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Porcine circoviruses (PCV) are present in pigs worldwide; they are grouped into two types: PCV1 comprising non-pathogenic viruses and PCV2 responsible for several clinical manifestations. Both types are frequently detected in domestic pigs, the prevalence and role of PCV in wild boars however, is not well studied. During the years 2002-2003 over 2000 organ samples of Hungarian wild boars were collected, grouped and samples from 307 different animals were tested by polymerase chain reaction for the presence of PCV. 35.5% of the wild boars were positive for one or both PCV types and PCV2 was detected in 20.5% of the animals. The PCV2 viruses were divided into 7 groups (WB-H1-7) based on sequencing data and genomes representing these groups were sequenced completely. The wild boar PCV2 groups were distributed evenly in the geographical region, regardless of the time and place of collection. The phylogenetic analysis of the PCV2 sequences of wild boar and domestic pig origin showed the possibility of an epidemiological link between wild boar and domestic pig infections. Interestingly, the complete nucleotide sequence of the viruses and the predicted amino acid sequence of the replication associated protein (ORF1) grouped the viruses similarly, whereas the capsid protein (ORF2) comparisons revealed different relations among the groups, suggesting the possibility of genomic recombination in PCV2.

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Circoviruses are present worldwide in birds and pigs but their occurrence in fish has not yet been reported. Recently, increased mortality was observed in barbel fry (Barbus barbus) in Hungary. This paper reports the detection of previously unknown circular viral DNA genomes in barbels by the use of a circovirus-specific wide-range nested PCR. The analysis of two complete genomes (Barbel circovirus, BaCV1 and BaCV2) indicated that they belonged into a new genetic group within the family Circoviridae, distinct from known circoviruses and circovirus-like genomes. Their genome size was 1957 bases and contained two major ORFs similar to the capsid and replication-associated protein genes of circoviruses. A connection between the presence of the virus and clinical manifestations of the infection could not be proved.Circoviruses are small non-enveloped viruses with a short single-stranded circular DNA genome of 1.7-2.3 kilobases. Since the first discovery of the virus in a porcine cell culture (Tischer et al., 1974(Tischer et al., , 1982 a number of novel viruses have been described with similar characteristics, providing a basis for the establishment of the family Circoviridae. The family is currently divided into two recognized genera (Fauquet et al., 2005). Chicken anaemia virus (CAV) is the only member of the genus Gyrovirus, the rest of the circoviruses belong to the genus Circovirus. Strangely enough, besides the first porcine circovirus (PCV1) identified, the only other circovirus of mammalian origin is a pathogenic variant of PCV, designated PCV2 genotype (Allan et al., 1998). The rest of the so far detected circoviruses are of avian origin. PCV is known to infect animals other than domestic pigs, like wild boars (Ellis et al., 2003; Cságola et al., 2006) or rodents (Lőrincz et al., 2010) and it was also detected in cattle (Nayar et al., 1999;Kappe et al., 2010), but circoviruses characteristic to mammalian species other than swine are not known at present.As molecular biology tools evolve the chances of discovering novel viral species or even virus families increase. Using viral metagenomics, novel circovirus-like genomes were detected recently in reclaimed water and marine samples (Rosario et al., 2009a, b). Ng et al. (2009) reported the presence of a single-stranded circular DNA virus in sea turtle fibropapilloma cases, a potential novel representative of circoviruses. Based on similar methods Li et al. (2010) identified distantly related circovirus-like genomes in human and chimpanzee stools, and suggested the establishment of a tentative new genus (Cyclovirus) within the family Circoviridae. Using random PCR amplification and sequencing Blinkova et al. (2010) described circular viral genomes resembling circoviruses, plant geminiviruses and nanoviruses in size and genome organization, suggesting an evolutionary link among them. These findings show that circoviruses were perhaps more widespread than previously thought, and samples from water sources suggest that fish might also be carriers of circovir...

Pigeon circoviruses (PiCV) had been identified worldwide and are responsible for immune suppression and a variety of diseases collectively referred to as young pigeon disease syndrome. Samples from racing pigeons were collected throughout Hungary and analyzed for the presence of PiCV by polymerase chain reaction. The capsid protein coding gene was amplified from ten PiCVs of different origins, and compared with known PiCV sequences. The results indicated that PiCV was highly variable, the viruses formed five distinct genetic groups. Differences of the 3' end of the gene suggested the possibility of genetic recombination among these groups.