Development and validation of a simplified serotyping ELISA based on monoclonal antibodies for the diagnosis of foot-and-mouth disease virus serotypes O, A, C and Asia 1

Validation of two multiplex lateral flow devices for the rapid detection and typing of foot-and-mouth disease viruses

Lateral Flow Devices (LFDs) represent a simple tool for the rapid diagnosis of FMD, particularly in endemic regions, often lacking adequate and equipped laboratories. Other experimental prototypes offer a user-friendly FMD confirmation tool, but serotype identification is crucial for transmission patterns evaluation and for vaccine selection and their serotyping capacity was limited. This study describes the validation of two multiplex devices based on well-characterized monoclonal antibodies: LFD1 (O, A and Asia1) and LFD2 (SAT1 and SAT2). First, the ability of the LFDs to recognize the widest spectrum of strains was assessed. Eighty-three tissue-cultured FMDV strains were tested with LFD1 and 15 with LFD2, confirming the capability to recognize and serotype a broad range of lineages and sub-lineages belonging to all 7 endemic pools. The diagnostic sensitivity related to FMDV detection was evaluated using 224 real-time RT-PCR positive samples collected in endemic countries, resulting in 87.5 % for LFD1 (140/160 detected) and 70 % for LFD2 (45/64 detected). The diagnostic sensitivity of serotyping capabilities was assessed by testing field samples in parallel with an antigen-ELISA kit: applied on 178 samples, LFD1 correctly typed 96 %, 94 % and 83 % of samples positive for type O (n = 95), A (n = 54) and Asia1 (n = 29) respectively, while LFD2 correctly typed 77 % SAT1 (n = 52) and 82 % SAT2 (n = 40) in 92 positive field samples. A 100 % diagnostic specificity was found testing 60 epithelium homogenates collected from animals negative for FMD. Obtained data highlighted the devices' potential value for field use to support the enhanced surveillance of FMD.

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.

Foot-and-mouth disease virus dynamics in border areas of Pakistan with Afghanistan

BACKGROUND

Foot and mouth disease (FMD) is a highly contagious disease that impacts cloven-hoofed animals globally. The illegal trade of livestock between the border regions of Pakistan and Afghanistan can contribute to the spread of this disease. This study focuses on investigating the outbreaks of FMD that occurred in this area from June 2020 to May 2021.

METHODS

RESULTS: A total of 233 epithelial tissue samples were collected, and 77% were found positive for FMDV through an antigen-detection by ELISA and molecular conformation through RT-PCR. The study found three serotypes of FMDV dominating in the border area of Pakistan with Afghanistan: O, A, and Asia-1. The outbreak activity was peaked between August/September followed by July/October 2020. Phylogenetic analysis conducted using the VP1 region sequence showed that serotype O isolates belonged to the Middle East-South Asia (ME-SA) topotype, PanAsia-2 lineage, and ANT-10 sub-lineage, while serotype Asia-1 isolates belonged to a novel lineage BD-18.The highest prevalence of serotype O of FMDV was found in cattle and buffalo of 1-2 year age group, while the highest outbreak ratio of serotype O was recorded in goats of 0-1 year age group and sheep of > 2 year age group. The serotype O was more prevalent in male than female sheep. The type A was more prevalent in females of sheep and goats than their corresponding males. The serotype Asia-1 was more prevalent in females of cattle and sheep than their corresponding males. The outbreak epidemiology of FMD varied significantly between various regions, months of study, animal species, age groups, and gender.

CONCLUSIONS

The study found that FMD outbreaks in the border area of Pakistan and Afghanistan were diverse and complicated, and that different types of FMDV were circulating. The study recommended effective actions to stop FMD transmission in this area.

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.

Relationship between neutralizing and opsonizing monoclonal antibodies against foot-and-mouth disease virus

Previous studies demonstrated that polyclonal antibodies against foot-and-mouth disease virus (FMDV) generated by vaccination can mediate immune functions not only through virus neutralization but also through promoting virus uptake by macrophages and dendritic cells that are otherwise resistant to FMDV infection. This causes abortive infections resulting in activation, enhanced antigen presentation but also cell death. Here we report the use of RAW264.7 cells representing a murine macrophage cells line to characterize opsonizing functions of a collection of monoclonal antibodies (mAbs) against FMDV O and A serotypes. We demonstrate that all neutralizing immunoglobulin G isotype mAbs are able to opsonize FMDV resulting in increased cell death of RAW264.7 cells. In contrast, neutralizing IgM antibodies did not possess this activity. Opsonization was observed with broader reactivity within the serotype when compared to neutralization. Importantly, the anti-O serotype D9 mAb reacting with the continuous epitope within the G-H loop of VP1 that contains the RGD binding site of FMDV, opsonized several FMDV serotypes despite its restricted neutralizing activity within the O serotype. Furthermore, by generating RAW264.7 cells expressing bovine CD32, an easy-to-use cell-based assay system to test for bovine antibody-dependent enhanced infection of FMDV was generated and tested with a collection of sera. The data indicate that opsonizing titers correlated better with vaccine dose when compared to neutralizing titers. On the other hand, neutralization and opsonization titers were similar predictive of protection. We conclude that low avidity interactions are sufficient to mediate Fcγ receptor-mediated immune functions that could contribute to protective immune responses against FMDV.

Genotyping of foot-and-mouth disease viruses collected in Sudan between 2009 and 2018

Foot-and-mouth disease (FMD) is widely distributed in Sudan where outbreaks occur on an annual basis especially during the winter months (December-February). This study aimed to increase our understanding of the epidemiological patterns of FMD in Sudan and connections to neighbouring countries by characterizing the genetic sequences of FMD viruses (FMDV) collected from samples collected in 10 Sudanese states over a 10-year period (between 2009 and 2018). FMDV was detected in 91 of the 265 samples using an antigen-detection ELISA. Three serotypes were detected: O (46.2%), A (34.0%), and SAT 2 (19.8%). Fifty-two of these samples were submitted for sequence analyses, generating sequences that were characterized as belonging to O/EA-3 (n = 17), A/AFRICA/G-IV (n = 23) and SAT 2/VII/Alx-12 (n = 12) viral lineages. Phylogenetic analyses provided evidence that FMDV lineages were maintained within Sudan, and also highlighted epidemiological connections to FMD outbreaks reported in neighbouring countries in East and North Africa (such as Ethiopia and Egypt). This study motivates continued FMD surveillance in Sudan to monitor the circulating viral lineages and broader initiatives to improve our understanding of the epidemiological risks in the region.

Characterization of the O/ME-SA/Ind-2001d foot-and-mouth disease virus epidemic recorded in the Maghreb during 2014-2015

The O/ME-SA/Ind-2001d has been the main foot-and-mouth disease virus (FMDV) lineage responsible for FMD epidemics outside the Indian subcontinent from 2013 to 2017. In 2014, outbreaks caused by this FMDV lineage were reported in Maghreb, where it was initially detected in Algeria and Tunisia and later in Morocco. This was the first incursion of an FMDV type O of exotic origin in the Maghreb region after 14 years of absence. In this study, we report analyses of both VP1 and whole-genome sequences (WGSs) generated from 22 isolates collected in Algeria and Tunisia between 2014 and 2015. All the WGSs analysed showed a minimum pairwise identity of 98.9% at the nucleotide level and 99% at the amino acid level (FMDV coding region). All Tunisian sequences shared a single putative common ancestor closely related to FMDV strains circulating in Libya during 2013. Whereas sequences from Algeria suggest the country experienced two virus introductions. The first introduction is represented by strains circulating in 2014 which are closely related to those from Tunisia, the second one, of which the origin is more uncertain, includes strains collected in Algeria in 2015 that gave origin to the 2015 outbreak reported in Morocco. Overall, our results demonstrated that a unique introduction of O/Ind-2001d FMDV occurred in Maghreb through Tunisia presumably in 2014, and from then the virus spread into Algeria and later into Morocco.

Cross-Serotype Reactivity of ELISAs Used to Detect Antibodies to the Structural Proteins of Foot-and-Mouth Disease Virus

Antibodies to the foot-and-mouth disease virus (FMDV) capsid induced by infection or vaccination can provide serotype-specific protection and be measured using virus neutralization tests and viral structural-protein (SP-)ELISAs. Separate tests are needed for each serotype, but cross-serotype reactions complicate serotyping. In this study, inter-serotypic responses were quantified for five SP-ELISA formats by testing 294 monovalent mainly bovine sera collected following infection, vaccination, or vaccination and infection with one of five serotypes of FMDV. Over half of the samples, representing all three immunization categories, scored positive for at least one heterologous serotype and some scored positive for all serotypes tested. A comparative approach to identifying the strongest reaction amongst serotypes O, A and Asia 1 improved the accuracy of serotyping to 73–100% depending on the serotype and test system, but this method will be undermined where animals have been infected and/or vaccinated with multiple FMDV serotypes. Preliminary studies with stabilized recombinant capsid antigens of serotypes O and A that do not expose internal epitopes showed reduced cross-reactivity, supporting the hypothesis that capsid integrity can affect the serotype-specificity of the SP-ELISAs. The residual cross-reactivity associated with capsid surface epitopes was consistent with the evidence of cross-serotype virus neutralization.

Diversity of SAT2 foot-and-mouth disease virus in Sudan: implication for diagnosis and control

Like other East African countries, Sudan experienced circulation of more than one topotype of SAT2 foot-and-mouth disease virus (FMDV). In Sudan, topotype XIII of SAT2 virus was recorded in 1977 and 2008 and topotype VII in 2007, 2010, 2013, 2014 and 2017. This work evaluated the impact of such diversity on diagnosis and control. After one or three doses of a vaccine derived from a Sudanese SAT2 virus of topotype VII originated in 2010, heterologous neutralizing antibody titres with Sudanese SAT2 viruses in 2008 were ≤ 1.2 log 10, not consistent with likely protection. Simultaneously, homologous titres were 1.65 (after one dose) or 1.95 and 2.55 log10 (after 3 doses). When r1 values between the vaccine virus and the SAT2 viruses isolated in 2008, whilst topotype XIII was circulating, were derived, values (≈ 0.00) suggested similarly poor antigenic relationship and unlikely cross protection. Concurrently, SAT2 positive field sera from Sudan in 2016 were not unvaryingly identified by virus neutralization tests (VNT) employing SAT2 viruses from 2010 and 2008. Proportions of positive sera by SAT2 virus from 2010 were always higher than those by viruses from 2008; consistent with the more frequent and recent circulation of topotype VII prior to 2016. Proportions by SAT2 virus from 2010 were 0.68 (± 0.1) in one location (n = 72), 0.39 (± 0.1) in another one (n = 94) and 0.52 (± 0.1) in the whole test group (n = 166). Corresponding values by viruses of 2008 were 0.53 (± 0.1), 0.27 (± 0.1) and 0.38 (± 0.1). In the whole test group, differences were statistically significant (p = .02339). Like post-vaccination sera, field sera (natural immunity) showed no considerable cross neutralization between topotype VII and presumably XIII; almost 45% (43/96) of SAT2 positive field sera were positive to one topotype but not to the other. Experimental and surveillance findings emphasized the implication of SAT2 diversity in Sudan. It is concluded that it is difficult to control SAT2 infection in Sudan using a monovalent vaccine. Beside a prophylactic vaccine from topotype VII, stockpiling of antigens from topotype XIII and enhanced virological surveillance with rapid genotyping and matching studies are necessary approaches. When more frequent circulation of more than one SAT2 topotype occurs, retrospective diagnosis by serological surveys could be problematic or imprecise.

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.

Recombinant cystatin-like protein-based competition ELISA for Trichinella spiralis antibody test in multihost sera

Objectives

Trichinella spiralis is a zoonotic parasite with a complex parasitic life cycle and exposed to animals or humans by infectious meat. To control transmissions of T. spiralis through the food chain to humans, sensitive and selective multihost sera-diagnosis is urgent needed for monitoring T. spiralis exposure.

Methods

A competition enzyme-linked immunosorbent assay (cELISA) for T. spiralis infection diagnosis in multihost sera was developed based on recombinant cystatin-like protein (rCLP-cELISA) as well as monoclonal antibodies. The sensitivity and accuracy of the rCLP-cELISA were quantified using swine (n = 1316), mice (n = 189) and human (n = 157) serum samples. T. spiralis-antibody targeting test ability of the rCLP-cELISA in swine (n = 22) and human (n = 36), instead of other parasites or viruses antibodies, was evaluated.

Results

The rCLP-cELISA showed high agreement with commercial ELISA kits in field swine sera assessed by Cohen’s kappa value (κ = 0.7963). And it showed 100% specificity in human trichinellosis detection with sensitivity of 96.49%, no cross-reaction with other parasite or virus infections, and high positive detection rate of 87.5% in low-dose infected swine. Besides, the rCLP-cELISA exhibited potential in the detection of T. spiralis, T. nelsoni and Trichinella T8 infections.

Conclusions

The rCLP-cELISA can be used for T. spiralis-associated antibody test in multihost sera.

Infections with T. spiralis that lives in host muscles for long periods of time are commonly difficult to diagnosis without causing a strong immune response or symptoms. The habit of eating raw/undercooked pork meat accidentally introduces humans into the exposure of T. spiralis that circulates between herds and rodents. There is an urgent need for serological antibody test of T. spiralis to monitor the infection of humans as well as hosts in the food chain, which is restricted by the mixture type of current used antigens and species-specific secondary antibodies for different hosts. We developed a novel recombinant cystatin-like protein-based competition enzyme-linked immunosorbent assay (rCLP-cELISA) employing monoclonal antibody. The proposed method showed considerable sensitivity and specificity in filed swine sera and human serum samples with good versatility in mice. Taking advantage of its controllable quality stability, the rCLP-cELISA had potential applications for screening of T. spiralis infections for multihost sera in one test. With the development of monoclonal antibody modification strategies and the discovery of antigenic proteins from parasitic pathogens, the proposed competition ELISA also provides useful reference for the improvement of serological assay for monitoring the exposure of zoonotic parasites.

Combining Multiple Assays Improves Detection and Serotyping of Foot-and-Mouth Disease Virus. A Practical Example with Field Samples from East Africa

Multiple serotypes and topotypes of foot-and-mouth disease virus (FMDV) circulate in endemic areas, posing considerable impacts locally. In addition, introductions into new areas are of great concern. Indeed, in recent years, multiple FMDV outbreaks, caused by topotypes that have escaped from their original areas, have been recorded in various parts of the world. In both cases, rapid and accurate diagnosis, including the identification of the serotype and topotype causing the given outbreaks, plays an important role in the implementation of the most effective and appropriate measures to control the spread of the disease. In the present study, we describe the performance of a range of diagnostic and typing tools for FMDV on a panel of vesicular samples collected in northern Tanzania (East Africa, EA) during 2012–2018. Specifically, we tested these samples with a real-time RT-PCR targeting 3D sequence for pan-FMDV detection; an FMDV monoclonal antibody-based antigen (Ag) detection and serotyping ELISA kit; virus isolation (VI) on LFBKαVβ6 cell line; and a panel of four topotype-specific real-time RT-PCRs, specifically tailored for circulating strains in EA. The 3D real-time RT-PCR showed the highest diagnostic sensitivity, but it lacked typing capacity. Ag-ELISA detected and typed FMDV in 71% of sample homogenates, while VI combined with Ag-ELISA for typing showed an efficiency of 82%. The panel of topotype-specific real-time RT-PCRs identified and typed FMDV in 93% of samples. However, the SAT1 real-time RT-PCR had the highest (20%) failure rate. Briefly, topotype-specific real-time RT-PCRs had the highest serotyping capacity for EA FMDVs, although four assays were required, while the Ag-ELISA, which was less sensitive, was the most user-friendly, hence suitable for any laboratory level. In conclusion, when the four compared tests were used in combination, both the diagnostic and serotyping performances approached 100%.

Scientific Opinion on the assessment of the control measures for category A diseases of Animal Health Law: Foot and Mouth Disease

EFSA received a mandate from the European Commission to assess the effectiveness of some of the control measures against diseases included in the Category A list according to Regulation (EU) 2016/429 on transmissible animal diseases ('Animal Health Law'). This opinion belongs to a series of opinions where these control measures will be assessed, with this opinion covering the assessment of control measures for foot and mouth disease (FMD). In this opinion, EFSA and the AHAW Panel of experts review the effectiveness of: i) clinical and laboratory sampling procedures, ii) monitoring period and iii) the minimum radius of the protection and surveillance zones, and the minimum length of time the measures should be applied in these zones. The general methodology used for this series of opinions has been published elsewhere; nonetheless, the transmission kernels used for the assessment of the minimum radius of the protection zone of 3 km and of the surveillance zone of 10 km are shown. Several scenarios for which these control measures had to be assessed were designed and agreed prior to the start of the assessment. The monitoring period of 21 days was assessed as effective, and it was concluded that the protection and the surveillance zones comprise > 99% of the infections from an affected establishment if transmission occurred. Recommendations, provided for each of the scenarios assessed, aim to support the European Commission in the drafting of further pieces of legislation, as well as for plausible ad hoc requests in relation to FMD.