Recombinant adenovirus expressing the haemagglutinin of Peste des petits ruminants virus (PPRV) protects goats against challenge with pathogenic virus; a DIVA vaccine for PPR

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.

Creation of poxvirus expressing foot-and-mouth and peste des petits ruminant disease virus proteins

OBJECTIVE

Foot-and-mouth disease (FMD) and Peste des petits ruminant disease (PPR) are acute and severe infectious diseases of sheep and are listed as animal diseases for compulsory immunization. However, there is no dual vaccine to prevent these two diseases. The Modified Vaccinia virus Ankara strain (MVA) has been widely used in the construction of recombinant live vector vaccine because of its large capacity of foreign gene, wide host range, high safety, and immunogenicity. In this study, MVA-GFP recombinant virus skeleton was used to construct dual live vector vaccines against FMD and PPR.

METHODS

The recombinant plasmid pUC57-FMDV P1-2A3CPPRV FH was synthesized and transfected into MVA-GFP infected CEF cells for homologous recombination.

RESULTS

The results showed that a recombinant virus without fluorescent labeling was obtained after multiple rounds of plaque screening. The recombinant virus successfully expressed the target proteins, and the empty capsid of FMDV could be observed by transmission electron microscope (TME), and the expression levels of foreign proteins (VP1 and VP3) detected by ELISA were like those detected in FMDV-infected cells. This study laid the foundation for the successful construction of a live vector vaccine against FMD and PPR.

KEY POINTS

• A recombinant MVA expressing FMDVP12A3C and PRRV HF proteins • Both the FMDV and PRRV proteins inserted into the virus were expressed • The proteins expressed by the recombinant poxvirus were assembled into VLPs.

Construction of Recombinant Rabies Virus Vectors Expressing H or F Protein of Peste des Petits Ruminants Virus

Simple Summary

Peste des petits ruminants (PPR) is one of the most contagious and fatal diseases of small ruminants. In this study, two recombinant viruses rSRV9-H and rSRV9-F, which express the envelope glycoprotein H (hemagglutinin protein) or F (fusion protein) protein, respectively, were successfully generated with a rabies virus as vector. The constructed viruses had good proliferative activity and stability and provided potential bivalent inactivated vaccine candidate strains for the prevention of PPR and livestock rabies.

Abstract

Peste des petits ruminants (PPR) is one of the most contagious and fatal diseases of small ruminants in the world and is classified as a category A epidemic disease. It is the target of a global eradication campaign led by the Office International des Epizooties (OIE) and Food and Agriculture Organization of the United Nations (FAO). The PPR live attenuated vaccine is currently the most widely used and approved vaccine, but the use of this vaccine interferes with the serological testing of the PPR elimination program, and there is a potential safety risk. Viral vector vaccines are one of the most promising methods to solve this dilemma. In this study, the full-length infectious clone plasmid of rabies virus (RABV), pD-SRV9-PM-LASV, was used as the backbone, and the envelope glycoprotein H (hemagglutinin protein) or F (fusion protein) gene of PPRV was inserted into the backbone plasmid to construct the infectious clones pD-SRV9-PM-PPRV-H and pD-SRV9-PM-PPRV-F, which express the PPRV H and PPRV F genes, respectively. The correct construction of these infectious clones was verified after sequencing and double digestion. The infectious clones were transfected with a helper plasmid into BSR/T7 cells, and recombinant viruses were successfully rescued by direct immunofluorescence, indirect immunofluorescence, Western blotting, and transmission electron microscopy and named rSRV9-H and rSRV9-F. The results of growth kinetics studies indicated that the inserted gene did not affect virus proliferation. Stability studies revealed that the inserted target gene was stably expressed in recombinant RABV for at least 15 generations. In this study, the recombinant viruses rSRV9-H and rSRV9-F were successfully rescued. The constructed viruses had good proliferative activity and stability and provided potential bivalent inactivated vaccine candidate strains for the prevention of PPR and livestock rabies.

Immunization With Bovine Herpesvirus-4-Based Vector Delivering PPRV-H Protein Protects Sheep From PPRV Challenge

The Morbillivirus peste des petits ruminants virus (PPRV) is the causal agent of a highly contagious disease that mostly affects sheep and goats and produces considerable losses in developing countries. Current PPRV control strategies rely on live-attenuated vaccines, which are not ideal, as they cannot differentiate infected from vaccinated animals (DIVA). Recombinant vector-based vaccines expressing viral subunits can provide an alternative to conventional vaccines, as they can be easily paired with DIVA diagnostic tools. In the present work, we used the bovine herpesvirus-4-based vector (BoHV-4-A) to deliver PPRV hemagglutinin H antigen (BoHV-4-A-PPRV-H-ΔTK). Vaccination with BoHV-4-A-PPRV-H-ΔTK protected sheep from virulent PPRV challenge and prevented virus shedding. Protection correlated with anti-PPRV IgGs, neutralizing antibodies and IFN-γ-producing cells induced by the vaccine. Detection of antibodies exclusively against H-PPRV in animal sera and not against other PPRV viral proteins such as F or N could serve as a DIVA diagnostic test when using BoHV-4-A-PPRV-H-ΔTK as vaccine. Our data indicate that BoHV-4-A-PPRV-H-ΔTK could be a promising new approach for PPRV eradication programs.

Determination of Intestinal Viral Loads and Distribution of Bovine Viral Diarrhea Virus, Classical Swine Fever Virus, and Peste Des Petits Ruminants Virus: A Pilot Study

The aim of this pilot study was to determine viral loads and distribution over the total length, at short distances, and in the separate layers of the intestine of virus-infected animals for future inactivation studies. Two calves, two pigs, and two goats were infected with bovine viral diarrhoea virus (BVDV), classical swine fever virus (CSFV), and peste des petits ruminants virus (PPRV), respectively. Homogenously distributed maximum BVDV viral loads were detected in the ileum of both calves, with a mean titer of 6.0 log10 TCID50-eq/g. The viral loads in colon and caecum were not distributed homogenously. In one pig, evenly distributed CSFV mean viral loads of 4.5 and 4.2 log10 TCID50-eq/g were found in the small and large intestines, respectively. Mucosa, submucosa, and muscular layer/serosa showed mean viral loads of 5.3, 3.4, and 4.0 log10 TCID50-eq/g, respectively. Homogenous distribution of PPRV was shown in the ileum of both goats, with a mean viral load of 4.6 log10 TCID50-eq/g. Mean mucosa, submucosa, and muscular layer/serosa viral loads were 3.5, 2.8, and 1.7 log10 TCID50-eq/g, respectively. This pilot study provides essential data for setting up inactivation experiments with intestines derived from experimentally infected animals, in which the level and the homogeneous distribution of intestinal viral loads are required.

A New Look at Vaccine Strategies Against PPRV Focused on Adenoviral Candidates

Peste des petits ruminants virus (PPRV) is a virus that mainly infects goats and sheep causing significant economic loss in Africa and Asia, but also posing a serious threat to Europe, as recent outbreaks in Georgia (2016) and Bulgaria (2018) have been reported. In order to carry out the eradication of PPRV, an objective set for 2030 by the Office International des Epizooties (OIE) and the Food and Agriculture Organization of the United Nations (FAO), close collaboration between governments, pharmaceutical companies, farmers and researchers, among others, is needed. Today, more than ever, as seen in the response to the SARS-CoV2 pandemic that we are currently experiencing, these goals are feasible. We summarize in this review the current vaccination approaches against PPRV in the field, discussing their advantages and shortfalls, as well as the development and generation of new vaccination strategies, focusing on the potential use of adenovirus as vaccine platform against PPRV and more broadly against other ruminant pathogens.

Progress towards Eradication of Peste des Petits Ruminants through Vaccination

Peste des petits ruminants (PPR) is a transboundary viral disease that threatens more than 1.74 billion goats and sheep in approximately 70 countries globally. In 2015, the international community set the goal of eradicating PPR by 2030, and, since then, Food and Agriculture Organization of the United Nations (FAO) and World Organization for Animal Health (OIE) have jointly developed and implemented the Global Control and Eradication Strategy for PPR. Here, data from the United Nations Food and Agriculture Organization Statistical Database (FAOSTAT), the OIE World Animal Health Information System (WAHIS), Regional Roadmap Meetings, and countries' responses to PPR Monitoring and Assessment Tool (PMAT) questionnaires were analyzed to inform on current progress towards PPR eradication. OIE recorded the use of over 333 million doses of vaccine in 12 countries from 2015 to 2018, 41.8% of which were used in Asia and 58.2% in Africa. Between 2015 and 2019, a total of 12,757 PPR outbreaks were reported to OIE: 75.1% in Asia, 24.8% in Africa, and 0.1% in Europe. The number of global outbreaks in 2019 fell to 1218, compared with 3688 in 2015. Analysis of vaccine use and PPR outbreaks in countries indicates that disease control strategies, particularly vaccination campaigns and vaccine distribution strategies, still require scientific evaluation. It is imperative that vaccination is undertaken based on the epidemiology of the disease in a region and is coordinated between neighboring countries to restrict transboundary movements. Strengthening surveillance and post-vaccination sero-monitoring at the national level is also essential. The PPR vaccine stock/bank established by FAO, OIE, and other partners have improved the quality assurance and supply of vaccines. However, to achieve PPR eradication, filling the funding gap for vaccination campaigns and other program activities will be critical.

Depletion of CD8+ T cells from vaccinated goats does not affect protection from challenge with wild-type peste des petits ruminants virus

Peste des petits ruminants (PPR) is a severe disease of goats and sheep that is widespread in Africa, the Middle East and Asia. The disease is caused by peste des petits ruminants virus (PPRV); cell culture-attenuated strains of PPRV have been shown, both experimentally and by extensive use in the field, to be effective vaccines and are widely used. We have previously demonstrated that these vaccines elicit both serological (PPRV-specific antibody) and cell-based (PPRV-specific CD4⁺ and CD8⁺ T cells) immune responses. However, it is not known which of these responses are required for protection from PPRV, information that would be useful in the evaluation of new vaccines that are being developed to provide the capability to differentiate infected and vaccinated animals (DIVA capability). To begin to address this issue, we have used a complement-fixing monoclonal antibody recognizing caprine CD8 to deplete >99.9% of circulating CD8⁺ T cells from vaccinated goats. Animals were then infected with wild-type PPRV. Despite the absence of the CD8⁺ T-cell component of the vaccine-induced immune response, the vaccinated animals were almost fully protected, showing no pyrexia or viraemia, and almost no clinical signs. These data suggest that a virus-specific CD8⁺ T-cell response is not critical for protection against PPRV and that virus-specific antibody and/or CD4⁺ T cells are the main mediators of protection. We have also shown that the leucopenia caused by infection with wild-type PPRV affects all major classes of circulating leucocytes.

A Novel Recombinant Newcastle Disease Virus Vectored DIVA Vaccine against Peste des Petits Ruminants in Goats

Peste des petits ruminants virus (PPRV, species: small ruminant morbillivirus) is the causative agent of the eponymous notifiable disease, the peste des petits ruminants (PPR) in wild and domestic sheep and goats. Mortality rates vary between 50% and 100%, causing significant losses of estimated 1.5 to 2 billion US Dollars per year. Live-attenuated PPRV vaccine strains are used in the field for disease prevention, but the application of a more thermostable vaccine enabling differentiation between infected and vaccinated animals (DIVA) would be highly desirable to achieve the goal of global disease eradication. We generated a recombinant Newcastle disease virus (rNDV) based on the live-attenuated NDV Clone 30 that expresses the surface protein hemagglutinin (H) of PPRV strain Kurdistan/11 (rNDV_H_Kur). In vitro analyses confirmed transgene expression as well as virus replication in avian, caprine, and ovine cells. Two consecutive subcutaneous vaccinations of German domestic goats with rNDV_H_Kur prevented clinical signs and hematogenic dissemination after an intranasal challenge with virulent PPRV Kurdistan/11. Virus shedding by different routes was reduced to a similar extent as after vaccination with the live-attenuated PPRV strain Nigeria 75/1. Goats that were either not vaccinated or inoculated with parental rNDV were used as controls. In summary, we demonstrate in a proof-of-concept study that an NDV vectored vaccine can protect against PPR. Furthermore, it provides DIVA-applicability and a high thermal tolerance.

Development of vaccines for prevention of peste-des-petits-ruminants virus infection

Peste des petits ruminants (PPR) is a highly contagious and fatal disease of small ruminants, particularly sheep and goats. This disease leads to high morbidity and mortality of small ruminants, thus resulting in devastating economic loss to the livestock industry globally. The severe disease impact has prompted the Food and Agriculture Organization of the United Nations (FAO) and the World Organization for Animal Health (OIE) to develop a global strategy for the control and eradication of PPR by 2030. Over the past decades, the control of PPR is mainly achieved through vaccinating the animals with live-attenuated vaccines, e.g., rinderpest vaccines. As a closely related disease to PPR of large ruminants, rinderpest was eradicated in 2011 and its vaccines subsequently got banned in order to keep rinderpest-free zones. Consequently, it is desirable to develop homologous PPR vaccines to control the disease. The present review summarizes the objectives of PPR control and eradication by focusing on the homologous PPR vaccines.

Paradigm shift in the diagnosis of peste des petits ruminants: scoping review

Peste des petits ruminants virus causes a highly contagious disease, which poses enormous economic losses in domestic animals and threatens the conservation of wild herbivores. Diagnosis remains a cornerstone to the Peste des petits ruminants Global Control and Eradication Strategy, an initiative of the World Organisation for Animal Health and the Food and Agriculture Organisation. The present review presents the peste des petits ruminants diagnostic landscape, including the practicality of commercially available diagnostic tools, prototype tests and opportunities for new technologies. The most common peste des petits ruminants diagnostic tools include; agar gel immunodiffusion, counter-immunoelectrophoresis, enzyme-linked immunosorbent assays, reverse transcription polymerase chain reaction either gel-based or real-time, reverse transcription loop-mediated isothermal amplification, reverse transcription recombinase polymerase amplification assays, immunochromatographic lateral flow devices, luciferase immunoprecipitation system and pseudotype-based assays. These tests vary in their technical demands, but all require a laboratory with exception of immunochromatographic lateral flow and possibly reverse transcription loop-mediated isothermal amplification and reverse transcription recombinase polymerase amplification assays. Thus, we are proposing an efficient integration of diagnostic tests for rapid and correct identification of peste des petits ruminants in endemic zones and to rapidly confirm outbreaks. Deployment of pen-side tests will improve diagnostic capacity in extremely remote settings and susceptible wildlife ecosystems, where transportation of clinical samples in the optimum cold chain is unreliable.

Safety and efficacy of ChAdOx1 RVF vaccine against Rift Valley fever in pregnant sheep and goats

Rift Valley fever virus (RVFV) is a zoonotic mosquito-borne virus that was first discovered in Kenya in 1930 and has since spread to become endemic in much of Africa and the Arabian Peninsula. Rift Valley fever (RVF) causes recurrent outbreaks of febrile illness associated with high levels of mortality and poor outcomes during pregnancy-including foetal malformations, spontaneous abortion and stillbirths-in livestock, and associated with miscarriage in humans. No vaccines are available for human use and those licensed for veterinary use have potential drawbacks, including residual virulence that may contraindicate their use in pregnancy. To address this gap, we previously developed a simian adenovirus vectored vaccine, ChAdOx1 RVF, that encodes RVFV envelope glycoproteins. ChAdOx1 RVF is fully protective against RVF in non-pregnant livestock and is also under development for human use. Here, we now demonstrate that when administered to pregnant sheep and goats, ChAdOx1 RVF is safe, elicits high titre RVFV neutralizing antibody, and provides protection against viraemia and foetal loss, although this protection is not as robust for the goats. In addition, we provide a description of RVFV challenge in pregnant goats and contrast this to the pathology observed in pregnant sheep. Together, our data further support the ongoing development of ChAdOx1 RVF vaccine for use in livestock and humans.

Toward peste des petits virus (PPRV) eradication: Diagnostic approaches, novel vaccines, and control strategies

Peste des petits ruminants (PPR) is an acute transboundary infectious viral disease affecting domestic and wild small ruminants' species besides camels reared in Africa, Asia and the Middle East. The virus is a serious paramount challenge to the sustainable agriculture advancement in the developing world. The disease outbreak was also detected for the first time in the European Union namely in Bulgaria at 2018. Therefore, the disease has lately been aimed for eradication with the purpose of worldwide clearance by 2030. Radically, the vaccines needed for effectively accomplishing this aim are presently convenient; however, the availableness of innovative modern vaccines to fulfill the desideratum for Differentiating between Infected and Vaccinated Animals (DIVA) may mitigate time spent and financial disbursement of serological monitoring and surveillance in the advanced levels for any disease obliteration campaign. We here highlight what is at the present time well-known about the virus and the different available diagnostic tools. Further, we interject on current updates and insights on several novel vaccines and on the possible current and prospective strategies to be applied for disease control.

Host Cellular Receptors for the Peste des Petits Ruminant Virus

Peste des Petits Ruminant (PPR) is an important transboundary, OIE-listed contagious viral disease of primarily sheep and goats caused by the PPR virus (PPRV), which belongs to the genus Morbillivirus of the family Paramyxoviridae. The mortality rate is 90–100%, and the morbidity rate may reach up to 100%. PPR is considered economically important as it decreases the production and productivity of livestock. In many endemic poor countries, it has remained an obstacle to the development of sustainable agriculture. Hence, proper control measures have become a necessity to prevent its rapid spread across the world. For this, detailed information on the pathogenesis of the virus and the virus host interaction through cellular receptors needs to be understood clearly. Presently, two cellular receptors; signaling lymphocyte activation molecule (SLAM) and Nectin-4 are known for PPRV. However, extensive information on virus interactions with these receptors and their impact on host immune response is still required. Hence, a thorough understanding of PPRV receptors and the mechanism involved in the induction of immunosuppression is crucial for controlling PPR. In this review, we discuss PPRV cellular receptors, viral host interaction with cellular receptors, and immunosuppression induced by the virus with reference to other Morbilliviruses.

Productive replication of peste des petits ruminants virus Nigeria 75/1 vaccine strain in vero cells correlates with inefficiency of maturation of the viral fusion protein

Peste des petits ruminants virus (PPRV), a member of the genus Morbillivirus, in the family Paramyxoviridae expresses two membrane glycoproteins, the fusion (F) and haemagglutinin (H) glycoproteins which mediate virus-to-cell fusion and cell-to-cell fusion leading to the induction of syncytia in PPRV infected cells. In the context of the characterization of the virulent lineage IV strain PPRV Kurdistan 2011, isolated from wild goats from the Kurdistan region in Iraq, we observed that both PPRV Kurdistan 2011 and the PPRV Nigeria 75/1 vaccine strain led to induction of large syncytia in Vero-dogSLAM cells within 48 h whereas both failed to induce detectable cell-cell fusion events in two Vero cell lines of differing passage histories. We were unable to detect syncytium formation in transiently transfected cells expressing PPRV F or H alone whereas co-expression of F and H induced large syncytia - in Vero-dogSLAM cells only. In Vero_Montpellier cells expressing PPRV F and H, fused cells were rarely detectable indicating that PPRV mediated cell fusion activity is impaired in this cell line. Surprisingly, on Vero-dogSLAM cells the vaccine strain grew to titers of 10^5.25 TCID₅₀/ml, whereas infectious virus yield was about 200-fold higher on Vero_Montpellier and Vero-76 cells. In contrast, the virulent Kurdistan 2011 strain grew to a maximum titer of 10^7.0 TCID₅₀/ml on Vero-dogSLAM cells and only 10^4.5 TCID50/ml on normal Vero cells. This was as expected since Vero cells lacking the SLAM receptor for PPRV are regarded as not so permissive for infection. To elucidate the divergent productive replication behaviour of PPRV Nigeria 75/1 vaccine strain on Vero vs Vero-dogSLAM cells, we examined whether intracellular transport and/or maturation of the viral envelope glycoproteins F and H might be implicated with this phenomenon. The results indicate that F in contrast to the H glycoprotein matures inefficiently during intracellular transport in Vero_Montpellier cells, thus leading to an absence of detectable syncytia formation. However, in the case of the PPRV Nigeria 75/1 vaccine strain this did not impair efficient virus assembly and release.

Peste des Petits Ruminants Virus Fusion and Hemagglutinin Proteins Trigger Antibody-Dependent Cell-Mediated Cytotoxicity in Infected Cells

The adaptive immune system utilizes multiple effector mechanisms to clear viral infections. Among those antibody-dependent cell-mediated cytotoxicity (ADCC) can help recognize and clear virus-infected cells. In the present work we evaluated ADCC contribution to immunity in two economically important viral diseases that affect ruminants: bluetongue and peste des petits ruminants. Immune sera obtained from sheep experimentally infected with bluetongue virus (BTV) serotype 8 or peste des petits ruminant virus (PPRV) IC'89 were used for this study. PPRV immune sera could bind to the surface of PPRV-infected ovine B cells while BTV immune sera was unable to bind to the surface of BTV-infected sheep cells but could recognize intracellular BTV antigens. BTV and PPRV immune serum ADCC potency was established using an ovine autologous cytotoxicity assay that employed an NK cell-enriched fraction as effector cells and a virus-infected B cell-enriched fraction as target cells. In this system, immune sera triggered ADCC against PPRV-infected cells, but not against BTV-infected cells. PPRV immune sera could recognize PPRV fusion and hemagglutinin proteins on the surface of transfected cells, and enhanced lysis of these cells in ADCC assays. This indicated that these viral antigens are natural ADCC targets during PPRV infection. The present work describes a novel effector immune mechanism against PPRV in the natural host that could contribute to virus clearance highlighting the importance of studying protective immune mechanisms to improve current vaccines by invoking all effector arms of immunity.

Comparison of the Immunogenicities and Cross-Lineage Efficacies of Live Attenuated Peste des Petits Ruminants Virus Vaccines PPRV/Nigeria/75/1 and PPRV/Sungri/96

Despite the widespread use of live attenuated PPRV vaccines, this is the first systematic analysis of the immune response elicited in small ruminants. These data will help in the establishment of the immunological determinants of protection, an important step in the development of new vaccines, especially DIVA vaccines using alternative vaccination vectors. This study is also the first controlled test of the ability of the two major vaccines used against virulent PPRV strains from all genetic lineages of the virus, showing conclusively the complete cross-protective ability of these vaccines.

Peste des petits ruminants (PPR) is a severe disease of goats and sheep that is widespread in Africa, the Middle East, and Asia. Several effective vaccines exist for the disease, based on attenuated strains of the virus (PPRV) that causes PPR. While the efficacy of these vaccines has been established by use in the field, the nature of the protective immune response has not been determined. In addition, while the vaccine derived from PPRV/Nigeria/75/1 (N75) is used in many countries, those developed in India have never been tested for their efficacy outside that country. We have studied the immune response in goats to vaccination with either N75 or the main Indian vaccine, which is based on isolate PPRV/India/Sungri/96 (S96). In addition, we compared the ability of these two vaccines, in parallel, to protect animals against challenge with pathogenic viruses from the four known genetic lineages of PPRV, representing viruses from different parts of Africa, as well as Asia. These studies showed that, while N75 elicited a stronger antibody response than S96, as measured by both enzyme-linked immunosorbent assay and virus neutralization, S96 resulted in more pronounced cellular immune responses, as measured by virus antigen-induced proliferation and interferon gamma production. While both vaccines induced comparable numbers of PPRV-specific CD8⁺ T cells, S96 induced a higher number of CD4⁺ T cells specifically responding to virus. Despite these quantitative and qualitative differences in the immune responses following vaccination, both vaccines gave complete clinical protection against challenge with all four lineages of PPRV.

IMPORTANCE Despite the widespread use of live attenuated PPRV vaccines, this is the first systematic analysis of the immune response elicited in small ruminants. These data will help in the establishment of the immunological determinants of protection, an important step in the development of new vaccines, especially DIVA vaccines using alternative vaccination vectors. This study is also the first controlled test of the ability of the two major vaccines used against virulent PPRV strains from all genetic lineages of the virus, showing conclusively the complete cross-protective ability of these vaccines.

Recent advances in viral vectors in veterinary vaccinology

Viral vectored vaccines, particularly using vectors such as adenovirus, herpesvirus and poxviruses, are used widely in veterinary medicine, where this technology has been adopted much more quickly than in human medicine. There are now a large number of programmes to develop viral vector vaccine platforms for humans and very similar or identical vectors are being developed for veterinary medicine. The shared experiences of developing these new vaccine platforms across the two disciplines is accelerating progress, a striking example of the value of a 'One Health' approach. In particular, there is growing use of adenoviruses, either replicating or replication-incompetent, to create new vaccines for use in livestock or companion animals. Live replicating avian herpesvirus vectors are increasingly used as vaccines against poultry diseases.

Bovine Herpesvirus-4-Based Vector Delivering Peste des Petits Ruminants Virus Hemagglutinin ORF Induces both Neutralizing Antibodies and Cytotoxic T Cell Responses

Peste des Petits Ruminants Virus (PPRV) is an extremely infective morbillivirus that primarily affects goats and sheep. In underdeveloped countries where livestock are the main economical resource, PPRV causes considerable economic losses. Protective live attenuated vaccines are currently available but they induce antibody responses similar to those produced in PPRV naturally infected animals. Effective vaccines able to distinguish between vaccinated and naturally infected animals are required to PPRV control and eradication programs. Hemagglutinin (H) is a highly immunogenic PPRV envelope glycoprotein displaying both hemagglutinin and neuraminidase activities, playing a crucial role in virus attachment and penetration. In this study, a recombinant Bovine Herpesvirus-4 (BoHV-4)-based vector delivering an optimized PPRV-Hemagglutinin expression cassette, BoHV-4-A-PPRV-H-ΔTK, was assessed in immunocompetent C57BL/6 mice. BoHV-4-A-PPRV-H-ΔTK-immunization elicited both cellular and humoral immune responses with specific T cell, cytotoxic T lymphocyte, and sero-neutralizing antibody against PPRV. These data suggest recombinant BoHV-4-A-PPRV-H-ΔTK as an effective vaccine candidate to protect against PPRV herd infection and potentially applicable for eradication programs.

Binding and entry of peste des petits ruminants virus into caprine endometrial epithelial cells profoundly affect early cellular gene expression

Peste des petits ruminants virus (PPRV), the etiological agent of peste des petits ruminants (PPR), causes an acute or subacute disease in small ruminants. Although abortion is observed in an unusually large proportion of pregnant goats during outbreaks of PPR, the pathogenic mechanism underlying remains unclear. Here, the gene expression profile of caprine endometrial epithelial cells (EECs) infected with PPRV Nigeria 75/1 was determined by DNA microarray to investigate the cellular response immediately after viral entry. The microarray analysis revealed that a total of 146 genes were significantly dysregulated by PPRV internalization within 1 h post-infection (hpi). Of these, 85 genes were upregulated and 61 genes were downregulated. Most of these genes, including NFKB1A, JUNB, and IL1A, have not previously been reported in association with PPRV infection in goats. Following viral replication (24 hpi), the expression of 307 genes were significantly upregulated and that of 261 genes were downregulated. The data for the genes differentially expressed in EECs were subjected to a time sequence profile analysis, gene network analysis and pathway analysis. The gene network analysis showed that 13 genes (EIF2AK3, IL10, TLR4, ZO3, NFKBIB, RAC1, HSP90AA1, SMAD7, ARG2, JUNB, ZFP36, APP, and IL1A) were located in the core of the network. We clearly demonstrate that PPRV infection upregulates the expression of nectin-4 after 1 hpi, which peaked at 24 hpi in EECs. In conclusion, this study demonstrates the early cellular gene expression in the caprine endometrial epithelial cells after the binding and entry of PPRV.

Vaccination with recombinant adenovirus expressing peste des petits ruminants virus-F or -H proteins elicits T cell responses to epitopes that arises during PPRV infection

Peste des petits ruminants virus (PPRV) causes an economically important disease that limits productivity in small domestic ruminants and often affects the livestock of the poorest populations in developing countries. Animals that survive PPRV develop strong cellular and humoral responses, which are probably necessary for protection. Vaccination should thus aim at mimicking these natural responses. Immunization strategies against this morbillivirus using recombinant adenoviruses expressing PPRV-F or -H proteins can protect PPRV-challenged animals and permit differentiation of infected from vaccinated animals. Little is known of the T cell repertoire these recombinant vaccines induce. In the present work, we identified several CD4⁺ and CD8⁺ T cell epitopes in sheep infected with PPRV. We also show that recombinant adenovirus vaccination induced T cell responses to the same epitopes, and led to memory T cell differentiation. T cells primed by these recombinant adenovirus vaccines expanded after PPRV challenge and probably contributed to protection. These data validate the use of recombinant adenovirus expressing PPRV genes as DIVA strategies to control this highly contagious disease.

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.

Field evaluation and confirmation of acute peste des petits ruminant outbreak in a flock of West African dwarf goats in Ibadan, Nigeria

This study utilised epidemiological, haematological, pathological findings and serological detection of specific antibodies to evaluate and confirm a peste des petit ruminants (PPR) outbreak in a herd of West African dwarf (WAD) goats in Ibadan, Nigeria. The morbidity and mortality rates post exposure (PE) were 96% and 60% respectively. Laboratory analyses revealed significant differences (P < 0.05) in mean values of the haematological and serum biochemical indices between the PE and control groups. The PE group experienced a significant (P < 0.05) increase in white blood cell (WBC), lymphocyte and monocytes after 10 days PE; the drop in glucose and high levels of alkaline phosphatase (ALP) and aspartate amino transferase (AST) indicated liver damage, while increased serum creatinine, blood urea nitrogen (BUN) and uric acid arose from kidney impairment. The electrolyte imbalance (potassium, sodium and chloride ions) resulting from the symptomatic diarrhea affected the functionality of the Na⁺–K⁺ pump mechanisms, hence pathologic damage to the liver, kidneys, skin, gastrointestinal, respiratory and cardiovascular systems. The competitive enzyme linked immuno-sorbent assay (c-ELISA) detected varying antibody levels in the PPR infected WAD goats; the percent inhibition was highest (P < 0.001) in survivors (70.00 ± 1.73), then in contact group (60.00 ± 2.00), and least in infected (23.33 ± 1.53), which were sero-negative. This study confirmed a PPR outbreak in a WAD goat flock in Ibadan, Nigeria.

The Opportunity To Eradicate Peste des Petits Ruminants

Peste des petits ruminants (PPR) is a highly infectious disease of sheep and goats that is caused by PPR virus, a member of the genus Morbillivirus that includes the viruses that cause rinderpest (RP) in cattle. RP was the first animal disease to be globally eradicated in 2011 and is only the second disease, after smallpox, to have ever been eradicated. PPR is one of the principal constraints to small ruminant production in Africa, Asia, and the Middle East. The epidemiology of PPR and RP as well as the technologies available for their diagnosis and control are similar. The conditions that favored the eradication of RP are also largely present for PPR. In this work, we outline the evolving strategy for eradication in light of current opportunities and challenges, as well as the lessons from other eradication programs in animal and human health. The global PPR situation and technology for its control are summarized. A strategy based on the lessons from previous eradication efforts that integrate epidemiology, social science, and economics as tools to target and motivate vaccination is summarized. Major aspects of the cost and benefit-cost analysis of the indicated program are presented. The overall undiscounted cost of eradication was estimated as $3.1 billion, and the benefit-cost ratio for the most likely scenario was estimated at 33.8. We close with a discussion of the possible next steps.

Advances in peste des petits ruminants vaccines

Peste des petits ruminants (PPR) is a highly contagious disease of small ruminants that leads to high morbidity and mortality thereby results in devastating economic consequences to the livestock industry. PPR is currently endemic across most parts of Asia and Africa, the two regions with the highest concentration of poor people in the world. Sheep and goats in particularly contribute significantly towards the upliftment of livelihood of the poor and marginal farmers in these regions. In this context, PPR directly affecting the viability of sheep and goat husbandry has emerged as a major hurdle in the development of these regions. The control of PPR in these regions could significantly contribute to poverty alleviation, therefore, the Office International des Epizooties (OIE) and Food and Agricultural Organization (FAO) have targeted the control and eradication of PPR by 2030 a priority. In order to achieve this goal, a potent, safe and efficacious live-attenuated PPR vaccine with long-lasting immunity is available for immunoprophylaxis. However, the live-attenuated PPR vaccine is thermolabile and needs maintenance of an effective cold chain to deliver into the field. In addition, the infected animals cannot be differentiated from vaccinated animals. To overcome these limitations, some recombinant vaccines have been developed. This review comprehensively describes about the latest developments in PPR vaccines.

A new immunoassay of serum antibodies against Peste des petits ruminants virus using quantum dots and a lateral-flow test strip

A fast and ultrasensitive test-strip system combining quantum dots (QDs) with a lateral-flow immunoassay strip (LFIAS) was established for detection of Peste des petits ruminants virus (PPRV) antibody. The highly luminescent water-soluble carboxyl-functionalized QDs were used as the signal output and were conjugated to streptococcal protein G (SPG), which was capable of binding to immunoglobulin G (IgG) from many species through an amide bond to capture the target PPRV IgGs. The PPRV N protein, which was immobilized on the detection zone of the test strip, was expressed by transfecting recombinant Bacmid-PPRV-N with Lipofect into Sf9 insect cells. When exposed to PPRV IgG, QD-SPG bound to PPRV N protein, resulting in the formation of a complex that subsequently produced a bright fluorescent band in response to 365 nm ultraviolet excitation. Sensitivity evaluation showed that the QD-LFIAS limit of detection (LOD) for PPRV antibody was superior to competitive enzyme-linked immunosorbent assay (c-ELISA) and the immunochromatographic strip. No cross reaction was observed when the positive sera of bluetongue virus, canine distemper virus, goat pox virus, and foot-and-mouth disease virus were tested. Further evaluation using field samples indicated that the diagnostic specificity and sensitivity of the QD-LFIAS was 99.47 and 97.67 %, respectively, with excellent agreement between QD-LFIAS and c-ELISA. The simple analysis step and objective results that can be obtained within 15 min indicate that this new method shows great promise for rapid, sensitive detection of PPRV IgG for onsite, point-of-care diagnosis and post vaccination evaluation (PVE). Graphical Abstract Ultrasensitive fluorescent QD immunochromotography in combination with recombinant PPRV N protein could be used to detect PPRV antibody in serum.

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.

Determination of the minimum fully protective dose of adenovirus-based DIVA vaccine against peste des petits ruminants virus challenge in East African goats

Peste des petits ruminants virus (PPRV) causes an economically important disease of sheep and goats, primarily in developing countries. It is becoming the object of intensive international control efforts. Current vaccines do not allow vaccinated and infected animals to be distinguished (no DIVA capability). We have previously shown that recombinant, replication-defective, adenovirus expressing the PPRV H glycoprotein (AdH) gives full protection against wild type PPRV challenge. We have now tested lower doses of the vaccine, as well as AdH in combination with a similar construct expressing the PPRV F glycoprotein (AdF). We show here that, in a local breed of goat in a country where PPR disease is common (Kenya), as little as 10(7) pfu of AdH gives significant protection against PPRV challenge, while a vaccine consisting of 10(8) pfu of each of AdH and AdF gives apparently sterile protection. These findings underline the utility of these constructs as DIVA vaccines for use in PPR control.

Peste des Petits Ruminants Virus

Peste des petits ruminants virus (PPRV) causes a severe contagious disease of sheep and goats and has spread extensively through the developing world. Because of its disproportionately large impact on the livelihoods of low-income livestock keepers, and the availability of effective vaccines and good diagnostics, the virus is being targeted for global control and eventual eradication. In this review we examine the origin of the virus and its current distribution, and the factors that have led international organizations to conclude that it is eradicable. We also review recent progress in the molecular and cellular biology of the virus and consider areas where further research is required to support the efforts being made by national, regional, and international bodies to tackle this growing threat.

Peste des petits ruminants

Peste des petits ruminants virus causes a highly infectious disease of small ruminants that is endemic across Africa, the Middle East and large regions of Asia. The virus is considered to be a major obstacle to the development of sustainable agriculture across the developing world and has recently been targeted by the World Organisation for Animal Health (OIE) and the Food and Agriculture Organisation (FAO) for eradication with the aim of global elimination of the disease by 2030. Fundamentally, the vaccines required to successfully achieve this goal are currently available, but the availability of novel vaccine preparations to also fulfill the requisite for differentiation between infected and vaccinated animals (DIVA) may reduce the time taken and the financial costs of serological surveillance in the later stages of any eradication campaign. Here, we overview what is currently known about the virus, with reference to its origin, updated global circulation, molecular evolution, diagnostic tools and vaccines currently available to combat the disease. Further, we comment on recent developments in our knowledge of various recombinant vaccines and on the potential for the development of novel multivalent vaccines for small ruminants.

Development of a helper cell-dependent form of peste des petits ruminants virus: a system for making biosafe antigen

Peste des petits ruminants (PPR) is a viral disease of sheep and goats that is spreading through many countries in the developing world. Work on the virus is often restricted to studies of attenuated vaccine strains or to work in laboratories that have high containment facilities. We have created a helper cell dependent form of PPR virus by removing the entire RNA polymerase gene and complementing it with polymerase made constitutively in a cell line. The resultant L-deleted virus grows efficiently in the L-expressing cell line but not in other cells. Virus made with this system is indistinguishable from normal virus when used in diagnostic assays, and can be grown in normal facilities without the need for high level biocontainment. The L-deleted virus will thus make a positive contribution to the control and study of this important disease.

Tomorrow's vector vaccines for small ruminants

Inactivated and attenuated vaccines have contributed to the control or even the eradication of significant animal pathogens. However, these traditional vaccine technologies have limitations and disadvantages. Inactivated vaccines lack efficacy against certain pathogens, while attenuated vaccines are not always as safe. New technology vaccines, namely DNA and recombinant viral vector vaccines, are being developed and tested against pathogens of small ruminants. These vaccines induce both humoral and cellular immune responses, are safe to manufacture and use and can be utilized in strategies for differentiation of infected from vaccinated animals. Although there are more strict regulatory requirements for the safety standards of these vaccines, once a vaccine platform is evaluated and established, effective vaccines can be rapidly produced and deployed in the field to prevent spread of emerging pathogens. The present article offers an introduction to these next generation technologies and examples of vaccines that have been tested against important diseases of sheep and goats.

Improving T cell-induced response to subunit vaccines: opportunities for a proteomic systems approach

Prophylactic vaccines are an effective strategy to prevent development of many infectious diseases. With new and re-emerging infections posing increasing risks to food stocks and the health of the population in general, there is a need to improve the rationale of vaccine development. One key challenge lies in development of an effective T cell-induced response to subunit vaccines at specific sites and in different populations.

OBJECTIVES

In this review, we consider how a proteomic systems-based approach can be used to identify putative novel vaccine targets, may be adopted to characterise subunit vaccines and adjuvants fully.

KEY FINDINGS

Despite the extensive potential for proteomics to aid our understanding of subunit vaccine nature, little work has been reported on identifying MHC 1-binding peptides for subunit vaccines generating T cell responses in the literature to date.

SUMMARY

In combination with predictive and structural biology approaches to mapping antigen presentation, proteomics offers a powerful and as yet un-tapped addition to the armoury of vaccine discovery to predict T-cell subset responses and improve vaccine design strategies.

Peste des petits ruminants virus-like particles induce both complete virus-specific antibodies and virus neutralizing antibodies in mice

Peste des petits ruminants virus (PPRV), an etiological agent of peste des petits ruminants (PPR), is classified into the genus Morbillivirus in the family Paramyxoviridae. In a previous study, a recombinant baculovirus has been constructed to co-express the PPRV matrix (M), haemagglutinin (H) and nucleocapsid (N) proteins in insect cells, causing budding of PPR virus-like particles (VLPs) from insect cell membranes by viewing of ultrathin section with a transmission electron microscope. In this follow-up study, these PPR VLPs were purified by sucrose density gradient centrifugation for immunizing mice twice. Three weeks post-primary immunization and 2 weeks post-secondary immunization, all serum samples were obtained and subsequently subjected to indirect ELISA detection on complete virus-specific antibodies. In addition, all serum samples, which were collected 2 weeks post-secondary immunization, were used for virus neutralization test on PPRV neutralizing antibodies. The results showed that the purified PPR VLPs induced both types of antibodies mentioned above in mice, indicating a given potential of VLP-based vaccine candidate against PPR.

Rescue of a vaccine strain of peste des petits ruminants virus: In vivo evaluation and comparison with standard vaccine

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Rescue of a vaccine strain of peste des petits ruminants virus.

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In vivo evaluation of rescued vaccine strain and comparison with standard vaccine.

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1SStrategy for Differentiating Infected from Vaccinated Animals (DIVA).

Across the developing world peste des petits ruminants virus places a huge disease burden on agriculture, primarily affecting the production of small ruminant. The disease is most effectively controlled by vaccinating sheep and goats with live attenuated vaccines that provide lifelong immunity. However, the current vaccines and serological tests are unable to enable Differentiation between naturally Infected and Vaccinated Animals (DIVA). This factor precludes meaningful assessment of vaccine coverage and epidemiological surveillance based on serology, in turn reducing the efficiency of control programmes. The availability of a recombinant PPRV vaccine with a proven functionality is a prerequisite for the development of novel vaccines that may enable the development of DIVA tools for PPRV diagnostics. In this study, we have established an efficient reverse genetics system for PPRV Nigeria 75/1 vaccine strain and, further rescued a version of PPRV Nigeria 75/1 vaccine strain that expresses eGFP as a novel transcription cassette and a version of PPRV Nigeria 75/1 vaccine strain with mutations in the haemagglutinin (H) gene to enable DIVA through disruption of binding to H by the C77 monoclonal antibody used in the competitive (c) H-ELISA. All three rescued viruses showed similar growth characteristics in vitro in comparison to parent vaccine strain and, following in vivo assessment the H mutant provided full protection in goats. Although the C77 monoclonal antibody used in the cH-ELISA was unable to bind to the mutated form of H in vitro, the mutation was not sufficient to enable DIVA in vivo.

Vaccination with recombinant adenoviruses expressing the peste des petits ruminants virus F or H proteins overcomes viral immunosuppression and induces protective immunity against PPRV challenge in sheep

Peste des petits ruminants (PPR) is a highly contagious disease of small ruminants caused by the Morbillivirus peste des petits ruminants virus (PPRV). Two recombinant replication-defective human adenoviruses serotype 5 (Ad5) expressing either the highly immunogenic fusion protein (F) or hemagglutinin protein (H) from PPRV were used to vaccinate sheep by intramuscular inoculation. Both recombinant adenovirus vaccines elicited PPRV-specific B- and T-cell responses. Thus, neutralizing antibodies were detected in sera from immunized sheep. In addition, we detected a significant antigen specific T-cell response in vaccinated sheep against two different PPRV strains, indicating that the vaccine induced heterologous T cell responses. Importantly, no clinical signs and undetectable virus shedding were observed after virulent PPRV challenge in vaccinated sheep. These vaccines also overcame the T cell immunosuppression induced by PPRV in control animals. The results indicate that these adenovirus constructs could be a promising alternative to current vaccine strategies for the development of PPRV DIVA vaccines.

Peste des petits ruminants virus infection of small ruminants: a comprehensive review

Peste des petits ruminants (PPR) is caused by a Morbillivirus that belongs to the family Paramyxoviridae. PPR is an acute, highly contagious and fatal disease primarily affecting goats and sheep, whereas cattle undergo sub-clinical infection. With morbidity and mortality rates that can be as high as 90%, PPR is classified as an OIE (Office International des Epizooties)-listed disease. Considering the importance of sheep and goats in the livelihood of the poor and marginal farmers in Africa and South Asia, PPR is an important concern for food security and poverty alleviation. PPR virus (PPRV) and rinderpest virus (RPV) are closely related Morbilliviruses. Rinderpest has been globally eradicated by mass vaccination. Though a live attenuated vaccine is available against PPR for immunoprophylaxis, due to its instability in subtropical climate (thermo-sensitivity), unavailability of required doses and insufficient coverage (herd immunity), the disease control program has not been a great success. Further, emerging evidence of poor cross neutralization between vaccine strain and PPRV strains currently circulating in the field has raised concerns about the protective efficacy of the existing PPR vaccines. This review summarizes the recent advancement in PPRV replication, its pathogenesis, immune response to vaccine and disease control. Attempts have also been made to highlight the current trends in understanding the host susceptibility and resistance to PPR.