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Avian Pox Virus | 371

Genome occur primarily in terminal and, notably, localized internal
Complete nucleotide sequence of a vaccine like US strain of genomic regions and suggest significant genomic diversity among
fowlpox virus (Afonso et al., 2000) and a high passaged, FP9 avipoxviruses. Divergent regions contain gene families, which
European strain of fowlpox virus (Laidlaw and Skinner, 2004), overall comprise over 49% of the CNPV genome and include
canarypox viruses (Tulman et al., 2004), two viruses from South genes encoding 51 proteins containing ankyrin repeats, 26 N1R/
Africa, from a penguin and pigeon (Offerman et al., 2014) have p28-like proteins, and potential immunomodulatory proteins,
been determined. In addition, the nucleotide sequences of including those similar to transforming growth factor and nerve
genomes of condorpox virus (CDPV), palilapox (PAPV), apap- growth factor. CNPV genes lacking homologues in FWPV
anepox (APPV) and Hawaiian goosepox (HGPV) viruses have encode proteins similar to ubiquitin, interleukin-10-like proteins,
been determined (Tripathy et al., 2015 – our unpublished data). tumour necrosis factor receptor, PIR1 RNA phosphatase, thiore-
doxin binding protein, MyD116 domain proteins, circovirus Rep
proteins, and the nucleotide metabolism proteins thymidylate
Genomic differences among avian pox kinase and ribonucleotide reductase small subunit (Tulman et al.,
viruses 2004).
Although the overall genomic organization of FWPV appears Nucleotide sequence of a poxvirus of feral pigeon (Fe2) and
to be similar to that of other members of the family Poxviridae, another virus from a penguin (PEPV) has been determined by
some genomic rearrangement has occurred. FWPV genome is Offerman et al. (2014). The genome of FeP2 is 282 kbp and has
composed of a single linear double-stranded DNA molecule 271 ORFs while the genome size of PEPV is 306 kbp which
with a hairpin loop at each end. The genome of an US FWPV encode 284 ORFs. They are more closely related to one another
contains a central coding region and two identical, inverted ter- (94.4%) than to either FWPV (85.3% and 84.0%, respectively)
minal repeat (ITR) regions of 9520 bp at both termini (Afonso or CNPV (62.0% and 63.4%, respectively). The most striking
et al., 2000). It contains 288,539 bp and encodes for 260 putative difference between FeP2 and the FWPV-like avipoxviruses is a
genes of 60–1949 amino acids in length. Based upon homologies large deletion of ≈ 16 kbp from the central region of the genome
with other viral or cellular genes, 101 ORFs of FWPV have been of FeP2.
assigned similar or putative functions. The nucleotide composi- Comparative analysis of the nucleotide sequence of a 4.5 kbp
tion of FWPV is 69% A + T, which is uniformly distributed over HindIII fragment of condorpox virus DNA with a corresponding
the entire length of the genome. Six small regions with higher region of FWPV genome showed marked differences. In FWPV,
G + C content (50%) are located in the terminal genomic regions. 11 ORFs are confined in this region, including sequences related
Because of the presence of multiple and in some cases large gene to reticuloendotheliosis virus (REV) integration. Condorpox
families, the genome of FWPV is larger than other completely virus, however, contains only eight ORFs and does not have any
sequenced pox virus genomes except canarypox virus and some REV sequences. Similarly, nucleotide sequences of a 5.3 kbp
other avian pox viruses, which have a larger genome than that of PstI-HindIII fragment of the genome of an avian pox virus from
FWPV. In this regard, 32% of the FWPV genome is composed of a Hawaiian goose revealed very high homology with CNPVs and
31 genes in the ankyrin repeat family, 10 genes in the N1R/p28 did not contain three FWPV ORFs including REV sequences
family, and 6 genes in the B22R family. The B22R ORFs alone (Kim et al., 2003; Kim and Tripathy, 2006a).
comprise 12% of the viral genome. As fewer ankyrin genes were
found in the genome of FWPV after extensive passages in tissue
culture, it is likely that in other avian pox viruses the number Virus replication
of ankyrin repeat genes also may vary. Since pox virus ankyrin Poxviruses replicate in the cytoplasm and encode proteins for
repeat genes have been associated with host range functions, loss DNA replication and gene expression. FWPV genes involved
or disruption of many of these genes may be associated with the in DNA replication and repair include a DNA ligase, ATP-GTP
narrowing of host range. The genome of a tissue culture passaged binding protein, uracil DNA glycosylase, DNA polymerase,
FWPV strain FP9 is approximately 260 kbp in size (Laidlaw and DNA topoisomerase, processivity factor and replication-essential
Skinner, 2004). protein kinase. Most of the information on poxvirus replication
Canarypox virus (CNPV) contains many genomic differ- comes from studies with vaccinia virus (VV). Fig. 13.10 simpli-
ences with FWPV which occur in terminal and localized internal fies the stages of virus replication (Hruby and Byrd, 2006). More
regions, suggesting significant genomic diversity among avipoxvi- related information is available elsewhere (Boulanger et al., 2000;
ruses. These differences may play role in virulence and host range. Hatano et al., 2001; Moss, 2006, 2013).
The 365-kbp canarypox virus genome (Tulman et al., 2004) con- FWPV encodes homologues of 31 known VV structural pro-
tains 328 potential genes in the central region and in the 6.5-kbp teins, and the majority of them are associated with the intracellular
inverted terminal repeats. mature virus particle (IMV). Eleven genes of FWPV contains hom-
CNPV contains many genomic differences with FWPV, ologues of VV core proteins. Seven genes of FWPV encode for VV
including over 75 kbp of additional sequence, 39 genes lacking IMV membrane associated proteins. Six FWPV structural proteins
FWPV homologues, and an average of 47% amino acid divergence like their VV homologues, contain the conserved AG proteolytic
between homologues. It is likely that the genomic differences in cleavage sites, which suggests that aspects of structural protein pro-
avian poxvirus affect the virulence and host range. Differences cessing are conserved in FWPV. FPV197 is the homologue of VV