Abstract
Sixty samples of bursa of Fabricius were collected from broiler chickens suspected to be infected with infectious bursal disease virus (IBDV) in different areas of Iraq for molecular evaluation. The extracted nucleic acid was amplified using reverse transcriptase polymerase chain reaction (RT-PCR) targeting genes of segment A (Vp2, Vp3, Vp4 and Vp5 genes) and segment B (VP1 genes). The products of amplification were sent to Korea for sequencing using Sanger method. The sequencing analysis of the IBDV from the Iraqi isolates revealed that each gene had different transition and transversion (nonsense and missense of point mutation) compared to reference genes. The phylogenetic tree analysis showed that the VP2 of segment A of the Iraqi samples was similar to that of an Egyptian strain with 96%similarity, the polypeptide VP2-3-4 of segment A of the Iraqi samples was similar to those of a Chinese strain with 99% similarity and the VP5 of segment A was similar to that of Chinese strain with 99% similarity. However, the phylogenetic tree analysis showed that the VP1 of segment B had 95% similarity with that of a Chinese strain.
Highlights
Infectious bursal disease virus (IBDV) is a double stranded RNA virus, which belongs to Avibirnavirus genus in the Birnaviridae family
The sequencing analysis of PCR products for segment A and segment B showed changes in different regions of nucleotide sequences with different percentages compared to other globally known infectious bursal disease virus (IBDV). These results revealed the exchange of amino acid at different positions in segment A (VP2, VP2-3-4, and VP5) and segment B (VP1) may be leading to changing of viral antigenic properties or viral replication and viral characteristics strains
These results are in agreement with [22, 23] who revealed the mutation at different positions leading to exchange of amino acid in hydrophilic part or hydrophobic part of VP2, resulted in the very virulent of IBDV (vvIBDV) has tolerated antigenic properties or resulted in lack of a neutralizing monoclonal antibody to vvIBDV strains
Summary
Infectious bursal disease virus (IBDV) is a double stranded RNA (dsRNA) virus, which belongs to Avibirnavirus genus in the Birnaviridae family. IBDV field strains were characterized in commercial broiler flocks in Tikrit city using RT-PCR to detect vvIBDV using a specific primer set [19] and the [20] who revealed the IBDV has antigenic drift. This means that the virus possesses antigenic variation in the VP2 (hydrophilic region) that preserves the neutralizing domine which is responsible for binding with monoclonal antibodies and this revealed that the vaccine should be prepared from a local strain, but the amplification of both genes (VP1 and VP2) sequencing is still not studied.
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