Generation of monoclonal antibodies against foot-and-mouth disease virus SAT 2 and the development of a lateral flow strip test for virus detection

Development and Validation of Serotype-Specific Blocking ELISA for the Detection of Anti-FMDV O/A/Asia1/SAT2 Antibodies

Foot-and-mouth disease (FMD) is one of the most infectious viral transboundary diseases of livestock, which causes devastating global economic losses. Different enzyme-linked immunosorbent assays (ELISAs) are used for sero-surveillance of the foot-and-mouth disease virus (FMDV). However, more sensitive, accurate, and convenient ELISAs are still required to detect antibodies against FMDV serotypes. The primary goal of this study was to establish serotype-specific monoclonal antibody (mAb)-based blocking ELISAs (mAb-bELISAs) that would provide better performance characteristics or be equivalent in performance characteristics compared with a conventional polyclonal antibody (pAb)-based competitive ELISA (pAb-cELISA). Four mAb-bELISAs were developed using FMDV serotype-specific mAbs for the detection of anti-FMDV/O/A/Asia1/SAT2 antibodies. Using a 50% cut-off, all four mAb-bELISAs exhibited species-independent 99.74%, 98.01%, 96.59%, and 98.55% diagnostic specificity (DSp) and 98.93%, 98.25%, 100%, and 87.50% diagnostic sensitivity (DSe) for FMDV serotypes O, A, Asia1, and SAT2, respectively. In addition, a 100% DSe of serotypes O- and SAT2-specific mAb-bELISAs was observed for porcine sera when the cut-off was 30%. All mAb-bELISAs developed in this study displayed high repeatability/reproducibility without cross-reactivity. Finally, the diagnostic performance of mAb-bELISAs was found to be better than or equivalent to compared with pAb-cELISAs, suggesting that mAb-bELISAs can be used to replace existing pAb-ELISAs for the detection of antibodies against these four FMDV serotypes.

Chimeric Porcine Parvovirus VP2 Virus-like Particles with Epitopes of South African Serotype 2 Foot-and-Mouth Disease Virus Elicits Specific Humoral and Cellular Responses in Mice

Southern Africa Territories 2 (SAT2) foot-and-mouth disease (FMD) has crossed long-standing regional boundaries in recent years and entered the Middle East. However, the existing vaccines offer poor cross-protection against the circulating strains in the field. Therefore, there is an urgent need for an alternative design approach for vaccines in anticipation of a pandemic of SAT2 Foot-and-mouth disease virus (FMDV). The porcine parvovirus (PPV) VP2 protein can embed exogenous epitopes into the four loops on its surface, assemble into virus-like particles (VLPs), and induce antibodies and cytokines to PPV and the exogenous epitope. In this study, chimeric porcine parvovirus VP2 VLPs (chimeric PPV-SAT2-VLPs) expressing the T-and/or B-cell epitopes of the structural protein VP1 of FMDV SAT2 were produced using the recombinant pFastBac™ Dual vector of baculoviruses in Sf9 and HF cells We used the Bac-to-Bac system to construct the recombinant baculoviruses. The VP2-VLP--SAT2 chimeras displayed chimeric T-cell epitope (amino acids 21-40 of VP1) and/or the B-cell epitope (amino acids 135-174) of SAT FMDV VP1 by substitution of the corresponding regions at the N terminus (amino acids 2-23) and/or loop 2 and/or loop 4 of the PPV VP2 protein, respectively. In mice, the chimeric PPV-SAT2-VLPs induced specific antibodies against PPV and the VP1 protein of SAT2 FMDV. The VP2-VLP-SAT2 chimeras induced specific antibodies to PPV and the VP1 protein specific epitopes of FMDV SAT2. In this study, as a proof-of-concept, successfully generated chimeric PPV-VP2 VLPs expressing epitopes of the structural protein VP1 of FMDV SAT2 that has a potential to prevent FMDV SAT2 and PPV infection in pigs.

Experimental design for the development of a multiplex antigen lateral flow immunoassay detecting the Southern African Territory (SAT) serotypes of foot-and-mouth disease virus

Antigenic lateral flow immunoassays (LFIAs) rely on the non-competitive sandwich format, including a detection (labelled) antibody and a capture antibody immobilised onto the analytical membrane. When the same antibody is used for the capture and the detection (single epitope immunoassay), the saturation of analyte epitopes by the probe compromises the capture and lowers the sensitivity. Hence, several factors, including the amount of the probe, the antibody-to-label ratio, and the contact time between the probe and the analyte before reaching the capture antibody, must be adjusted. We explored different designs of experiments (full-factorial, optimal, sub-optimal models) to optimise a multiplex sandwich-type LFIA for the diagnosis and serotyping of two Southern African Territory (SAT) serotypes of the foot-and-mouth disease virus, and to evaluate the reduction of the number of experiments in the development. Both assays employed single epitope sandwich, so most influencing variables on the sensitivity were studied and individuated. We upgraded a previous device increasing the sensitivity by a factor of two and reached the visual limit of detection of 103.7 and 104.0 (TCID/mL) for SAT 1 and SAT 2, respectively. The positioning of the capture region along the LFIA strip was the most influent variable to increase the detectability. Furthermore, we confirmed that the 13-optimal DoE was the most convenient approach for designing the device.

Detection Methods for Foodborne Viruses: Current State-of-Art and Future Perspectives

Foodborne viruses have been recognized as important threats to food safety and human health. Rapid and accurate detection is one of the most crucial measures for food safety control. With the development of biology, chemistry, nanoscience, and related interdisciplines, detection strategies have been devised and advanced continuously. This review mainly focuses on the progress of detection methods for foodborne viruses. The current detection methods for foodborne viruses are summarized, including traditional electron microscopy and cultural isolation, immunoassay, molecular technology, biosensors, and newly emerging CRISPR/Cas-based detection technology. Furthermore, a comparison of the detection methods was objectively discussed. This review provides a comprehensive account of foodborne virus detection methods from fundamentals to state-of-the-art and illustrates the advantages and disadvantages of the current methods and proposes the future trends and directions for foodborne virus detection. It is hoped that this review can update current knowledge and present blueprints in order to accelerate futuristic development.

Detection of Nipah and Hendra Viruses Using Recombinant Human Ephrin B2 Capture Virus in Immunoassays

Nipah virus (NiV) and Hendra virus (HeV) are classified as high-consequence zoonotic viruses characterized by high pathogenicity and high mortality in animals and humans. Rapid diagnosis is essential to containing the outbreak. In this study, the henipavirus receptor ephrin B2 was examined to determine whether it could be used as a universal ligand for henipavirus detection in immunoassays. Enzyme-linked immunosorbent assays (ELISAs) were developed using recombinant ephrin B2 as the capture ligand and two monoclonal antibodies (mAbs) as detection reagents. Using mAb F27NiV-34, which cross-reacts with NiV and HeV, we were able to detect NiV and HeV, while mAb F20NiV-65 was used to detect NiV. Therefore, using these two ELISAs, we were able to differentiate between NiV and HeV. Furthermore, we developed a rapid lateral flow strip test for NiV detection using ephrin B2 as the capture ligand combined with mAb F20NiV-65 as the detector. Taken together, our results show that the combination of ephrin B2 and a specific mAb provides an excellent pairing for NiV and HeV detection.

Combining a Universal Capture Ligand and Pan-Serotype Monoclonal Antibody to Develop a Pan-Serotype Lateral Flow Strip Test for Foot-and-Mouth Disease Virus Detection

Foot-and-mouth disease virus (FMDV) causes FMD, a highly contagious disease of cloven-hoofed animals including cattle, goats, pigs and sheep. Rapid detection of FMDV is critical to limit the devastating economic losses due to FMD. Current laboratory methods for FMDV detection such as virus isolation, real-time reverse transcription PCR and antigen detection enzyme-linked immunosorbent assay (AgELISA) are labor-intensive, requiring trained personnel and specialized equipment. We present the development and validation of a pan-serotype lateral flow strip test (LFST) that uses recombinant bovine integrin αvβ6 as a universal capture ligand and a pan-serotype monoclonal antibody (mAb) to detect FMDV. The LFST detected all seven FMDV serotypes, where the diagnostic sensitivity was comparable to the AgELISA, and the diagnostic specificity was 100% without cross-reactivity to other viruses causing vesicular disease in livestock. This rapid test will be useful for on-site FMDV detection, as well as in laboratories in endemic countries where laboratory resources are limited.

Design of multiplexing lateral flow immunoassay for detection and typing of foot-and-mouth disease virus using pan-reactive and serotype-specific monoclonal antibodies: Evidence of a new hook effect

The foot-and-mouth disease (FMD) is the most important transboundary viral disease of livestock in the international context, because of its extreme contagiousness, widespread diffusion, and severe impact on animal trade and animal productions. The rapid and on-field detection of the virus responsible for the FMD represents an urgent demand to efficiently control the diffusion of the infection, especially in low resource setting where the FMD is endemic. Colorimetric lateral flow immunoassay (LFIA) is largely used for the development of rapid tests, due to the extreme simplicity, cost-effectiveness, and on-field operation. In this work, two multiplex LFIA devices were designed for the diagnosis of FMD and the simultaneous identification of major circulating serotypes of the FMD virus. The LFIAs relied on the sandwich-type immunoassay and combined a set of well-characterised monoclonal antibodies (mAb) pairs. One LFIA aimed at detecting and identifying O, A and Asia-1 serotypes, the second device enabled the detection and differentiation of the SAT 1 and SAT 2 serotypes. Both devices also incorporated a broad-specific test line reporting on infection from FMDV, regardless the strain and the serotype involved. Accordingly, five and four reactive zones were arranged in the two devices to achieve a total of six simultaneous analyses. The development of the two multiplex systems highlighted for the first time the relevance of the mAb positioning along the LFIA strip in connection with the use of the same or different mAb as capture and detector ligands. In fact, the excess of detector mAb typically employed for increasing the sensitivity of sandwich immunoassay induced a new type of hook effect when combined with the same ligand used as the capture. This effect strongly impacted assay sensitivity, which could be improved by an intelligent alignment of the mAb pairs along the LFIA strip. The analytical and diagnostic performances of the two LFIAs were studied by testing reference FMDV strains grown in cell cultures and some representative field samples (epithelium homogenates). Almost equivalent sensitivity and specificity to those of a reference Ag-ELISA kit were shown, except for the serotype SAT 2. These simple devices are suitable in endemic regions for in-field diagnosis of FMD accompanied by virus serotyping and, moreover, could be deployed and used for rapid confirmation of secondary outbreaks after FMD incursions in free-areas, thus contributing to promptly implement control measures.

Ten Years of Lateral Flow Immunoassay Technique Applications: Trends, Challenges and Future Perspectives

The Lateral Flow Immunoassay (LFIA) is by far one of the most successful analytical platforms to perform the on-site detection of target substances. LFIA can be considered as a sort of lab-in-a-hand and, together with other point-of-need tests, has represented a paradigm shift from sample-to-lab to lab-to-sample aiming to improve decision making and turnaround time. The features of LFIAs made them a very attractive tool in clinical diagnostic where they can improve patient care by enabling more prompt diagnosis and treatment decisions. The rapidity, simplicity, relative cost-effectiveness, and the possibility to be used by nonskilled personnel contributed to the wide acceptance of LFIAs. As a consequence, from the detection of molecules, organisms, and (bio)markers for clinical purposes, the LFIA application has been rapidly extended to other fields, including food and feed safety, veterinary medicine, environmental control, and many others. This review aims to provide readers with a 10-years overview of applications, outlining the trends for the main application fields and the relative compounded annual growth rates. Moreover, future perspectives and challenges are discussed.

High selectivity detection of FMDV- SAT-2 using a newly-developed electrochemical nanosensors

Foot-and-mouth disease virus serotype South-Africa territories-2 (FMDV-SAT-2) is the most fastidious known type in Aphthovirus which is subsequently reflected in the diagnosis regime. Rapid and early diagnostic actions are usually taken in response to the FMDV outbreak to prevent the dramatic spread of the disease. Virus imprinted sensor (VIP sensor) is gathering huge attention for the selective detection of pathogens. Thus, the whole virus particles of SAT-2 together with an electropolymerized film of poly(o-phenylenediamine) (PoPD) on gold-copper modified screen-printed electrode were applied to fabricate SAT-2-virus imprinted polymer (SAT-2-VIP). The SAT-2-VIPs were fully characterized using cyclic voltammetry (CV), linear sweep voltammetry (LSV), Atomic force microscopy (AFM), Scanning electron microscope (SEM), and Fourier transform Infra-Red (FTIR) spectroscopy. Excellent selective binding affinity towards the targeted virus particle was achieved with limits of detection and quantification of 0.1 ng/mL and 0.4 ng/mL, respectively. In terms of viral interference, the sensor did not show cross-reactivity towards other animal viruses including FMDV serotype A, O, or even SAT-2 subtype Libya and the un-related virus Lumpy skin disease virus (LSDV). This high selectivity provides a sensible platform with 70 folds more sensitivity than the reference RT-PCR as revealed from the application of SAT-2-VIP sensor for rapid analysis of clinical samples with no need for treatment or equipped labs. Thus, as diagnostic and surveillance technologies, on-site point of care diagnostics for SAT-2 virus are supported.

Phage Display Screening of Bovine Antibodies to Foot-and-Mouth Disease Virus and Their Application in a Competitive ELISA for Serodiagnosis

For serodiagnosis of foot-and-mouth disease virus (FMDV), monoclonal antibody (MAb)-based competitive ELISA (cELISA) is commonly used since it allows simple and reproducible detection of antibody response to FMDV. However, the use of mouse-origin MAb as a detection reagent is questionable, as antibody responses to FMDV in mice may differ in epitope structure and preference from those in natural hosts such as cattle and pigs. To take advantage of natural host-derived antibodies, a phage-displayed scFv library was constructed from FMDV-immune cattle and subjected to two separate pannings against inactivated FMDV type O and A. Subsequent ELISA screening revealed high-affinity scFv antibodies specific to a serotype (O or A) as well as those with pan-serotype specificity. When BvO17, an scFv antibody specific to FMDV type O, was tested as a detection reagent in cELISA, it successfully detected FMDV type O antibodies for both serum samples from vaccinated cattle and virus-challenged pigs with even higher sensitivity than a mouse MAb-based commercial FMDV type O antibody detection kit. These results demonstrate the feasibility of using natural host-derived antibodies such as bovine scFv instead of mouse MAb in cELISA for serological detection of antibody response to FMDV in the susceptible animals.

Development of two rapid lateral flow test strips for detection of foot-and-mouth disease virus SAT 1 and SAT 3

Foot-and-mouth disease (FMD) is a highly contagious disease that affects cattle, sheep, goats, pigs, and over 70 species of wildlife. FMD continues to be a major economic concern for livestock productivity in many countries. FMDV has seven serotypes O, A, Asia 1, C, and Southern Africa Territories (SAT) 1, 2, and 3. Although SAT 1, and SAT 3 outbreaks are not as common as serotypes O, A, Asia 1, and SAT 2, outbreaks have also been reported. The recent outbreaks of SAT 1 occurred in Cameroon, Zimbabwe, South Africa, and Uganda, while most recent SAT 3 occurred in Namibia in 2019. The development of rapid and easy-to-perform FMDV detection tests is critical to control the outbreak and spread of FMD. The current project has produced monoclonal antibodies (mAb) against FMDV serotypes SAT 1, and SAT 3. Using these mAbs, two lateral flow immunochromatographic (LFI) strip tests for the detection of FMDV SAT 1, and SAT 3 have been developed. SAT 1 strip test detected 14 out of 15 SAT 1 field isolates. The SAT 3 strip test detected all four SAT 3 isolates tested, but the signal is weak for UGA 10/97 and showed no cross-reactivity with other FMDV serotypes. The diagnostic specificities of the SAT 1 and the SAT 3 tests are 100 %, which are higher than double antibody sandwich (DAS) ELISA. The diagnostic sensitivity of the SAT 1 test strip is lower than that of DAS ELISA, while the diagnostic sensitivity of the SAT 3 test strip is similar to that of DAS ELISA. The first reported SAT 1 and SAT 3 strip test combined with the previously developed SAT 2 strip test can be used for quick diagnosis in endemic countries in Africa. Rapid identification of FMDV serotypes is critical for disease control and vaccine selection. Also, these strip tests can be used in the laboratory to quickly screen samples from the field.

Detection of Foot-and-Mouth Disease Virus in Swine Meat Juice

Foot-and-mouth disease virus (FMDV) is a highly contagious agent that impacts livestock industries worldwide, leading to significant financial loss. Its impact can be avoided or minimized if the virus is detected early. FMDV detection relies on vesicular fluid, epithelial tags, swabs, serum, and other sample types from live animals. These samples might not always be available, necessitating the use of alternative sample types. Meat juice (MJ), collected after freeze-thaw cycles of skeletal muscle, is a potential sample type for FMDV detection, especially when meat is illegally imported. We have performed experiments to evaluate the suitability of MJ for FMDV detection. MJ was collected from pigs that were experimentally infected with FMDV. Ribonucleic acid (RNA) was extracted from MJ, sera, oral swabs, and lymph nodes from the same animals and tested for FMDV by real-time reverse transcription polymerase chain reaction (rRT-PCR). MJ was also tested for FMDV antigen by Lateral Flow Immunoassay (LFI). FMDV RNA was detected in MJ by rRT-PCR starting at one day post infection (DPI) and as late as 21 DPI. In contrast, FMDV RNA was detected in sera at 1–7 DPI. Antigen was also detected in MJ at 1–9 DPI by LFI. Live virus was not isolated directly from MJ, but was recovered from the viral genome by transfection into susceptible cells. The data show that MJ is a good sample type for FMDV detection.

Multiplexed DIVA tests for rapid detection of FMDV infection/circulation in endemic countries

Foot-and-mouth disease (FMD) is an important transboundary disease affecting domestic and wild ruminants. Due to FMD outbreaks, the annual economic losses in endemic countries range from USD 6.1 billion to 200 billion. It also restricts the export of animals/animal by-products to FMD-free countries. FMD-free countries can experience a more severe economic loss due to the culling of infected animals as experienced by the UK in 2001 outbreaks. In endemic countries outbreaks occur mainly due to unrestricted animal movements. This creates a difficult situation in an endemic setting for controlling FMD spread to nearby areas. During post-vaccination surveillance, testing of serum samples using single test may not be able to substantiate complete freedom from infection. Thus, there is a requirement of more sensitive, robust, and accurate diagnostic tests to detect the FMDV infection/virus circulation in the vaccinated population with more accuracy than the available diagnostic tests. This can be achieved by using multiple antigens and setting the criteria for the positivity/negativity of the samples. Thus, this review emphasizes the comparison and the practical utility of the available diagnostic tests which detect antibodies against single antigen with those which detect antibodies against multiple antigens in single testing. It also emphasizes the utility of these tests in PCP-FMD (Progressive Control Pathway for Foot-and-Mouth Disease) going on in endemic countries.

Foot-and-mouth disease virus detection on a handheld real-time polymerase chain reaction platform

Foot-and-mouth disease (FMD) is a highly contagious disease of livestock that requires rapid control. Early detection is critical but transportation of samples to laboratory delays testing. Sensitive and specific field-deployable assays are therefore desirable. Real-time reverse transcription polymerase chain reaction (RRT-PCR) and RRT-loop-mediated isothermal amplification assays for FMDV on portable platforms have been described but none of these are handheld. In this report, we have evaluated a handheld Biomeme two3™ Real-Time PCR Thermocycler (two3) as a field-deployable platform for FMDV RRT-PCR targeting the 3D gene segment. Two3's performance was compared with the laboratory-based reference assay on the ABI7500 platform. RNA extraction using a rapid Biomeme proprietary sample prep technology (M1) was compared with MagMax RNA extraction. Two3 successfully detected FMDV isolates for six serotypes (O, A, Asia 1, SAT 1, 2 and 3). Serotype C was excluded since it has not been detected in the field since 2004. The limits of detection for serial 10-fold dilutions of cell culture isolates were equal or one log different between two3 and ABI7500. Furthermore, two3 detected FMDV RNA in multiple sample types including serum, vesicular fluid, tissue suspensions, oral fluid, oral and nasal swabs. Two3 also detected FMDV RNA directly in vesicular fluid and other samples without prior RNA extraction. Comparison of the time to first detection of a positive result in serial samples in MagMax RNA extraction/ABI7500 (MgMx/ABI) system vs. M1 RNA extraction/Two3 system revealed similar or slightly better analytical sensitivity for the MgMx/ABI system. Overall, RNA extraction by M1 yielded good results and FMDV RNA detection on two3 was not significantly different from the ABI7500. Therefore, two3 could potentially enable sensitive penside detection of FMDV within an hour using M1-extracted RNA or direct testing of vesicular fluid and swabs without RNA extraction thereby ensuring prompt implementation of appropriate control measures.