Selected aspects of infectious bursal disease – the current state of knowledge

Infectious bursal disease (IBD) is a highly infectious and contagious immunosuppressive viral disease of chickens with a worldwide economic significance to the poultry industry. Over fifty years have passed since the first confirmed occurrence of the disease, and the virus has spread all over world and evolved into multiple genetic, antigenic and pathotypic variants, becoming a serious threat to the poultry industry. The primary tool in IBD eradication is the maintenance of strict biosecurity in poultry farms and implementation of vaccination programmes which should take into account the current epidemiological knowledge about the IBDV strains circulating in the field. This review article presents the current state of knowledge about the infectious bursal disease virus (IBDV) with special regard to the molecular biology of the virus, immunological aspects, as well as current and future prevention strategies.

Molecular Survey of Viral Poultry Diseases with an Indirect Public Health Significance in Central Ethiopia

The importance of poultry production is globally increasing, in Ethiopia as well, where high-quality protein and contained costs make poultry a valuable food resource. However, this entails some problems linked to rural, backyard and intensively reared flock proximity and pathogen circulation. This study is aimed at monitoring the presence of important viral pathogens in poultry (infectious bronchitis virus (IBV), avian metapneumovirus (aMPV), infectious bursal disease virus (IBDV) and Newcastle disease virus (NDV)) in Ethiopia. Respiratory and cloacal swabs and bursa of Fabricius and kidney imprints on FTA cards were collected in 2021 from 16 farms and tested for IBV, aMPV, NDV and IBDV. One farm was positive for IBDV, resulting in strains similar to those present in vaccines, belonging to genogroup A1a; two farms were positive for IBV but, due to sensitivity limits, only one sample was sequenced, resulting in a 4/91-like strain (GI-13); a layer farm tested positive for NDV with a Lasota-like vaccine strain. These findings suggest a low presence of these pathogens, probably due to the implementation of vaccination strategies, which is also testified by the detection of vaccine strains. A close diagnostic activity should be implemented on a routine basis in order to monitor pathogen circulation, ameliorate biosecurity measures and protect animal health and production levels.

Single-Dose Vaccination of Recombinant Chimeric Newcastle Disease Virus (NDV) LaSota Vaccine Strain Expressing Infectious Bursal Disease Virus (IBDV) VP2 Gene Provides Full Protection against Genotype VII NDV and IBDV Challenge

Newcastle disease virus (NDV) and infectious bursal disease virus (IBDV) are the two most important and widespread viruses causing huge economic losses in the global poultry industry. Outbreaks of genotype VII NDV and IBDV variants in vaccinated poultry flocks call for genetically matched vaccines. In the present study, a genetic matched chimeric NDV LaSota vaccine strain expressing VP2 gene of IBDV variant, rLaS-VIIF/HN-VP2 was generated for the first time, in which both the F and HN genes of LaSota were replaced with those of the genotype VII NDV strain FJSW. The cleavage site of the FJSW strain F protein in the rLaS-VIIF/HN-VP2 genome was mutated to the avirulent motif found in LaSota. Expression of IBDV VP2 protein was confirmed by western blot. The rLaS-VIIF/HN-VP2 maintained the efficient replication ability in embryonated eggs, low pathogenicity and genetic stability comparable to that of parental LaSota virus. One dose oculonasal vaccination of one-week-old SPF chickens with rLaS-VIIF/HN-VP2 induced full protection against genotype VII NDV and IBDV lethal challenge. These results indicate that the rLaS-VIIF/HN-VP2 is a promising bivalent vaccine to prevent infections of IBDV and genotype VII NDV.

Development of multiplex reverse transcription-polymerase chain reaction for differentiation of strains of infectious bursal disease virus and primary screening of the virus in Thailand

Background and Aim: A new set of primers (400 base pairs partial of VP2) was designed and used for the infectious bursal disease virus (IBDV) screening test. Using this new primer set, the enzymes MboI and BstNI were unable to differentiate the field and vaccine strains. As a result, a new simple, cheap, and appropriate tool for strain differentiation is required. The objective of this study was to develop the appropriate restriction fragment length polymorphism (RFLP) and multiplex reverse transcription-polymerase chain reaction (RT-PCR) for the differentiation of classic IBDV (cIBDV) strains and very virulent IBDV (vvIBDV) strains in Thailand. Materials and Methods: Ninety seven bursa of Fabricius from 16 farms were collected from farms in the eastern and central regions of Thailand. RT-PCR screening showed that 82 samples were positive for IBDV and 15 samples were negative. Then, selected samples were sequenced from each farm with a positive test. Results: The sequencing results showed that samples from six of the farms were vvIBDV and samples from the other six farms were cIBDV. Although the whole genome sequencing was incomplete, both the sequencing results of segment A and segment B showed high similarity between cIBDV and vvIBDV. Restriction enzyme cutting site and primers for multiplex RT-PCR were hard to design. An RT-PCR-RFLP method was developed, but it failed to differentiate IBDV strains. However, the multiplex RT-PCR was able to differentiate cIBDV from vvIBDV. Four primers were used in the multiplex RT-PCR. Conclusion: These four primers were used together in one reaction at an annealing temperature of 45°C. Therefore, multiplex RT-PCR is a less complicated, cheaper, and less time-consuming method for the differentiation of cIBDV and vvIBDV strains.

The Autophagy Cargo Receptor SQSTM1 Inhibits Infectious Bursal Disease Virus Infection through Selective Autophagic Degradation of Double-Stranded Viral RNA

Selective autophagy mediates the degradation of cytoplasmic cargos, such as damaged organelles, invading pathogens, and protein aggregates. However, whether it targets double-stranded RNA (dsRNA) of intracellular pathogens is still largely unknown. Here, we show that selective autophagy regulates the degradation of the infectious bursal disease virus (IBDV) dsRNA genome. The amount of dsRNA decreased greatly in cells that overexpressed the autophagy-required protein VPS34 or autophagy cargo receptor SQSTM1, while it increased significantly in SQSTM1 or VPS34 knockout cells or by treating wild-type cells with the autophagy inhibitor chloroquine or wortmannin. Confocal microscopy and structured illumination microscopy showed SQSTM1 colocalized with dsRNA during IBDV infection. A pull-down assay further confirmed the direct binding of SQSTM1 to dsRNA through amino acid sites R139 and K141. Overexpression of SQSTM1 inhibited the replication of IBDV, while knockout of SQSTM1 promoted IBDV replication. Therefore, our findings reveal the role of SQSTM1 in clearing viral dsRNA through selective autophagy, highlighting the antiviral role of autophagy in the removal of the viral genome.