Quantitative one-step real-time RT-PCR for the fast detection of the four genotypes of PPRV

Comparative study of HA and HNB staining RT-LAMP assays for peste des petits ruminants virus detection in West African Dwarf goats

Peste des petits ruminants (PPR) cause severe economic losses to many countries of the world where the disease is endemic. It has been targeted for global eradication by 2030 following the successful eradication of rinderpest in 2011. The proposed eradication program would benefit from efficient and relatively reliable diagnostic tools for early PPR virus (PPRV) detection. A total of 33 eight to 12 months old West African Dwarf (WAD) goats were used. Nineteen goats infected by commingling with two PPR virus-positive animals formed the infected group (PPRV-infected goats) while 14 non-infected goats formed the control group (CTG). The suitability of hydroxyl naphthol blue (HNB) staining of reverse transcription loop-mediated isothermal amplification (RT-LAMP) and haemagglutination (HA) assays was compared for their sensitivity to detect the PPRV in PPRV-infected goats and non-infected CTG. PPR disease severity in WAD goats at different days post infection (dpi) was evaluated by clinical scoring and haemagglutination titre (HAT). HNB staining RT-LAMP reaction and HA showed sensitivities of 100% and 73.68%, respectively, for PPRV detection. Expression of PPR clinical signs began from 3 dpi, attained peak at 5 dpi, thereafter showed irregular patterns till 24 dpi. Evaluation of HAT in PPRV-infected goats at 12 dpi ranged from 2 to 64 haemagglutination units (HAU), while CTG goats had 0 HAU. In conclusion, HA could be a good tool for rapid diagnosis of PPRV in a developing country setting. However, HNB staining RT-LAMP assay demonstrated high sensitivity for accurate diagnoses of PPRV and as an important diagnostic tool when precise phenotyping is desired.

Development and Evaluation of a Nested PCR for Improved Diagnosis and Genetic Analysis of Peste des Petits Ruminants Virus (PPRV) for Future Use in Nascent PPR Eradication Programme

Peste des petits ruminants (PPR) is a highly contagious viral disease of small ruminants caused by PPR virus (PPRV). PPR is endemic in Asia, the Middle East and across large areas of Africa and is currently targeted for global eradication by 2030. The virus exists as four different lineages that are usually limited to specific geographical areas. However, recent reports of spread of PPRV, in particular of lineage IV viruses to infection-free countries and previously PPR endemic areas are noteworthy. A rapid and accurate laboratory diagnosis and reports on its epidemiological linkage for virus spread play a major role in the effective control and eradication of the disease. Currently, molecular assays, including conventional reverse transcription-polymerase chain reaction (RT-PCR) and real-time RT-PCR (RT-qPCR) are usually used for diagnosis of PPR while the sequencing of part of the nucleocapsid gene is usually carried out for the viral lineage identification. However, it is difficult to diagnose and sequence the genetic material if the animal excreted a low level of virus at the initial stage of infection or if the PPRV is degraded during the long-distance transportation of samples to the reference laboratories. This study describes the development of a novel nested RT-PCR assay for the detection of the PPRV nucleic acid by targeting the N-protein gene, compares the performance of the assay with the existing conventional RT-PCR and also provides good-quality DNA suitable for sequencing in order to identify circulating lineages. The assay was evaluated using cell culture propagated PPRVs, field samples from clinically infected animals and samples from experimentally infected animals encompassing all four lineages (I-IV) of PPRV. This assay provides a solution with an easy, accurate, rapid and cost-effective PPR diagnostic and partial genome sequencing for use in resource-limited settings.

Complete Genome Sequencing of Field Isolates of Peste des Petits Ruminants Virus from Tanzania Revealed a High Nucleotide Identity with Lineage III PPR Viruses

Peste des petits ruminants virus (PPRV) causes a highly devastating disease of sheep and goats that threatens food security, small ruminant production and susceptible endangered wild ruminants. With policy directed towards achieving global PPR eradication, the establishment of cost-effective genomic surveillance tools is critical where PPR is endemic. Genomic data can provide sufficient in-depth information to identify the pockets of endemicity responsible for PPRV persistence and viral evolution, and direct an appropriate vaccination response. Yet, access to the required sequencing technology is low in resource-limited settings and is compounded by the difficulty of transporting clinical samples from wildlife across international borders due to the Convention on International Trade in Endangered Species (CITES) of Wild Fauna and Flora, and Nagoya Protocol regulations. Oxford nanopore MinION sequencing technology has recently demonstrated an extraordinary performance in the sequencing of PPRV due to its rapidity, utility in endemic countries and comparatively low cost per sample when compared to other whole-genome (WGS) sequencing platforms. In the present study, Oxford nanopore MinION sequencing was utilised to generate complete genomes of PPRV isolates collected from infected goats in Ngorongoro and Momba districts in the northern and southern highlands of Tanzania during 2016 and 2018, respectively. The tiling multiplex polymerase chain reaction (PCR) was carried out with twenty-five pairs of long-read primers. The resulting PCR amplicons were used for nanopore library preparation and sequencing. The analysis of output data was complete genomes of PPRV, produced within four hours of sequencing (accession numbers: MW960272 and MZ322753). Phylogenetic analysis of the complete genomes revealed a high nucleotide identity, between 96.19 and 99.24% with lineage III PPRV currently circulating in East Africa, indicating a common origin. The Oxford nanopore MinION sequencer can be deployed to overcome diagnostic and surveillance challenges in the PPR Global Control and Eradication program. However, the coverage depth was uneven across the genome and amplicon dropout was observed mainly in the GC-rich region between the matrix (M) and fusion (F) genes of PPRV. Thus, larger field studies are needed to allow the collection of sufficient data to assess the robustness of nanopore sequencing technology.

Inhibiting pyrimidine biosynthesis impairs Peste des Petits Ruminants Virus replication through depletion of nucleoside pools and activation of cellular immunity

Replication of peste des petits ruminants virus (PPRV) strongly depends on the cellular environment and resources of host cells including nucleoside pool. Thus, enzymes involved in nucleoside biosynthesis (such as pyrimidine biosynthesis pathway) are regarded as attractive targets for antiviral drug development. Here, we demonstrate that brequinar (BQR) and leflunomide (LFM) which are two specific inhibitors of DHODH enzyme and 6-azauracil (6-AU) which is an ODase enzyme inhibitor robustly inhibit PPRV replication in HEK293T cell line as well as in peripheral blood mononuclear cells isolated from goat. We further demonstrate that these agents exert anti-PPRV activity via the depletion of purimidine nucleotide. Interestingly, these inhibitors can trigger the transcription of antiviral interferon-stimulated genes (ISGs). However, the induction of ISGs is largely independent of the classical JAK-STAT pathway. Combination of BQR with interferons (IFNs) exerts enhanced ISG induction and anti-PPRV activity. Taken together, this study reveals an unconventional novel mechanism of crosstalk between nucleotide biosynthesis pathways and cellular antiviral immunity in inhibiting PPRV replication. In conclusion, targeting pyrimidine biosynthesis represents a potential strategy for developing antiviral strategies against PPRV.

In vitro and in vivo analyses of co-infections with peste des petits ruminants and capripox vaccine strains

BACKGROUND

Peste des petits ruminants (PPR) and goat pox (GTP) are two devastating animal epidemic diseases that affect small ruminants. Vaccination is one of the most important measures to prevent and control these two severe infectious diseases.

METHODS

In this study, we vaccinated sheep with PPR and POX vaccines to compare the changes in the antibody levels between animals vaccinated with PPRV and POX vaccines alone and those co-infected with both vaccines simultaneously. The cell infection model was used to explore the interference mechanism between the vaccines in vitro. The antibody levels were detected with the commercial ELISA kit. The Real-time Quantitative PCR fluorescent quantitative PCR method was employed to detect the viral load changes and cytokines expression after the infection.

RESULTS

The concurrent immunization of GTP and PPR vaccine enhanced the PPR vaccine's immune effect but inhibited the immune effect of the GTP vaccine. After the infection, GTP and PPR vaccine strains caused cytopathic effect; co-infection with GTP and PPR vaccine strains inhibited the replication of PPR vaccine strains; co-infection with GTP and PPR vaccine strains enhanced the replication of GTP vaccine strains. Moreover, virus mixed infection enhanced the mRNA expressions of TNF-α, IL-1β, IL-6, IL-10, IFN-α, and IFN-β by 2-170 times. GTP vaccine strains infection alone can enhanced the mRNA expression of IL-1β, TNF-α, IL-6, IL-10, while the expression of IFN-α mRNA is inhibited. PPR vaccine strains alone can enhanced the mRNA expression of IFN-α, IFN-β, TNF-α, and has little effect the mRNA expression of IL-1β, IL-6 and IL-10. The results showed that GTP and PPR vaccine used simultaneously in sheep enhanced the PPR vaccine's immune effect but inhibited the immune effect of the GTP vaccine in vivo. Furthermore, an infection of GTP and PPR vaccine strains caused significant cell lesions in vitro; co-infection with GTP + PPR vaccine strains inhibited the replication of PPR vaccine strains, while the co-infection of GTP followed by PPR infection enhanced the replication of GTP vaccine strains. Moreover, virus infection enhanced the expressions of TNF-α, IL-1β, IL-6, IL-10, IFN-α, and IFN-β.

CONCLUSIONS

Peste des petits ruminants and capripox vaccine strains interfere with each other in vivo and vitro.

"FastCheckFLI PPR-like"-A Molecular Tool for the Fast Genome Detection of PPRV and Differential Diagnostic Pathogens

To assist the global eradication of peste des petits ruminants virus (PPRV), a molecular test for the rapid and reliable detection of PPRV was developed which additionally enables the detection of pathogens relevant for differential diagnostics. For this purpose, the necessary time frame of a magnetic bead-based nucleic acid extraction protocol was markedly shortened to 7 min and 13 s. The optimized extraction was run on a BioSprint 15 platform. Furthermore, a high-speed multi-well RT-qPCR for the genome detection of PPRV and additional important pathogens such as Foot-and-mouth disease virus, Parapoxvirus ovis, Goatpox virus, and Mycoplasma capricolum subsp. capripneumoniae was established and combined with suitable internal control assays. The here-described qPCR is based on a lyophilized master mix and takes only around 30 to 40 min. Several qPCR cyclers were evaluated regarding their suitability for fast-cycling approaches and for their diagnostic performance in a high-speed RT-qPCR. The final evaluation was conducted on the BioRad CFX96 and also on a portable Liberty16 qPCR cycler. The new molecular test designated as "FastCheck^FLI PPR-like", which is based on rapid nucleic acid extraction and high-speed RT-qPCR, delivered reliable results in less than one hour, allowing its use also in a pen-side scenario.

Peste des petits ruminants in Africa: a review of currently available molecular epidemiological data, 2020

Small ruminants (e.g., sheep and goats) contribute considerably to the cash income and nutrition of small farmers in most countries in Africa and Asia. Their husbandry is threatened by the highly infectious transboundary viral disease peste des petits ruminants (PPR) caused by peste-des-petits-ruminants virus (PPRV). Given its social and economic impact, PPR is presently being targeted by international organizations for global eradication by 2030. Since its first description in Côte d’Ivoire in 1942, and particularly over the last 10 years, a large amount of molecular epidemiological data on the virus have been generated in Africa. This review aims to consolidate these data in order to have a clearer picture of the current PPR situation in Africa, which will, in turn, assist authorities in global eradication attempts.

Identification of a murine cell line that distinguishes virulent from attenuated isolates of the morbillivirus Peste des Petits Ruminants, a promising tool for virulence studies

Comprehensive pathogenesis studies on Peste des Petits Ruminants virus (PPRV) have been delayed so far by the absence of a small animal model reproducing the disease or an in vitro biological system revealing virulence differences. In this study, a mouse 10T1/2 cell line has been identified as presenting different susceptibility to virulent and attenuated PPRV strains. As evidenced by immunofluorescence test and RT-PCR, both virulent and attenuated PPR viruses penetrated and initiated the replication cycle in 10T1/2 cells, independently of the presence of the SLAM goat receptor. However, only virulent strains successfully completed their replication cycle while the vaccine strains did not. Since 10T1/2 cells are interferon-producing cells, the role of the type I interferon (type I IFN) response on this differentiated replication between virulent and attenuated strains was verified by stimulation or repression. Modulation of the type I IFN response did not improve the replication of the vaccine strains, indicating that other cell factor(s) not yet established may hinder the replication of attenuated PPRV in 10T1/2. This 10T1/2 cell line can be proposed as a new in vitro tool for PPRV-host interaction and virulence studies.

Detection of melon necrotic spot virus by one-step reverse transcription loop-mediated isothermal amplification assay

Melon necrotic spot virus (MNSV) can cause significant economic losses due to decreased quality in cucurbit crops. The current study is the first to use reverse transcription loop-mediated isothermal amplification (RT-LAMP) for detection of MNSV. A set of four LAMP primers was designed based on the coat protein gene sequence of MNSV, and a RT-LAMP reaction was successfully performed for 1 h at 62°C. The results of RT-LAMP showed high specificity for MNSV and no cross-reaction with other viruses. Compared to traditional reverse transcription-PCR (RT-PCR), the RT-LAMP assay was 10³-fold more sensitive in detecting MNSV. Due to its sensitivity, speed and visual assessment, RT-LAMP is appropriate for detecting MNSV in the laboratory.

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.

A versatile dual-use RT-PCR control for use in assays for the detection of peste des petits ruminants virus

Peste des petits ruminants (PPR) is an acute and highly contagious disease with high mortality in small ruminants and significant socioeconomic impact in developing countries. The causative agent is peste des petits ruminants virus (PPRV). The Food and Agriculture Organization of the United Nations (FAO) and the World Organization for Animal Health (OIE) have set up a goal for the global eradication of PPR by 2030. To assist in this effort, an easily produced, specific, non-pathogenic bacteriophage Qβ based real-time RT-PCR (qRT-PCR) PPRV positive control was developed. This control is compatible for use with two previously described PPRV qRT-PCR assays either as singleplex or multiplex platform. Additionally, the control can also be used for assembling proficiency testing panels for competency testing in diagnostic laboratories. Use of the Qβ phage based PPRV control as a positive control or in proficiency testing panels reduces the risk of inadvertent release of pathogenic PPRV from diagnostic laboratories, which would be especially important should PPR be eradicated in the future.

A rapid RT-LAMP assay for the detection of all four lineages of Peste des Petits Ruminants Virus

Peste des petits ruminants (PPR) is a viral disease of small ruminants that is caused by the PPR virus (PPRV) and is a significant burden on subsistence farmers across the developing world. Loop-mediated isothermal amplification (LAMP) provides cost-effective, rapid, specific and sensitive detection of nucleic acid and has been demonstrated to have field application for a range of viruses. We describe the development of a novel PPRV RT-LAMP assay utilising carefully-selected primers (targeting the N-gene) allowing for the detection of all known PPRV lineages in < 20 min. The assay was evaluated in comparison with a "gold standard" real-time RT-PCR assay using more than 200 samples, comprising samples from recent PPRV outbreaks, experimentally-infected goats, well-characterised cell culture isolates and samples collected from uninfected animals. The RT-LAMP assay demonstrated 100% diagnostic specificity and greater than 97% diagnostic sensitivity in comparison with the real-time RT-PCR assay. The limit of detection was between 0.3 and 0.8 log₁₀ TCID₅₀ ml^-1 equating to a C_T value of 31.52 to 33.48. In experimentally-infected animals, the RT-LAMP could detect PPRV as early as 4 days post infection (dpi) - before clinical signs were observed at 7 dpi. The RT-LAMP assay can support the global PPR eradication campaign.

Peste des Petits Ruminants Virus Surveillance in Domestic Small Ruminants, Mozambique (2015 and 2017)

Peste des Petits Ruminants (PPR), a transboundary animal disease affecting mainly goats and sheep is caused by a morbillivirus and threatens food security and livelihoods as morbidity and mortality rates can reach 90%. There are no records of PPR in Mozambique, but the disease situation in Tanzania and the ability of PPR virus to rapidly spread across countries constitute a high risk for about 4.7 million goats and sheep in Mozambique. A total of 4,995 goats and sheep were sampled in several provinces during 2015 and 2017 to assess the status of PPR virus (PPRV) in Mozambique and to contribute to surveillance along the border with Tanzania. The sera were screened for anti-PPRV antibodies using a commercial PPR competition ELISA (c-ELISA) and the haemagglutinin based PPR blocking ELISA (HPPR-bELISA). The swabs were tested using one-step RT-PCR for detection of PPRV RNA. The overall percentage of animals with anti-PPRV antibodies by c-ELISA, was 0.46% [0.30–0.70]. However, all the sera positive on c-ELISA were confirmed to be negative by the HPPR-bELISA. Considering that all the swabs were negative for detection of PPRV, no clinical cases were observed during passive surveillance and active sampling, and no symptoms were reported, these results suggest that PPRV is not present in Mozambique.

Improved PCR diagnostics using up-to-date in silico validation: An F-gene RT-qPCR assay for the detection of all four lineages of peste des petits ruminants virus

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Designed F-gene RT-qPCR using all full-genomes available on genbank.

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Performed in silico evaluation of existing and new PPRV RT-qPCR assays.

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F-gene RT-qPCR assay shows the greatest in silico performance.

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The assay demonstrates excellent diagnostic and analytical sensitivity.

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The assay may be useful during the global PPR eradication campaign.

Peste des petits ruminants (PPR) is a globally significant disease of small ruminants caused by the peste des petits ruminants virus (PPRV) that is considered for eradication by 2030 by the United Nations Food and Agriculture Organisation (FAO). Critical to the eradication of PPR are accurate diagnostic assays. RT-qPCR assays targeting the nucleocapsid gene of PPRV have been successfully used for the diagnosis of PPR. We describe the development of an RT-qPCR assay targeting an alternative region (the fusion (F) gene) based on the most up-to-date PPRV sequence data. In silico analysis of the F-gene RT-qPCR assay performed using PCRv software indicated 98% sensitivity and 100% specificity against all PPRV sequences published in Genbank. The assay indicated the greatest in silico sensitivity in comparison to other previously published and recommended PPRV RT-qPCR assays. We evaluated the assay using strains representative of all 4 lineages in addition to samples obtained from naturally and experimentally-infected animals. The F-gene RT-qPCR assay showed 100% diagnostic specificity and demonstrated a limit of detection of 10 PPRV genome copies per μl. This RT-qPCR assay can be used in isolation or in conjunction with other assays for confirmation of PPR and should support the global efforts for eradication.

Rapid Detection of Peste des Petits Ruminants Virus (PPRV) Nucleic Acid Using a Novel Low-Cost Reverse Transcription Loop-Mediated Isothermal Amplification (RT-LAMP) Assay for Future Use in Nascent PPR Eradication Programme

Peste des petits ruminants (PPR) is a disease of small ruminants caused by peste des petits ruminants virus (PPRV), and is endemic in Asia, the Middle East and Africa. Effective control combines the application of early warning systems, accurate laboratory diagnosis and reporting, animal movement restrictions, suitable vaccination and surveillance programs, and the coordination of all these measures by efficient veterinary services. Molecular assays, including conventional reverse transcription-polymerase chain reaction (RT-PCR) and real-time RT-PCR (RT-qPCR) have improved the sensitivity and rapidity of diagnosing PPR. However, currently these assays are only performed within laboratory settings; therefore, the development of field diagnostics for PPR would improve the fast implementation of control policies, particularly when PPR has been targeted to be eradicated by 2030. Loop-mediated isothermal amplification (LAMP) assays are simple to use, rapid, and have sensitivity and specificity within the range of RT-qPCR; and can be performed in the field using disposable consumables and portable equipment. This study describes the development of a novel RT-LAMP assay for the detection of PPRV nucleic acid by targeting the N-protein gene. The RT-LAMP assay was evaluated using cell culture propagated PPRVs, field samples from clinically infected animals and samples from experimentally infected animals encompassing all four lineages (I-IV) of PPRV. The test displayed 100% concordance with RT-qPCR when considering an RT-qPCR cut-off value of C_T >40. Further, the RT-LAMP assay was evaluated using experimental and outbreak samples without prior RNA extraction making it more time and cost-effective. This assay provides a solution for a pen-side, rapid and inexpensive PPR diagnostic for use in the field in nascent PPR eradication programme.

Optimization and evaluation of a non-invasive tool for peste des petits ruminants surveillance and control

Peste des petits ruminants (PPR) is a highly contagious and devastating viral disease affecting mainly sheep and goats, but also a large number of wild species within the order Artiodactyla. A better understanding of PPR transmission dynamics in multi-host systems is necessary to efficiently control the disease, in particular where wildlife and livestock co-occur. Notably, the role of wildlife in PPR epidemiology is still not clearly understood. Non-invasive strategies to detect PPR infection without the need for animal handling could greatly facilitate research on PPR epidemiology and management of the disease in atypical hosts and in complex field situations. Here, we describe optimized methods for the direct detection of PPR virus genetic material and antigen in fecal samples. We use these methods to determine the detection window of PPR in fecal samples, and compare the sensitivity of these methods to standard invasive sampling and PPR diagnostic methods using field samples collected at a wildlife-livestock interface in Africa. Our results show that quantitative reverse transcription PCR (RT-QPCR) amplification of PPRV from fecal swabs has good sensitivity in comparison to ocular swabs. Animals infected by PPRV could be identified relatively early on and during the whole course of infection based on fecal samples using RT-QPCR. Partial gene sequences could also be retrieved in some cases, from both fecal and ocular samples, providing important information about virus origin and relatedness to other PPRV strains. Non-invasive strategies for PPRV surveillance could provide important data to fill major gaps in our knowledge of the multi-host PPR epidemiology.

Molecular characterization of Peste des petits ruminants viruses in the Marmara Region of Turkey

Recent outbreaks of Peste des petits ruminants (PPR) in the Marmara region of Turkey including the European part of Thrace is important due to its proximity to Europe (Greece and Bulgaria) and the potential threat of spread of PPR into mainland Europe. In order to investigate the circulation of PPRV in the region suspect clinical and necropsy samples were collected from domestic sheep (n = 211) in the Marmara region of Turkey between 2011 and 2012. PPR virus (PPRV) genome was detected in 10.4% (22 out of 211) of sheep samples by real-time RT-PCR, and PPR virus was isolated from lungs of two sheep that died from infection. Of the 22 positive samples nine were used for partial N-gene amplification and sequencing. The phylogenetic analyses indicated that the virus belongs to lineage IV, the same lineage that is circulating in eastern and central part of Turkey since its first official report in 1999. In addition, samples from 100 cattle were collected to investigate potential subclinical circulation of PPRV. However all were found to be negative by real-time RT-PCR, and also in serological tests indicating the large ruminants were likely not exposed or infected with the virus. The impact of these findings on the potential threat of spread of PPR to Europe including the first PPR outbreak in Europe in Bulgaria on 23rd June 2018 is discussed.

Development and validation of an epitope-blocking ELISA using an anti-haemagglutinin monoclonal antibody for specific detection of antibodies in sheep and goat sera directed against peste des petits ruminants virus

Peste des petits ruminants (PPR) is a contagious and economically important disease affecting production of small ruminants (i.e., sheep and goats). Taking into consideration the lessons learnt from the Global Rinderpest Eradication Programme (GREP), PPR is now targeted by the international veterinary community as the next animal disease to be eradicated. To support the African continental programme for the control of PPR, the Pan African Veterinary Vaccine Centre of the African Union (AU-PANVAC) is developing diagnostics tools. Here, we describe the development of a blocking enzyme-linked immunosorbent assay (bELISA) that allows testing of a large number of samples for specific detection of antibodies directed against PPR virus in sheep and goat sera. The PPR bELISA uses an anti-haemagglutinin (H) monoclonal antibody (MAb) as a competitor antibody, and tests results are interpreted using the percentage of inhibition (PI) of MAb binding generated by the serum sample. PI values below or equal to 18% (PI ≤ 18%) are negative, PI values greater than or equal to 25% (PI ≥ 25%) are positive, and PI values greater than 18% and below 25% are doubtful. The diagnostic specificity (DSp) and diagnostic sensitivity (DSe) were found to be 100% and 93.74%, respectively. The H-based PPR-bELISA showed good correlation with the virus neutralization test (VNT), the gold standard test, with a kappa value of 0.947. The H-based PPR-bELISA is more specific than the commercial kit ID Screen® PPR Competition (N-based PPR-cELISA) from IDvet (France), but the commercial kit is slightly more sensitive than the H-based PPR-bELISA. The validation process also indicated good repeatability and reproducibility of the H-based PPR-bELISA, making this new test a suitable tool for the surveillance and sero-monitoring of the vaccination campaign.

Development of real-time and lateral flow strip reverse transcription recombinase polymerase Amplification assays for rapid detection of peste des petits ruminants virus

BACKGROUND

Peste des petits ruminants (PPR) is an economically important, Office International des Epizooties (OIE) notifiable, transboundary viral disease of small ruminants such as sheep and goat. PPR virus (PPRV), a negative-sense single-stranded RNA virus, is the causal agent of PPR. Therefore, sensitive, specific and rapid diagnostic assay for the detection of PPRV are necessary to accurately and promptly diagnose suspected case of PPR.

METHODS

In this study, reverse transcription recombinase polymerase amplification assays using real-time fluorescent detection (real-time RT-RPA assay) and lateral flow strip detection (LFS RT-RPA assay) were developed targeting the N gene of PPRV.

RESULTS

The sensitivity of the developed real-time RT-RPA assay was as low as 100 copies per reaction within 7 min at 40 °C with 95% reliability; while the sensitivity of the developed LFS RT-RPA assay was as low as 150 copies per reaction at 39 °C in less than 25 min. In both assays, there were no cross-reactions with sheep and goat pox viruses, foot-and-mouth disease virus and Orf virus.

CONCLUSIONS

These features make RPA assay promising candidates either in field use or as a point of care diagnostic technique.

Peste des petits ruminants diagnosis and diagnostic tools at a glance: perspectives on global control and eradication

Peste des petits ruminants (PPR) is a highly contagious, economically important viral disease of small ruminants, targeted for global eradication by the year 2030. The recent geographic surge in PPR virus distribution, economic implications, the success of the rinderpest eradication campaign, and ongoing national/regional efforts convinced the FAO and OIE to initiate a global PPR control and eradication strategy. Since its discovery, a series of diagnostic tools have been developed for detecting PPR virus and virus-specific antibodies. Furthermore, it is understood that diagnostic and vaccine-monitoring tools are inevitable components of the four-stage strategy of global PPR eradication from assessment to the post-eradication phase. However, these tools may not be suitable for all stages of PPR control and eradication. For instance, diagnostics such as ELISA could be used for mass screening of clinical and serum samples, whereas immunochromatographic tests can be used at the field level as a pen-side test. Yet, assays with higher sensitivity, such as RT-PCR, RT-PCR ELISA, real-time RT-PCR and LAMP are important for early diagnosis of PPR and also, theoretically, during the late stages of eradication or when sampling non-natural hosts. Moreover, during the later stages of any control program, suspected/doubtful outbreaks will have to be reconfirmed using multiple laboratory tests. Hence, diagnostics can and should be efficiently applied at different stages of the PPR control and eradication campaign based on available resources and the number of samples to be tested. This article provides an overview of the various PPR diagnostic tools and suggests where and how they should be logically applied during the different phases of global PPR control and eradication.

One-Step Multiplex RT-qPCR Assay for the Detection of Peste des petits ruminants virus, Capripoxvirus, Pasteurella multocida and Mycoplasma capricolum subspecies (ssp.) capripneumoniae

Respiratory infections, although showing common clinical symptoms like pneumonia, are caused by bacterial, viral or parasitic agents. These are often reported in sheep and goats populations and cause huge economic losses to the animal owners in developing countries. Detection of these diseases is routinely done using ELISA or microbiological methods which are being reinforced or replaced by molecular based detection methods including multiplex assays, where detection of different pathogens is carried out in a single reaction. In the present study, a one-step multiplex RT-qPCR assay was developed for simultaneous detection of Capripoxvirus (CaPV), Peste de petits ruminants virus (PPRV), Pasteurella multocida (PM) and Mycoplasma capricolum ssp. capripneumonia (Mccp) in pathological samples collected from small ruminants with respiratory disease symptoms. The test performed efficiently without any cross-amplification. The multiplex PCR efficiency was 98.31%, 95.48%, 102.77% and 91.46% whereas the singleplex efficiency was 93.43%, 98.82%, 102.55% and 92.0% for CaPV, PPRV, PM and Mccp, respectively. The correlation coefficient was greater than 0.99 for all the targets in both multiplex and singleplex. Based on cycle threshold values, intra and inter assay variability, ranged between the limits of 2%-4%, except for lower concentrations of Mccp. The detection limits at 95% confidence interval (CI) were 12, 163, 13 and 23 copies/reaction for CaPV, PPRV, PM and Mccp, respectively. The multiplex assay was able to detect CaPVs from all genotypes, PPRV from the four lineages, PM and Mccp without amplifying the other subspecies of mycoplasmas. The discriminating power of the assay was proven by accurate detection of the targeted pathogen (s) by screening 58 viral and bacterial isolates representing all four targeted pathogens. Furthermore, by screening 81 pathological samples collected from small ruminants showing respiratory disease symptoms, CaPV was detected in 17 samples, PPRV in 45, and PM in six samples. In addition, three samples showed a co-infection of PPRV and PM. Overall, the one-step multiplex RT-qPCR assay developed will be a valuable tool for rapid detection of individual and co-infections of the targeted pathogens with high specificity and sensitivity.

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.

Dried fluid spots for peste des petits ruminants virus load evaluation allowing for non-invasive diagnosis and genotyping

BACKGROUND

Active surveillance of peste des petits ruminants (PPR) should ease prevention and control of this disease widely present across Africa, Middle East, central and southern Asia. PPR is now present in Turkey at the gateway to the European Union. In Bangladesh, the diagnosis and genotyping of PPR virus (PPRV) may be hampered by inadequate infrastructures and by lack of proper clinical material, which is often not preserved under cold chain up to laboratories. It has been shown previously that Whatman® 3MM filter paper (GE Healthcare, France) preserves the nucleic acid of PPRV for at least 3 months at 32°C.

RESULTS

In this study, we demonstrate the performances of filter papers for archiving RNA from local PPRV field isolates for further molecular detection and genotyping of PPRV, at -70°C combined with ambient temperature, for periods up to 16 months. PPR-suspected live animals were sampled and their blood and nasal swabs were applied on filter papers then air dried. Immediately after field sampling, RT-PCR amplifying a 448-bp fragment of the F gene appeared positive for both blood and nasal swabs when animals were in febrile stage and only nasal swabs were detected positive in non-febrile stage. Those tested positive were monitored by RT-PCR up to 10 months by storage at -70°C. At 16 months, using real time RT-PCR adapted to amplify the N gene from filter paper, high viral loads could still be detected (~2 x 10(7) copy numbers), essentially from nasal samples. The material was successfully sequenced and a Bayesian phylogenetic reconstruction achieved adequate resolution to establish temporal relationships within or between the geographical clusters of the PPRV strains.

CONCLUSIONS

This clearly reveals the excellent capacity of filter papers to store genetic material that can be sampled using a non-invasive approach.

Development and testing of a field diagnostic assay for peste des petits ruminants virus

We have developed an immunochromatographic test for the diagnosis of peste des petits ruminants (PPR) under field conditions. The diagnostic assay has been tested in the laboratory and also under field conditions in Ivory Coast, Pakistan, Ethiopia and Uganda. The test is carried out on a superficial swab sample (ocular or nasal) and showed a sensitivity of 84% relative to PCR. The specificity was 95% over all nasal and ocular samples. The test detected as little as 10³ TCID₅₀ (50% tissue culture infectious doses) of cell culture-grown virus, and detected virus isolates representing all four known genetic lineages of peste des petits ruminants virus. Virus could be detected in swabs from animals as early as 4 days post-infection, at a time when clinical signs were minimal. Feedback from field trials was uniformly positive, suggesting that this diagnostic tool may be useful for current efforts to control the spread of PPR.

Protective efficacy of a single immunization with capripoxvirus-vectored recombinant peste des petits ruminants vaccines in presence of pre-existing immunity

Sheeppox, goatpox and peste des petits ruminants (PPR) are highly contagious ruminant diseases widely distributed in Africa, the Middle East and Asia. Capripoxvirus (CPV)-vectored recombinant PPR vaccines (rCPV-PPR vaccines), which have been developed and shown to protect against both Capripox (CP) and PPR, would be critical tools in the control of these important diseases. In most parts of the world, these disease distributions overlap each other leaving concerns about the potential impact that pre-existing immunity against either disease may have on the protective efficacy of these bivalent rCPV-PPR vaccines. Currently, this question has not been indisputably addressed. Therefore, we undertook this study, under experimental conditions designed for the context of mass vaccination campaigns of small ruminants, using the two CPV recombinants (Kenya sheep-1 (KS-1) strain-based constructs) developed previously in our laboratory. Pre-existing immunity was first induced by immunization either with an attenuated CPV vaccine strain (KS-1) or the attenuated PPRV vaccine strain (Nigeria 75/1) and animals were thereafter inoculated once subcutaneously with a mixture of CPV recombinants expressing either the hemagglutinin (H) or the fusion (F) protein gene of PPRV (10(3) TCID50/animal of each). Finally, these animals were challenged with a virulent CPV strain followed by a virulent PPRV strain 3 weeks later. Our study demonstrated full protection against CP for vaccinated animals with prior exposure to PPRV and a partial protection against PPR for vaccinated animals with prior exposure to CPV. The latter animals exhibited a mild clinical form of PPR and did not show any post-challenge anamnestic neutralizing antibody response against PPRV. The implications of these results are discussed herein and suggestions made for future research regarding the development of CPV-vectored vaccines.

Experimental infection of sheep and goats with a recent isolate of peste des petits ruminants virus from Kurdistan

Peste des petits ruminants (PPR) is a contagious viral disease of sheep and goats common in Africa and Asia. Its high morbidity and mortality has a devastating impact on agriculture in developing countries. As an example, an Asian lineage IV strain of PPRV was responsible for mass fatalities among wild goats in Kurdistan in 2010/2011. In separate experiments, three sheep and three goats of German domestic breeds were subcutaneously inoculated with the Kurdish virus isolate; three uninfected sheep and goats were housed together with the inoculated animals. All inoculated animals, all in-contact goats and two in-contact sheep developed high fever (up to 41.7 °C), depression, severe diarrhea, ocular and nasal discharge as well as ulcerative stomatitis and pharyngitis. Infected animals seroconverted within a few days of the first detection of viral genome. Clinical signs were more pronounced in goats; four out of six goats had to be euthanized. Necropsy revealed characteristic lesions in the alimentary tract. Peste des petits ruminants virus (PPRV) RNA was detected in blood as well as nasal, oral and fecal swabs and tissues. The 2011 Kurdish strain of PPRV is highly virulent in European goats and spreads easily to in-contact animals, while disease severity and contagiosity in sheep are slightly lower. PPRV strains like the tested recent isolate can have a high impact on small ruminants in the European Union, and therefore, both early detection methods and intervention strategies have to be improved and updated regularly.

A SYBR Green I based real time RT-PCR assay for specific detection and quantitation of Peste des petits ruminants virus

Background

Peste des petits ruminants (PPR) is an economically important disease of small ruminants such as sheep and goats. The disease is characterized by severe pyrexia, oculo-nasal discharge, pneumonia, necrosis and ulceration of the mucous membrane and inflammation of the gastro-intestinal tract leading to severe diarrhea. A SYBR Green I based real time RT-PCR targeting the N gene of PPRV has not been established for PPRV detection. Thus, the objective of present study was to develop highly sensitive N gene target SYBR Green I real time RT-PCR for specific detection and quantification of PPRV in clinical samples. A set of primers was designed to detect the nucleocapsid (N) gene of PPRV.

Results

The assay exhibited high specificity as all the viruses which have clinical and structural similarities to PPRV including Canine distemper virus (CDV), Measles virus (MV), Bluetongue virus (BTV) and Newcastle disease virus (NDV) failed to show an amplification signal. The lower detection limit of the assay was 5.11 copies/μl (Ct value of 33.67 ± 0.5) and 0.001 TCID₅₀/ml (Ct value of 34.7 ± 0.5) based on plasmid copy number and tissue culture infectivity titre. The assay was 3-log more sensitive than the conventional RT-PCR. The coefficient of variation (CV) values for intra- and inter-assay variability were low, ranging from 0.32% - 2.31%, and 0.71% - 5.32%, respectively. To evaluate the performance of the newly developed assay, a total of 36 clinical samples suspected of PPR were screened for the presence of PPRV in parallel with conventional RT-PCR. The real time RT-PCR assay detected PPRV in 30 (83.3%) of clinical samples compared to 16 (44.4%) by conventional RT-PCR.

Conclusions

The two-step SYBR Green I based real time RT-PCR assay reported here is highly sensitive, specific, reproducible and rapid for detection and quantification of PPRV nucleic acids.

Development and Preliminary Evaluation of a New Real-Time RT-PCR Assay For Detection of Peste des petits Ruminants Virus Genome

A duplex real-time reverse transcription-polymerase chain reaction (qRT-PCR) assay was developed for a simple and rapid diagnosis of Peste des petits ruminants (PPR). qRT-PCR primers and TaqMan probe were designed on a conserved region of nucleocapsid protein (Np) of PPR virus (PPRV) genome. An in vitro transcript of the target region was constructed and tested to determine analytical sensitivity. Commercial heterologous Armored RNA(®) was used as an internal positive control (IPC) for either RNA isolation or RT-PCR steps. The detection limit of the newly designed duplex real-time RT-PCR (qRT-PCR PPR_Np) was approximately 20 copies/μl with a 95% probability. No amplification signals were recorded when the qRT-PCR PPR_Np was applied to viruses closely related or clinically similar to PPRV- or to PPR-negative blood samples. A preliminary evaluation of the diagnostic performance was carried out by testing a group of 43 clinical specimens collected from distinct geographic areas of Africa and Middle East. qRT-PCR PPR_Np showed higher sensitivity than the conventional gel-based RT-PCR assays, which have been used as reference standards. Internal positive control made it possible to identify the occurrence of 5 false-negative results caused by the amplification failure, thus improving the accuracy of PPRV detection.

Molecular characterization of peste des petits ruminants viruses from outbreaks caused by unrestricted movements of small ruminants in pakistan

Peste des petits ruminants (PPR) is an endemic disease of small ruminants, and vaccination has been the method of control but outbreaks are continuously occurring in Pakistan. The following study presents a detailed investigation of an outbreak, suspected to be PPR, probably introduced by PPRV-infected sheep and goats from Sindh Province (north-west) to Punjab Province (central) of Pakistan during the flood relief campaign in 2011. A total of 70 serum samples from 28 different flocks were tested with competitive ELISA (H antibodies), which detected 24 (34.2%) samples positive for PPRV antibodies. Nasal swabs and faeces were tested with immunocapture ELISA (N antigen), which detected 18 (25.7%) samples positive for PPRV antigen. The RNA detected positive (n = 28, 40%) using real-time PCR was subjected to conventional PCR for the amplification of the fusion and nucleoprotein genes. Sequencing of both genes and subsequent phylogenetic analysis indicated the grouping of all the sequences to be in lineage IV along with other Asian isolates of PPRV. However, sequences of both genes were divided into two groups within lineage IV. One group of viruses clustered with previously characterized Pakistani isolates, whereas the other group was distinctly clustered with isolates from the Middle East or India. The sequence identity indicated the introduction of at least one population of PPRV from a different source and circulation in the local flocks of small ruminants, which emphasized the need to obtain health clearance certificate before movement of animals. The results of this study provide baseline data for the genetic characterization of different PPRV populations in Pakistan.

Genetic analysis of peste des petits ruminants virus from Pakistan

Background

Peste des petits ruminants (PPR) is an endemic and highly contagious disease in small ruminants of Pakistan. Despite the fact that an effective vaccine is available, outbreaks are regularly occurring in the country. Thus so far, the diagnosis has primarily been made based on clinical outcome or serology. This study was carried out to characterize PPRV from an emerging wave of outbreaks from Punjab, Pakistan.

Results

A total of 32 blood samples from five different flocks were tested with real-time PCR for the presence of PPRV genome. The samples detected positive in real-time PCR (n = 17) were subjected to conventional PCR for the amplification of the nucleoprotein (N) gene. Phylogenetic analysis of the sequenced N genes (n = 8) indicated the grouping of all the sequences in lineage IV along with PPRV strains from Asian and Middle East. However, interestingly sequences were divided into two groups. One group of viruses (n = 7) clustered with previously characterized Pakistani isolates whereas one strain of PPRV was distinct and clustered with Saudi Arabian and Iranian strains of PPRV.

Conclusions

Results demonstrated in this study expanded the information on the genetic nature of different PPRV population circulating in small ruminants. Such information is essential to understand genetic nature of PPRV strains throughout the country. Proper understanding of these viruses will help to devise control strategies in PPRV endemic countries such as Pakistan.

Peste des Petits Ruminants, the next eradicated animal disease?

Peste des Petits Ruminants (PPR) is a widespread viral disease caused by a Morbillivirus (Paramyxoviridae). There is a single serotype of PPR virus, but four distinct genetic lineages. Morbidity and mortality are high when occurring in naive sheep and goats populations. Cattle and African buffaloes (Syncerus caffer) are asymptomatically infected. Other wild ruminants and camels may express clinical signs and mortality. PPR has recently spread in southern and northern Africa, and in central and far-east Asia. More than one billion sheep and goats worldwide are at risk. PPR is also present in Europe through western Turkey. Because of its clinical incidence and the restrictions on animal movements, PPR is a disease of major economic importance. A live attenuated vaccine was developed in the 1980s, and has been widely used in sheep and goats. Current researches aim (i) to make it more thermotolerant for use in countries with limited cold chain, and (ii) to add a DIVA mark to shorten and reduce the cost of final eradication. Rinderpest virus-another Morbillivirus-was the first animal virus to be eradicated from Earth. PPRV has been proposed as the next candidate. Considering its wide distribution and its multiple target host species which have an intense mobility, it will be a long process that cannot exclusively rely on mass vaccination. PPR specific epidemiological features and socio-economic considerations will also have to be taken into account, and sustained international, coordinated, and funded strategy based on a regional approach of PPR control will be the guarantee toward success.

Fatalities in wild goats in Kurdistan associated with Peste des Petits Ruminants virus

Between August 2010 and February 2011, over 750 deaths were recorded among wild goats (Capra aegagrus, the endangered progenitor of the domestic goat) in Kurdistan. Based on the clinical signs and post-mortem findings, the involvement of peste des petits ruminants virus (PPRV) was suspected. This was confirmed by laboratory analysis, and the virus was found to be closely related to a Turkish strain isolated in 2000. During the outbreak in wild goats, no disease in domestic animals was reported. Domestic ruminants in the region are routinely vaccinated with an attenuated vaccine based on the 'Nigeria/75/1' strain of PPRV. This is the first report of active PPRV infection in Kurdistan and most likely the immunity afforded by vaccination prevented spillover infections. It is therefore recommended to continue with the campaign. Conversely, there is no justification for the use of force to keep the endangered wild goats away from domestic flocks.

Peste des petits ruminants: a suitable candidate for eradication?

This year will see the final announcement, accompanied by much justifiable celebration, of the eradication from the wild of rinderpest, the 'cattle plague' that has been with us for so many centuries. The only known rinderpest virus (RPV) remaining is in a relatively small number of laboratories around the world, and in the stockpiles of vaccine held on a precautionary basis. As we mark this achievement, only the second virus ever eradicated through human intervention, it seems a good time to look at rinderpest's less famous cousin, peste des petits ruminants ('the plague of small ruminants') and assess if it should, and could, also be targeted for global eradication.

Tissue distribution and expression of signaling lymphocyte activation molecule receptor to peste des petits ruminant virus in goats detected by real-time PCR

In the present study, we investigated the tissue distribution and expression of signaling lymphocyte activation molecule (SLAM) in 40 tissues and organs of goats by real-time RT-PCR, in order to determine the role of these receptors in tissue tropism. SLAM mRNA was detected in all the samples investigated. The expression of SLAM mRNA was detected at high levels in spleen, mesenteric lymph node, hilar lymph node, mandibular lymph node, superficial cervical lymph node, nasal mucosa, duodenum, heart, gallbladder, thymus and blood; this is similar to the tissue tropism of peste des petits ruminant virus. However, it was surprising that expression of SLAM was low in lungs, colon and rectum which are the major sites of replication of PPRV. In addition, very low levels were detected in larynx, tongue and esophagus, which suggest the possible presence of an alternative receptor for PPRV. This study provided the first data on caprine SLAM for use in further studies of the pathogenesis of PPRV in goats.

Detection and phylogenetic analysis of peste des petits ruminants virus isolated from outbreaks in Punjab, Pakistan

Peste des Petits Ruminants (PPR) is an important viral disease of small ruminants and is endemic in Pakistan. In the following study, samples from two outbreaks of PPR in goats have been subjected to laboratory investigations. The Peste des Petits Ruminants virus (PPRV) genome was detected using both conventional and real-time PCR. Genetic characterization of the local PPRV field isolates was conducted by sequencing 322 bp of the fusion (F) gene and 255 bp of the nucleoprotein (N) gene. The phylogenetic tree based on the F gene clustered samples from both outbreaks into lineage 4 along with other Asian isolates, specifically into subcluster 1 along with isolates from Middle East. Analysis of N gene revealed a different pattern. In this case, the Pakistani samples clustered with Chinese, Tajikistani and Iranian isolates, which probably represents the true geographical pattern of virus circulation. This is the first report presenting the phylogenetic tree based on N gene as well as performing a parallel comparison of the trees of F and N gene together from Pakistani isolates. The results of this study shed light on the PPRV population in Pakistan and emphasize the importance of using molecular methods to understand the epidemiology. Such understanding is essential in any efforts to control the number and impact of outbreaks that are occurring in endemic countries such as Pakistan, especially in the current scenario where OIE and FAO are eager to control and subsequently eradicate PPR from the globe, as has been achieved for Rinderpest.

Design and Application of Nucleic Acid Standards for Quantitative Detection of Enteric Viruses by Real-Time PCR

Synthetic multiple-target RNA and DNA oligonucleotides were constructed for use as quantification standards for nucleic acid amplification assays for human norovirus genogroup I and II, hepatitis E virus, murine norovirus, human adenovirus, porcine adenovirus and bovine polyomavirus. This approach overcomes the problems related to the difficulty of obtaining practical quantities of viral RNA and DNA from these viruses. The quantification capacity of assays using the standards was excellent in each case (R(2) > 0.998 and PCR efficiency > 0.89). The copy numbers of the standards were equivalent to the genome equivalents of representative viruses (murine norovirus and human adenovirus), ensuring an accurate determination of virus presence. The availability of these standards should facilitate the implementation of nucleic acid amplification-based methods for quantitative virus detection.

A real time RT-PCR assay for the specific detection of Peste des petits ruminants virus

Peste des petits ruminants virus (PPRV) causes a devastating disease of small ruminants present across much of Africa and Asia. Recent surveillance activities and phylogenetic analyses have suggested that the virus is an emerging problem as it is now being detected in areas previously free of the disease. As such, the virus not only is threatening small ruminant production and agricultural stability in the developing world, but also poses an economic threat to livestock in the European Union (EU) through introduction from European Turkey and North Africa. This report describes the development of a high throughput, rapid, real time RT-PCR method for the sensitive and specific detection of PPRV using robotic RNA extraction. This assay targets the nucleocapsid (N) gene of PPRV and has been shown to detect all four genetic lineages of PPRV in tissues, ocular and nasal swabs and blood samples collected in the field. The lowest detection limit achieved was approximately 10 genome copies/reaction, making this assay an ideal tool for the sensitive and rapid detection of PPRV in diagnostic laboratories.

Rapid detection of peste des petits ruminants virus by a reverse transcription loop-mediated isothermal amplification assay

Peste des petits ruminants virus (PPRV) is the causative agent of peste des petits ruminants (PPR), an economically important viral disease of small ruminants. In this report, a one-step, single-tube, reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay was developed for the detection of PPRV. A set of six LAMP primers were designed based on the matrix gene sequence of PPRV to amplify the target RNA by incubation at 63°C for 60min with Bst DNA polymerase and reverse transcriptase. The amplified products could be observed by the naked eye. The specificity of the RT-LAMP assay was validated by amplifying eight strains of PPRV isolated in different geographical areas. No cross-reactivity with other related viruses, including rinderpest virus, canine distemper virus and measles virus, was detected. The sensitivity of the assay was similar to that of real-time reverse transcription polymerase chain reaction (RT-PCR) and 10-fold higher than that of conventional RT-PCR. Twenty clinical samples were evaluated by the RT-LAMP assay, and the results were consistent with those of real-time RT-PCR. As a simple, rapid and accurate detection method, this RT-LAMP assay has important potential applications in the clinical diagnosis of PPR and the surveillance of PPRV.

Application of semi-quantitative M gene-based hydrolysis probe (TaqMan) real-time RT-PCR assay for the detection of peste des petits ruminants virus in the clinical samples for investigation into clinical prevalence of disease

Peste des petits ruminants (PPR) is a contagious, notifiable and economically important transboundary viral disease of small ruminants. In this study, a hydrolysis probe-based real-time reverse transcription-polymerase chain reaction (rt RT-PCR) assay for the detection and semi-quantification of PPR virus (PPRV) nucleic acid was developed using the virus RNA and matrix (M) gene-specific primers with Hex-labelled fluorescent probe and applied for the detection of PPRV in clinical samples to identify outbreaks and to monitor the prevalence of disease. The assay was found specific with a sensitivity detection limit of 0.5 pg of total PPRV RNA. Based on a serial dilution of the live-attenuated PPR vaccine virus, the detection limits were approximately 0.1 and 1 TCID₅₀ for the hydrolysis probe and conventional RT-PCR assays, respectively. The assay was linear within a range of 50 ng to 0.5 pg total virus RNA with an intra-assay coefficient of variation (CV) in the range of 0.91-2.86% and an inter-assay CV ranging between 0.59% and 2.37%. The standardized rt RT-PCR was easily employed for the detection of PPRV nucleic acid directly in the experimental/field clinical samples. This assay detected the PPRV in pre-clinical swab materials as early as the 4th day post-infection (dpi) and up to 17th dpi in nasal, ocular and oral swabs collected from experimentally infected animals. The rt RT-PCR was rapid, specific and 10 times more sensitive than conventional RT-PCR. It is an alternative test to the existing diagnostic assays and could be useful with enhanced applicability in field clinical diagnosis by avoiding the use of expensive commercial real-time PCR reagents. This assay was adopted directly in the detection of PPRV nucleic acid in clinical samples collected from sheep and goats suspected of PPR to monitor outbreak situations and the clinical prevalence of PPR in India.