Detection and Phylogeny of Infectious Bursal Disease Virus (IBDV) during Field Outbreaks in Broilers Umm-i-Habiba 1, *, Ayesha Maqbool 2 , Muhammad Safdar 3 , Nida Zia 1 , Altaf Mehmood 4 , Muhammad Usman 5 , Mehwish Sharif 6 , Amanullah Khan 7 and Sajid Umar 8 1 Department of Biology, Virtual University, Lahore, Pakistan 2 Department of molecular Biology, Virtual University of Pakistan 3 Department of Breeding and Genetics, Cholistan University of Veterinary & Animal Sciences, Bahawalpur 4 Punjab Livestock and Dairy Development Department, Chakwal, Pakistan 5 Poultry Research Institute, Rawalpindi, Pakistan 6 University of Veterinary and Animal Sciences, Lahore, Pakistan 7 Department of Microbiology, Friedrich Loeffler Institute, Jena, Germany 8 Department of Pathology, PMAS-Arid Agriculture University, Rawalpindi, Pakistan Article Information Received 10 February 2019 Revised 22 March 2019 Accepted 30 March 2019 Available online27 January 2020 Authors’ Contribution UH conducted the research and collected data. AM, MS and SU supervised the study and designed the study. NZ, AM, MU, MS and AK helped in sample collection, interpretation of results and article writing. Key words Infectious bursal disease, RT-PCR, Phylogenetic, Commercial poultry, Pakistan. Infectious bursal disease (IBD) is economically important disease causing great losses to poultry industry worldwide. Field outbreaks of IBD in 18 different poultry farms in the Chakwal district were confirmed by clinicopathologic examination and PCR. A total of 6 isolates of IBDV from these outbreaks were genetically characterized based on hyper-variable region of the VP2 gene. IBDV strains were grouped into two distinct clusters on the basis of nucleotide sequences of hyper-variable region of the VP2 gene. According to phylogenetic analysis, 5 IBDV strains showed characteristic amino acid signatures in the VP2 gene (A222, I242, I256, I294, S299) and classified as vvIBDV. Furthermore, the sequencing analysis of detected field strains revealed the high similarity and close clustering with vvIBDV strains isolated from neighboring countries, suggesting geographic and temporal relationships among these strains. Interestingly, one IBDV strain clustered togather with vaccinal IBDV strains and showed 99% sequence homology with attenuated vaccine strains. Our study revealed exclusive circulation of vvIBDV and these evidences emphasize the need of further detailed and more systemic approaches to study IBDV distribution for the implementation of effective control measures. INTRODUCTION I nfectious bursal disease (IBD), continues to be a serious threat to the poultry industry worldwide. Despite the availability and application of IBDV vaccines, the emergence of new IBDV variants can threaten poultry health and production all over the world causing significant economic losses (Yilmaz et al., 2018). It is one of the most devastating viral diseases and targets immune cells thus lead to severe immunosuppression (Alkie and Rautenschlein, 2016). Chickens are the primary host species for IBDV, but the antibodies and the virus are also found in wild birds including guinea fowls, ducks, quails, pheasants and ostriches with no signs of infection * Corresponding author: Umihabiba25@gmail.com 0030-9923/2020/0002-0659 $ 9.00/0 Copyright 2020 Zoological Society of Pakistan (Lukert and Saif, 2003). It is caused by infectious bursal disease virus (IBDV), which was first discovered in Del- aware in the United States of America (USA) in 1962. IBDV primarily infects immature B cells causing patho- logical changes in the bursa of Fabricius of chickens, resulting in immunosuppression which in turn facilitates secondary infections and poor immune response to patho- gens and vaccination (OIE, 2016). IBDV is a non-enveloped, icosahedral, bi-segmented (segment A and Segment B), double-stranded RNA (dsRNA) virus belonging to the genus Avibirnavirus within the family Birnaviridae (OIE, 2016; Lukert and Saif, 2003; Alkie and Rautenschlein, 2016). The larger segment A (3.2 kbp) of the bisegmented dsRNA genome of IBDV encodes a precursor poly-protein that is processed in three mature proteins; VP2 (outer capsid), VP3 (inner capsid), and VP4 (protease). The VP2 is the major structural protein that contains antigenic regions, that is, those responsible for ABSTRACT Pakistan J. Zool., vol. 52(2), pp 659-667, 2020. DOI: https://dx.doi.org/10.17582/journal.pjz/20190210070218