Genotyping and Molecular Characterization of Infectious Bursal Disease Virus Identified in Important Poultry-Raising Areas of China During 2019 and 2020

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.

Dynamics of the Emerging Genogroup of Infectious Bursal Disease Virus Infection in Broiler Farms in South Korea: A Nationwide Study

“…This clustered area is known to have the highest density of chicken farms in South Korea and has experienced several highly infectious disease outbreaks, such as highly pathogenic avian influenza [ 33 ]. A similar finding was reported in China, where G2d IBDV was also prevalent in the major poultry-raising regions of this country [ 17 ]. This implies that the novel sub-genogroup of IBDV is likely to harbor a vulnerable area and facilitate inter-farm transmission at close distances during the course of the epidemic.…”

“…This novel variant of IBDV was first found in China and was later classified as sub-lineage G2d, whose molecular characterization was different from that of the early variant IBDVs originally reported in America [ 9 ]. G2d IBDV has become widespread in China, mostly driven by evading the immune protection conferred by available vaccines [ 15 , 16 , 17 ]. More recently, G2d IBDV epidemics have also been reported in other Asian countries, including Japan [ 18 ] and Malaysia [ 19 ].…”

The Over-40-Years-Epidemic of Infectious Bursal Disease Virus in China

“…Since 2017, atypical IBD caused by nVarIBDV has become widespread in China, and nVarIBDV sequence numbers have shown a rapid growth trend, even exceeding the number of vvIBDV sequences ( Figure 1 b). Currently, the newly emerging nVarIBDV, and persistently circulating vvIBDV are the two predominant epidemic strains endangering the healthy development of the poultry industry, which is consistent with a recent clinical epidemiological survey from 2019 to 2020 [ 25 ]. The geographical distribution of IBDV in China was also analyzed.…”

“…Since then, with the rapid development of the chicken industry, vvIBDV has rapidly swept across almost the entire country of China ( Figure 1 ). Owing to the high mortality and severe immunosuppression associated with this disease, vvIBDV has become one of the most important threats to the healthy development of the poultry industry in the past 30 years in China [ 24 , 25 , 27 , 33 , 34 , 35 , 36 , 37 , 38 ]. IBD is an important disease that must be immunized and prevented in all chicken farms in China.…”

Genetics and Pathogenicity of Natural Reassortant of Infectious Bursal Disease Virus Emerging in Latvia

“…Epidemiological data on the incidence of Gumboro disease show that IBDV reassortants are increasingly being isolated from field cases [ 10 , 39 , 40 , 41 ], indicating that the virus is continuously evolving, seeking new characteristics to facilitate its persistence in the environment. Strain 25/11/Latvia/2011 is a good example of this trend; its reduced virulence results in a subclinical course of the disease.…”