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.

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.

Trial Control of Infectious Bursal Disease Virus Isolated From Broiler Chicken Using Iron Oxide Chitosan Nanocomposite

A severe outbreak of Infectious Bursal Disease (IBD) recorded in (30) chicken flocks at different districts in Sharqia Governorate during 2019 that showed high mortalities (30%) and severe immunosuppression. Attempts to control (IBD) by antiviral iron oxide chitosan nanocomposite (characterized nano-size 35.1±5 nm with a stable state, zeta potentials16.8 ± 10.9, the PDI. 0.91 and iron concentration in nanocomposite is 2625 mg/L,).Eighty Baladi broiler chicks at the age of 21 days were divided into 4 groups. Group A (as the negative control group), group B (as the positive control group), group C (as the nanocomposite treatment group), and group D (only received nanocomposite). The used treatment was iron oxide chitosan nanocomposite with the concentration of (1 mg/ 100ml) IC50 orally administered for 3 days post infection.The virus shedding showed marked significant decrease (P<0.05) in group C compared to group B was 0.5 to 1 log 10 compared to group B was 3 to 6.4 log 10.Histopathological lesions of bursa, spleen, thymus, liver, and kidney in group C after 6 days PI showed hyper activity of lymphoid population compared to chicks infected group which revealed necrosis and depletion of lymphoid elements of the bursa, thymus, and spleen with blood vessels had marked congestion and hemorrhages in parenchyma.Base on this study, iron oxide chitosan nanocomposite showed an antiviral activity that could significantly reduce viral shedding, and could decrease pathological changes in lymphoid organs which is considered to be better protection for solving health problems in infected chicks.