Efficient generation of vesicular stomatitis virus (VSV)-pseudotypes bearing morbilliviral glycoproteins and their use in quantifying virus neutralising antibodies

Development and characterization of a novel nanobody with SRMV neutralizing activity

Peste des petits ruminants (PPR) is an acute, contact infectious disease caused by the small ruminant morbillivirus (SRMV), and its morbidity in goats and sheep can be up to 100% with significant mortality. Nanobody generated from camelid animals such as alpaca has attracted wide attention because of its unique advantages compared with conventional antibodies. The main objective of this study was to produce specific nanobodies against SRMV and identify its characteristics. To obtain the coding gene of SRMV-specific nanobodies, we first constructed an immune phage-displayed library from the VHH repertoire of alpaca that was immunized with SRMV-F and -H proteins. By using phage display technology, the target antigen-specific VHHs can be obtained after four consecutive rounds of biopanning. Results showed that the size of this VHH library was 2.26 × 1010 CFU/mL and the SRMV-F and -H specific phage particles were greatly enriched after four rounds of biopanning. The positive phage clones were selected and sequenced, and total of five independent different sequences of SRMV-specific nanobodies were identified. Subsequently, the DNA fragments of the five nanobodies were cloned into E. coli BL21(DE3), respectively, and three of them were successfully expressed and purified. Specificity and affinity towards inactivated SRMV of these purified nanobodies were then evaluated using the ELISA method. Results demonstrated that NbSRMV-1-1, NbSRMV-2-10, and NbSRMV-1-21 showed no cross-reactivity with other antigens, such as inactivated BTV, inactivated FMDV, His-tag labeled protein, and BSA. The ELISA titer of these three nanobodies against inactivated SRMV was up to 1:1000. However, only NbSRMV-1-21 displayed SRMV neutralizing activity at a maximum dilution of 1:4. The results indicate that the nanobodies against SRMV generated in this study could be useful in future applications. This study provided a novel antibody tool and laid a foundation for the treatment and detection of SRMV.

Correlation between pseudotyped virus and authentic virus neutralisation assays, a systematic review and meta-analysis of the literature

Background

The virus neutralization assay is a principal method to assess the efficacy of antibodies in blocking viral entry. Due to biosafety handling requirements of viruses classified as hazard group 3 or 4, pseudotyped viruses can be used as a safer alternative. However, it is often queried how well the results derived from pseudotyped viruses correlate with authentic virus. This systematic review and meta-analysis was designed to comprehensively evaluate the correlation between the two assays.

Methods

Using PubMed and Google Scholar, reports that incorporated neutralisation assays with both pseudotyped virus, authentic virus, and the application of a mathematical formula to assess the relationship between the results, were selected for review. Our searches identified 67 reports, of which 22 underwent a three-level meta-analysis.

Results

The three-level meta-analysis revealed a high level of correlation between pseudotyped viruses and authentic viruses when used in an neutralisation assay. Reports that were not included in the meta-analysis also showed a high degree of correlation, with the exception of lentiviral-based pseudotyped Ebola viruses.

Conclusion

Pseudotyped viruses identified in this report can be used as a surrogate for authentic virus, though care must be taken in considering which pseudotype core to use when generating new uncharacterised pseudotyped viruses.

The evaluation of five serological assays in determining seroconversion to peste des petits ruminants virus in typical and atypical hosts

Peste des petits ruminants (PPR) is an infectious viral disease, primarily of small ruminants such as sheep and goats, but is also known to infect a wide range of wild and domestic Artiodactyls including African buffalo, gazelle, saiga and camels. The livestock-wildlife interface, where free-ranging animals can interact with captive flocks, is the subject of scrutiny as its role in the maintenance and spread of PPR virus (PPRV) is poorly understood. As seroconversion to PPRV indicates previous infection and/or vaccination, the availability of validated serological tools for use in both typical (sheep and goat) and atypical species is essential to support future disease surveillance and control strategies. The virus neutralisation test (VNT) and enzyme-linked immunosorbent assay (ELISA) have been validated using sera from typical host species. Still, the performance of these assays in detecting antibodies from atypical species remains unclear. We examined a large panel of sera (n = 793) from a range of species from multiple countries (sourced 2015-2022) using three tests: VNT, ID VET N-ELISA and AU-PANVAC H-ELISA. A sub-panel (n = 30) was also distributed to two laboratories and tested using the luciferase immunoprecipitation system (LIPS) and a pseudotyped virus neutralisation assay (PVNA). We demonstrate a 75.0-88.0% agreement of positive results for detecting PPRV antibodies in sera from typical species between the VNT and commercial ELISAs, however this decreased to 44.4-62.3% in sera from atypical species, with an inter-species variation. The LIPS and PVNA strongly correlate with the VNT and ELISAs for typical species but vary when testing sera from atypical species.

LRP6 Is a Functional Receptor for Attenuated Canine Distemper Virus

Wild-type canine distemper virus (CDV) is an important pathogen of dogs as well as wildlife that can infect immune and epithelial cells through two known receptors: the signaling lymphocytic activation molecule (SLAM) and nectin-4, respectively. Conversely, the ferret and egg-adapted CDV-Onderstepoort strain (CDV-OP) is employed as an effective vaccine for dogs. CDV-OP also exhibits promising oncolytic properties, such as its abilities to infect and kill multiple cancer cells in vitro. Interestingly, several cancer cells do not express SLAM or nectin-4, suggesting the presence of a yet unknown entry factor for CDV-OP. By conducting a genome-wide CRISPR/Cas9 knockout (KO) screen in CDV-OP-susceptible canine mammary carcinoma P114 cells, which neither express SLAM nor nectin-4, we identified low-density lipoprotein receptor-related protein 6 (LRP6) as a host factor that promotes CDV-OP infectivity. Whereas the genetic ablation of LRP6 rendered cells resistant to infection, ectopic expression in resistant LRP6^KO cells restored susceptibility. Furthermore, multiple functional studies revealed that (i) the overexpression of LRP6 leads to increased cell-cell fusion, (ii) a soluble construct of the viral receptor-binding protein (solHOP) interacts with a soluble form of LRP6 (solLRP6), (iii) an H-OP point mutant that prevents interaction with solLRP6 abrogates cell entry in multiple cell lines once transferred into recombinant viral particles, and (iv) vesicular stomatitis virus (VSV) pseudotyped with CDV-OP envelope glycoproteins loses its infectivity in LRP6^KO cells. Collectively, our study identified LRP6 as the long sought-after cell entry receptor of CDV-OP in multiple cell lines, which set the molecular bases to refine our understanding of viral-cell adaptation and to further investigate its oncolytic properties. IMPORTANCE Oncolytic viruses (OV) have gathered increasing interest in recent years as an alternative option to treat cancers. The Onderstepoort strain of canine distemper virus (CDV-OP), an enveloped RNA virus belonging to the genus Morbillivirus, is employed as a safe and efficient vaccine for dogs against distemper disease. Importantly, although CDV-OP can infect and kill multiple cancer cell lines, the basic mechanisms of entry remain to be elucidated, as most of those transformed cells do not express natural receptors (i.e., SLAM and nectin-4). In this study, using a genome-wide CRISPR/Cas9 knockout screen, we describe the discovery of LRP6 as a novel functional entry receptor for CDV-OP in various cancer cell lines and thereby uncover a basic mechanism of cell culture adaptation. Since LRP6 is upregulated in various cancer types, our data provide important insights in order to further investigate the oncolytic properties of CDV-OP.

Canine Distemper Virus in Tigers (Panthera tigris) and Leopards (P. pardus) in Nepal

From wild dogs (Lycaon pictus) in the Serengeti to tigers (Panthera tigris altaica) in the Russian Far East, canine distemper virus (CDV) has been repeatedly identified as a threat to wild carnivores. Between 2020 and 2022, six Indian leopards (P. pardus fusca) presented to Nepali authorities with fatal neurological disease, consistent with CDV. Here, we report the findings of a serosurvey of wild felids from Nepal. A total of 48 serum samples were tested, comprising 28 Bengal tigers (P. t. tigris) and 20 Indian leopards. Neutralizing antibodies were identified in three tigers and six leopards, equating to seroprevalences of 11% (CI: 2.8-29.3%, n = 28) and 30% (CI: 12.8-54.3%, n = 20), respectively. More than one-third of seropositive animals were symptomatic, and three died within a week of being sampled. The predation of domestic dogs (Canis lupus familiaris) has been posited as a potential route of infection. A comparison of existing diet studies revealed that while leopards in Nepal frequently predate on dogs, tigers do not, potentially supporting this hypothesis. However, further work, including molecular analyses, would be needed to confirm this.

Correlating IgG Levels with Neutralising Antibody Levels to Indicate Clinical Protection in Healthcare Workers at Risk during a Measles Outbreak

The rapid transmission of measles poses a great challenge for measles elimination. Thus, rapid testing is required to screen the health status in the population during measles outbreaks. A pseudotype-based virus neutralisation assay was used to measure neutralising antibody titres in serum samples collected from healthcare workers in Sheffield during the measles outbreak in 2016. Vesicular stomatitis virus (VSV) pseudotypes bearing the haemagglutinin and fusion glycoproteins of measles virus (MeV) and carrying a luciferase marker gene were prepared; the neutralising antibody titre was defined as the dilution resulting in 90% reduction in luciferase activity. Spearman’s correlation coefficients between IgG titres and neutralising antibody levels ranged from 0.40 to 0.55 (p < 0.05) or from 0.71 to 0.79 (p < 0.0001) when the IgG titres were obtained using different testing kits. In addition, the currently used vaccine was observed to cross-neutralise most circulating MeV genotypes. However, the percentage of individuals being “well-protected” was lower than 95%, the target rate of vaccination coverage to eliminate measles. These results demonstrate that the level of clinical protection against measles in individuals could be inferred by IgG titre, as long as a precise correlation has been established between IgG testing and neutralisation assay; moreover, maintaining a high vaccination coverage rate is still necessary for measles elimination.

Evaluation of the effect of maternally derived antibody on response to MMR vaccine in Thai infants

Background

Although the number of measles cases declined globally in response to anti-measles immunisation campaigns, measles has re-emerged. A review of current vaccination policies is required to improve measles elimination strategies.

Methods

A pseudotype-based virus neutralisation assay (PVNA) was used to measure neutralising antibody titres in serum samples collected from Thai infants at six timepoints before and after two-doses of MMR (1&2) vaccination (ClinicalTrials.gov no. NCT02408926). Vesicular stomatitis virus (VSV) luciferase pseudotypes bearing the haemaglutinin (H) and fusion (F) glycoproteins of measles virus (MeV) were prepared. Serial dilutions of serum samples were incubated with VSV (MeV) pseudotypes and plated onto HEK293-human SLAM1 cells; the neutralising antibody titre was defined as the dilution resulting in 90% reduction in luciferase activity.

Results

Neutralising antibody titres in infants born with high levels of maternal immunity (H group) persisted at the time of the first MMR vaccination, and those infants did not respond effectively by developing protective titres. In contrast, infants with lower maternal immunity (L group) developed protective titres of antibody following vaccination. Responses to the second MMR vaccination were significantly higher (P = 0.0171, Wilcoxon signed-rank test) in the H group. The observed correlation between anti-MeV IgG level and neutralising antibody titre in Thai infants indicates the possibility of using rapid IgG testing as a surrogate measure for neutralising activity to define clinical protection levels within populations.

Conclusion

These results demonstrate that varying the timing of the first MMR immunisation according to the level of acquired maternal immunity could increase vaccination immunogenicity and hence accelerate measles eradication.

Production of Recombinant Replication-defective Lentiviruses Bearing the SARS-CoV or SARS-CoV-2 Attachment Spike Glycoprotein and Their Application in Receptor Tropism and Neutralisation Assays

For enveloped viruses, such as SARS-CoV-2, transmission relies on the binding of viral glycoproteins to cellular receptors. Conventionally, this process is recapitulated in the lab by infection of cells with isolated live virus. However, such studies can be restricted due to the availability of high quantities of replication-competent virus, biosafety precautions and associated trained staff. Here, we present a protocol based on pseudotyping to produce recombinant replication-defective lentiviruses bearing the SARS-CoV or SARS-CoV-2 attachment Spike glycoprotein, allowing the investigation of viral entry in a lower-containment facility. Pseudoparticles are produced by cells transiently transfected with plasmids encoding retroviral RNA packaging signals and Gag-Pol proteins, for the reconstitution of lentiviral particles, and a plasmid coding for the viral attachment protein of interest. This approach allows the investigation of different aspects of viral entry, such as the identification of receptor tropism, the prediction of virus host range, and zoonotic transmission potential, as well as the characterisation of antibodies (sera or monoclonal antibodies) and pharmacological inhibitors that can block entry. Graphic abstract: SARS-CoV and SARS-CoV-2 pseudoparticle generation and applications.

Exposure of Wild Sumatran Tiger (Panthera tigris sumatrae) to Canine Distemper Virus

Canine distemper virus (CDV) is recognized as a conservation threat to Amur tigers (Panthera tigris altaica) in Russia, but the risk to other subspecies remains unknown. We detected CDV neutralizing antibodies in nine of 21 wild-caught Sumatran tigers (42.9%), including one sampled on the day of capture, confirming exposure in the wild.

Severe Acute Respiratory Syndrome Coronavirus 2 Serosurveillance in a Patient Population Reveals Differences in Virus Exposure and Antibody-Mediated Immunity According to Host Demography and Healthcare Setting

Identifying drivers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exposure and quantifying population immunity is crucial to prepare for future epidemics. We performed a serial cross-sectional serosurvey throughout the first pandemic wave among patients from the largest health board in Scotland. Screening of 7480 patient serum samples showed a weekly seroprevalence ranging from 0.10% to 8.23% in primary and 0.21% to 17.44% in secondary care, respectively. Neutralization assays showed that highly neutralizing antibodies developed in about half of individuals who tested positive with enzyme-linked immunosorbent assay, mainly among secondary care patients. We estimated the individual probability of SARS-CoV-2 exposure and quantified associated risk factors. We show that secondary care patients, male patients, and 45–64-year-olds exhibit a higher probability of being seropositive. The identification of risk factors and the differences in virus neutralization activity between patient populations provided insights into the patterns of virus exposure during the first pandemic wave and shed light on what to expect in future waves.

Distemper, extinction, and vaccination of the Amur tiger

Canine distemper virus (CDV) has recently emerged as an extinction threat for the endangered Amur tiger (Panthera tigris altaica). CDV is vaccine-preventable, and control strategies could require vaccination of domestic dogs and/or wildlife populations. However, vaccination of endangered wildlife remains controversial, which has led to a focus on interventions in domestic dogs, often assumed to be the source of infection. Effective decision making requires an understanding of the true reservoir dynamics, which poses substantial challenges in remote areas with diverse host communities. We carried out serological, demographic, and phylogenetic studies of dog and wildlife populations in the Russian Far East to show that a number of wildlife species are more important than dogs, both in maintaining CDV and as sources of infection for tigers. Critically, therefore, because CDV circulates among multiple wildlife sources, dog vaccination alone would not be effective at protecting tigers. We show, however, that low-coverage vaccination of tigers themselves is feasible and would produce substantive reductions in extinction risks. Vaccination of endangered wildlife provides a valuable component of conservation strategies for endangered species.

Rhabdoviruses as vectors for vaccines and therapeutics

Appropriate choice of vaccine vector is crucial for effective vaccine development. Rhabdoviral vectors, such as rabies virus and vesicular stomatitis virus, have been used in a variety of vaccine strategies. These viruses have small, easily manipulated genomes that can stably express foreign glycoproteins due to a well-established reverse genetics system for virus recovery. Both viruses have well-described safety profiles and have been demonstrated to be effective vaccine vectors. This review will describe how these Rhabdoviruses can be manipulated for use as vectors, their various applications as vaccines or therapeutics, and the advantages and disadvantages of their use.

Characterisation of SARS-CoV-2 Lentiviral Pseudotypes and Correlation between Pseudotype-Based Neutralisation Assays and Live Virus-Based Micro Neutralisation Assays

The recent outbreak of a novel Coronavirus (SARS-CoV-2) and its rapid spread across the continents has generated an urgent need for assays to detect the neutralising activity of human sera or human monoclonal antibodies against SARS-CoV-2 spike protein and to evaluate the serological immunity in humans. Since the accessibility of live virus microneutralisation (MN) assays with SARS-CoV-2 is limited and requires enhanced bio-containment, the approach based on "pseudotyping" can be considered a useful complement to other serological assays. After fully characterising lentiviral pseudotypes bearing the SARS-CoV-2 spike protein, we employed them in pseudotype-based neutralisation assays in order to profile the neutralising activity of human serum samples from an Italian sero-epidemiological study. The results obtained with pseudotype-based neutralisation assays mirrored those obtained when the same panel of sera was tested against the wild type virus, showing an evident convergence of the pseudotype-based neutralisation and MN results. The overall results lead to the conclusion that the pseudotype-based neutralisation assay is a valid alternative to using the wild-type strain, and although this system needs to be optimised and standardised, it can not only complement the classical serological methods, but also allows serological assessments to be made when other methods cannot be employed, especially in a human pandemic context.

A tool with many applications: vesicular stomatitis virus in research and medicine

INTRODUCTION

Vesicular stomatitis virus (VSV) has long been a useful research tool in virology and recently become an essential part of medicinal products. Vesiculovirus research is growing quickly following its adaptation to clinical gene and cell therapy and oncolytic virotherapy.

AREAS COVERED

This article reviews the versatility of VSV as a research tool and biological reagent, its use as a viral and vaccine vector delivering therapeutic and immunogenic transgenes and an oncolytic virus aiding cancer treatment. Challenges such as the immune response against such advanced therapeutic medicinal products and manufacturing constraints are also discussed.

EXPERT OPINION

The field of in vivo gene and cell therapy is advancing rapidly with VSV used in many ways. Comparison of VSV's use as a versatile therapeutic reagent unveils further prospects and problems for each application. Overcoming immunological challenges to aid repeated administration of viral vectors and minimizing harmful host-vector interactions remains one of the major challenges. In the future, exploitation of reverse genetic tools may assist the creation of recombinant viral variants that have improved onco-selectivity and more efficient vaccine vector activity. This will add to the preferential features of VSV as an excellent advanced therapy medicinal product (ATMP) platform.

Eradication of Peste des Petits Ruminants Virus and the Wildlife-Livestock Interface

Growing evidence suggests that multiple wildlife species can be infected with peste des petits ruminants virus (PPRV), with important consequences for the potential maintenance of PPRV in communities of susceptible hosts, and the threat that PPRV may pose to the conservation of wildlife populations and resilience of ecosystems. Significant knowledge gaps in the epidemiology of PPRV across the ruminant community (wildlife and domestic), and the understanding of infection in wildlife and other atypical host species groups (e.g., camelidae, suidae, and bovinae) hinder our ability to apply necessary integrated disease control and management interventions at the wildlife-livestock interface. Similarly, knowledge gaps limit the inclusion of wildlife in the FAO/OIE Global Strategy for the Control and Eradication of PPR, and the framework of activities in the PPR Global Eradication Programme that lays the foundation for eradicating PPR through national and regional efforts. This article reports on the first international meeting on, "Controlling PPR at the livestock-wildlife interface," held in Rome, Italy, March 27-29, 2019. A large group representing national and international institutions discussed recent advances in our understanding of PPRV in wildlife, identified knowledge gaps and research priorities, and formulated recommendations. The need for a better understanding of PPRV epidemiology at the wildlife-livestock interface to support the integration of wildlife into PPR eradication efforts was highlighted by meeting participants along with the reminder that PPR eradication and wildlife conservation need not be viewed as competing priorities, but instead constitute two requisites of healthy socio-ecological systems.

Production of Pseudotyped Particles to Study Highly Pathogenic Coronaviruses in a Biosafety Level 2 Setting

The protocol aims to generate coronavirus (CoV) spike (S) fusion protein pseudotyped particles with a murine leukemia virus (MLV) core and luciferase reporter, using a simple transfection procedure of the widely available HEK-293T cell line. Once formed and released from producer cells, these pseudovirions incorporate a luciferase reporter gene. Since they only contain the heterologous coronavirus spike protein on their surface, the particles behave like their native coronavirus counterparts for entry steps. As such, they are the excellent surrogates of native virions for studying viral entry into host cells. Upon successful entry and infection into target cells, the luciferase reporter gets integrated into the host cell genome and is expressed. Using a simple luciferase assay, transduced cells can be easily quantified. An important advantage of the procedure is that it can be performed in biosafety level 2 (BSL-2) facilities instead of BSL-3 facilities required for work with highly pathogenic coronaviruses such as Middle East respiratory syndrome coronavirus (MERS-CoV) and severe acute respiratory syndrome coronavirus (SARS-CoV). Another benefit comes from its versatility as it can be applied to envelope proteins belonging to all three classes of viral fusion proteins, such as the class I influenza hemagglutinin (HA) and Ebola virus glycoprotein (GP), the class II Semliki forest virus E1 protein, or the class III vesicular stomatitis virus G glycoprotein. A limitation of the methodology is that it can only recapitulate virus entry steps mediated by the envelope protein being investigated. For studying other viral life cycle steps, other methods are required. Examples of the many applications these pseudotype particles can be used in include investigation of host cell susceptibility and tropism and testing the effects of virus entry inhibitors to dissect viral entry pathways used.

Structure-Guided Identification of a Nonhuman Morbillivirus with Zoonotic Potential

Morbilliviruses infect a broad range of mammalian hosts, including ruminants, carnivores, and humans. The recent eradication of rinderpest virus (RPV) and the active campaigns for eradication of the human-specific measles virus (MeV) have raised significant concerns that the remaining morbilliviruses may emerge in so-called vacated ecological niches. Seeking to assess the zoonotic potential of nonhuman morbilliviruses within human populations, we found that peste des petits ruminants virus (PPRV)-the small-ruminant morbillivirus-is restricted at the point of entry into human cells due to deficient interactions with human SLAMF1-the immune cell receptor for morbilliviruses. Using a structure-guided approach, we characterized a single amino acid change, mapping to the receptor-binding domain in the PPRV hemagglutinin (H) protein, which overcomes this restriction. The same mutation allowed escape from some cross-protective, human patient, anti-MeV antibodies, raising concerns that PPRV is a pathogen with zoonotic potential. Analysis of natural variation within human and ovine SLAMF1 also identified polymorphisms that could correlate with disease resistance. Finally, the mechanistic nature of the PPRV restriction was also investigated, identifying charge incompatibility and steric hindrance between PPRV H and human SLAMF1 proteins. Importantly, this research was performed entirely using surrogate virus entry assays, negating the requirement for in situ derivation of a human-tropic PPRV and illustrating alternative strategies for identifying gain-of-function mutations in viral pathogens.IMPORTANCE A significant proportion of viral pandemics occur following zoonotic transmission events, where animal-associated viruses jump species into human populations. In order to provide forewarnings of the emergence of these viruses, it is necessary to develop a better understanding of what determines virus host range, often at the genetic and structural levels. In this study, we demonstrated that the small-ruminant morbillivirus, a close relative of measles, is unable to use human receptors to enter cells; however, a change of a single amino acid in the virus is sufficient to overcome this restriction. This information will be important for monitoring this virus's evolution in the field. Of note, this study was undertaken in vitro, without generation of a fully infectious virus with this phenotype.

Rapid quantification of vesicular stomatitis virus in Vero cells using Laser Force Cytology

The ability to rapidly and accurately determine viral infectivity can help improve the speed of vaccine product development and manufacturing. Current methods to determine infectious viral titers, such as the end-point dilution (50% tissue culture infective dose, TCID50) and plaque assays are slow, labor intensive, and often subjective. In order to accelerate virus quantification, Laser Force Cytology (LFC) was used to monitor vesicular stomatitis virus (VSV) infection in Vero (African green monkey kidney) cells. LFC uses a combination of optical and fluidic forces to interrogate single cells without the use of labels or antibodies. Using a combination of variables measured by the Radiance™ LFC instrument (LumaCyte), an infection metric was developed that correlates well with the viral titer as measured by TCID50 and shortens the timeframe from infection to titer determination from 3 days to 16 h (a 4.5 fold reduction). A correlation was also developed between in-process cellular measurements and the viral titer of collected supernatant, demonstrating the potential for real-time infectivity measurements. Overall, these results demonstrate the utility of LFC as a tool for rapid infectivity measurements throughout the vaccine development process.

Current status on the development of pseudoviruses for enveloped viruses

Emerging and reemerging infectious diseases have a strong negative impact on public health. However, because many of these pathogens must be handled in biosafety level, 3 or 4 containment laboratories, research and development of antivirals or vaccines against these diseases are often impeded. Alternative approaches to address this issue have been vigorously pursued, particularly the use of pseudoviruses in place of wild‐type viruses. As pseudoviruses have been deprived of certain gene sequences of the virulent virus, they can be handled in biosafety level 2 laboratories. Importantly, the envelopes of these viral particles may have similar conformational structures to those of the wild‐type viruses, making it feasible to conduct mechanistic investigation on viral entry and to evaluate potential neutralizing antibodies. However, a variety of challenging issues remain, including the production of a sufficient pseudovirus yield and the inability to produce an appropriate pseudotype of certain viruses. This review discusses current progress in the development of pseudoviruses and dissects the factors that contribute to low viral yields.

Future research to underpin successful peste des petits ruminants virus (PPRV) eradication

Peste des petits ruminants virus (PPRV) is a significant pathogen of small ruminants and is prevalent in much of Africa, the Near and Middle East and Asia. Despite the availability of an efficacious and cheap live-attenuated vaccine, the virus has continued to spread, with its range stretching from Morocco in the west to China and Mongolia in the east. Some of the world's poorest communities rely on small ruminant farming for subsistence and the continued endemicity of PPRV is a constant threat to their livelihoods. Moreover, PPRV's effects on the world's population are felt broadly across many economic, agricultural and social situations. This far-reaching impact has prompted the Food and Agriculture Organization of the United Nations (FAO) and the World Organisation for Animal Health (OIE) to develop a global strategy for the eradication of this virus and its disease. PPRV is a morbillivirus and, given the experience of these organizations in eradicating the related rinderpest virus, the eradication of PPRV should be feasible. However, there are many critical areas where basic and applied virological research concerning PPRV is lacking. The purpose of this review is to highlight areas where new research could be performed in order to guide and facilitate the eradication programme. These areas include studies on disease transmission and epidemiology, the existence of wildlife reservoirs and the development of next-generation vaccines and diagnostics. With the support of the international virology community, the successful eradication of PPRV can be achieved.

Enhanced immunosurveillance for animal morbilliviruses using vesicular stomatitis virus (VSV) pseudotypes

The measurement of virus-specific neutralising antibodies represents the “gold-standard” for diagnostic serology. For animal morbilliviruses, such as peste des petits ruminants (PPRV) or rinderpest virus (RPV), live virus-based neutralisation tests require high-level biocontainment to prevent the accidental escape of the infectious agents. In this study, we describe the adaptation of a replication-defective vesicular stomatitis virus (VSVΔG) based pseudotyping system for the measurement of neutralising antibodies against animal morbilliviruses. By expressing the haemagglutinin (H) and fusion (F) proteins of PPRV on VSVΔG pseudotypes bearing a luciferase marker gene, neutralising antibody titres could be measured rapidly and with high sensitivity. Serological responses against the four distinct lineages of PPRV could be measured simultaneously and cross-neutralising responses against other morbilliviruses compared. Using this approach, we observed that titres of neutralising antibodies induced by vaccination with live attenuated PPRV were lower than those induced by wild type virus infection and the level of cross-lineage neutralisation varied between vaccinates. By comparing neutralising responses from animals infected with either PPRV or RPV, we found that responses were highest against the homologous virus, indicating that retrospective analyses of serum samples could be used to confirm the nature of the original pathogen to which an animal had been exposed. Accordingly, when screening sera from domestic livestock and wild ruminants in Tanzania, we detected evidence of cross-species infection with PPRV, canine distemper virus (CDV) and a RPV-related bovine morbillivirus, suggesting that exposure to animal morbilliviruses may be more widespread than indicated previously using existing diagnostic techniques.

Protection of Cattle against Rinderpest by Vaccination with Wild-Type but Not Attenuated Strains of Peste des Petits Ruminants Virus

Although rinderpest virus (RPV) has been eradicated in the wild, efforts are still continuing to restrict the extent to which live virus is distributed in facilities around the world and to prepare for any reappearance of the disease, whether through deliberate or accidental release. In an effort to find an alternative vaccine which could be used in place of the traditional live attenuated RPV strains, we have determined whether cattle can be protected from rinderpest by inoculation with vaccine strains of the related morbillivirus, peste des petits ruminants virus (PPRV). Cattle were vaccinated with wild-type PPRV or either of two established PPRV vaccine strains, Nigeria/75/1 or Sungri/96. All animals developed antibody and T cell immune responses to the inoculated PPRV. However, only the animals given wild-type PPRV were protected from RPV challenge. Animals given PPRV/Sungri/96 were only partially protected, and animals given PPRV/Nigeria/75/1 showed no protection against RPV challenge. While sera from animals vaccinated with the vaccine strain of RPV showed cross-neutralizing ability against PPRV, none of the sera from animals vaccinated with any strain of PPRV was able to neutralize RPV although sera from animals inoculated with wild-type PPRV were able to neutralize RPV-pseudotyped vesicular stomatitis virus.

IMPORTANCE

Rinderpest virus has been eradicated, and it is only the second virus for which this is so. Significant efforts are still required to ensure preparedness for a possible escape of RPV from a laboratory or its deliberate release. Since RPV vaccine protects sheep and goats from PPRV, it is important to determine if the reverse is true as this would provide a non-RPV vaccine for dealing with suspected RPV outbreaks. This is probably the last in vivo study with live RPV that will be approved.