INTRODUCTION
Members of the Circoviridae , within the order Circovirus ,
contain a small, circular, non-enveloped, single stranded DNA genomes
that range from 1.7 to 2.5 kb in size (Stenzel et al., 2017). ThePigeon circovirus (PiCV) or the columbid circovirus (CoCV),
together with porcine circoviruses (PCV) types 1 and 2,
psittacine
beak and feather disease virus (BFDV), duck circovirus (DuCV), goose
circovirus (GoCV), canary circovirus (CaCV), raven (RaCV), starling
(StCV), swan (SwCV), finch and gull (FiCV and GuCV)
circoviruses
belongs to the genus Circovirus and the familyCircoviridae(http://www.ictvonline.org/).
PiCV is a small, circular,
non-enveloped
DNA virus that contains single-stranded DNA approximately 2.0 kb in
size. The genome of PiCV forms two main open reading frames (ORFs). The
ORF-V1, located on the virion sense strand, encodes a
replication-associated protein (rep ) and the ORF–C1, located on
the complementary sense strand, encodes a capsid protein (cap )
(Mankertz et al., 2000; Todd et al., 2001). In contrast to the gene
forming ORF-V1, the gene forming ORF-C1 of PiCV had been demonstrated to
be highly
genetically
diverse (Stenzel & Koncicki, 2017; Zhang et al., 2015). The other ORFs
(ORF-C2, ORF-C3 and ORF-C4), located on the complementary sense strand,
encode three PiCV proteins with unknown functions (Mankertz et al.,
2000; Todd et al., 2008). The circovirus infection in pigeons was first
diagnosed in 1993 in the USA (Woods et al., 1993) and had been
considered to be strongly associated with young pigeon disease syndrome
(YPDS) including weakened racing performance, weight loss, lethargy,
anorexia,
respiratory distress and diarrhea (Raue et al., 2005).
Various methods have been applied to detect PiCV infection in clinical
specimens. The original diagnose methods including electron microscopy,
histology, dot blot hybridization (DBH), and in situ hybridization
(Yamamoto et al., 2015) are time consuming (Smyth et al., 2001; Soike et
al., 2001; Todd et al., 2002; Tsai et al., 2014). The molecular biology
techniques, such as the standard PCR, real-time PCR (Duchatel et al.,
2009), NGS techniques (Wang et al., 2017) and the loop-mediated
isothermal amplification method (Tsai et al., 2014), enabled the more
rapid and accurate detection of PiCV infections. As a result,
cases
of PiCV infections in pigeons were subsequently reported in various
countries, including Northern Ireland (Todd et al., 2001), Germany
(Mankertz et al., 2000; Raue et al., 2005), Italy (Franciosini et al.,
2005), France (Abadie et al., 2001), Czech Republic (Taras et al.,
2003),
Belgium
(Duchatel et al., 2005; Duchatel et al., 2006), Poland (Stenzel et al.,
2012; Stenzel et al., 2014c), Slovenia (Krapez et al., 2012), Hungary
(Cságola
et al., 2012), United Arab Emirates (Ledwoń et al., 2011), Iran
(Mahzounieh et al., 2014), China (Liao et al., 2015; Wang et al., 2017;
Zhang et al., 2015), Japan (Yamamoto et al., 2015) and the USA (Roy et
al., 2003). The previous studies also had demonstrated that PiCV has
been detected in different types of pigeons including racing, fancy,
feral, meat pigeons (Stenzel et al., 2014b; Stenzel et al., 2012; Wang
et al., 2017). However, all of the mentioned above birds belong toColumba livia species.
In China, the first PiCV infection was detected from meat pigeons of
Zhejiang province in 2009 and the full genome was sequenced (Yu et al.,
2009). In recent years, several studies had proved that PiCV was
prevalent among meat pigeons in eastern and southern of China (Wang et
al., 2017; Zhang et al., 2015). The competitions of racing pigeons are
becoming increasingly popular in China, and even, pigeon racing is
considered to be a national sport. The Chinese Association of Racing
Pigeon Breeders has over 5 million members. The Chinese breeders compete
in numerous races at different distances in their sections through the
racing season, and more than 25 million of racing pigeons were selected
to attend the competitions in a total of approximately 750 racing clubs
every year. However, there is no epidemiologic data on PiCV infections
among racing pigeons. In order to investigate the prevalence, evolution
and genome characterization of PiCV in racing pigeons in China, an
extensive epidemiological investigation and bioinformatics analysis of
PiCV from racing pigeons were undertaken. A total of 571 serum samples
collected from healthy pigeons and 51 tissues samples collected from
sick pigeons were obtained from 39 racing pigeon clubs in 11 provinces
or municipalities of China between 2016 and 2019. The purpose of our
study is to provide novel epidemiologic data and genome characterization
about PiCV isolated from racing pigeons in China.