Full-length coding sequence analysis of genome segments A and B of infectious bursal disease virus in Thailand: identification of Chinese-like and recombinant virus in the field

Abstract

ABSTRACT Infectious bursal disease virus (IBDV) causes immunosuppression in chickens, with distinctive bursal lesions. Genomic sequence information is essential to understand the epidemiology of antigenically and/or pathogenically variable IBDV strains. The present study investigated the full-length coding sequences of genome segments A and B of IBDV circulating in Thailand during 2010–2015. Five clinical samples of pooled bursas obtained from five commercial chicken farms experiencing problems with IBD in five different provinces of Thailand were identified by using a one-step reverse transcriptase polymerase chain reaction. The full-length coding sequences of genome segments A and B of three and five isolates, respectively, were successfully characterized. Phylogenetic analysis showed that two groups of IBDV were circulating in Thailand. The first group was similar to strain HLJ-504, genotype A3B3, isolated in China, but it had some minor variations in both genome segments A and B. The second group, which had a recombination event in segment A, was clustered with genotype A1B1. Its segment A originated from the intermediate vaccine W2512-like strain and isolate 9109, whereas segment B shared characteristics of a classical strain without recombination events. This study characterized the full-length coding sequences of genome segments A and B of Thai IBDV and demonstrated the presence of recombinant IBDV in Thailand for the first time. Therefore, the molecular characterization of the full-length coding sequences of both genome segments of IBDV is essential to monitor the emergence of new variant viruses, which is important for effective control and appropriate vaccine development. RESEARCH HIGHLIGHTS For the first time, this work demonstrated a recombinant IBDV strain in Thailand. Two genogroups of IBDV were found in Thailand: including HLJ-504-like and recombinant virus. Analysis of the full coding sequence is essential for monitoring emerging variant IBDV.