Development of recombinase polymerase amplification assays for the rapid detection of peste des petits ruminants virus

Research Progress on Emerging Viral Pathogens of Small Ruminants in China during the Last Decade

China is the country with the largest number of domestic small ruminants in the world. Recently, the intensive and large-scale sheep/goat raising industry has developed rapidly, especially in nonpastoral regions. Frequent trading, allocation, and transportation result in the introduction and prevalence of new pathogens. Several new viral pathogens (peste des petits ruminants virus, caprine parainfluenza virus type 3, border disease virus, enzootic nasal tumor virus, caprine herpesvirus 1, enterovirus) have been circulating and identified in China, which has attracted extensive attention from both farmers and researchers. During the last decade, studies examining the etiology, epidemiology, pathogenesis, diagnostic methods, and vaccines for these emerging viruses have been conducted. In this review, we focus on the latest findings and research progress related to these newly identified viral pathogens in China, discuss the current situation and problems, and propose research directions and prevention strategies for different diseases in the future. Our aim is to provide comprehensive and valuable information for the prevention and control of these emerging viruses and highlight the importance of surveillance of emerging or re-emerging viruses.

A rapid and convenient method for on-site detection of MON863 maize through real-time fluorescence recombinase polymerase amplification

As large-scale planting of genetically modified (GM) crops increases, the development of a rapid and convenient method for on-site detection of GM crops is important. We combined the advantages of recombinase polymerase amplification (RPA) and fluorescence detection to establish a rapid, sensitive, specific, and simple detection platform for on-site detection of MON863 maize. Test samples were added directly to the platform after simple pre-treatment with a DNA extraction-free method. Results were obtained through real-time monitoring with a portable instrument, which facilitated sample-in/answer-out on-site detection. The entire detection process, including sample preparation, RPA and identification of amplification results, was accomplished in approximately 10 min. Furthermore, the detection was achieved with a simple and inexpensive portable device. This method has high potential for application in other fields requiring rapid detection of DNA targets, such as in field research, resource-limited areas, and science education.

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.

Development of real-time reverse transcription recombinase polymerase amplification (RPA) for rapid detection of peste des petits ruminants virus in clinical samples and its comparison with real-time PCR test

Peste des petits ruminants (PPR), caused by small ruminant morbillivirus (SRMV), formerly called peste des petits ruminants virus (PPRV), is one of the most important pathogens in small ruminants, and has tremendous negative economic impact on the sheep industry worldwide. Current detection of PPRV in clinical samples mainly relies on real-time RT-PCR. Particularly, samples collected from rural area require highly equipped laboratories for screening. A rapid, real-time reverse-transcription recombinase polymerase amplification assay (RT-RPA), employing primers and exo probe, was thus developed to perform at 42 °C for 20 min, and the detection limit at 95% probability was 14.98 copies per reaction and 0.326 TCID₅₀/mL based on plasmid copy number and tissue culture infectivity titre. All the four lineages of PPRV could be detected with no cross-reaction to other pathogens including measles virus (MeV), goatpox virus (GTPV), canine distemper virus (CDV), foot-and-mouth disease virus (FMDV) and Mycoplasma capricolum subsp. capripneumoniae (Mccp). The performance of real-time RT-RPA assay was validated by testing 138 field samples and compared to real-time RT-PCR. The results indicated an excellent diagnostic agreement between real-time RT-RPA and a reference real-time RT-PCR method with the kappa value of 0.968. Compared to real-time RT-PCR, the sensitivity of real-time RT-RPA was 100%, while the specificity was 97.80%. The developed RT-RPA assay offers a promising platform for simple, rapid, and reliable detection of PPRV, especially in the resource-limited settings.

Development of a droplet digital PCR assay for sensitive detection of porcine circovirus 3

Porcine circovirus 3 (PCV3), a newly emerged circovirus, is associated with porcine dermatitis and nephropathy syndrome, reproductive failure and multi-systemic inflammation disease, and is widely distributed in pig populations worldwide. Therefore, developing specific diagnostic assays will be important for controlling this emerging pathogen. In this study, we developed a novel droplet digital PCR (ddPCR) assay targeting the PCV3 cap gene to improve the sensitivity of PCV3 detection. The established assay is highly specific to PCV3, and does not cross react with other important swine pathogens. The assay's detection limit was 1.68 ± 0.29 copies of PCV3 DNA per reaction (n = 8), an approximately 10-fold greater sensitivity than that of our previously developed quantitative real-time PCR (qPCR) assay for the same virus. The ddPCR assay results were highly reproducible, with intra- and inter-assay coefficient of variation values of <9.0%. Of the 239 archived pig tissue and serum samples, 42 tested positive for PCV3 by the ddPCR assay. Among the 42 positive samples, 31 tested positive by the qPCR assay. Notably, PCV3 was detected in the serum samples collected from commercially imported healthy boars from the US, France and the UK during 2011-2017. The overall agreement between the two assays was 95.39% (228/239). Furthermore, the linear regression analysis showed that the ddPCR and the qPCR results were significantly correlated with an R² value of 0.9945. Collectively, these results indicate that the ddPCR assay is a robust diagnostic tool for sensitive detection of PCV3, even in samples with low viral loads.