Optimization of peptide-based ELISA for serological diagnostics: a retrospective study of human monkeypox infection

Rapid and highly sensitive colorimetric LAMP assay and integrated device for visual detection of monkeypox virus

BACKGROUND

The monkeypox virus (MPXV) is a linear double-stranded DNA virus with a large genome that causes tens of thousands of infections and hundreds of deaths in at least 40 countries and regions worldwide. Therefore, timely and accurate diagnostic testing could be an important measure to prevent the ongoing spread of MPXV and widespread epidemics.

RESULTS

Here, we designed multiple sets of primers for the target region of MPXV for loop-mediated isothermal amplification (LAMP) detection and identified the optimal primer set. Then, the specificity in fluorescent LAMP detection was verified using the plasmids containing the target gene, pseudovirus and other DNA/RNA viruses. We also evaluated the sensitivity of the colorimetric LAMP detection system using the plasmid and pseudovirus samples, respectively. Besides, we used monkeypox pseudovirus to simulate real samples for detection. Subsequent to the establishment and introduction of a magnetic beads (MBs)-based nucleic acid extraction technique, an integrated device was developed, characterized by rapidity, high sensitivity, and remarkable specificity. This portable system demonstrated a visual detection limit of 137 copies/mL, achieving sample-to-answer detection within 1 h.

SIGNIFICANCE

The device has the advantages of integration, simplicity, miniaturization, and visualization, which help promote the realization of accurate, rapid, portable, and low-cost testing. Meanwhile, this platform could facilitate efficient, cost-effective and easy-operable point-of-care testing (POCT) in diverse resource-limited settings in addition to the laboratory.

Development of a multiplex real-time PCR assay for the simultaneous detection of mpox virus and orthopoxvirus infections

Since May 2022, the multi-country outbreak of monkeypox (mpox) has raised a great concern worldwide. Early detection of mpox virus infection is recognized as an efficient way to prevent mpox transmission. Mpox specific detection methods reported up to now are based on the SNPs among mpox virus and other orthopoxviruses. We have therefore developed a real-time PCR based mpox detection method targeting mpox virus specific sequences (N3R and B18Rplus). We have also optimized an orthopoxvirus detection system which targets the highly conserved E9L and D6R genes. The mpox and orthopoxvirus real-time PCR assays have a high sensitivity (1 copy/reaction) and specificity. Mpox viral DNA and clinical samples from mpox patients are detected with the mpox detection system. Furthermore, we have established a multiplex real-time PCR detection system allowing simultaneous and efficient detection of mpox and orthopoxvirus infections.

Electrochemical Immunoassay Platform for Human Monkeypox Virus Detection

In this study, we reported a selective impedimetric biosensor for the detection of A29 which is the target protein of the monkeypox virus (MPXV). The working principle of the biosensor relies on the interaction mechanism between A29, which is an internal membrane protein of MPXV, and the heparan sulfate receptor. For this purpose, after immobilizing heparan sulfate onto the gold screen-printed electrode surface, its interaction with A29 protein was monitored using electrochemical impedance spectroscopy. After the optimization of experimental parameters, the analytical characteristics of the developed MPVX immunosensor were examined. The developed immunosensor exhibited a linear detection range between 2.0 and 50 ng mL-1, with a detection limit of 2.08 ng mL-1 and a quantification limit of 6.28 ng mL-1. Furthermore, a relative standard deviation value of 2.82% was determined for 25 ng mL-1. Apart from that, sample application studies were also performed with the standard addition of A29 protein to 1:10 diluted real serum samples that were taken from healthy individuals, and very good recovery values were obtained.

Monkeypox Virus Neutralizing Antibodies at Six Months from Mpox Infection: Virologic Factors Associated with Poor Immunologic Response

A natural monkeypox virus infection may not induce sufficient neutralizing antibody responses in a subset of healthy individuals. The aim of this study was to evaluate monkeypox virus-neutralizing antibodies six months after infection and to assess the virological factors predictive of a poor immunological response. Antibodies were assessed using a plaque reduction neutralization test at six months from mpox infection; mpox cutaneous, oropharyngeal, and anal swabs, semen, and plasma samples were tested during infection. Overall, 95 people were included in the study; all developed detectable antibodies. People who were positive for the monkeypox virus for more days had higher levels of antibodies when considering all tested samples (p = 0.029) and all swabs (p = 0.005). Mpox cycle threshold values were not predictive of antibody titers. This study found that the overall days of monkeypox virus detection in the body, irrespective of the viral loads, were directly correlated with monkeypox virus neutralizing antibodies at six months after infection.

Mpox: An Overview of Pathogenesis, Diagnosis, and Public Health Implications

Mpox, caused by viruses of the genus Orthopoxvirus, is an emerging threat to human and animal health. With increasing urbanization and more frequent interaction between humans and wild animals, the risk of Mpox transmission to humans has increased significantly. This review aims to examine in depth the epidemiology, pathogenesis, and diagnosis of Mpox, with a special focus on recent discoveries and advances in understanding the disease. Molecular mechanisms involved in viral replication will be examined, as well as risk factors associated with interspecific transmission and spread of the disease in human populations. Currently available diagnostic methods will also be discussed, with a critical analysis of their limitations and possible future directions for improving the accuracy and timeliness of diagnosis. Finally, this review will explore the public health implications associated with Mpox, emphasizing the importance of epidemiological surveillance, vaccination, and emergency preparedness to prevent and manage possible outbreaks. Understanding the epidemiology and control strategies for Mpox is critical to protecting the health of human and animal communities and mitigating the risk of interspecific transmission and spread of the disease.

How the Orthodox Features of Orthopoxviruses Led to an Unorthodox Mpox Outbreak: What We've Learned, and What We Still Need to Understand

Orthopoxviruses have repeatedly confounded expectations in terms of the clinical illness they cause and their patterns of spread. Monkeypox virus (MPXV), originally characterized in the late 1950s during outbreaks among captive primates, has been recognized since the 1970s to cause human disease (mpox) in West and Central Africa, where interhuman transmission has largely been associated with nonsexual, close physical contact. In May 2022, a focus of MPXV transmission was detected, spreading among international networks of gay, bisexual, and other men who have sex with men. The outbreak grew in both size and geographic scope, testing the strength of preparedness tools and public health science alike. In this article we consider what was known about mpox before the 2022 outbreak, what we learned about mpox during the outbreak, and what continued research is needed to ensure that the global public health community can detect, and halt further spread of this disease threat.

Monkeypox virus: insights into pathogenesis and laboratory testing methods

The monkeypox virus (MPXV) is a zoonotic pathogen that transmits between monkeys and humans, exhibiting clinical similarities with the smallpox virus. Studies on the immunopathogenesis of MPXV revealed that an initial strong innate immune response is elicited on viral infection that subsequently helps in circumventing the host defense. Once the World Health Organization (WHO) declared it a global public health emergency in July 2022, it became essential to clearly demarcate the MPXV-induced symptoms from other viral infections. We have exhaustively searched the various databases involving Google Scholar, PubMed, and Medline to extract the information comprehensively compiled in this review. The primary focus of this review is to describe the diagnostic methods for MPXV such as polymerase chain reaction (PCR), and serological assays, along with developments in viral isolation, imaging techniques, and next-generation sequencing. These innovative technologies have the potential to greatly enhance the accuracy of diagnostic procedures. Significant discoveries involving MPXV immunopathogenesis have also been highlighted. Overall, this will be a knowledge repertoire that will be crucial for the development of efficient monitoring and control strategies in response to the MPXV infection helping clinicians and researchers in formulating healthcare strategies.

Antibody response to mycobacterial Rpf B protein and its immunodominant peptides in HIV-TB co-infected individuals

Diagnosis of TB at early stages of HIV infection may lead to timely intervention for improving patient outcome. Antibodies to Mycobacterium tuberculosis recombinant RpfB protein and two immunodominant peptides of Rpf B protein were evaluated in the sera of HIV +TB+, HIV+ and HIV- pulmonary TB patients by ELISA. Serum antibodies from 90 % and 65 % of HIV+TB+ patients reacted to recombinant RpfB protein and synthetic peptide RpfP1 respectively. Overall, this study shows that resuscitation promoting factor B elicits humoral antibody response in HIV+TB+ co-infected individuals and be proposed as a potential biomarker for diagnosis of HIV+TB+ patients, however further longitudinal follow up studies are warranted.

Role of the Laboratory in the Diagnosis of Poxvirus Infections

Although WHO-led global efforts led to eradication of smallpox over four decades ago, other poxviruses, especially monkeypox, have re-emerged to occupy the ecological niche vacated by smallpox. Many of these viruses produce similar lesions thus mandating a prompt laboratory confirmation. There has been considerable evolution in the techniques available to diagnose these infections and differentiate between them. With the 2022 multi-country outbreak of monkeypox, significant efforts were made to apprise the laboratory diagnosis of the virus and numerous real-time-PCR-based assays were made commercially available. This chapter discusses the sample collection and biosafety aspects along with the repertoire of diagnostic modalities, both traditional and emerging, for poxviruses which a special focus on monkeypox. The advantages and disadvantages of each technique have been illustrated. We have also reflected upon the newer advances and the existing lacunae.

Characterizing the acute antibody response of monkeypox and MVA-BN vaccine following an Australian outbreak

In response to the emergence of the monkeypox virus (MPXV) in Australia in May 2022, we developed and evaluated indirect immunofluorescence assays (IFA) for MPXV and Vaccinia virus (VACV) IgG and IgM antibodies using serum samples from patients with nucleic acid amplification test (NAAT)-confirmed mpox and uninfected unvaccinated controls. Additionally, 47 healthcare workers receiving two doses of the third-generation smallpox vaccine Modified Vaccinia Ankara-Bavarian Nordic (MVA-BN) undertook serial serum collection to describe the serological response to vaccination. MPXV antibodies were detected in 16/18 individuals with NAAT-confirmed mpox (sensitivity 0.89, specificity 1.00), and VACV antibodies were detected in 28/29 individuals who received two doses of MVA-BN vaccine (sensitivity 0.97, specificity 1.00). Detectable antibody in subjects historically vaccinated with early-generation vaccines against smallpox was found in 7/7 subjects, at a median of 48 years following vaccination. MPXV NAAT-positive patients with serum samples collected within the first 14 days after rash onset had detectable IgG and IgM in 9/12 and 5/12 of patients, respectively, with maintenance of IgG and disappearance of IgM titers after 60 days. While specificity was high when testing unvaccinated and uninfected subjects, significant cross-reactivity between MPXV and VACV antibodies was observed.

Serological methods for the detection of antibodies against monkeypox virus applicable for laboratories with different biosafety levels

The monkeypox virus (MPXV) outbreak in 2022 has renewed interest in the detection of antibodies against orthopox viruses (OPXV) and MPXV, as serological methods can aid diagnostics and are key to epidemiological studies. Here three complementary serological methods are described with different strengths to aid the development and evaluation of in-house assays: An immunofluorescence assay (IFA) for specific detection of IgG and IgM, an enzyme-linked immunosorbent assay for higher sample throughput to aid epidemiological studies and a neutralization test to detect virus neutralizing antibodies. As implementation of MPXV-specific diagnostics is often hampered by the requirement for a dedicated biosafety level 3 laboratory (BSL-3), the focus of this study is on biosafety aspects to facilitate safe testing also under BSL-2 conditions. To this aim, it was analyzed whether OPXV, which can be handled under BSL-2 conditions, could be used as less virulent alternatives to MPXV. Furthermore, an inactivation method was established to remove up to five log-steps of infectious virus particles from viraemic sera without compromising antibody detection. The results show that immunological cross-reactivity between OPXV provides an opportunity for the interchangeable usage of different OPXV species in serological assays, enabling MPXV serology outside of BSL-3 facilities.

Harnessing Attenuation-Related Mutations of Viral Genomes: Development of a Serological Assay to Differentiate between Capripoxvirus-Infected and -Vaccinated Animals

Sheeppox, goatpox, and lumpy skin disease caused by the sheeppox virus (SPPV), goatpox virus (GTPV), and lumpy skin disease virus (LSDV), respectively, are diseases that affect millions of ruminants and many low-income households in endemic countries, leading to great economic losses for the ruminant industry. The three viruses are members of the Capripoxvirus genus of the Poxviridae family. Live attenuated vaccines remain the only efficient means for controlling capripox diseases. However, serological tools have not been available to differentiate infected from vaccinated animals (DIVA), though crucial for proper disease surveillance, control, and eradication efforts. We analysed the sequences of variola virus B22R homologue gene for SPPV, GTPV, and LSDV and observed significant differences between field and vaccine strains in all three capripoxvirus species, resulting in the truncation and absence of the B22R protein in major vaccines within each of the viral species. We selected and expressed a protein fragment present in wildtype viruses but absent in selected vaccine strains of all three species, taking advantage of these alterations in the B22R gene. An indirect ELISA (iELISA) developed using this protein fragment was evaluated on well-characterized sera from vaccinated, naturally and experimentally infected, and negative cattle and sheep. The developed wildtype-specific capripox DIVA iELISA showed >99% sensitivity and specificity for serum collected from animals infected with the wildtype virus. To the best of our knowledge, this is the first wildtype-specific, DIVA-capable iELISA for poxvirus diseases exploiting changes in nucleotide sequence alterations in vaccine strains.

Determination of seroprevalence and kinetics of humoral response using mpox virus A29 protein

BACKGROUND

Mpox virus (MPXV), previously known as monkeypox virus, has spread globally in 2022. An accurate and convenient antibody test is essential for the determination of seroprevalence and for studying immune response after natural infection or vaccination. Most seroprevalence or vaccine studies used either live MPXV (or vaccinia virus [VACV]) or inactivated MPXV (or VACV) culture lysate for serological assays, but MPXV culture can only be performed in biosafety level 3 (BSL-3) facilities. Here, we developed and evaluated an enzyme immunoassay (EIA) based on the MPXV A29 surface envelope protein.

METHODS

We compared the specificity of the MPXV A29, VACV A27, and VACV lysate EIA using serum specimens collected prior to the global spread of MPXV. Next, we performed these EIAs for serum specimens collected from two mpox patients and an MVA-BN vaccine recipient. We also assessed the kinetics of plasmblast and MPXV A29-specific B-cell response.

RESULTS

Using sera collected from different age groups in Hong Kong, we found that most individuals, including those born before 1981 who have received the smallpox vaccine, tested negative using the MPXV A29 protein. MPXV A29-specific antibody could be detected in the serum of mpox patients and an MVA-BN recipient. In a mpox patient, the frequency of plasmablast and MPXV A29-specific B cell peaked on day 8 post-symptom onset and gradually decreased. Finally, we demonstrated that antibodies against the A29 protein can be used for immunofluorescence staining of MPXV-infected cells.

CONCLUSIONS

MPXV A29 protein is suitable for studying the immune response against MPXV infection.

Serosurvey of Immunity to Monkeypox (Mpox) Virus Antigens in People Living with HIV in South Florida

Mpox is an infectious disease caused by the monkeypox virus (MPXV) belonging to the Orthopoxvirus (OPXV) genus, which includes smallpox and vaccinia virus (VACV). A global mpox outbreak which began in May 2022 has infected more than 88,000 people. VACV-based vaccines provide protection against mpox disease but complicate the use of serological assays for disease surveillance. We tested the reactivity of serum IgG from Modified Vaccinia Ankara-Bavarian Nordic (MVA-BN)-vaccinated (n = 12) and convalescent mpox-infected (n = 5) individuals and uninfected, non-vaccinated controls (n = 32) to MPXV/VACV proteins A27, A29, A30, A35, B16, B21, C19, D6, E8, H3, I1, and L1. Using a subset of MPXV antigen-based assays (A35, B16, E8, H3, and I1), we conducted a mpox antibody survey of serum from 214 individuals, including 117 (54.7%) people with HIV (PWH) collected between June 2022 and January 2023, excluding individuals who reported recent mpox vaccination or infection, and 32 young, pre-pandemic controls. The convalescent sera reacted strongly to most tested antigens. Vaccine sera responses were limited to A35, E8, H3, and I1. IgG antibody to E8 was markedly elevated in all vaccinated individuals. B16 IgG showed high sensitivity (100% [95% CI: 56.55-100.0%]) and specificity (91.67% [64.61-99.57%]) for distinguishing infection from MVA-BN vaccination, while E8 IgG showed 100% [75.75-100] sensitivity and 100% [79.61-100] specificity for detecting and distinguishing vaccinated individuals from controls. We identified 11/214 (5.1%) recent serum samples and 1/32 (3.1%) young, pre-pandemic controls that were seropositive for ≥2 MPXV antibodies, including 6.8% of PWH. Seropositivity was 10/129 (7.8%) among males compared to 1/85 (1.2%) among females. Our findings provide insight into the humoral immune response to mpox and demonstrate the usefulness of inexpensive, antigen-based serosurveillance in identifying asymptomatic or unreported infections.

Development of a novel serological assay for the detection of mpox infection in vaccinated populations

In 2022 the World Health Organization declared a Public Health Emergency for an outbreak of mpox, the zoonotic Orthopoxvirus (OPV) affecting at least 104 nonendemic locations worldwide. Serologic detection of mpox infection is problematic, however, due to considerable antigenic and serologic cross-reactivity among OPVs and smallpox-vaccinated individuals. In this report, we developed a high-throughput multiplex microsphere immunoassay using a combination of mpox-specific peptides and cross-reactive OPV proteins that results in the specific serologic detection of mpox infection with 93% sensitivity and 98% specificity. The New York State Non-Vaccinia Orthopoxvirus Microsphere Immunoassay is an important tool to detect subclinical mpox infection and understand the extent of mpox spread in the community through retrospective analysis.

Mpox: a review of laboratory detection techniques

Mpox (formerly monkeypox) is a zoonotic disease caused by monkeypox virus (MPXV), which, like smallpox, is characterised by skin rashes. While the world is currently grappling with the coronavirus disease 2019 pandemic, the appearance of MPXV has presented a global threat and raised concerns worldwide. Since May 2022, MPXV has spread rapidly in non-endemic mpox areas. As of 27 June 2023, the virus has spread to more than 112 countries and regions, with over 88,060 laboratory-confirmed cases and 147 deaths. Thus, measures to control the mpox epidemic are urgently needed. As the principal methods for identifying and monitoring mpox, laboratory detection techniques play an important role in mpox diagnosis. This review summarises the currently-used laboratory techniques for MPXV detection, discusses progress in improving these methods, and compares the benefits and limitations of various diagnostic detection methods. Currently, nucleic acid amplification tests, such as the polymerase chain reaction, are the most commonly used. Immunological methods have also been applied to diagnose the disease, which can help us discover new features of MPXV, improve diagnostic accuracy, track epidemic trends, and guide future prevention and control strategies, which are also vital for controlling mpox epidemics. This review provides a resource for the scientific community and should stimulate more research and development in alternative diagnostics to be applied to this and future public health crises.

The prospective outcome of the monkeypox outbreak in 2022 and characterization of monkeypox disease immunobiology

A new threat to global health re-emerged with monkeypox's advent in early 2022. As of November 10, 2022, nearly 80,000 confirmed cases had been reported worldwide, with most of them coming from places where the disease is not common. There were 53 fatalities, with 40 occurring in areas that had never before recorded monkeypox and the remaining 13 appearing in the regions that had previously reported the disease. Preliminary genetic data suggest that the 2022 monkeypox virus is part of the West African clade; the virus can be transmitted from person to person through direct interaction with lesions during sexual activity. It is still unknown if monkeypox can be transmitted via sexual contact or, more particularly, through infected body fluids. This most recent epidemic's reservoir host, or principal carrier, is still a mystery. Rodents found in Africa can be the possible intermediate host. Instead, the CDC has confirmed that there are currently no particular treatments for monkeypox virus infection in 2022; however, antivirals already in the market that are successful against smallpox may mitigate the spread of monkeypox. To protect against the disease, the JYNNEOS (Imvamune or Imvanex) smallpox vaccine can be given. The spread of monkeypox can be slowed through measures such as post-exposure immunization, contact tracing, and improved case diagnosis and isolation. Final Thoughts: The latest monkeypox epidemic is a new hazard during the COVID-19 epidemic. The prevailing condition of the monkeypox epidemic along with coinfection with COVID-19 could pose a serious condition for clinicians that could lead to the global epidemic community in the form of coinfection.

Use of Mpox Multiplex Serology in the Identification of Cases and Outbreak Investigations in the Democratic Republic of the Congo (DRC)

Human Mpox cases are increasingly reported in Africa, with the highest burden in the Democratic Republic of Congo (DRC). While case reporting on a clinical basis can overestimate infection rates, laboratory confirmation by PCR can underestimate them, especially on suboptimal samples like blood, commonly used in DRC. Here we used a Luminex-based assay to evaluate whether antibody testing can be complementary to confirm cases and to identify human transmission chains during outbreak investigations. We used left-over blood samples from 463 patients, collected during 174 outbreaks between 2013 and 2022, with corresponding Mpox and VZV PCR results. In total, 157 (33.9%) samples were orthopox-PCR positive and classified as Mpox+; 124 (26.8%) had antibodies to at least one of the three Mpox peptides. The proportion of antibody positive samples was significantly higher in Mpox positive samples (36.9%) versus negative (21.6%) (p < 0.001). By combining PCR and serology, 66 additional patients were identified, leading to an Mpox infection rate of 48.2% (223/463) versus 33.9% when only PCR positivity is considered. Mpox infections were as such identified in 14 additional health zones and 23 additional outbreaks (111/174 (63.8%) versus 88/174 (50.6%)). Our findings highlight the urgent need of rapid on-site diagnostics to circumvent Mpox spread.

CRISPR/Cas12a-mediated ultrasensitive and on-site monkeypox viral testing

The spread of the monkeypox virus (MPXV) from Central and West Africa to previously non-endemic regions has caused a global panic. In this context, the rapid, specific, and ultrasensitive detection of MPXV is crucial to contain its spread, though such technology has seldom been reported. Herein, we proposed an MPXV assay combining recombinase-aided amplification (RAA) and CRISPR/Cas12a. This assay targeted the highly conserved MPXV F3L gene and demonstrates a low detection limit (LOD) of 10¹ copies per μL. By leveraging the high specificity nature of RAA and CRISPR/Cas12a, we rationally optimized probes and conditions to achieve high selectivity that differentiates MPXV from other orthopox viruses and current high-profile viruses. To facilitate on-site screening of potential MPXV carriers, a kit integrating lateral flow strips was developed, enabling naked-eye MPXV detection with a LOD of 10⁴ copies per μL. Our RAA-Cas12a-MPXV assay was able to detect MPXV without the need for sophisticated operation and expensive equipment. We believe that this assay can be rapidly deployed in emerging viral outbreaks for on-site surveillance of MPXV.

Development of a Novel Serological Assay for the Detection of Mpox Infection in Vaccinated Populations

In 2022 the World Health Organization declared a Public Health Emergency for an outbreak of mpox, the zoonotic Orthopoxvirus (OPV) affecting at least 103 non-endemic locations world-wide. Serologic detection of mpox infection is problematic, however, due to considerable antigenic and serologic cross-reactivity among OPVs and smallpox-vaccinated individuals. In this report, we developed a high-throughput multiplex microsphere immunoassay (MIA) using a combination of mpox-specific peptides and cross-reactive OPV proteins that results in the specific serologic detection of mpox infection with 93% sensitivity and 98% specificity. The New York State Non-Vaccinia Orthopoxvirus Microsphere Immunoassay is an important diagnostic tool to detect subclinical mpox infection and understand the extent of mpox spread in the community through retrospective analysis.

A systematic review of peptide-based serological tests for the diagnosis of leishmaniasis

Serological methods should meet the needs of leishmaniasis diagnosis due to their high sensitivity and specificity, economical and adaptable rapid diagnostic test format, and ease of use. Currently, the performances of serological diagnostic tests, despite improvements with recombinant proteins, vary greatly depending on the clinical form of leishmaniasis and the endemic area. Peptide-based serological tests are promising as they could compensate for antigenic variability and improve performance, independently of Leishmania species and subspecies circulating in the endemic areas. The objective of this systematic review was to inventory all studies published from 2002 to 2022 that evaluate synthetic peptides for serological diagnosis of human leishmaniases and also to highlight the performance (e.g., sensitivity and specificity) of each peptide reported in these studies. All clinical forms of leishmaniasis, visceral and tegumentary, and all Leishmania species responsible for these diseases were considered. Following PRISMA statement recommendations, 1,405 studies were identified but only 22 articles met the selection criteria and were included in this systematic review. These original research articles described 77 different peptides, of which several have promising performance for visceral or tegumentary leishmaniasis diagnosis. This review highlights the importance of and growing interest in synthetic peptides used for serological diagnosis of leishmaniases, and their performances compared to some widely used tests with recombinant proteins.

Design and Optimization of a Monkeypox virus Specific Serological Assay

Monkeypox virus (MPXV), a member of the Orthopoxvirus (OPXV) genus, is a zoonotic virus, endemic to central and western Africa that can cause smallpox-like symptoms in humans with fatal outcomes in up to 15% of patients. The incidence of MPXV infections in the Democratic Republic of the Congo, where the majority of cases have occurred historically, has been estimated to have increased as much as 20-fold since the end of smallpox vaccination in 1980. Considering the risk global travel carries for future disease outbreaks, accurate epidemiological surveillance of MPXV is warranted as demonstrated by the recent Mpox outbreak, where the majority of cases were occurring in non-endemic areas. Serological differentiation between childhood vaccination and recent infection with MPXV or other OPXVs is difficult due to the high level of conservation within OPXV proteins. Here, a peptide-based serological assay was developed to specifically detect exposure to MPXV. A comparative analysis of immunogenic proteins across human OPXVs identified a large subset of proteins that could potentially be specifically recognized in response to a MPXV infection. Peptides were chosen based upon MPXV sequence specificity and predicted immunogenicity. Peptides individually and combined were screened in an ELISA against serum from well-characterized Mpox outbreaks, vaccinee sera, and smallpox sera collected prior to eradication. One peptide combination was successful with ~86% sensitivity and ~90% specificity. The performance of the assay was assessed against the OPXV IgG ELISA in the context of a serosurvey by retrospectively screening a set of serum specimens from the region in Ghana believed to have harbored the MPXV-infected rodents involved in the 2003 United States outbreak.

The pathophysiological and immunological background of the monkeypox virus infection: An update

In addition to the COVID-19 waves, the globe is facing global monkeypox (MPX) outbreak. MPX is an uncommon zoonotic infection characterized by symptoms similar to smallpox. It is caused by the monkeypox virus (MPXV), a double-stranded DNA virus that belongs to the genus Orthopoxvirus (OPXV). MPXV, which causes human disease, has been confined to Africa for many years, with only a few isolated cases in other areas. Outside of Africa, the continuing MPXV outbreak in multiple countries in 2022 is the greatest in recorded history. The current outbreak, with over 10 000 confirmed cases in over 50 countries between May and July 2022, demonstrates that MPXV may travel rapidly among humans and pose a danger to human health worldwide. The rapid spread of such outbreaks in recent times has elevated MPX to the status of a rising zoonotic disease with significant epidemic potential. While the MPXV is not as deadly or contagious as the variola virus that causes smallpox, it poses a threat because it could evolve into a more potent human pathogen. This review assesses the potential threat to the human population and provides a brief overview of what is currently known about this reemerging virus. By analyzing the biological effects of MPXV on human health, its shifting epidemiological footprint, and currently available therapeutic options, this review has presented the most recent insights into the biology of the virus. This study also clarifies the key potential causes that could be to blame for the present MPX outbreak and draw attention to major research questions and promising new avenues for combating the current MPX epidemic.

Mpox diagnostics: Review of current and emerging technologies

Mpox is a zoonotic disease caused by monkeypox virus (MPXV) from the Orthopoxvirus genus. Unprecedented transmission events have led to more than 70 000 cases reported worldwide by October 2022. The change in mpox epidemiology has raised concerns of its ability to establish endemicity beyond its traditional geographical locations. In this review, we discuss the current understanding of mpox virology and viral dynamics that are relevant to mpox diagnostics. A synopsis of the traditional and emerging laboratory technologies useful for MPXV detection and in guiding "elimination" strategies is outlined in this review. Importantly, development in MPXV genomics has rapidly advanced our understanding of the role of viral evolution and adaptation in the current outbreak.

Development and Validation of an LC-MS/MS Method for Simultaneous Determination of Short Peptide-Based Drugs in Human Blood Plasma

A novel HPLC-ESI-MS/MS method for simultaneous gonadotropin-releasing hormone (GnRH) analogs and somatostatin analog quantitation was developed and validated. The developed method was successfully applied to pharmacokinetic studies. The sample preparation process included solid-phase extraction (SPE). Effective chromatographic separation of the analytes and internal standard (dalargin) was achieved with a C18 column, using a gradient elution with two mobile phases: 0.1% v/v formic acid (aqueous solution) and 0.1% v/v formic acid (acetonitrile solution). The linearity of the method was demonstrated within a concentration range of 0.5-20 ng/mL, with correlation coefficients between 0.998-0.999 for goserelin, buserelin, triptorelin, and octreotide, respectively. The relative standard deviation (RSD, %) values for method accuracy and precision did not exceed 20% at the lower level of quantitation (LLOQ) or 15% at other concentration levels.

Monkeypox: epidemiology, pathogenesis, treatment and prevention

Monkeypox is a zoonotic disease that was once endemic in west and central Africa caused by monkeypox virus. However, cases recently have been confirmed in many nonendemic countries outside of Africa. WHO declared the ongoing monkeypox outbreak to be a public health emergency of international concern on July 23, 2022, in the context of the COVID-19 pandemic. The rapidly increasing number of confirmed cases could pose a threat to the international community. Here, we review the epidemiology of monkeypox, monkeypox virus reservoirs, novel transmission patterns, mutations and mechanisms of viral infection, clinical characteristics, laboratory diagnosis and treatment measures. In addition, strategies for the prevention, such as vaccination of smallpox vaccine, is also included. Current epidemiological data indicate that high frequency of human-to-human transmission could lead to further outbreaks, especially among men who have sex with men. The development of antiviral drugs and vaccines against monkeypox virus is urgently needed, despite some therapeutic effects of currently used drugs in the clinic. We provide useful information to improve the understanding of monkeypox virus and give guidance for the government and relative agency to prevent and control the further spread of monkeypox virus.

Monkeypox: disease epidemiology, host immunity and clinical interventions

Monkeypox virus (MPXV), which causes disease in humans, has for many years been restricted to the African continent, with only a handful of sporadic cases in other parts of the world. However, unprecedented outbreaks of monkeypox in non-endemic regions have recently taken the world by surprise. In less than 4 months, the number of detected MPXV infections has soared to more than 48,000 cases, recording a total of 13 deaths. In this Review, we discuss the clinical, epidemiological and immunological features of MPXV infections. We also highlight important research questions and new opportunities to tackle the ongoing monkeypox outbreak.

In this Review, Ng and colleagues examine the clinical, epidemiological and immunological aspects of monkeypox virus (MPXV) infections, with a focus on mechanisms of host immunity to MPXV. The authors also consider the unique epidemiological and pathological characteristics of the current non-endemic outbreak of the virus and discuss vaccines, therapeutics and outstanding research questions.

Mapping of Antibody Epitopes on the Crimean-Congo Hemorrhagic Fever Virus Nucleoprotein

Crimean-Congo hemorrhagic fever virus (CCHFV), a nairovirus, is a tick-borne zoonotic virus that causes hemorrhagic fever in humans. The CCHFV nucleoprotein (NP) is the antigen most used for serological screening of CCHFV infection in animals and humans. To gain insights into antibody epitopes on the NP molecule, we produced recombinant chimeric NPs between CCHFV and Nairobi sheep disease virus (NSDV), which is another nairovirus, and tested rabbit and mouse antisera/immune ascites, anti-NP monoclonal antibodies, and CCHFV-infected animal/human sera for their reactivities to the NP antigens. We found that the amino acids at positions 161–320 might include dominant epitopes recognized by anti-CCHFV IgG antibodies, whereas cross-reactivity between anti-CCHFV and anti-NSDV antibodies was limited. Their binding capacities were further tested using a series of synthetic peptides whose sequences were derived from CCHFV NP. IgG antibodies in CCHFV-infected monkeys and patients were reactive to some of the synthetic peptide antigens (e.g., amino acid residues at positions 131–150 and 211–230). Only a few peptides were recognized by IgG antibodies in the anti-NSDV serum. These results provide useful information to improve NP-based antibody detection assays as well as antigen detection tests relying on anti-NP monoclonal antibodies.

A novel click chemistry-based peptide ELISA protocol: development and technical evaluation

ELISA is the current standard for (auto)antibody diagnostics. Once established, ELISA protocols can be easily adapted for novel antigens; however, peptide-based protocols are rarely available. Herein the authors describe the results of a technical investigation of an indirect ELISA protocol using peptides conjugated onto a protein carrier based on click chemistry and immobilized in standard plastics. The authors compared this approach with the common biotin-avidin system and obtained a slightly improved limit of detection for purified IgG of 25-100 ng/well compared with 25-1000 ng/well. Reproducibility and stability of the methodological approach were conducted for further technical characterization. Indirect ELISA using immunoreactive peptides conjugated to bovine serum albumin offers a reliable method that is complementary to standard plastics and plate readers.

Epitope Profiling Reveals the Critical Antigenic Determinants in SARS-CoV-2 RBD-Based Antigen

The ongoing COVID-19 pandemic caused by SARS-CoV-2 is a huge public health crisis for the globe. The receptor-binding domain (RBD) of SARS-CoV-2 spike (S) protein plays a vital role in viral infection and serves as a major target for developing neutralizing antibodies. In this study, the antibody response to the RBD of SARS-CoV-2 S protein was analyzed by a panel of sera from animals immunized with RBD-based antigens and four linear B-cell epitope peptides (R345, R405, R450 and R465) were revealed. The immunogenicity of three immunodominant peptides (R345, R405, R465) was further accessed by peptide immunization in mice, and all of them could induced potent antibody response to SARS-CoV-2 S protein, indicating that the three determinants in the RBD were immunogenic. We further generated and characterized monoclonal antibodies (15G9, 12C10 and 10D2) binding to these epitope peptides, and finely mapped the three immunodominant epitopes using the corresponding antibodies. Neutralization assays showed that all three monoclonal antibodies had neutralization activity. Results from IFA and western blotting showed that 12C10 was a cross-reactive antibody against both of SARS-CoV-2 and SARS-CoV. Results from conservative and structural analysis showed that ³⁵⁰VYAWN³⁵⁴ was a highly conserved epitope and exposed on the surface of SARS-CoV-2 S trimer, whereas ⁴⁷³YQAGSTP⁴⁷⁹ located in the receptor binding motif (RBM) was variable among different SARS-CoV-2 strains. ⁴⁰⁷VRQIAP⁴¹² was a highly conserved, but cryptic epitope shared between SARS-CoV-2 and SARS-CoV. These findings provide important information for understanding the humoral antibody response to the RBD of SARS-CoV-2 S protein and may facilitate further efforts to design SARS-CoV-2 vaccines and the target of COVID-19 diagnostic.

Multiple antigenic peptide-based flow through dot-blot assay for simultaneous antibody detection of infectious bronchitis virus and Newcastle disease virus

The present study describes the development of a novel affordable and rapid visual dot-blot assay using synthetic multiple antigenic peptides (MAP) for simultaneous detection of antibodies to infectious bronchitis virus (IBV) and Newcastle disease virus (NDV). Antibody detection efficiencies of MAP peptides namely, NP1 MAP (Nucleoprotein IBV) and HN MAP (Haemagglutinin-neuraminidase NDV) were studied in solid-phase indirect peptide ELISA. In comparison with the commercial kit, the NP1 MAP showed 89.20% diagnostic sensitivity (DSn) and 85.90% diagnostic specificity (DSp) at 19.45% ROC cut-off. Similarly, HN MAP was evaluated and showed 89.70% DSn and 92.90% DSp at 19.90 % ROC cut-off. The peptides after evaluating their ELISA performance were further used to device a flow-through dot-blot assay (FT-DBA) for simultaneous detection of IBV and NDV antibodies. The kappa value for IBV by FT-DBA in comparison to commercial ELISA was 0.64 whereas for NDV, FT-DBA gave a kappa value of 0.68 in comparison to commercial ELISA indicating substantial agreement between the assays. In essence, the divergent MAP based diagnostic design could provide an alternative for antibody detection of IBV and NDV. Further, the FT-DBA approach could be used for low cost, rapid and pen-side detection of IBV and NDV antibodies simultaneously.

Development and characterization of monoclonal antibodies against the N-terminal domain of African swine fever virus structural protein, p54

African swine fever virus (ASFV), a re-emerging DNA virus, causes a highly contagious disease for domestic pigs. It is running rife worldwide and threatening the global swine industry. Protein p54 is an attractive candidate for ASFV diagnostic and vaccine design. In this work, we designed a peptide to mimic the N-terminal domain (NTD) of ASFV p54 and pretested it with sera from ASFV-infected pigs. The peptide could be well recognized by the sera, implying that the NTD of p54 contained some potential linear B cell epitopes. Then, the conjugates of the peptide with bovine serum albumin were used as the immunogen to generate monoclonal antibodies (mAbs). A total of six mAbs specific to the NTD of ASFV p54 protein were developed. Five of them well reacted with ASFV HLJ/18 strain and recognized a same linear B cell epitope ⁵FFQPV⁹. Furthermore, epitope ⁵FFQPV⁹ could be well recognized by ASFV-positive sera from natural infected pigs, suggesting that it was a natural linear B-cell epitope. Conservation analysis indicated that epitope ⁵FFQPV⁹ were highly conserved among ASFV epidemic isolates belonging to genotype I and II. Alanine-scanning mutagenesis further revealed that the residues (6F to 9V) of epitope ⁵FFQPV⁹ were the core binding sites for antibody recognition. This is the first research to characterize specific mAbs against NTD of p54 protein. These findings may help further understand the function of p54 protein and the improvement of ASFV diagnosis.

A bio-safe multiple antigenic peptide (MAP) enzyme-linked immunoassay for the detection of antibodies to infectious bronchitis virus in chickens

The objective of the study was to develop a bio-safe synthetic peptide ELISA for the detection of antibodies against the infectious bronchitis virus (IBV) using a novel multiple antigenic peptide approach (MAP). After initial ELISA optimization, diagnostic sensitivity (DSn) and specificity (DSp) for the linear peptides were determined using receiver operator curve (ROC) analysis. The peptide IBVP1 showed 90.44% DSn and 88.64% DSp at ROC cut off 22.8% while IBVP2 showed 88.24% DSn and 85.23% DSp at ROC cut off 23.05%. The multimerization of linear peptides to MAP design resulted in the improvement of the diagnostic efficiency up to 94.85% DSn and 92.05% DSp for IBVM1 with 19.95% cut off. A similar improvement in the performance was also observed with 92.65% DSn and 90.91% DSp for IBVM2 at 20.72% cut off. All the peptides were tested for diagnostic specificity and did not show the cross-reactivity with Newcastle disease virus and infectious bursal disease virus positive serum samples. In addition, repeatability testing for all linear and multimeric peptide showed that the coefficient of variation for intra-assay was within the expected limits, ranging from 2.4 to 10.4% and inter-assay coefficient of variation was ranging from 5.56 to 14.3%. In a nutshell, the present study used predicted B cell epitope, the synthetic peptide in linear and multimeric design for IBV antibody detection. The study also highlights peptide antigen with modified scaffold design could be a safe alternative to whole virion-based ELISA for IBV antibody detection.

ReScan, a Multiplex Diagnostic Pipeline, Pans Human Sera for SARS-CoV-2 Antigens

Comprehensive understanding of the serological response to SARS-CoV-2 infection is important for both pathophysiologic insight and diagnostic development. Here, we generate a pan-human coronavirus programmable phage display assay to perform proteome-wide profiling of coronavirus antigens enriched by 98 COVID-19 patient sera. Next, we use ReScan, a method to efficiently sequester phage expressing the most immunogenic peptides and print them onto paper-based microarrays using acoustic liquid handling, which isolates and identifies nine candidate antigens, eight of which are derived from the two proteins used for SARS-CoV-2 serologic assays: spike and nucleocapsid proteins. After deployment in a high-throughput assay amenable to clinical lab settings, these antigens show improved specificity over a whole protein panel. This proof-of-concept study demonstrates that ReScan will have broad applicability for other emerging infectious diseases or autoimmune diseases that lack a valid biomarker, enabling a seamless pipeline from antigen discovery to diagnostic using one recombinant protein source.

ReScan is a whole proteome screen to isolate and identify serologic assay targets

Antibodies to linear peptides in COVID-19 sera bind spike and nucleocapsid proteins

Rapid workflow that seamlessly translates biomarkers into a functional diagnostic

Multiplexing linear S and N SARS-CoV-2 peptides can increase diagnostic specificity

Identification of B-Cell Epitopes with Potential to Serologicaly Discrimnate Dengue from Zika Infections

Dengue is currently one of the most important arbovirus infections worldwide. Early diagnosis is important for disease outcome, particularly for those afflicted with the severe forms of infection. The goal of this work was to identify conserved and polymorphic linear B-cell Dengue virus (DENV) epitopes that could be used for diagnostic purposes. To this end, we aligned the predicted viral proteome of the four DENV serotype and performed in silico B-cell epitope mapping. We developed a script in Perl integrating alignment and prediction information to identify potential serotype-specific epitopes. We excluded epitopes that were similarly present in the yellow fever and zika viruses' proteomes. A total of 15 polymorphic and nine conserved peptides among DENV serotypes were selected. Peptides were spotted on cellulose membranes and tested against sera from rabbits that were monoinfected with each DENV serotype. Although serotype-specific peptides failed to recognize any sera, three conserved peptides were recognized by all anti-dengue sera and were included on an ELISA test employing a well-characterized human sera bank. Of the three peptides, one was able to efficiently identify sera from all four DENV serotypes and to discriminate them from Zika virus positive sera.

Glycoprotein D peptide-based diagnostic approach for the detection of avian infectious laryngotracheitis antibodies

Infectious laryngotracheitis (ILT) is a highly contagious respiratory disease of chickens, pheasants, and peafowl. It is caused by the alpha herpesvirus, infectious laryngotracheitis virus (ILTV). Glycoprotein D (gD) of ILTV is immunogenic and helps in its binding to the susceptible host cell receptor. In the present study, a recombinant gD protein was expressed in a prokaryotic system to develop a single serum dilution ELISA. In addition, two immunogenic peptides, corresponding to regions 77-89 and 317-328, were identified in gD protein. The peptides were synthesized using solid-phase peptide synthesis, purified using reversed-phase HPLC, and characterized using mass spectrometry. The peptides displayed a good titre and were found to be promising antigens to coat the ELISA plate to detect the ILTV antibodies in the serum sample. The developed ELISA showed 96.9% sensitivity, 87.5% specificity, and 95.3% accuracy as compared to OIE referenced standard indirect ILTV ELISA (whole viral coated). The assay may not differentiate vaccinated from infected birds when the flocks are administered with live attenuated vaccines. However, the assay could be useful to detect the disease condition in birds vaccinated with recombinant vaccine expressing glycoproteins other than gD. The developed ILTV single serum dilution ELISA could be an alternative to the existing diagnostics for the detection of ILTV antibodies.

Performance evaluation of 3 serodiagnostic peptide epitopes and the derived multi-epitope peptide OvNMP-48 for detection of Onchocerca volvulus infection

Current diagnostic tools to determine infection with the helminth parasite Onchocerca volvulus have limited performance characteristics. In previous studies, a proteome-wide screen was conducted to identify linear epitopes in this parasite’s proteome, resulting in the discovery of 1110 antigenic peptide fragments. Here, we investigated three of these peptides using peptide ELISA’s and evaluated their sensitivity and specificity. Epitope mapping was performed, and peptides were constructed that contained only the minimal epitope, flanked by a linker. Investigation of the performance of these minimal epitope peptides demonstrated that all three of them have a specificity (as defined by lack of response in non-helminth-infected individuals) of 100%, low cross-reactivity (5.6%, 5.6%, and 9.3%, respectively), but low sensitivity (36.9%, 46.5%, and 41.2%, respectively). Some cross-reactivity was observed in samples from individuals infected with soil-transmitted helminths or Brugia malayi. Combining these three minimal epitopes in a single peptide, called OvNMP-48, resulted in a performance that exceeded the sum of the individual epitopes, with a sensitivity of 76.0%, a specificity of 97.4%, and a cross-reactivity of 11.1%. Cross-reactivity was observed in some STH and Brugia malayi-infected individuals. This work opens the opportunity to start exploring how these novel linear epitope markers might become part of the O. volvulus diagnostic toolbox.

Discovery of Leptospira spp. seroreactive peptides using ORFeome phage display

Background

Leptospirosis is the most common zoonotic disease worldwide. The diagnostic performance of a serological test for human leptospirosis is mainly influenced by the antigen used in the test assay. An ideal serological test should cover all serovars of pathogenic leptospires with high sensitivity and specificity and use reagents that are relatively inexpensive to produce and can be used in tropical climates. Peptide-based tests fulfil at least the latter two requirements, and ORFeome phage display has been successfully used to identify immunogenic peptides from other pathogens.

Methodology/Principal findings

Two ORFeome phage display libraries of the entire Leptospira spp. genomes from five local strains isolated in Malaysia and seven WHO reference strains were constructed. Subsequently, 18 unique Leptospira peptides were identified in a screen using a pool of sera from patients with acute leptospirosis. Five of these were validated by titration ELISA using different pools of patient or control sera. The diagnostic performance of these five peptides was then assessed against 16 individual sera from patients with acute leptospirosis and 16 healthy donors and was compared to that of two recombinant reference proteins from L. interrogans. This analysis revealed two peptides (SIR16-D1 and SIR16-H1) from the local isolates with good accuracy for the detection of acute leptospirosis (area under the ROC curve: 0.86 and 0.78, respectively; sensitivity: 0.88 and 0.94; specificity: 0.81 and 0.69), which was close to that of the reference proteins LipL32 and Loa22 (area under the ROC curve: 0.91 and 0.80; sensitivity: 0.94 and 0.81; specificity: 0.75 and 0.75).

Conclusions/Significance

This analysis lends further support for using ORFeome phage display to identify pathogen-associated immunogenic peptides, and it suggests that this technique holds promise for the development of peptide-based diagnostics for leptospirosis and, possibly, of vaccines against this pathogen.

Leptospirosis is an infectious disease that is transmitted from animals to humans. It is associated with a broad range of clinical presentations, and diagnostic tests with high diagnostic accuracy are required in order to enable accurate diagnosis. Leptospirosis is diagnosed by detecting DNA of the pathogen or antibodies against it in patients’ blood; the latter are preferred in resource limited regions, and diagnostics based on peptides (small fragments of proteins) are advantageous because they are inexpensive to produce and more stable in hot climates than full-length proteins. We used a technique called open reading frame phage display to identify peptides from Leptospira spp. that could be used to detect antibodies against them in human blood. In this method, the pathogen’s genome is fragmented, the corresponding peptides displayed on the surfaces of phages (viruses that infect bacteria), and the peptides that bind most strongly to the patients’ antibodies are then selected by screening. Using this method, we identified 2 leptospiral peptides that accurately identified antibodies against Leptospira spp. in sera from patients with leptospirosis. These results are encouraging because they demonstrate that ORFeome phage display may be a powerful tool to develop better diagnostics for leptospirosis for use in less developed areas.

Identification of novel B-cell epitope in gp85 of subgroup J avian leukosis virus and its application in diagnosis of disease

Background

The gp85 is the main envelope protein of avian leukosis subgroup J (ALV-J) involved in virus neutralization. Here, we mapped the epitope in ALV-J gp85 by ELISA using synthetic peptides and developed epitope based diagnostic methods for ALV-J infection.

Results

The results revealed that monoclonal antibody (mAb) JE9 recognized ⁸³WDPQEL⁸⁸ motif, which was highly conserved in gp85 among different ALV-J strains by homology analysis. Moreover, after evaluation with two hundred and forty sera samples obtained from different chicken farms, the epitope-based peptide ELISA had much higher sensitivity than commercial ELISA kit for antibody detection of ALV-J.

Conclusions

A novel B-cell epitope recognized by the mAb JE9 was identified. The developed peptide-ELISA based on this novel B-cell epitope could be useful in laboratory viral diagnosis, routine surveillance in chicken farms, and also in understanding the pathogenesis of ALV-J.

Retrospective Proteomic Analysis of Serum After Akhmeta Virus Infection: New Suspect Case Identification and Insights Into Poxvirus Humoral Immunity

Serologic cross-reactivity, a hallmark of orthopoxvirus (OPXV) infection, makes species-specific diagnosis of infection difficult. In this study, we used a variola virus proteome microarray to characterize and differentiate antibody responses to nonvaccinia OPXV infections from smallpox vaccination. The profile of 2 case patients infected with newly discovered OPXV, Akhmeta virus, exhibited antibody responses of greater intensity and broader recognition of viral proteins and includes the B21/22 family glycoproteins not encoded by vaccinia virus strains used as vaccines. An additional case of Akhmeta virus, or nonvaccinia OPXV infection, was identified through community surveillance of individuals with no or uncertain history of vaccination and no recent infection. The results demonstrate the utility of microarrays for high-resolution mapping of antibody response to determine the nature of OPXV exposure.

A Cross-Sectional Serosurvey of Anti-Orthopoxvirus Antibodies in Central and Western Africa

Since the eradication of smallpox and the subsequent discontinuation of the worldwide smallpox vaccination program, other Orthopoxviruses beside Variola virus have been increasingly representing a risk to human health. To investigate the extent of natural contact with Orthopoxviruses and possible demographic risk factors for such an exposure, we performed a cross-sectional serosurvey of anti-Orthopoxvirus IgG antibodies in West and Central Africa. To this end, people living in forest regions in Côte d’Ivoire (CIV, n = 737) and the Democratic Republic of the Congo (COD, n = 267) were assigned into groups according to their likely smallpox vaccination status. The overall prevalence of anti-Orthopoxvirus antibodies was 51% in CIV and 60% in COD. High rates of seropositivity among the vaccinated part of the population (80% in CIV; 96% COD) indicated a long-lasting post vaccination immune response. In non-vaccinated participants, seroprevalences of 19% (CIV) and 26% (COD) indicated regular contact with Orthopoxviruses. Multivariate logistic regression revealed that the antibody level in the vaccinated part of the population was higher in COD than in CIV, increased with age and was slightly higher in females than males. In the unvaccinated part of the population none of these factors influenced antibody level significantly. In conclusion, our results confirm expectedly high anti-Orthopoxvirus seroprevalences in previously smallpox-vaccinated people living in CIV and the COD but more unexpectedly imply regular contact with Orthopoxviruses both in Western and Central Africa, even in the absence of recognized outbreaks.

Identification of three immunodominant motifs with atypical isotype profile scattered over the Onchocerca volvulus proteome

Understanding the immune response upon infection with the filarial nematode Onchocerca volvulus and the mechanisms that evolved in this parasite to evade immune mediated elimination is essential to expand the toolbox available for diagnostics, therapeutics and vaccines development. Using high-density peptide microarrays we scanned the proteome-wide linear epitope repertoire in Cameroonian onchocerciasis patients and healthy controls from Southern Africa which led to the identification of 249 immunodominant antigenic peptides. Motif analysis learned that 3 immunodominant motifs, encompassing 3 linear epitopes, are present in 70, 43, and 31 of these peptides, respectively and appear to be scattered over the entire proteome in seemingly non-related proteins. These linear epitopes are shown to have an atypical isotype profile dominated by IgG1, IgG3, IgE and IgM, in contrast to the commonly observed IgG4 response in chronic active helminth infections. The identification of these linear epitope motifs may lead to novel diagnostic development but further evaluation of cross-reactivity against common co-infecting human nematode infections will be needed.

Infection with the filarial parasite Onchocerca volvulus is the cause of river blindness. We analyzed the immune response against this parasite in infected individuals in order to identify linear epitopes. Using high-density peptide microarrays we discovered three immunodominant motifs in the Onchocerca volvulus proteome that induce a broad IgG response, but the typical IgG4 immune response against parasites was absent. Our study led to the identification of novel potential epitope sequences that can potentially be used for detection of infection with Onchocerca volvulus.

Identification of human linear B-cell epitope sites on the envelope glycoproteins of Crimean-Congo haemorrhagic fever virus

A peptide library was used to screen for regions containing potential linear B-cell epitope sites in the glycoproteins and nucleoprotein of Crimean-Congo haemorrhagic fever virus (CCHFV) in an enzyme-linked immunosorbent assay (ELISA). The library consisted of 156 peptides, spanning the nucleoprotein and mature GN and GC proteins in a 19-mer with 9-mer overlap format. Using pooled serum samples from convalescent patients to screen the library, six peptides were identified as potential epitope sites. Further testing of these six peptides with individual patient sera identified two of these peptides as probable epitope sites, with peptide G1451-1469 reacting to 13/15 and peptide G1613-1631 to 14/15 human sera. These peptides are situated on the GC protein at amino acid positions 1451-1469 (relative to CCHFV isolate SPU103/97) (TCTGCYACSSGISCKVRIH) and 1613-1631 (FMFGWRILFCFKCCRRTRG). Identified peptides may have application in ELISA for diagnostic or serosurveillance purposes.

A highly specific monoclonal antibody against monkeypox virus detects the heparin binding domain of A27

The eradication of smallpox and the cessation of global vaccination led to the increased prevalence of human infections in Central Africa. Serologic and protein-based diagnostic assay for MPXV detection is difficult due to cross-reactive antibodies that do not differentiate between diverse orthopoxvirus (OPXV) species. A previously characterized monoclonal antibody (mAb 69-126-3-7) against MPXV [1] was retested for cross-reactivity with various OPXVs. The 14.5 kDa band protein that reacted with mAb 69-126-3 was identified to be MPXV A29 protein (homolog of vaccinia virus Copenhagen A27). Amino acid sequence analysis of the MPXV A29 with other OPXV homologs identified four amino acid changes. Peptides corresponding to these regions were designed and evaluated for binding to mAb 69-126-3 by ELISA and BioLayer Interferometry (BLI). Further refinement and truncations mapped the specificity of this antibody to a single amino acid difference in a 30-mer peptide compared to other OPXV homologs. This particular residue is proposed to be essential for heparin binding by VACV A27 protein. Despite this substitution, MPXV A29 bound to heparin with similar affinity to that of VACV A27 protein, suggesting flexibility of this motif for heparin binding. Although binding of mAb 69-126-3-7 to MPXV A29 prevented interaction with heparin, it did not have any effect on the infectivity of MPXV. Characterization of 69-126-3-7 mAb antibody allows for the possibility of the generation of a serological based species-specific detection of OPXVs despite high proteomic homology.

Conserved B-cell epitopes among human bocavirus species indicate potential diagnostic targets

BACKGROUND

Human bocavirus species 1-4 (HBoV1-4) have been associated with respiratory and enteric infections in children. However, the immunological mechanisms in response to HBoV infections are not fully understood. Though previous studies have shown cross-reactivities between HBoV species, the epitopes responsible for this phenomenon remain unknown. In this study, we used genomic and immunologic approaches to identify the reactive epitopes conserved across multiple HBoV species and explored their potential as the basis of a novel diagnostic test for HBoVs.

METHODOLOGY/PRINCIPAL FINDINGS

We generated HBoV1-3 VP2 gene fragment phage display libraries (GFPDLs) and used these libraries to analyze mouse antisera against VP2 protein of HBoV1, 2, and 3, and human sera positive for HBoVs. Using this approach, we mapped four epitope clusters of HBoVs and identified two immunodominant peptides--P1 (¹MSDTDIQDQQPDTVDAPQNT²⁰), and P2 (¹⁶²EHAYPNASHPWDEDVMPDL¹⁸⁰)--that are conserved among HBoV1-4. To confirm epitope immunogenicity, we immunized mice with the immunodominant P1 and P2 peptides identified in our screen and found that they elicited high titer antibodies in mice. These two antibodies could only recognize the VP2 of HBoV 1-4 in Western blot assays, rather than those of the two other parvoviruses human parvovirus B19 and human parvovirus 4 (PARV4). Based on our findings, we evaluated epitope-based peptide-IgM ELISAs as potential diagnostic tools for HBoVs IgM antibodies. We found that the P1+P2-IgM ELISA showed a higher sensitivity and specificity in HBoVs IgM detection than the assays using a single peptide.

CONCLUSIONS/SIGNIFICANCE

The identification of the conserved B-cell epitopes among human bocavirus species contributes to our understanding of immunological cross-reactivities of HBoVs, and provides important insights for the development of HBoV diagnostic tools.