Avipoxviruses have low G+C content (30 to 40%) and consist of a single linear molecule of double-stranded DNA of between 260-365 kb. The central region of the genome is flanked by two identical inverted terminal repeats (ITRs) which are covalently linked by hairpin loops and contains several hundred closely spaced open reading frames [7] . The central region contains about 90-106 homologous genes that are involve in basic replication mechanisms, including viral transcription and RNA modification, viral DNA replication, and proteins involved in structure and assembly of intracellular mature virions and extracellular enveloped virions [8] .