VP5-deficient mutant virus induced protection against challenge with very virulent infectious bursal disease virus of chickens

Genetic Insight into the Interaction of IBDV with Host-A Clue to the Development of Novel IBDV Vaccines

Infectious bursal disease virus (IBDV) is an immunosuppressive pathogen causing enormous economic losses to the poultry industry across the globe. As a double-stranded RNA virus, IBDV undergoes genetic mutation or recombination in replication during circulation among flocks, leading to the generation and spread of variant or recombinant strains. In particular, the recent emergence of variant IBDV causes severe immunosuppression in chickens, affecting the efficacy of other vaccines. It seems that the genetic mutation of IBDV during the battle against host response is an effective strategy to help itself to survive. Therefore, a comprehensive understanding of the viral genome diversity will definitely help to develop effective measures for prevention and control of infectious bursal disease (IBD). In recent years, considerable progress has been made in understanding the relation of genetic mutation and genomic recombination of IBDV to its pathogenesis using the reverse genetic technique. Therefore, this review focuses on our current genetic insight into the IBDV's genetic typing and viral genomic variation.

Reverse genetics approaches for live-attenuated vaccine development of infectious bursal disease virus

Infectious bursal disease (IBD), which is caused by infectious bursal disease virus (IBDV) infection, leads to severe immunosuppression in young chickens and results in significant economic losses in the poultry industry. To date, vaccination with live-attenuated vaccine (LAV) is a convenient method to provide effective protection against IBDV infection. Classical attenuated viruses are usually obtained by either passaging virus in cultured cells or natural isolation. However, these empiric attenuation methods, which are time-consuming and not guaranteed, are not reliable for emergent antigenic variant and very virulent IBDV strains. The reverse genetics (RG) system opens a new avenue for the development of IBDV LAV. In this review, we summarize the current knowledge on the biological characteristics of IBDV structure and genome organization, as well as the established RG systems. We also describe the details for the strategies used to develop IBDV LAV based on the RG systems.

Infectious Bursal Disease Virus-Host Interactions: Multifunctional Viral Proteins that Perform Multiple and Differing Jobs

Infectious bursal disease (IBD) is an acute, highly contagious and immunosuppressive poultry disease caused by IBD virus (IBDV). The consequent immunosuppression increases susceptibility to other infectious diseases and the risk of subsequent vaccination failure as well. Since the genome of IBDV is relatively small, it has a limited number of proteins inhibiting the cellular antiviral responses and acting as destroyers to the host defense system. Thus, these virulence factors must be multifunctional in order to complete the viral replication cycle in a host cell. Insights into the roles of these viral proteins along with their multiple cellular targets in different pathways will give rise to a rational design for safer and effective vaccines. Here we summarize the recent findings that focus on the virus-cell interactions during IBDV infection at the protein level.

Infectious bursal disease virus VP5 polypeptide: a phosphoinositide-binding protein required for efficient cell-to-cell virus dissemination

Infectious bursal disease virus (IBDV), a member of the Birnaviridae family, is a major avian pathogen responsible for an immunosuppressive disease affecting juvenile chickens. The IBDV genome is formed by two dsRNA segments. The largest one harbors two partially overlapping open reading frames encoding a non-structural polypeptide, known as VP5, and a large polyprotein, respectively. VP5 is non-essential for virus replication. However, it plays a major role in IBDV pathogenesis. VP5 accumulates at the plasma membrane (PM) of IBDV-infected cells. We have analyzed the mechanism underlying the VP5 PM targeting. Updated topological prediction algorithm servers fail to identify a transmembrane domain within the VP5 sequence. However, the VP5 polycationic C-terminal region, harboring three closely spaced patches formed by two or three consecutive basic amino acid residues (lysine or arginine), might account for its PM tropism. We have found that mutations, either C-terminal VP5 deletions or replacement of basic amino acids by alanine residues, that reduce the electropositive charge of the VP5 C-terminus abolish PM targeting. Lipid overlay assays performed with an affinity-purified Flag-tagged VP5 (FVP5) protein version show that this polypeptide binds several phosphoinositides (PIP), exhibiting a clear preference for monophosphate species. Experiments performed with FVP5 mutant proteins lacking the polycationic domain demonstrate that this region is essential for PIP binding. Data gathered with IBDV mutants expressing C-terminal deleted VP5 polypeptides generated by reverse genetics demonstrate that the VP5-PIP binding domain is required both for its PM targeting in infected cells, and for efficient virus dissemination. Data presented here lead us to hypothesize that IBDV might use a non-lytic VP5-dependent cell-to-cell spreading mechanism.

Seasonal variations in health indices of free-ranging asymptomatic guinea fowls (Numida meleagris) in Zambia

OBJECTIVE

To determine the impact of seasonal variations on health indices of free-ranging asymptomatic guinea fowls (Numida meleagris) in Zambia.

METHODS

A time series analysis was carried out on a prospective cohort study over a 12 month period between March 2010 and February 2011 by examining a total 147 guinea fowls for haematological and morphometric data of selected organs.

RESULTS

There was a strong correlation in erythrocytic indices between packed cell volume and red blood cell counts (=0.824, P<0.001) as well as between packed cell volume and hemoglobulin (Hb) counts (r=0.648, P<0.001). Seasonal differences showed that erythrocytic indices were higher in the males than the females and that the difference was significantly higher (P<0.001) during the rainy season, which coincided with the breeding period when females were laying eggs. Increase in total plasma protein was positively correlated with overall body weight. Generally, females had higher body weights and total plasma protein levels than the males in the rain season. Of the 147 birds examined, 51% (n=147) had the bursa of Fabricius. For birds that had the bursa of Fabricius, the weights of bursae were higher (P<0.05) in the cold-dry season than the other seasons and no sex differences were observed. Spleen morphometric data did not show any seasonal nor sex differences.

CONCLUSIONS

Overall, data presented herein demonstrate that seasonal variations have a significant influence on health indices of free-ranging guinea fowls and that these factors could influence the susceptibility of this species of birds to disease infections at different times of the year.

The infectious bursal disease virus RNA-binding VP3 polypeptide inhibits PKR-mediated apoptosis

Infectious bursal disease virus (IBDV) is an avian pathogen responsible for an acute immunosuppressive disease that causes major losses to the poultry industry. Despite having a bipartite dsRNA genome, IBDV, as well as other members of the Birnaviridae family, possesses a single capsid layer formed by trimers of the VP2 capsid protein. The capsid encloses a ribonucleoprotein complex formed by the genome associated to the RNA-dependent RNA polymerase and the RNA-binding polypeptide VP3. A previous report evidenced that expression of the mature VP2 IBDV capsid polypeptide triggers a swift programmed cell death response in a wide variety of cell lines. The mechanism(s) underlying this effect remained unknown. Here, we show that VP2 expression in HeLa cells activates the double-stranded RNA (dsRNA)-dependent protein kinase (PKR), which in turn triggers the phosphorylation of the eukaryotic initiation factor 2α (eIF2α). This results in a strong blockade of protein synthesis and the activation of an apoptotic response which is efficiently blocked by coexpression of a dominant negative PKR polypeptide. Our results demonstrate that coexpression of the VP3 polypeptide precludes phosphorylation of both PKR and eIF2α and the onset of programmed cell death induced by VP2 expression. A mutation blocking the capacity of VP3 to bind dsRNA also abolishes its capacity to prevent PKR activation and apoptosis. Further experiments showed that VP3 functionally replaces the host-range vaccinia virus (VACV) E3 protein, thus allowing the E3 deficient VACV deletion mutant WRΔE3L to grow in non-permissive cell lines. According to results presented here, VP3 can be categorized along with other well characterized proteins such us VACV E3, avian reovirus sigmaA, and influenza virus NS1 as a virus-encoded dsRNA-binding polypeptide with antiapoptotic properties. Our results suggest that VP3 plays a central role in ensuring the viability of the IBDV replication cycle by preventing programmed cell death.

Critical role for voltage-dependent anion channel 2 in infectious bursal disease virus-induced apoptosis in host cells via interaction with VP5

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by IBD virus (IBDV). Although IBDV-induced host cell apoptosis has been established, the underlying molecular mechanism is still unclear. We report here that IBDV viral protein 5 (VP5) is a major apoptosis inducer in DF-1 cells by interacting with the voltage-dependent anion channel 2 (VDAC2) in the mitochondrion. We found that in DF-1 cells, VP5-induced apoptosis can be completely abolished by 4,4'-diisothiocyanatostibene-2,2'-disulfonic acid (DIDS), an inhibitor of VDAC. Furthermore, knockdown of VDAC2 by small interfering RNA markedly inhibits IBDV-induced apoptosis associated with decreased caspase-9 and -3 activation and cytochrome c release, leading to increased IBDV growth in host cells. Thus, VP5-induced apoptosis during IBDV infection is mediated by interacting with VDAC2, a protein that appears to restrict viral replication via induction of cell death.