Newcastle disease virus (NDV) marker vaccine: an immunodominant epitope on the nucleoprotein gene of NDV can be deleted or replaced by a foreign epitope

Newcastle disease virus: the past and current situation in Indonesia

The Newcastle disease virus (NDV) outbreak was first reported in Java Island, Indonesia, in 1926, which was then reported further in Newcastle-upon-Tyne, England. Nevertheless, the NDV is still endemic in Indonesia, with outbreaks occurring in free-range and commercial chicken farms. The dynamic evolution of the NDV has led to the further development of vaccines and diagnostic tools for more effective control of this virus. This paper discusses the history of the NDV occurrence, vaccines, the development of diagnostic tools, and the epidemiological condition of the NDV in Indonesia. Indonesia, which has the largest poultry population in the world after China, has challenges in preventing and controlling this virus that causes economic losses to the farmers and has an impact on the welfare of the poultry farming community in Indonesia.

Current situation and future direction of Newcastle disease vaccines

Newcastle disease (ND) is one of the most economically devastating infectious diseases affecting the poultry industry. Virulent Newcastle disease virus (NDV) can cause high mortality and severe tissue lesions in the respiratory, gastrointestinal, neurological, reproductive and immune systems of poultry. Tremendous progress has been made in preventing morbidity and mortality caused by ND based on strict biosecurity and wide vaccine application. In recent decades, the continual evolution of NDV has resulted in a total of twenty genotypes, and genetic variation may be associated with disease outbreaks in vaccinated chickens. In some countries, the administration of genotype-matched novel vaccines in poultry successfully suppresses the circulation of virulent NDV strains in the field. However, virulent NDV is still endemic in many regions of the world, especially in low- and middle-income countries, impacting the livelihood of millions of people dependent on poultry for food. In ND-endemic countries, although vaccination is implemented for disease control, the lack of genotype-matched vaccines that can reduce virus infection and transmission as well as the inadequate administration of vaccines in the field undermines the effectiveness of vaccination. Dissection of the profiles of existing ND vaccines is fundamental for establishing proper vaccination regimes and developing next-generation vaccines. Therefore, in this article, we provide a broad review of commercial and experimental ND vaccines and promising new platforms for the development of next-generation vaccines.

The Role of Nucleoprotein in Immunity to Human Negative-Stranded RNA Viruses—Not Just Another Brick in the Viral Nucleocapsid

Negative-stranded RNA viruses (NSVs) are important human pathogens, including emerging and reemerging viruses that cause respiratory, hemorrhagic and other severe illnesses. Vaccine design traditionally relies on the viral surface glycoproteins. However, surface glycoproteins rarely elicit effective long-term immunity due to high variability. Therefore, an alternative approach is to include conserved structural proteins such as nucleoprotein (NP). NP is engaged in myriad processes in the viral life cycle: coating and protection of viral RNA, regulation of transcription/replication processes and induction of immunosuppression of the host. A broad heterosubtypic T-cellular protection was ascribed very early to this protein. In contrast, the understanding of the humoral immunity to NP is very limited in spite of the high titer of non-neutralizing NP-specific antibodies raised upon natural infection or immunization. In this review, the data with important implications for the understanding of the role of NP in the immune response to human NSVs are revisited. Major implications of the elicited T-cell immune responses to NP are evaluated, and the possible multiple mechanisms of the neglected humoral response to NP are discussed. The intention of this review is to remind that NP is a very promising target for the development of future vaccines.

Exchange of C-Terminal Variable Sequences within Morbillivirus Nucleocapsid Protein Are Tolerated: Development and Evaluation of Two Marker (DIVA) Vaccines (Sungri/96 DIVA, Nigeria/75/1 DIVA) against PPR

Across Africa, the Middle East, and Asia, peste des petits ruminants virus (PPRV) places a huge disease burden on agriculture, affecting, in particular, small ruminant production. The recent PPR outbreaks in Northern Africa, the European part of Turkey, and Bulgaria represent a significant threat to mainland Europe, as a source of disease. Although two safe and efficacious live attenuated vaccines (Sungri/96 and Nigeria/75/1) are available for the control of PPR, current serological tests do not enable the differentiation between naturally infected and vaccinated animals (DIVA). The vaccinated animals develop a full range of immune responses to viral proteins and, therefore, cannot be distinguished serologically from those that have recovered from a natural infection. This poses a serious problem for the post-vaccinal sero-surveillance during the ongoing PPR eradication program. Furthermore, during the latter stages of any eradication program, vaccination is only possible if the vaccine used is fully DIVA compliant. Using reverse genetics, we have developed two live attenuated PPR DIVA vaccines (Sungri/96 DIVA and Nigeria/75/1 DIVA), in which the C-terminal variable region of the PPRV N-protein has been replaced with dolphin morbillivirus (DMV). As a proof of principle, both the DIVA vaccines were evaluated in goats in pilot studies for safety and efficacy, and all the animals were clinically protected against the intranasal virulent virus challenge, similar to the parent vaccines. Furthermore, it is possible to differentiate between infected animals and vaccinated animals using two newly developed ELISAs. Therefore, these DIVA vaccines and associated tests can facilitate the sero-monitoring process and speed up the implementation of global PPR eradication through vaccination.

Development of a T7 RNA polymerase expressing cell line using lentivirus vectors for the recovery of recombinant Newcastle disease virus

The development of a T7 RNA polymerase (T7 RNAP) expressing cell line i.e. BSR T7/5 cells marks an improvement of reverse genetics for the recovery of recombinant Newcastle disease virus (rNDV). BSR T7/5 is developed by transient transfection of plasmid encoding T7 RNAP gene for rNDV rescue. However, the gene expression decreases gradually over multiple passages and eventually hinders the rescue of rNDV. To address this issue, lentiviral vector was used to develop T7 RNAP-expressing HEK293-TA (HEK293-TA-Lv-T7) and SW620 (SW620-Lv-T7) cell lines, evidenced by the expression of T7 RNAP after subsequent 20 passages. rNDV was rescued successfully using HEK293-TA-Lv-T7 clones (R1D3, R1D8, R5B9) and SW620-Lv-T7 clones (R1C11, R3C5) by reverse transfection, yielding comparable virus rescue efficiency and virus titres to that of BSR T7/5. This study provides new tools for rNDV rescue and insights into cell line development and virology by reverse genetics.

Structure analysis of the nucleoprotein of Newcastle disease virus: An insight towards its multimeric form in solution

Newcastle disease virus (NDV) has been explored to a great extent to understand the biology of negative-sense RNA viruses. Nucleoprotein (N) is the most abundant protein in the virus particles, and its primary function is to encapsidate the virus genome for its transcription, replication, and packaging. Here, we report the structural investigations of the N protein of NDV (NDV-N) in solution. The N gene of NDV was cloned and expressed in E. coli as a soluble protein of ~53 kDa in size. The FE-TEM imaging of the purified NDV-N displayed a nearly spherical shape with a diameter of 28 nm and the DLS analysis of the purified NDV-N displayed a monodispersed nature, with averaged hydrodynamic radius, 26.5 nm. The conformational behavior of the NDV-N in solution was studied by SAXS analysis, which suggested two ring structures of NDV-N formed by thirteen monomeric units each. Each ring interacts with RNA molecules and forms a large molecule with a size of ~1450 kDa and are stacked on each other in a spiral arrangement. More profound knowledge of the N protein structure will help us in deciphering the control of viral RNA synthesis at the early stage of NDV life-cycle.

Therapeutic potential of Nitazoxanide against Newcastle disease virus: A possible modulation of host cytokines

Newcastle disease (ND) is prevalent among the domesticated and the wild birds and is caused by the avian paramyxovirus serotype-I (APMV-I). It is commonly known to affect chicken, pheasant, ostrich, pigeon and waterfowl. Depending on the virulence, the velogenic NDV strains cause severe respiratory and nervous disorders with a high mortality rate. The live and killed vaccines are available for the prevention of infection in the market, but the drug for the treatment is not available. Nitazoxanide (NTZ), a member of thiazolides, is an antiparasitic drug. In the present study, the effect of NTZ on the NDV replication was explored. The experiments were conducted in chicken fibroblast cells (DF-1), PBMC, embryonated chicken eggs, and two-week old chickens. The inhibition of the NDV was observed upon post-treatment of NTZ at a concentration of ~12.5 μM. Cytokine profiling of the DF-1, PBMC, and chicken embryonic tissue treated with NTZ revealed significant upregulation in all the cytokines studied except for IL-1β in DF-1 cells. It is plausible that NTZ is involved in causing immune-modulatory effects in poultry. NTZ treatment in two weeks old chicken showed significant reduction in NDV replication in trachea, and lungs, respectively, at 72 h post-infection. Encouraging results from the present study warrants repurposing NTZ as a drug for the treatment of viral infection in poultry. It will also pave the way towards understanding of similar effect against other animal pathogens.

Identification of Two Distinct Linear B Cell Epitopes of the Matrix Protein of the Newcastle Disease Virus Vaccine Strain LaSota

Matrix (M) protein of Newcastle disease virus (NDV) is an abundant protein that can induce a robust humoral immune response. However, its antigenic epitopes remain unknown. In this study, we used a pepscan approach to map linear B cell immunodominant epitopes (IDEs) of M protein with NDV-specific chicken antisera. The six epitopes with the highest reactivity by peptide scanning were obtained as IDE candidates. Among them, aa71-85 and aa349-363 were identified by immunological assays with NDV-specific or IDE-specific antisera. The minimal antigenic epitopes of the two IDEs were further characterized as ⁷⁷MIDDKP⁸² and ³⁵⁴HTLAKYNPFK³⁶³. Moreover, an amino acid sequence alignment and immunoblot analysis revealed the conservation of the two IDEs in the M protein of strains of different genotypes. These two IDEs of M protein could be genetically eliminated as negative markers in recombinant NDV for serologically differential diagnosis in the development of marker vaccines.

The Ntail region of nucleocapsid protein is associated with the pathogenicity of pigeon paramyxovirus type 1 in chickens

The nucleoprotein (NP) of pigeon paramyxovirus type 1 (PPMV-1) and other paramyxoviruses plays an important role in virus proliferation. A previous study found that NP is associated with the low pathogenicity of PPMV-1 strains in chickens. Here, we investigated which domain of NP is responsible for regulating the pathogenicity of PPMV-1. We found that the Ntail sequences were more diverse for different viral genotypes compared to Ncore sequences. The chimeric rBJ-SG10Ntail strain caused more severe clinical symptoms than the parental rBJ strain, increased the viral copy number in sampled tissues and induced higher IFN-γ gene expression. This demonstrated that the Ntail sequence plays a role in regulating viral virulence. These findings increase our understanding of the Ntail of NP protein and the virulence factors associated with PPMV-1.

Chimaeric Rift Valley Fever Virus-Like Particle Vaccine Candidate Production in Nicotiana benthamiana

Rift Valley fever virus (RVFV) is an emerging mosquito-borne virus and hemorrhagic fever agent, which causes abortion storms in farmed small ruminants and potentially causes miscarriages in humans. Although live-attenuated vaccines are available for animals, they can only be used in endemic areas and there are currently no commercially available vaccines for humans. Here the authors describe the production of chimaeric RVFV virus-like particles transiently expressed in Nicotiana benthamiana by Agrobacterium tumefaciens-mediated gene transfer. The glycoprotein (Gn) gene is modified by removing its ectodomain (Gne) and fusing it to the transmembrane domain and cytosolic tail-encoding region of avian influenza H5N1 hemagglutinin. This is expressed transiently in N. benthamiana with purified protein yields calculated to be ≈57 mg kg-1 fresh weight. Transmission electron microscopy shows putative chimaeric RVFV Gne-HA particles of 49-60 nm which are immunogenic, eliciting Gn-specific antibody responses in vaccinated mice without the use of adjuvant. To our knowledge, this is the first demonstration of the synthesis of Gne-HA chimaeric RVFV VLPs and the first demonstration of a detectable yield of RVFV Gn in plants.

Expression and serological application of recombinant epitope-repeat protein carrying an immunodominant epitope of Newcastle disease virus nucleoprotein

Purpose

The aim of the present study was to develop a serodiagnostic test for differentiation infected from vaccinated animal (DIVA) strategy accompanying the marker vaccine lacking an immunodominant epitope (IDE) of nucleoprotein of Newcastle disease virus (NDV).

Materials and Methods

Recombinant epitope-repeat protein (rERP) gene encoding eight repeats of the IDE sequence (ETQFLDLMRAVANSMR) by tetra-glycine linker was synthesized. Recombinant baculovirus carrying the rERP gene was generated to express the rERP in insect cells. Specificity and sensitivity of an indirect enzyme-linked immunosorbent assay (ELISA) employing the rERP was evaluated.

Results

The rERP with molecular weight of 20 kDa was successfully expressed by the recombinant baculovirus in an insect-baculovirus system. The rERP was antigenically functional as demonstrated by Western blotting. An indirect ELISA employing the rERP was developed and its specificity and sensitivity was determined. The ELISA test allowed discrimination of NDV infected sera from epitope deletion virus vaccinated sera.

Conclusion

The preliminary results represent rERP ELISA as a promising DIVA diagnostic tool.

Genetic Changes in Pigeon Paramyxovirus Type-1 Induced by Serial Passages in Chickens and Microscopic Lesions Caused by the Virus in Various Avian Hosts

INTRODUCTION

Genotype VI of avian avulavirus 1 (AAvV-1) has pigeons and doves as its reservoir and is often termed pigeon paramyxovirus type-1 (PPMV-1). The pathogenesis of PPMV-1 infections in poultry is largely obscure. It is known that PPMV-1 requires a series of passages in chickens before it becomes adapted to gallinaceous poultry.

MATERIAL AND METHODS

Changes in the genome of PPMV-1 were analysed after serial passages in specific pathogen free (SPF) chickens, using high-throughput sequencing. Additionally, histopathological lesions induced by PPMV-1 in experimentally inoculated pigeons, chickens, and turkeys were evaluated.

RESULTS

Following six passages of PPMV-1 in chickens, 10 nonsynonymous substitutions were found including one (in the NP protein) which dominated the genetic pool of viral quasispecies. Histopathological changes induced by the post-passage PPMV-1 strain were more prominent than changes wrought by the pre-passaged PPMV-1 strain and the lesions were most intense in pigeons followed by chickens and turkeys.

CONCLUSION

PPMV-1 is highly adapted to pigeons and passaging through chickens results in the acquisition of novel amino acids in the polymerase complex, which may alter the pathogenic potential of the virus.

Analysis of molecular evolution of nucleocapsid protein in Newcastle disease virus

The present study investigated the molecular evolution of nucleocapsid protein (NP) in different Newcastle disease virus (NDV) genotypes. The evolutionary timescale and rate were estimated using the Bayesian Markov chain Monte Carlo (MCMC) method. The p-distance, Bayesian skyline plot (BSP), and positively selected sites were also analyzed. The MCMC tree indicated that NDV diverged about 250 years ago with a rapid evolution rate (1.059 × 10^-2 substitutions/site/year) and that different NDV genotypes formed three lineages. The p-distance results reflected the great genetic diversity of NDV. BSP analysis suggested that the effective population size of NDV has been increasing since 2000 and that the basic reproductive number (R₀) of NDV ranged from 1.003 to 1.006. The abundance of negatively selected sites in the NP and the mean dN/dS value of 0.07 indicated that the NP of NDV may have undergone purifying selection. However, the predicted positively selected site at position 370 was located in the known effective epitopic region of the NP. In conclusion, although NDV evolved at a high rate and showed great genetic diversity, the structure and function of the NP had been well conserved. However, R₀>1 suggests that NDV might have been causing an epidemic since the time of radiation.

The role of vaccination in risk mitigation and control of Newcastle disease in poultry

Newcastle disease is regarded as one of the most important avian diseases throughout the world and continues to be a threat and economic burden to the poultry industry. With no effective treatment, poultry producers rely primarily on stringent biosecurity and vaccination regimens to control the spread of this devastating disease. This concise review provides an historical perspective of Newcastle disease vaccination and how fundamental research has paved the way for the development of instrumental techniques which are still in use today. Although vaccination programmes have reduced the impact of clinical disease, they have historically been ineffective in controlling the spread of virulent viruses and therefore do not always offer an adequate solution to the world's food security problems. However, the continued development of novel vaccine technology and improved biosecurity measures through education may offer a solution to help reduce the global threat of Newcastle disease on the poultry industry.

Identification of Optimal Insertion Site in Recombinant Newcastle Disease Virus (rNDV) Vector Expressing Foreign Gene to Enhance Its Anti-Tumor Effect

Recombinant Newcastle disease virus (rNDV) is tumor selective and intrinsically oncolytic, which has been developed as a vector to express exogenous genes to enhance its oncolytic efficacy. Our previous studies found that insertion sites of foreign gene in rNDV vector affected its expression and anti-tumor activities. However, the optimal insertion site for foreign genes remains unknown. In this study, we inserted the enhanced green fluorescence protein (EGFP) and IL2 genes into four different intergenic regions of the rNDV using reverse genetics technology. Recombinants rNDV-EGFPs and rNDV-IL2s were successfully rescued, which displayed the similar growth kinetics with parental virus. Both EGFP mRNA and protein levels were most abundant in HepG2 cells, when EGFP gene was inserted between the NP/P site of the rNDV. Similarly, the IL-2 expressed by HepG2 cells infected with rNDV-IL2 was highest, when IL2 was inserted into NP/P site. To test whether these rNDVs that express higher foreign genes could induce stronger anti-tumor response, we treated the H22-oxter-tumor-bearing C57BL/6J mice with rNDV-IL2s and then examined the oncolytic efficacy. The results showed that rNDV-IL2-NP/P had the strongest inhibition of murine hepatoma carcinoma tumors. The splenocytes isolated from the mice treated with rNDV-IL2-NP/P reached the highest degrees of CD4+ T and CD8+ T cells. In addition, animals' survival rate in rNDV-IL2-NP/P-treated group was higher than that of other groups. Taken together, these results demonstrate that NP and P gene junction in rNDV is the optimal insertion site for foreign genes expression to enhance rNDV's anti-tumor effects.

Generation and evaluation of a chimeric classical swine fever virus expressing a visible marker gene

Classical swine fever virus (CSFV) is a noncytopathogenic virus, and the incorporation of an enhanced green fluorescent protein (EGFP) tag into the viral genome provides a means of direct monitoring of viral infection without immunostaining. It is well established that the 3' untranslated region (3'-UTR) of the CSFV plays an important role in viral RNA replication. Although CSFV carrying a reporter gene and chimeric CSFV have been generated and evaluated, a chimeric CSFV with a visible marker has not yet been reported. Here, we generated and evaluated a chimeric virus containing the EGFP tag and the 3'-UTR from vaccine strain HCLV (C-strain) in the genetic background of the highly virulent CSFV Shimen strain. The chimeric marker CSFV was fluorescent and had an approximately 100-fold lower viral titer, lower replication level of viral genome, and weaker fluorescence intensity than the recombinant CSFV with only the EGFP tag or the parental virus. Furthermore, the marker chimera was avirulent and displayed no viremia in inoculated pigs, which were completely protected from lethal CSFV challenge as early as 15 days post-inoculation. The chimeric marker virus was visible in vitro and attenuated in vitro and in vivo, which suggests that CSFV can be engineered to produce attenuated variants with a visible marker to facilitate in vitro studies of CSFV infection and replication and to develop of novel vaccines against CSF.

Spectrum of Newcastle disease virus stability in gradients of temperature and pH

Newcastle disease (ND) is one of the highly pathogenic viral diseases of avian species. The disease is endemic in many developing countries where agriculture serves as the primary source of national income. Newcastle disease virus (NDV) belongs to the family Paramyxoviridae and is well characterized member among the avian paramyxovirus serotypes. The failure of vaccination is one of the major causes of NDV outbreaks in field condition. The present study gives a brief picture about the biology of NDV genome and its proteins under different conditions of temperature and pH. Our results indicate that the NDV is non-infective above 42 °C and unstable above 72 °C. The study will be useful in defining an optimum storage condition for NDV without causing any deterioration in its viability.

Newcastle disease virus: current status and our understanding

Newcastle disease (ND) is one of the highly pathogenic viral diseases of avian species. ND is economically significant because of the huge mortality and morbidity associated with it. The disease is endemic in many third world countries where agriculture serves as the primary source of national income. Newcastle disease virus (NDV) belongs to the family Paramyxoviridae and is well characterized member among the avian paramyxovirus serotypes. In recent years, NDV has lured the virologists not only because of its pathogenic potential, but also for its oncolytic activity and its use as a vaccine vector for both humans and animals. The NDV based recombinant vaccine offers a pertinent choice for the construction of live attenuated vaccine due to its modular nature of transcription, minimum recombination frequency, and lack of DNA phase during replication. Our current understanding about the NDV biology is expanding rapidly because of the availability of modern molecular biology tools and high-throughput complete genome sequencing.

Recombinant DNA technology for producing new rinderpest virus vaccines

With few exceptions, vaccination aims to control rather than eliminate or eradicate disease. The eradication of smallpox in the 1970s led to two other human diseases, polio and measles, being targeted for eradication by the World Health Organization. In general, animal diseases are ignored by the public, however, recent targeting of the rinderpest virus, the agent of cattle plague, has put this virus on the verge of global extinction. For centuries, this virus was responsible for major cattle plagues in Europe, Asia and Africa. The success of the Global Rinderpest Eradication Program is an illustration of the power of vaccines to alter people's lives economically and socially when used in an internationally coordinated way. In this review, the history of the development of rinderpest vaccines and the new research being undertaken to produce marker vaccines, using recombinant DNA technology and reverse genetics, are described. In addition, the valuable contribution that marker vaccines can make in the final stages of the rinderpest eradication program is outlined.

Virus-like particles: promising platforms with characteristics of DIVA for veterinary vaccine design

In general, it is difficult to differentiate infected from vaccinated animals through vaccination with conventional vaccines, thereby impeding the serological surveillance of animal diseases. DIVA (differentiating infected from vaccinated animals) vaccine, originally known as marker vaccine, usually based on the absence of at least one immunogenic protein in the vaccine strain, allows DIVA in conjunction with a diagnostic test that detects antibodies against the antigens lacking in the vaccine strain. Virus-like particles (VLPs), composed of one or more structural proteins but no genomes of native viruses, mimic the organization and conformation of authentic virions but have no ability to self-replicate in cells, potentially yielding safer vaccine candidates. Since VLPs containing either monovalent or multivalent antigen can be produced in compliance with the requirements for serological surveillance, the use of VLP-based vaccines plays a promising role in DIVA vaccination strategies against animal diseases. Here, we critically reviewed VLPs and companion diagnostics with properties of DIVA for veterinary vaccine design, and three different VLPs as promising platforms for DIVA vaccination strategies in animals.

Paramyxovirus fusion and entry: multiple paths to a common end

The paramyxovirus family contains many common human pathogenic viruses, including measles, mumps, the parainfluenza viruses, respiratory syncytial virus, human metapneumovirus, and the zoonotic henipaviruses, Hendra and Nipah. While the expression of a type 1 fusion protein and a type 2 attachment protein is common to all paramyxoviruses, there is considerable variation in viral attachment, the activation and triggering of the fusion protein, and the process of viral entry. In this review, we discuss recent advances in the understanding of paramyxovirus F protein-mediated membrane fusion, an essential process in viral infectivity. We also review the role of the other surface glycoproteins in receptor binding and viral entry, and the implications for viral infection. Throughout, we concentrate on the commonalities and differences in fusion triggering and viral entry among the members of the family. Finally, we highlight key unanswered questions and how further studies can identify novel targets for the development of therapeutic treatments against these human pathogens.

A mutant of Asia 1 serotype of Foot-and-mouth disease virus with the deletion of an important antigenic epitope in the 3A protein

Foot-and-mouth disease is a highly contagious viral disease of cloven-hoofed animals. The availability of a vaccine for differentiating infected from vaccinated animals (DIVA) is crucial for the control and eradication of Foot-and-mouth disease virus (FMDV). Because traditional inactivated vaccines may contain trace nonstructural proteins interfering with the DIVA, we hypothesized that mutant FMDV with deletion of immunodominant epitopes may be valuable. Our previous study has generated a full-length cDNA clone (pBSAs) of FMDV serotype Asia 1 isolated in China. In this study, a B-cell epitope was identified in the 3A region of a nonstructural protein (NSP) by anti-FMDV cattle sera. Furthermore, we generated recombinant FMDV (rvAs-3A14D) by selectively deleting 14 amino acids (position 91–104) in the 3A region of the NSP. Following in vitro transcription and transfection in BHK-21 cells, we successfully rescued the rvAs-3A14D from BHK-21 cells. Characterization of the rvAs-3A14D revealed that the infectivity, antigenicity, and replication kinetics in BHK-21 cells and virulence in mice of the rvAs-3A14D were similar to that of its parent virus. Notably, the mutant rvAs-3A14D only replicated well in BHK-21 but did poorly in primary calf kidney cells. These data suggest that the recombinant FMDV with deletion of this epitope in the NSP may be potentially used as a candidate inactivated vaccine. Therefore, the application of the marker vaccine and differential diagnostic tests may open a promising new avenue for the development of a vaccine for DIVA.

Recombinant infectious bursal disease virus carrying hepatitis C virus epitopes

The delivery of foreign epitopes by a replicating nonpathogenic avian infectious bursal disease virus (IBDV) was explored. The aim of the study was to identify regions in the IBDV genome that are amenable to the introduction of a sequence encoding a foreign peptide. By using a cDNA-based reverse genetics system, insertions or substitutions of sequences encoding epitope tags (FLAG, c-Myc, or hepatitis C virus epitopes) were engineered in the open reading frames of a nonstructural protein (VP5) and the capsid protein (VP2). Attempts were also made to generate recombinant IBDV that displayed foreign epitopes in the exposed loops (P(BC) and P(HI)) of the VP2 trimer. We successfully recovered recombinant IBDVs expressing c-Myc and two different virus-neutralizing epitopes of human hepatitis C virus (HCV) envelope glycoprotein E in the VP5 region. Western blot analyses with anti-c-Myc and anti-HCV antibodies provided positive identification of both the c-Myc and HCV epitopes that were fused to the N terminus of VP5. Genetic analysis showed that the recombinants carrying the c-Myc/HCV epitopes maintained the foreign gene sequences and were stable after several passages in Vero and 293T cells. This is the first report describing efficient expression of foreign peptides from a replication-competent IBDV and demonstrates the potential of this virus as a vector.

Molecular characterization of partial fusion gene and C-terminus extension length of haemagglutinin-neuraminidase gene of recently isolated Newcastle disease virus isolates in Malaysia

Background

Newcastle disease (ND), caused by Newcastle disease virus (NDV), is a highly contagious disease of birds and has been one of the major causes of economic losses in the poultry industry. Despite routine vaccination programs, sporadic cases have occasionally occurred in the country and remain a constant threat to commercial poultry. Hence, the present study was aimed to characterize NDV isolates obtained from clinical cases in various locations of Malaysia between 2004 and 2007 based on sequence and phylogenetic analysis of partial F gene and C-terminus extension length of HN gene.

Results

The coding region of eleven NDV isolates fusion (F) gene and carboxyl terminal region of haemagglutinin-neuraminidase (HN) gene including extensions were amplified by reverse transcriptase PCR and directly sequenced. All the isolates have shown to have non-synonymous to synonymous base substitution rate ranging between 0.081 - 0.264 demonstrating presence of negative selection. Analysis based on F gene showed the characterized isolates possess three different types of protease cleavage site motifs; namely ¹¹²RRQKRF¹¹⁷, ¹¹²RRRKRF¹¹⁷ and ¹¹²GRQGRL¹¹⁷ and appear to show maximum identities with isolates in the region such as cockatoo/14698/90 (Indonesia), Ch/2000 (China), local isolate AF2240 indicating the high similarity of isolates circulating in the South East Asian countries. Meanwhile, one of the isolates resembles commonly used lentogenic vaccine strains. On further characterization of the HN gene, Malaysian isolates had C-terminus extensions of 0, 6 and 11 amino acids. Analysis of the phylogenetic tree revealed that the existence of three genetic groups; namely, genotype II, VII and VIII.

Conclusions

The study concluded that the occurrence of three types of NDV genotypes and presence of varied carboxyl terminus extension lengths among Malaysian isolates incriminated for sporadic cases.

The PRRSV replicase: exploring the multifunctionality of an intriguing set of nonstructural proteins

Our knowledge about the structure and function of the nonstructural proteins (nsps) encoded by the arterivirus replicase gene has advanced in recent years. The continued characterization of the nsps of the arterivirus prototype equine arteritis virus has not only corroborated several important functional predictions, but also revealed various novel features of arteriviral replication. For porcine reproductive and respiratory syndrome virus (PRRSV), based on bioinformatics predictions and experimental studies, a processing map for the pp1a and pp1ab replicase polyproteins has been developed. Crystal structures have been resolved for two of the PRRSV nonstructural proteins that possess proteinase activity (nsp1α and nsp4). The functional characterization of the key enzymes for arterivirus RNA synthesis, the nsp9 RNA polymerase and nsp10 helicase, has been initiated. In addition, progress has been made on nsp functions relating to the regulation of subgenomic mRNAs synthesis (nsp1), the induction of replication-associated membrane rearrangements (nsp2 and nsp3), and an intriguing replicative endoribonuclease (nsp11) for which the natural substrate remains to be identified. The role of nsps in viral pathogenesis and host immunity is also being explored, and specific nsps (including nsp1α/β, nsp2, nsp4, nsp7, and nsp11) have been implicated in the modulation of host immune responses to PRRSV infection. The nsp3–8 region was identified as containing major virulence factors, although mechanistic information is scarce. The biological significance of PRRSV nsps in virus-host interactions and the technical advancements in engineering the PRRSV genome by reverse genetics are also reflected in recent developments in the area of vaccines and diagnostic assays.

Development and characterization of monoclonal antibodies against Rift Valley fever virus nucleocapsid protein generated by DNA immunization

This paper describes the generation of monoclonal antibodies directed to immunogenic nucleoprotein N epitopes of Rift Valley fever virus (RVFV), and their application in diagnostics, both for antibody detection in competitive ELISA and for antigen capture in a sandwich ELISA. Monoclonal antibodies (mAbs) were generated after DNA immunization of Balb/c mice and characterized by western blot, ELISA and cell immunostaining assays. At least three different immunorelevant epitopes were defined by mAb competition assays. Interestingly, two of the mAbs generated were able to distinguish between RVFV strains from Egyptian or South African lineages. These monoclonal antibodies constitute useful tools for diagnosis, especially for the detection of serum anti-RVFV antibodies from a broad range of species by means of competitive ELISA.

Marker vaccine potential of a foot-and-mouth disease virus with a partial VP1 G-H loop deletion

Previous work in cattle and pigs demonstrated that protection against foot-and-mouth disease (FMD) could be achieved following vaccination with chimeric foot-and-mouth disease virus (FMDV) vaccines, in which the VP1 G-H loop had been substituted with that from another serotype. This indicated that the VP1 G-H loop may not be essential for the protection of natural hosts against FMDV. If this could be substantiated there would be potential to develop FMD marker vaccines, characterised by the absence of this region. Here, we investigate the serological responses to vaccination with a virus with a partial VP1 G-H loop deletion in order to determine the likelihood of achieving protection and the potential of this virus as a marker vaccine. Inactivated, oil adjuvanted, vaccines, consisting of chemically inactivated virus with or without a partially deleted VP1 G-H loop, were used to immunise cattle. Serum was collected on days 0, 7, 14 and 21 and antibody titres calculated using the virus neutralisation test (VNT) to estimate the likelihood of protection. We predict a good likelihood that cattle vaccinated with a vaccine characterised by a partial VP1 G-H loop would be protected against challenge with the same virus containing the VP1 G-H loop. We also present evidence on the potential of such a construct to act as a marker vaccine, when used in conjunction with a novel serological test.

Antigen delivery systems for veterinary vaccine development. Viral-vector based delivery systems

The recent advances in molecular genetics, pathogenesis and immunology have provided an optimal framework for developing novel approaches in the rational design of vaccines effective against viral epizootic diseases. This paper reviews most of the viral-vector based antigen delivery systems (ADSs) recently developed for vaccine testing in veterinary species, including attenuated virus and DNA and RNA viral vectors. Besides their usefulness in vaccinology, these ADSs constitute invaluable tools to researchers for understanding the nature of protective responses in different species, opening the possibility of modulating or potentiating relevant immune mechanisms involved in protection.

Immunoprophylaxis against important virus disease of horses, farm animals and birds

Since the refinement of tissue culture techniques for virus isolation and propagation from the mid 1960s onwards, veterinary virology has received much academic and industrial interest, and has now become a major global industry largely centred on vaccine development against economically important virus diseases of food animals. Bio-tech approaches have been widely used for improved vaccines development. While many viral diseases are controlled through vaccination, many still lack safe and efficacious vaccines. Additional challenges faced by academia, industry and governments are likely to come from viruses jumping species and also from the emergence of virulent variants of established viruses due to natural mutations. Also viral ecology is changing as the respective vectors adapt to new habitats as has been shown in the recent incursion by bluetongue virus into Europe. In this paper the current vaccines for livestock, horses and birds are described in a species by species order. The new promising bio-tech approaches using reverse genetics, non-replicating viral vectors, alpha virus vectors and genetic vaccines in conjunction with better adjuvants and better ways of vaccine delivery are discussed as well

Development of genetic markers in the non-structural protein 2 region of a US type 1 porcine reproductive and respiratory syndrome virus: implications for future recombinant marker vaccine development

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to be a major problem in the pork industry worldwide. The limitations of current PRRSV vaccines require the development of a new generation of vaccines. One of the key steps in future vaccine development is to include markers for diagnostic differentiation of vaccinated animals from those naturally infected with wild-type virus. Using a cDNA infectious clone of type 1 PRRSV, this study constructed a recombinant green fluorescent protein (GFP)-tagged PRRSV containing a deletion of an immunogenic epitope, ES4, in the nsp2 region. In a nursery pig disease model, the recombinant virus was attenuated with a lower level of viraemia in comparison with that of the parental virus. To complement the marker identification, GFP and ES4 epitope-based ELISAs were developed. Pigs immunized with the recombinant virus lacked antibodies directed against the corresponding deleted epitope, but generated a high-level antibody response to GFP by 14 days post-infection. These results demonstrated that this recombinant marker virus, in conjunction with the diagnostic tests, enables serological differentiation between marker virus-infected animals and those infected with the wild-type virus. This rationally designed marker virus will provide a basis for further development of PRRSV marker vaccines to assist with the control of PRRS.

Characterization of a recombinant Newcastle disease virus vaccine strain

A recombinant La Sota strain (KBNP-C4152R2L) in which fusion (F) and hemagglutinin-neuraminidase (HN) genes were replaced with those of a contemporary genotype VIId virus, KBNP-4152, has been developed. To attenuate the virulence of the recombinant strain, the F cleavage motif was mutated from (112)RRQKR(116) to (112)GRQAR(116), and to reduce pathogenic instability, a codon which does not allow changes to basic amino acids by single point mutation was inserted at codon 115. In addition a six-nucleotide sequence was inserted into the intergenic region between matrix protein and F genes for attenuation without breaking the "rule-of-six." The HN protein length was increased from 571 to 577 as a marker. Serological tests revealed that the antigenicity of KBNP-C4152R2L was similar to that of KBNP-4152 but distinct from that of the La Sota strain. KBNP-C4152R2L was avirulent (intracerebral pathogenicity index, 0.0; mean death time, >168 h) and stable in pathogenicity through in vivo passages. The killed oil emulsion of and live KBNP-C4152R2L were completely protective against mortality and egg drop caused by virulent strains, and KBNP-C4152R2L was applicable to in ovo vaccination. Therefore, KBNP-C4152R2L is a promising vaccine strain and viral vector in terms of antigenicity, productivity, safety, and pathogenic stability.

Priming with DNA plasmids encoding the nucleocapsid protein and glycoprotein precursors from Rift Valley fever virus accelerates the immune responses induced by an attenuated vaccine in sheep

In this work we tested the ability of plasmid DNA constructs encoding structural Rift Valley fever virus (RVFV) antigens to induce specific immune responses in sheep. The sole immunization of DNA constructs encoding the glycoprotein precursor NSm/G2/G1 did not suffice to induce a detectable antibody response. In contrast, immunization of sheep with a plasmid vector encoding the viral nucleocapsid protein N elicited a potent and long lasting induction of antibodies but with low neutralizing titers. After DNA immunization, no antigen-specific proliferating cells were detected in sheep PBLs. Boosting with the attenuated vaccine strain MP12 was able to increase the levels of proliferating memory cell pools and induction of IFN-gamma in response to purified virus or recombinant proteins, particularly in sheep vaccinated with a combination of both plasmid constructs. These results open the possibility to exploit this strategy to improve the induction of immune responses against RVFV in sheep.

Localization of the antigenic sites of newcastle disease virus nucleocapsid using a panel of monoclonal antibodies

A panel of six monoclonal antibodies (mAbs) against the nucleocapsid (NP) protein of Newcastle disease virus (NDV) was produced by immunization of Balb/c mice with purified recombinant NP protein. Western Blot analysis showed that all the mAbs recognized linearized NP epitopes. Three different NP antigenic sites were identified using deleted truncated NP mutants purified from Escherichia coli. One of the antigenic sites was located at the C-terminal end (residues 441 to 489) of the NP protein. Two other antigenic sites were located within the N-terminal end (residues 26-121 and 122-375). This study demonstrates that the N- and C-terminal ends of the NP proteins are responsible in eliciting immune response, thus it is most likely that these ends are exposed on the NP.

Development of a porcine reproductive and respiratory syndrome virus differentiable (DIVA) strain through deletion of specific immunodominant epitopes

The availability of a DIVA (differentiating infected from vaccinated animals) vaccine is very important for the control and eradication of endemic infectious diseases such as porcine reproductive and respiratory syndrome (PRRS). Previous studies in our laboratory identified several B-cell linear epitopes consistently recognized by convalescent sera obtained from pigs infected with a North American porcine reproductive and respiratory syndrome virus (PRRSV) strain. To ascertain if one or more of these immunodominant epitopes can be used as the basis of DIVA differentiation, we selected two epitope markers previously identified on the non-structural protein 2 (PRRSV NSP2, predictably the viral protein most likely to tolerate large deletions). The choice of these epitopes was primarily based on their immunodominance and their deletion were performed along the backbone of the wild-type cDNA infectious clone (FL12). We were able to successfully rescue a mutant that fulfilled the requirements for a DIVA marker strain, such as: efficient growth of the deletion mutant in vitro and in vivo and induction of specific seroconversion as measured by a commercial ELISA kit, with absence of a marker-specific peptide-ELISA response in 100% (n=15) of the inoculated animals. In summary, our results provide proof of concept that DIVA PRRSV vaccines can potentially be developed by deletion of individual "marker" immunodominant epitopes.

Rescue of a chimeric rinderpest virus with the nucleocapsid protein derived from peste-des-petits-ruminants virus: use as a marker vaccine

The nucleocapsid (N) protein of all morbilliviruses has a highly conserved central region that is thought to interact with and encapsidate the viral RNA. The C-terminal third of the N protein is highly variable among morbilliviruses and is thought to be located on the outer surface and to be available to interact with other viral proteins such as the phosphoprotein, the polymerase protein and the matrix protein. Using reverse genetics, a chimeric rinderpest virus (RPV)/peste-des-petits-ruminants virus (PPRV) was rescued in which the RPV N gene open reading frame had been replaced with that of PPRV (RPV-PPRN). The chimeric virus maintained efficient replication in cell culture. Cattle vaccinated with this chimeric vaccine showed no adverse reaction and were protected from subsequent challenge with wild-type RPV, indicating it to be a safe and efficacious vaccine. The carboxyl-terminal variable region of the rinderpest N protein was cloned and expressed in Escherichia coli. The expressed protein was used to develop an indirect ELISA that could clearly differentiate between RPV- and PPRV-infected animals. The possibility of using this virus as a marker vaccine in association with a new diagnostic ELISA in the rinderpest eradication programme is discussed.

Analyses of the results of different test systems in the 2005 global proficiency testing schemes for infectious bursal disease virus and Newcastle disease virus antibody detection in chicken serum

The results of global proficiency testing schemes (PTS) for serological tests to detect antibodies against infectious bursal disease virus (IBDV) and Newcastle disease virus (NDV) in chicken serum, in which 125 and 120 laboratories, respectively, participated from Africa, Asia, Europe, Central and South America, were used to analyse the performances of different antibody test systems such as virus neutralization tests, haemagglutination inhibition tests, enzyme-linked immunosorbent assays and agar gel precipitation tests. All laboratories were asked to carry out their routine diagnostic tests for the detection of IBDV and NDV antibodies as usual. This global ring trial provided a large amount of data on variation within and between laboratories and test systems used worldwide. The data showed that the variation between the quantitative test results of different laboratories (R(between)) using the IBDV virus neutralization tests and the NDV haemagglutination inhibition test was higher (about double) compared with the variation within commercial enzyme-linked immunosorbent assay systems. Although both tests are often referred to and used as the "gold standard" in experimental and scientific studies, official procedures and for the validation of tests, this study shows that there is an urgent need for a global implementation of recommended test procedures and/or the inclusion of international reference sera in these studies.

Serologic marker candidates identified among B-cell linear epitopes of Nsp2 and structural proteins of a North American strain of porcine reproductive and respiratory syndrome virus

We describe B-cell linear epitopes detected by Pepscan in the Nsp2 and all of the structural proteins of a US PRRSV strain, using sera of 15 experimentally infected pigs. The Nsp2 was found to contain the highest frequency of immunodominant epitopes (n = 18) when compared to structural proteins. Ten of these 18 Nsp2 peptides were reactive with 80 to 100% of the examined sera. In the structural proteins, epitopes consistently recognized by immune sera were located at gp2 (n = 2), gp3 (n = 4), gp5 (n = 3), M (n = 2) and N (n = 2). Overall, the highest degree of immunogenicity and conservation was exhibited by two epitopes identified in the C-terminal end of the M protein (ORF6). The antibodies recognizing the immunodominant epitopes of each protein were detected as early as days 7 to 15 pi and remained detectable until the end of the experiment (day 90 pi). These findings have direct implications for PRRSV differential diagnostics and eventual eradication as the identified epitopes may represent serologic marker candidates for differential (DIVA) PRRSV vaccines, derived from infectious cDNA clones.

Identification of epitopes in the nucleocapsid protein of Nipah virus using a linear phage-displayed random peptide library

A random peptide library of heptamers displayed on the surface of M13 bacteriophage was used to identify specific epitopes of antibodies in pooled sera of swine naturally infected by Nipah virus. The selected heptapeptides were aligned with protein sequences of Nipah virus and several putative epitopes were identified within the nucleocapsid protein. A total of 41 of 60 (68%) selected phage clones had inserts resembling a region with the sequence SNRTQGE, located at the C-terminal end (amino acids 503-509) of the nucleocapsid protein. The binding of antibodies in the swine and human antisera to the phage clone was inhibited by a synthetic peptide corresponding to this region. Epitopes identified by phage display are consistent with the predicted antigenic sites for the Nipah virus nucleocapsid protein. The selected phage clone used as a coating antigen discriminated swine and human Nipah virus sera-positive from sera-negative samples exhibiting characteristics, which might be attractive for diagnostic tests.

Rabies virus nucleoprotein as a carrier for foreign antigens

Rabies virus (RV) nucleoprotein (N) tightly encapsidates the genomic and antigenomic RNA of RV to form the viral ribonucleoprotein (RNP) complex. Antigens, such as N, presented in a highly organized structure are sufficient and even desirable to activate B cells to proliferate and produce antibodies. In addition to activating B cells to proliferate, it has been shown that RV N in the RNP complex induces potent T helper cell responses resulting in long-lasting and strong humoral immune responses against RV. The possibility to systematically incorporate foreign genes into the genome of RV and produce a recombinant virus allows us to examine whether the immunogenicity of foreign antigens can be enhanced by incorporation into the RV RNP structure. To test this hypothesis we constructed a recombinant RV expressing a RV N-GFP fusion protein. The chimeric N-GFP fusion protein was efficiently expressed and incorporated into RV RNP and virions. Moreover, the recombinant RNP induces a strong humoral immune response against GFP in mice. In contrast, mice inoculated with GFP alone or a combination of wild-type RV RNPs and GFP did not trigger any GFP-specific humoral responses using the same immunization schedule. These data indicate the usefulness of RV-based vectors as killed vaccines against other infectious diseases.

Generation of a candidate live marker vaccine for equine arteritis virus by deletion of the major virus neutralization domain

Equine arteritis virus (EAV) is an enveloped plus-strand RNA virus of the family Arteriviridae (order Nidovirales) that causes respiratory and reproductive disease in equids. Protective, virus-neutralizing antibodies (VNAb) elicited by infection are directed predominantly against an immunodominant region in the membrane-proximal domain of the viral envelope glycoprotein G(L), allowing recently the establishment of a sensitive peptide enzyme-linked immunosorbent assay (ELISA) based on this particular domain (J. Nugent et al., J. Virol. Methods 90:167-183, 2000). By using an infectious cDNA we have now generated, in the controlled background of a nonvirulent virus, a mutant EAV from which this immunodominant domain was deleted. This virus, EAV-G(L)Delta, replicated to normal titers in culture cells, although at a slower rate than wild-type EAV, and caused an asymptomatic infection in ponies. The antibodies induced neutralized the mutant virus efficiently in vitro but reacted poorly to wild-type EAV strains. Nevertheless, when inoculated subsequently with virulent EAV, the immunized animals, in contrast to nonvaccinated controls, were fully protected against disease; replication of the challenge virus occurred briefly at low though detectable levels. The levels of protection achieved suggest that an immune effector mechanism other than VNAb plays an important role in protection against infection. As expected, infection with EAV-G(L)Delta did not induce a measurable response in our G(L)-peptide ELISA while the challenge infection of the animals clearly did. EAV-G(L)Delta or similar mutants are therefore attractive marker vaccine candidates, enabling serological discrimination between vaccinated and wild-type virus-infected animals.

An overview on the development of newcastle disease virus as an anti-cancer therapy

Newcastle disease virus (NDV) is one of the most economically important avian virus which affects the poultry industry worldwide. Although NDV is being very actively studied in Malaysia, there are still no studies on its potential as an anticancer agent, a new approach to treating cancer known as virotherapy. Currently, a collaborative research is being undertaken between Universiti Putra Malaysia (UPM), Universiti Sains Malaysia (USM) and Majlis Kanser Nasional (MAKNA) in characterising various local NDV isolates as anticancer agent. This paper describes an overview of the research that have been carried out worldwide in the use of NDV for cancer treatment and also some of our findings in characterising local NDVs with oncolytic properties.