Arboviruses collectively account for thousands of deaths every year. These viruses are transmitted to humans via infected arthropods, mostly mosquitoes and ticks. The severity of arboviral infections is diverse and ranges from asymptomatic infection to severe disease that can lead to death. In 2024, the World Health Organization (WHO) recorded over 10,000 deaths caused by the four serotypes of the dengue virus (DENV) alone1. The same year, the virus infected over 14 million people, including 50,000 severe cases1. While DENV is the most prominent arbovirus, the group includes other life-threatening pathogens that have been responsible for multiple outbreaks worldwide. A recent summary review of arboviral infections in Africa found that these viruses, including DENV, yellow fever virus (YFV), chikungunya virus (CHIKV), Crimean-Congo hemorrhagic fever virus (CCHFV), Rift Valley fever virus (RVFV), West Nile virus (WNV), and Zika virus (ZIKV), caused at least 29 outbreaks across the continent in 20232. In 2022, a report published by the WHO Regional Office for Africa highlighted the current limitations in arbovirus surveillance across the region, emphasizing the urgent need to develop methods for arbovirus surveillance and control3.
Clinical diagnosis of arboviral infections is challenging due to the similarities in symptoms, such as fever, arthralgia, and general malaise, that are common to other pathogens present in endemic regions4. In addition, due to the co-circulation and potentially co-infection of the viruses, distinction of the etiological pathogen is difficult5. Laboratory confirmation is crucial for differential diagnosis. Several methods exist for the detection of arborviruses in human samples. Direct methods, including molecular diagnostic tests, viral antigen detection, and viral isolation, detect the presence of the pathogen, while indirect methods, such as serological diagnosis, measure the immune response to the viral infection6.
A plethora of methods for the detection of antibody responses to arboviruses has been developed. These include enzyme-linked immunosorbent assays (ELISAs), complement fixation, hemagglutination inhibition, and microsphere immunoassays6,7. This report presents a multiplex fluorescence microsphere-based immunoassay (FMIA) for the detection of antibody responses to arbovirus antigens. Microsphere-based assays8 are extensively used in serology and offer several advantages, most importantly, the ability for the detection of multiple analytes in a single reaction with minimal sample volume. Optically coded microspheres (magnetic polystyrene beads) coated with recombinant antigens of interest are used in an indirect serological immunoassay. The coupled beads are then incubated with samples, and antigen-specific antibodies are detected using an anti-human IgG secondary antibody conjugated to a Phycoerythrin (PE) fluorophore reporter. Several analyzers are available for the detection of emitted fluorescence, which is reported as MFI.
The principle of the assay is detailed in Angeloni et al.8. Briefly, the antigens of interest are chemically bound to color-coded microspheres. For this, the beads are initially treated with 1-ethyl-3-[3-dimethylaminopropyl] Carbodiimide (EDC) and N-hydroxysulfosuccinimide (sulfo-NHS), which activate the carboxyl group on the surface of the beads, creating an amine-reactive compound. This intermediate semi-stable compound is then mixed with the protein of interest, whereby amine moieties of the protein are covalently bound to the beads, generating stable microbeads coated with the protein of interest at the surface. The antigen-bound beads are incubated with samples, allowing antibodies to bind to specific antigens. Antigen-bound antibodies are detected using an anti-immunoglobulin secondary antibody conjugated to a fluorescent dye. We use PE-labelled secondary antibody. MFIs are measured using a light imager (details of the instrument are provided in the Table of Materials). The instrument uses two LED lights, a red LED and a green LED, which separately excite the beads' internal dyes and a reporter fluorescence on the surface of the beads9. Filters are then used to classify beads based on the color and to quantify fluorescence emitted by the analytes.
We have previously applied the technology for the detection of antibody responses to SARS-CoV-210 and vaccine-preventable diseases11 and showed that multiplex assays constitute an invaluable tool for seroprevalence and surveillance studies. The goal of this project is to extend the use of the FMIA to the detection of antibody responses to multiple antigens belonging to arboviruses with an aim to apply the assay to screen samples from the African region.
Arbovirus multiplex assays using multiplex technology have been described elsewhere using different antigen targets such as non-structural protein 1 (NS1)12,13 or envelope domain III (EDIII)14. A 50-plex assay, which includes 26 arbovirus antigens (including NS1, EDIII, viral-like particles (VLPs), and multiple other antigens to test for pathogens that are co-circulating in the region, is presented. The assay will allow assessment of transmission intensity for these pathogens. A summary of recombinant antigens used for the development of the assay is provided in Table 1. The protocol presented in this report was developed in complement to an extensive method development study focused on optimizing the detection of arboviruses.
Ordinarily, the coupling (or fixation) of antigens to the microsphere beads is carried out in single tubes8 (manual coupling). This process is time-consuming, cumbersome, and prone to reproducibility errors. This article reports a protocol using an automated instrument to perform the successive steps involved in the chemical binding of antigens to the beads. In this manuscript, we report steps undertaken for the validation of the new protocol. The validation of the new protocol was performed by comparing IgG responses measured with a 50-plex FMIA using antigen-coupled beads prepared with either the manual method or the automated protocol. Further validation of the method was performed by analyzing human serum samples from African and French cohorts.
The automated beads coupling protocol is fast, allowing simultaneous coupling of up to 96 analytes in a single run. More importantly, results are comparable to those obtained using the established manual protocol, with reduced batch-to-batch variation.