains detected in ornamental, racing, meat, and feral pigeons.

Molecular characterization and epidemiological investigation of Pigeon circovirus isolated in eastern China

To investigate the prevalence and genetic characterization of Pigeon circovirus (PiCV) circulating in Chinese flocks, the genomic DNA of 144 samples collected from pigeons in 6 different geographic regions of eastern China between 2009 and 2010 were amplified using previously published PiCV primers. The PiCV sequence was detected in 83 of 104 unhealthy pigeons (79.8%) and 25 of 40 healthy pigeons (62.5%). The overall positive rate was 75% for all samples. An inverse primer polymerase chain reaction (IP-PCR) assay was performed to amplify the full-length sequence from a random sample of each region, and 6 specific DNA fragments were gel-purified and sequenced. The 6 full-length sequences were designated as SHWH-AB4 (2,031 bp), NJPK-21 (2,035 bp), HBLF-E2 (2,031 bp), JSJN (2,039 bp), SDDZ (2,037 bp), and AHBZ (2,035 bp) after BLAST analyses. The phylogenic tree and amino acid comparison indicated that all the strains examined were derived from a common strain, but had undergone genetic mutations through time. Pairwise comparisons revealed 93.4%–100% amino acid identity for the putative replication-associated proteins and 67.5%–100% for the putative capsid proteins.

Quantification of pigeon circovirus in serum, blood, semen and different tissues of naturally infected pigeons using a real-time polymerase chain reaction

The development of a real-time polymerase chain reaction (PCR) based on SYBR Green chemistry is described for the quantification of pigeon circovirus (PiCV) DNA in various samples. Plasmid containing a fragment of the PiCV genome was used to create a standard curve and to estimate the viral DNA copies in analysed samples. Both primers were designed in highly conserved regions to avoid false negatives, and amplified a 139-base-pair amplicon. When the amplifications were performed in the presence of cellular DNA extracted from PCR-negative liver, bursa and spleen samples, the detection limits were respectively 20, 20 and 60 copies of genome per milligram of tissue. These limits were 10, 160 and 25 copies/microl for control blood, sera and semen, respectively. For cloacal swab, the detection limit was 200 copies. The assay showed a linear detection over a six-log range (R(2)>0.99) and displayed reliable inter-assay and intra-assay reproducibility. Application of the test to sera samples indicated the presence of the virus in Belgium in 1991, 6 years before PiCV infections were histologically diagnosed. Testing of samples from pigeons with "young pigeon sickness" showed that the viral loads were high in the bursa of Fabricius (up to 2.07 x 10(9) copies/mg), the liver (up to 2.88 x 10(8) copies/mg) and spleen (up to 5.57 x 10(8) copies/mg). For liver, the viral load was significantly higher in sick pigeons than in apparently healthy pigeons. Detection of high quantities of PiCV DNA (up to 1.6 x 10(9) copies/microl) in the sera or blood of some young healthy pigeons indicated that the viral load in this sample type would not be useful as predictive indicator of disease. This work also showed that PiCV DNA can be detected in relatively large amounts in semen (up to 1.0 x 10(7) copies/ejaculate) and cloacal swabs (up to 3.6 x 10(10) copies/swab), confirming that PiCV may be transmitted by vertical and horizontal routes.

Sequence comparison of pigeon circoviruses

The genome sequences of eight pigeon circoviruses (PiCV) were determined and compared with four previously published sequences. The viruses compared were from the USA, five European countries, China and Australia and included PiCVs from racing, feral, ornamental and meat pigeons and a Senegal dove (Streptopelia senegalensis). The 12 PiCV genomes, ranging from 2032 to 2040 nucleotides in length, displayed similar organizations. Pairwise comparisons showed that the genome nucleotide sequence identities ranged from 85.1% to 97.8% and that the amino acid identities of the putative replication associated (Rep) and putative capsid (Cap) proteins displayed ranges of 91.5-99.1% and 73.0-99.3%, respectively. Comparative analyses identified conserved nucleotide sequences within the Rep gene and 3' intergenic regions, which would be suitable for diagnostic PCR primers, and variable amino acid sequences within the capsid proteins, which should be considered when selecting virus isolates for vaccine development.

Observations on detection, excretion and transmission of pigeon circovirus in adult, young and embryonic pigeons

Infections with pigeon circovirus (PiCV) occur in young racing pigeons and pigeons raised for meat production and have been reported worldwide, but relatively little is known about the disease induced by PiCV infection. The aim of this study was to investigate how PiCV is transmitted. Using a sensitive polymerase chain reaction (PCR) test, the presence of PiCV was investigated in a wide range of samples from adult pigeons, embryos, breeders and young birds, which were derived from a racing loft that had a clinical history of "young pigeon sickness" and in which PiCV had been previously been diagnosed. Using PCR, PiCV DNA was detected in tissues of 13/20 apparently healthy older birds, aged from 1 to 9 years. Viral DNA was most commonly detected in the respiratory organs, including the trachea, pharynx and lung, followed by tissues such as the spleen, kidney and liver. It was also detected in the ovary and/or testes of some birds. This finding, and the detection of viral DNA in tissues from 8/22 embryos, suggested that PiCV may be vertically transmitted. Testing of pharyngeal and cloacal swabs, and blood samples, collected immediately before the death of the adult pigeons, failed to detect all birds found to be infected at necropsy, suggesting that testing of potential breeding birds would not enable exclusion of infected birds from breeding programmes. Additional PCR testing of cloacal swab samples obtained sequentially from 19 young pigeons showed that while four were excreting virus when 15 days old, only one bird was excreting at the time of weaning (28 days old). The detection of viral DNA in cloacal swab samples from 15.8% of the birds when 37 days old and 100% of birds when 51 days old suggested that most young pigeons probably became infected in the rearing loft.

Avian circoviruses of the genus Circovirus: A potential trigger in Pigeon breeder’s lung (PBL)/Bird fancier’s lung (BFL)

Pigeon breeder's lung (PBL) or Bird fancier's lung (BFL) is one of the most common extrinsic allergic alveolitis or hypersensitivity pneumonitis. It is caused after prolonged inhalation of avian antigens and provokes a hypersensitivity reaction in the lungs of sensitised people. Although the pathogenic mechanism is unclear, the epidemiology of BFL shows that it occurs worldwide, and has been described in adults keeping birds and also in their children. Laboratory findings associated with the disease classified as a type III immunologic reaction that produces blood precipitin antibodies against birds' serum, feathers, intestinal mucin and/or faeces. In particular, the fine dust from pigeon feathers has strong antigenic properties. There is an interaction between host and antigen that seems to be influenced by both genetic and environmental factors. Avian circoviruses (ACV) of the genus Circovirus, has been detected in free-ranging and captive birds worldwide, such as pigeons, canaries, psittacines, Senegal doves, finches, gulls, Australian ravens and geese. T lymphocytes are the main target cells of the ACV and in the above avian species circovirus-like particles were detected in blood, macrophages, feathers, crop secretions, intestinal contents and/or faeces. Most of the ACV was demonstrated that are pantropic and viral antigen in pigeon tissues was most commonly detected in respiratory organs, including the trachea, pharynx and lung. The transmission of the circovirus between the birds usually occurs through inhalation of feathers dust. There is evidence that animal circoviruses may originate when vertebrates become "infected" with DNA from a plant nanovirus. So, it seems that further investigation for the avian circoviruses is needed to determine if they are host specific or not. This study attempts to demonstrate ACV or ACV-like particles as potential triggers in the BFL aetiology, and the possible involvement in BFL's pathogenic mechanism.

Viral infections in pigeons

This review provides a current update on the major viral diseases of the domestic pigeon (Columba livia domestica), based on scientific reports and clinical experience. Paramyxovirus 1, adenovirus, rotavirus, herpesvirus 1, poxvirus and circovirus infections are described according to common clinical signs and target tissues. Since pigeons are sometimes treated as if they were poultry, the review also summarises the common viral infections of poultry for which pigeons are considered resistant. It is hoped that the review will provide a useful reference for veterinarians and others and offer advice on the diagnosis, treatment and prevention of the major infectious diseases of pigeons.

Development of a Polymerase Chain Reaction-BasedIn VivoMethod in the Diagnosis of Subclinical Pigeon Circovirus Infection

This paper describes a polymerase chain reaction (PCR)-based method performed on blood samples and intestinal content to detect subclinical pigeon circovirus (PiCV) infection in live pigeons. In addition, two sets of primers (primer set 1 and 2), designed in two different regions of the viral genome, were used to provide evidence of possible differences in PCR responses. Blood and intestinal content samples were randomly collected from a total of 50 apparently healthy meat pigeons, aged 1 to 5 wk, which came from central Italy. Samples of primary lymphoid organs were also collected. Results showed a high level of PiCV infection, although clinical signs were not present. The results obtained with the two sets of primers showed that primer set 2 was able to detect a higher number of PCR-positive pigeons (45 of 50 pigeons) than primer set 1 (11 of 50 pigeons). In both cases an increase in positive results with pigeon age indicates that the major direction of transmission is likely horizontal. In these circumstances feces can play an important epidemiologic role, as supported by the consistent circovirus detection in intestinal content. The high sensitivity of this PCR test, which is able to detect very low amounts of viral DNA (5.5 x 10(-3) fg of plasmid containing the cloned PiCV genome), makes it suitable for possible application as an epidemiologic tool for identifying virus carriers for subsequent removal from lofts.

Diagnosis of goose circovirus infection in Hungarian geese samples using polymerase chain reaction and dot blot hybridization tests

A polymerase chain reaction (PCR) and dot blot hybridization (DBH) test have been developed for the diagnosis of infection by a novel circovirus of geese (GoCV). These tests were applied to samples of bursae of Fabricius from sick and dead birds from commercial goose farms in Hungary. In this second report of the occurrence of circovirus infection in diseased geese, 103 of 214 (48.1%) and 37 of 150 (24.6%) birds, and 49 of 76 (64.5%) and 18 of 76 (23.7%) flocks were positive by PCR and DBH respectively. The sensitivity of the PCR test was such that 0.10 fg of virus DNA was detectable. The DBH test was less sensitive, only detecting larger amounts (40 pg) of DNA, but was used as a semi-quantitative method for detecting the presence of virus. The incidence of infection was affected by factors such as the age of the birds and rearing methods.

Evaluation of polymerase chain reaction and dot blot hybridisation tests in the diagnosis of pigeon circovirus infections

Polymerase chain reaction (PCR) and dot blot hybridisation (DBH) tests for detecting pigeon circovirus (PiCV) DNA were developed and evaluated using tissue samples obtained from diseased and clinically normal pigeons, which originated in Belgium and Northern Ireland. When PCR product was visually detected, the limit of detection of the PCR test was 31 fg, while that of the DBH was 1.6p g. For evaluation purposes, the results of the PCR and DBH tests, performed with DNAs extracted from samples of bursa of Fabricius (BF), were compared with those of in situ hybridisation (ISH) and histology. In 32 samples tested by all four tests, 27 (84%) were positive by PCR, 24 (75%) were positive by ISH, 20 (63%) were positive by DBH, and 13 (41%) were positive by histology. Additional PCR testing showed that in some disease-affected birds, PiCV DNA could be detected in a range of tissues including thymus, spleen, liver, kidney and brain. The PCR detection of PiCV DNA in BF samples from clinically normal birds indicated that PCR can detect infections in the absence of disease, a finding that mitigates against its use as a disease diagnostic. In addition, nucleotide sequence determinations indicated that PCR test performance was adversely affected by the sequence diversity exhibited by selected PiCVs. The application of the DBH test to dilutions of test samples indicated that the BF from some diseased pigeons contained very large amounts of virus DNA, as much as 10(13)genome copies/g tissue, and suggested that this test may be a convenient method of providing a semi-quantitative estimate of virus load.

Detection of circovirus infection in pigeons by in situ hybridization using cloned DNA probes

Degenerate primers were designed based on known sequence information for the circoviruses psittacine beak and feather disease virus and porcine circovirus and applied by polymerase chain reaction (PCR) to known virus-infected bursa of Fabricius (BF) from a pigeon. A 548-bp DNA fragment was amplified and shown to be specific to a novel circovirus, named pigeon circovirus (PiCV), and was used to produce sensitive and specific probes for detection of circovirus DNA by in situ hybridization (ISH). Using ISH on BF from 107 pigeons submitted for necropsy, infection was detected in 89%, compared with a histologic detection rate of 66%. Using the ISH technique, infected cells were also found in liver, kidney, trachea, lung, brain, crop, intestine, spleen, bone marrow, and heart of some birds. Large quantities of DNA were present in some of these tissues, and in the absence of BF, liver in particular is identified as a potentially useful organ to examine for presence of PiCV. This high prevalence of infection in diseased birds is noteworthy, emphasizing the need for studies to determine the precise role of this virus as a disease-producing agent.

Genome sequence determinations and analyses of novel circoviruses from goose and pigeon

The genomes of novel circoviruses from goose and pigeon, which were isolated using degenerate primer and inverse primer PCR methods, were cloned and sequenced. Comparative nucleotide (nt) sequence analyses showed that the goose circovirus (GCV) and pigeon circovirus (PiCV) possessed genomes which were 1821 and 2037 or 2036 nt, respectively, and which had features in common with the genomes of porcine circoviruses types 1 and 2 (PCV1, PCV2) and psittacine beak and feather disease virus (BFDV), such that they can now be assigned to the genus Circovirus of the family Circoviridae. Common features include the possession of (i) a potential stem-loop/nonanucleotide motif with which the initiation of rolling circle replication of the virus DNA is associated; (ii) two major ORFs, located on the virus (V1 ORF) and complementary (C1 ORF) strands, which encode the replication-associated protein (Rep) and capsid protein, respectively; (iii) high levels of amino acid identity (41.2--58.2%) shared with other circovirus Rep proteins; and (iv) direct/inverted repeat sequences within the putative intergenic region. On the basis of nt and amino acid sequence identities, GCV is substantially less closely related to BFDV than PiCV is to BFDV.