Molecular Characterization of a Novel Budgerigar Fledgling Disease Virus Strain From Budgerigars in China.

Xiaoliang Hu,Hongzhi Cao,Zhige Tian,Hongli Pu,Lulu Chen,Lili Zhao,Yan Li,Tiankuo Yang,Yucan He,Xiangxiao Liu,Dongdong Cai,Guangmei Luo,Siru Liu

doi:10.3389/fvets.2021.813397

Abstract

Budgerigar fledgling disease virus (BFDV) is the causative polyomavirus of budgerigar fledgling disease, an important avian immunosuppressive disease in budgerigars (Melopsittacus undulatus). In the current study, we explored the etiological role and molecular characteristics of BFDV. We identified a novel BFDV strain, designated as SC-YB19, belonging to a unique cluster with three other domestic strains (WF-GM01, SD18, and APV-P) and closely related to Polish isolates based on complete sequences. Sequence analysis showed that SC-YB19 had an 18-nucleotide (nt) deletion in the enhancer region, corresponding to the sequence position 164–181 nt, which differed significantly from all other BFDV strains. Based on sequence alignment, three unique nucleotide substitutions were found in VP4 (position 821), VP1 (position 2,383), and T-antigen (position 3,517) of SC-YB19, compared with SD18, WF-GM01, QDJM01, HBYM02, APV7, and BFDV1. Phylogenetic analyses based on complete sequences suggested that SC-YB19, along with the domestic WF-GM01, SD18, and APV-P strains, formed a single branch and were closely related to Polish, Japanese, and American isolates. These results demonstrate that BFDV genotype variations are co-circulating in China, thus providing important insight into BFDV evolution.

Highlights

Budgerigar fledgling disease virus (BFDV), called avian polyomavirus (APV), is the causative agent of budgerigar fledgling disease, an important immunosuppressive disease in budgerigars (Melopsittacus undulatus)
We identified an 18-nt deletion in the enhancer section in SC-YB19, but not in the other BFDV isolates (Supplementary Figures 2A,B)
Whether this deletion affects the transcription, replication, and virulence of SC-YB19 is unknown, and further experiments are required to investigate its potential influence on biological effects

Summary

Introduction

Budgerigar fledgling disease virus (BFDV), called avian polyomavirus (APV), is the causative agent of budgerigar fledgling disease, an important immunosuppressive disease in budgerigars (Melopsittacus undulatus). The disease was first reported in 1981, with typical symptoms including abdominal distention, lack of down feathers on the back and abdomen, subcutaneous hemorrhage of nestlings, and acute death [1,2,3]. Polyomaviruses have a wide host range, and have been identified in vertebrates such as humans [4, 5], bats [6, 7], non-human primates [8], and horses [9]. BFDV was identified as the first non-mammalian member of the genus polyomavirus [11, 12]. BFDV is a circular, doublestranded molecule with a 4 981-nt genome, which can be divided into early and late regions. The late region contains four structural proteins, i.e., VP1, VP2, VP3, and VP4 [13]. The genome contains four regulatory elements, i.e., promoter, polyadenylation signal, DNA replication origin, and enhancer regions [14]

Methods

Results

Conclusion