Abstract
Infectious bursal disease (IBD) is an acute and highly contagious immunosuppressive disease caused by the infectious bursal disease virus (IBDV), which seriously threatens the healthy development of the poultry industry. Since its spread to China in the early 1990s, the very virulent IBDV (vvIBDV) characterized by high lethality, has been the focus of prevention and control. However, the novel variant IBDV (nVarIBDV), which has been widely prevalent in China since 2017, has brought a new threat to the poultry industry. In this study, the prevalence of IBDV in the important poultry-raising areas of China from 2019 to 2020 was detected. Of these, 45.1% (101/224) of the samples and 61.9% (26/42) of the chicken flocks were shown to be positive for IBDV. For 50 IBDVs, the sequences of the hypervariable region of the VP2 gene in segment A and of the B-marker of the VP1 gene in segment B were analyzed. The results revealed the coexistence of a number of different IBDV genotypes, including A2dB1 (nVar, 26/50, 52.0%), A3B3 (HLJ0504-like, 15/50, 30.0%), A1B1 (classical, 1/50, 2.0%), and A8B1 (attenuated, 1/50, 2.0%). This indicated that the newly emerging nVarIBDV of A2dB1 and the persistently circulating HLJ0504-like vvIBDV of A3B3 are the two important epidemic strains. Furthermore, we established that segment reassortment has occurred among these circulating strains. This study is the first to reveal the novel epidemic characteristics of IBDV since the report of the emerging nVarIBDV of A2dB1 in China.
Highlights
Infectious bursal disease (IBD), known as the Gumboro disease, is an economically important viral disease that affects young birds and causes acute death or immunosuppression [1]
These samples were subjected to an RT-polymerase chain reaction (PCR) detection, which revealed that 45.1% (101/224) of the samples and 61.9% (26/42) of the flocks were positive for IBD virus (IBDV)
According to the current scheme used for IBDV genotype classification [19], genogroup is identified by individual segment and genotype is synthetically determined by both segments
Summary
Infectious bursal disease (IBD), known as the Gumboro disease, is an economically important viral disease that affects young birds and causes acute death or immunosuppression [1]. It is characterized by bursal damage secondary to an invasion of immature lymphocytes. The hypervariable region (HVR) of VP2 (amino acids 206–350) is a fragment representative of the gene characteristics of segment A, which is widely used in analyses of the genetic evolution of IBDV [3, 5]. Similar to the HVR of VP2, the B-marker of VP1 (amino acids 110–252) is a fragment representative of the gene characteristics of segment B [6]
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