Development of recombinant nucleoprotein-based diagnostic systems for Lassa fever

Novel Tools for Lassa Virus Surveillance in Peri-domestic Rodents

Background

Lassa fever (LF) is a rodent-borne disease endemic to West Africa. In the absence of licensed therapeutics or vaccines, rodent exclusion from living spaces remains the primary method of preventing LF. Zoonotic surveillance of Lassa virus (LASV), the etiologic agent of LF, can assess the burden of LASV in a region and guide public health measures against LF.

Methods

In this study, we adapted commercially available LASV human diagnostics to assess the prevalence of LASV in peri-domestic rodents in Eastern Sierra Leone. Small mammal trapping was conducted in Kenema district, Sierra Leone between November 2018-July 2019. LASV antigen was detected using a commercially available LASV NP antigen rapid diagnostic test. LASV IgG antibodies against LASV nucleoprotein (NP) and glycoprotein (GP) were tested by adapting a commercially available semi-quantitative enzyme linked immunosorbent assay (ELISA) for detection of mouse-related and rat-related species IgG.

Findings

Of the 373 tested specimens, 74 (20%) tested positive for LASV antigen. 40 (11%) specimens tested positive for LASV NP IgG, while an additional 12 (3%) specimens only tested positive for LASV GP IgG. Simultaneous antigen presence and IgG antibody presence was linked in Mastomys sp. specimens (p < 0.01), but not Rattus sp. specimens (p = 1). Despite the link between antigen presence and IgG antibody presence in Mastomys sp., the strength of antigen response did not correlate with the strength of IgG response to either GP IgG or NP IgG.

Interpretation

The tools developed in this study can aid in the generation of valuable public health data for rapid field assessment of LASV burden during outbreak investigations and general LASV surveillance.

Funding

Funding for this work was supported by the National Institute of Allergy and Infectious Diseases National Institute of Health, Department of Health and Human Services under the following grants: International Collaboration in Infectious Disease Research on Lassa fever and Ebola - ICIDR - U19 AI115589, Consortium for Viral Systems Biology - CViSB - 5U19AI135995, West African Emerging Infectious Disease Research Center - WARN-ID - U01AI151812, West African Center for Emerging Infectious Diseases: U01AI151801.

Seroprevalence of Jamestown Canyon virus in the Japanese general population

Background

Jamestown Canyon virus (JCV) is a mosquito-borne orthobunyavirus that causes acute febrile illness, meningitis, and meningoencephalitis, mainly among adults. JCV is widely distributed in North America and the number of JCV cases in the U.S. has increased in recent years. Therefore, the central nervous system disease caused by JCV can be considered a potentially re-emerging viral disease. However, the seroprevalence of JCV is unknown in Japan. The purpose of this study is to evaluate the seroprevalence of JCV in the Japanese population.

Methods

We used an IgG enzyme-linked immunosorbent assay (IgG-ELISA) with JCV-infected cell-lysates and/or a neutralizing (NT) antibody assay. The cut-off value of IgG-ELISA was determined using IgG-ELISA to analyze serum specimens from 37 healthy Japanese donors. IgG-ELISA was validated by assessing its sensitivity and specificity, using 38 human serum samples previously tested for the presence or absence of antibodies against JCV and snowshoe hare virus (SSHV), in an in-house NT antibody assay conducted by the Public Health Agency of Canada. The seroepidemiological study was performed using IgG-ELISA and NT antibody assay to analyze 246 human serum samples from the serum bank of the National Institute of Infectious Diseases (NIID) in Japan.

Results

The cut-off value of IgG-ELISA was determined at 0.20, based on the mean (− 0.075) and standard deviation (0.092) values using Japanese donors’ sera. The sensitivity and the specificity of IgG-ELISA determined using 25 JCV-positive and 4 JCV-negative serum samples were 96 and 100%, respectively. Analysis of the 246 Japanese serum samples revealed that no specimen showed a higher value than the cut-off value of IgG-ELISA, and no sample tested positive by the NT antibody assay.

Conclusions

Our results showed that JCV is not circulating significantly in Japan. To the best of our knowledge, this is the first report to demonstrate the seroprevalence of JCV in the general population in Japan.

Analysis of the Function of the Lymphocytic Choriomeningitis Virus S Segment Untranslated Region on Growth Capacity In Vitro and on Virulence In Vivo

Lymphocytic choriomeningitis virus (LCMV) is a prototypic arenavirus. The function of untranslated regions (UTRs) of the LCMV genome has not been well studied except for the extreme 19 nucleotide residues of both the 5′ and 3′ termini. There are internal UTRs composed of 58 and 41 nucleotide residues in the 5′ and 3′ UTRs, respectively, in the LCMV S segment. Their functional roles have yet to be elucidated. In this study, reverse genetics and minigenome systems were established for LCMV strain WE and the function of these regions were analyzed. It was revealed that nucleotides 20–40 and 20–38 located downstream of the 19 nucleotides in the 5′ and 3′ termini, respectively, were involved in viral genome replication and transcription. Furthermore, it was revealed that the other internal UTRs (nucleotides 41–77 and 39–60 in the 5′ and 3′ termini, respectively) in the S segment were involved in virulence in vivo, even though these regions did not affect viral growth capacity in Vero cells. The introduction of LCMV with mutations in these regions attenuates the virus and may enable the production of LCMV vaccine candidates.

Enzyme-Antibody-Modified Gold Nanoparticle Probes for the Ultrasensitive Detection of Nucleocapsid Protein in SFTSV

As humans and climate change continue to alter the landscape, novel disease risk scenarios have emerged. Sever fever with thrombocytopenia syndrome (SFTS), an emerging tick-borne infectious disease first discovered in rural areas of central China in 2009, is caused by a novel bunyavirus (SFTSV). The potential for SFTS to spread to other countries in combination with its high fatality rate, possible human-to-human transmission, and extensive prevalence among residents and domesticated animals in endemic regions make the disease a severe threat to public health. Because of the lack of preventive vaccines or useful antiviral drugs, diagnosis of SFTS is the key to prevention and control of the SFTSV infection. The development of serological detection methods will greatly improve our understanding of SFTSV ecology and host tropism. We describe a highly sensitive protein detection method based on gold nanoparticles (AuNPs) and enzyme-linked immunosorbent assay (ELISA)—AuNP-based ELISA. The optical sensitivity enhancement of this method is due to the high loading efficiency of AuNPs to McAb. This enhances the concentration of the HRP enzyme in each immune sandwich structure. The detection limit of this method to the nucleocapsid protein (NP) of SFTSV was 0.9 pg mL⁻¹ with good specificity and reproducibility. The sensitivity of AuNP-based ELISA was higher than that of traditional ELISA and was comparable to real-time quantitative polymerase chain reaction (qRT-PCR). The probes are stable for 120 days at 4 °C. This can be applied to diagnosis and hopefully can be developed into a commercial ELISA kit. The ultrasensitive detection of SFTSV will increase our understanding of the distribution and spread of SFTSV, thus helping to monitor the changes in tick-borne pathogen SFTSV risk in the environment.

A point-of-care diagnostic for differentiating Ebola from endemic febrile diseases

Hemorrhagic fever outbreaks such as Ebola are difficult to detect and control because of the lack of low-cost, easily deployable diagnostics and because initial clinical symptoms mimic other endemic diseases such as malaria. Current molecular diagnostic methods such as polymerase chain reaction require trained personnel and laboratory infrastructure, hindering diagnostics at the point of need. Although rapid tests such as lateral flow can be broadly deployed, they are typically not well-suited for differentiating among multiple diseases presenting with similar symptoms. Early detection and control of Ebola outbreaks require simple, easy-to-use assays that can detect and differentiate infection with Ebola virus from other more common febrile diseases. Here, we developed and tested an immunoassay technology that uses surface-enhanced Raman scattering (SERS) tags to simultaneously detect antigens from Ebola, Lassa, and malaria within a single blood sample. Results are provided in <30 min for individual or batched samples. Using 190 clinical samples collected from the 2014 West African Ebola outbreak, along with 163 malaria positives and 233 negative controls, we demonstrated Ebola detection with 90.0% sensitivity and 97.9% specificity and malaria detection with 100.0% sensitivity and 99.6% specificity. These results, along with corresponding live virus and nonhuman primate testing of an Ebola, Lassa, and malaria 3-plex assay, indicate the potential of the SERS technology as an important tool for outbreak detection and clinical triage in low-resource settings.

Sensitivity and specificity of diagnostic tests for Lassa fever: a systematic review

BACKGROUND

Lassa fever virus has been enlisted as a priority pathogen of epidemic potential by the World Health organization Research and Development (WHO R & D) Blueprint. Diagnostics play a crucial role in epidemic preparedness. This systematic review was conducted to determine the sensitivity and specificity of Lassa fever diagnostic tests for humans.

METHODS

We searched OVID Medline, OVID Embase, Scopus and Web of Science for laboratory based and field studies that reported the performance of diagnostic tests for Lassa fever in humans from 1 January 1990 to 25 January 2019. Two reviewers independently screened all the studies and included only studies that involved the evaluation of a Lassa fever diagnostic test and provided data on the sensitivity and specificity. The quality of the studies was assessed using the QUADAS-2 criteria. Data on the study location, study design, type of sample, index test, reference tests and diagnostic performance were extracted from the studies.

RESULTS

Out of a total of 1947 records identified, 1245 non-duplicate citations were obtained. Twenty-six (26) full-text articles examined which identified 08 studies meeting pre-defined criteria. Only one study was a field evaluation study. The sensitivity and specificity of the point of care (RDT) against the Nikisins qPCR were 91.2%(95% CI:75.2-97.7) and 86%(95% CI: 71.4-94.2) at temperatures 18-30 °C, while the sensitivity and specificity of the single IgM ELISA assay against standard RT-PCR were 31.1%(95%CI: 25.6-37) and 95.7%(95%CI:92.8-97.7). The sensitivity of the combined ELISA Antigen/IgM assay(against virus isolation), the recombinant IgM/IgG ELISA(against standard RT-PCR), and the IgM/IgG immunoblot(against IFA) were 88%(95%CI:77-95), 25.9%(95%CI:20.8-31.6), and 90.7%(95%CI:84.13-97.27) respectively. The specificity of the combined ELISA Antigen/IgM assay(against virus isolation), the recombinant IgM/IgG ELISA(against standard RT-PCR), and the IgM/IgG immunoblot(against IFA) were 90%(95%CI:88-91), 100%(95%CI:98.2-100), and 96.3%(95%CI:92.2-100) respectively.

CONCLUSION

Lassa fever has assays for antigenaemia, IgM, IgG and PCR detection. The RDT reportedly performed well but more data are needed from other countries and at temperatures above 30 °C. Most combined immunoassays perform better than the single IgM. Multiplex and pan-Lassa assays are needed. More well conducted field studies are needed.

TRIAL REGISTRATION

Prospero registration number: CRD42018091585 .

[Arenavirus research and antiviral candidate]

Arenavirus is a genetic term for viruses belonging to the family Arenaviridae and is presented from lymphocytic choriomeningitis virus (LCMV), which shows almost no pathogenicity to humans, to Lassa virus, Junin virus, Machupo virus, Chapare virus, Lujo virus, Sabia virus, and Guanarito virus, which shows high pathogenicity to humans. These viruses except for LCMV are risk group 4 pathogens specified by World Health Organization. Based on this designation, it is designated as Class I pathogens in Japan. Although there have been no reports excluding one imported case of the Lassa fever patient, it is not surprising whenever imported cases occur in our country. Considering the disease severity and mortality rate, it is an urgent matter to develop vaccines and therapeutic drugs in endemic areas, and maintenances of these are also important in countries other than endemic areas. However, basic research on highly pathogenic arenavirus infections and development of therapeutic drugs are not easily progressed, because handling in highly safe research facilities is indispensable. In this article, we will outline the current knowledge from the recent basic research on arenavirus to the development situation of antivirals against arenaviruses.

Diagnostics for Lassa fever virus: a genetically diverse pathogen found in low-resource settings

Lassa fever virus (LASV) causes acute viral haemorrhagic fever with symptoms similar to those seen with Ebola virus infections. LASV is endemic to West Africa and is transmitted through contact with excretions of infected Mastomys natalensis rodents and other rodent species. Due to a high fatality rate, lack of treatment options and difficulties with prevention and control, LASV is one of the high-priority pathogens included in the WHO R&D Blueprint. The WHO LASV vaccine strategy relies on availability of effective diagnostic tests. Current diagnostics for LASV include in-house and commercial (primarily research-only) laboratory-based serological and nucleic acid amplification tests. There are two commercially available (for research use only) rapid diagnostic tests (RDTs), and a number of multiplex panels for differential detection of LASV infection from other endemic diseases with similar symptoms have been evaluated. However, a number of diagnostic gaps remain. Lineage detection is a challenge due to the genomic diversity of LASV, as pan-lineage sensitivity for both molecular and immunological detection is necessary for surveillance and outbreak response. While pan-lineage ELISA and RDTs are commercially available (for research use only), validation and external quality assessment (EQA) is needed to confirm detection sensitivity for all known or relevant strains. Variable sensitivity of LASV PCR tests also highlights the need for improved validation and EQA. Given that LASV outbreaks typically occur in low-resource settings, more options for point-of-care testing would be valuable. These requirements should be taken into account in target product profiles for improved LASV diagnostics.

Development and evaluation of antibody-capture immunoassays for detection of Lassa virus nucleoprotein-specific immunoglobulin M and G

Background

The classical method for detection of Lassa virus-specific antibodies is the immunofluorescence assay (IFA) using virus-infected cells as antigen. However, IFA requires laboratories of biosafety level 4 for assay production and an experienced investigator to interpret the fluorescence signals. Therefore, we aimed to establish and evaluate enzyme-linked immunosorbent assays (ELISA) using recombinant Lassa virus nucleoprotein (NP) as antigen.

Methodology/Principal findings

The IgM ELISA is based on capturing IgM antibodies using anti-IgM, and the IgG ELISA is based on capturing IgG antibody–antigen complexes using rheumatoid factor or Fc gamma receptor CD32a. Analytical and clinical evaluation was performed with 880 sera from Lassa fever endemic (Nigeria) and non-endemic (Ghana and Germany) areas. Using the IFA as reference method, we observed 91.5–94.3% analytical accuracy of the ELISAs in detecting Lassa virus-specific antibodies. Evaluation of the ELISAs for diagnosis of Lassa fever on admission to hospital in an endemic area revealed a clinical sensitivity for the stand-alone IgM ELISA of 31% (95% CI 25–37) and for combined IgM/IgG detection of 26% (95% CI 21–32) compared to RT-PCR. The specificity of IgM and IgG ELISA was estimated at 96% (95% CI 93–98) and 100% (95% CI 99–100), respectively, in non-Lassa fever patients from non-endemic areas. In patients who seroconverted during follow-up, Lassa virus-specific IgM and IgG developed simultaneously rather than sequentially. Consistent with this finding, isolated IgM reactivity, i.e. IgM in the absence of IgG, had no diagnostic value.

Conclusions/Significance

The ELISAs are not equivalent to RT-PCR for early diagnosis of Lassa fever; however, they are of value in diagnosing patients at later stage. The IgG ELISA may be useful for epidemiological studies and clinical trials due its high specificity, and the higher throughput rate and easier operation compared to IFA.

Lassa fever is endemic in several West African countries. However, only few hospitals and laboratories in the region have the capacity to conduct molecular or serological Lassa fever diagnostics. One reason is that the classical serological technique for Lassa fever—the immunofluorescence assay (IFA)—requires biosafety level 4 laboratories, which are not available in the Lassa fever endemic countries. In addition, IFA does not feature an objective read-out. Therefore, we established enzyme-linked immunosorbent assays (ELISA) for detection of Lassa virus-specific IgM and IgG in 96-well format, which do not require expensive equipment and can be implemented in diagnostic laboratories in West Africa. The ELISAs are based on recombinant antigen facilitating future production according to industry standards. In our evaluation, the ELISAs have shown a performance comparable to IFA. They allow in particular the diagnosis of Lassa fever patients at later stages of the acute illness. In addition, reliable serological assays, such as those described here, are urgently needed to conduct large-scale epidemiological investigations to better understand the epidemiology of Lassa fever across West Africa as well as for clinical trials evaluating novel medical countermeasures including vaccines and drugs.

Preventive, Diagnostic and Therapeutic Applications of Baculovirus Expression Vector System

Different strategies are being worked out for engineering the original baculovirus expression vector (BEV) system to produce cost-effective clinical biologics at commercial scale. To date, thousands of highly variable molecules in the form of heterologous proteins, virus-like particles, surface display proteins/antigen carriers, heterologous viral vectors and gene delivery vehicles have been produced using this system. These products are being used in vaccine production, tissue engineering, stem cell transduction, viral vector production, gene therapy, cancer treatment and development of biosensors. Recombinant proteins that are expressed and post-translationally modified using this system are also suitable for functional, crystallographic studies, microarray and drug discovery-based applications. Till now, four BEV-based commercial products (Cervarix^®, Provenge^®, Glybera^® and Flublok^®) have been approved for humans, and myriad of others are in different stages of preclinical or clinical trials. Five products (Porcilis^® Pesti, BAYOVAC CSF E2^®, Circumvent^® PCV, Ingelvac CircoFLEX^® and Porcilis^® PCV) got approval for veterinary use, and many more are in the pipeline. In the present chapter, we have emphasized on both approved and other baculovirus-based products produced in insect cells or larvae that are important from clinical perspective and are being developed as preventive, diagnostic or therapeutic agents. Further, the potential of recombinant adeno-associated virus (rAAV) as gene delivery vector has been described. This system, due to its relatively extended gene expression, lack of pathogenicity and the ability to transduce a wide variety of cells, gained extensive popularity just after the approval of first AAV-based gene therapy drug alipogene tiparvovec (Glybera^®). Numerous products based on AAV which are presently in different clinical trials have also been highlighted.

Laboratory Diagnosis of Lassa Fever

Lassa virus remains an important cause of illness in West Africa and among the travelers returning from this region with an acute febrile illness. The symptoms of Lassa fever can be nonspecific and mimic those of other endemic infections, especially early in illness, making a clinical diagnosis difficult; therefore, laboratory testing is needed to confirm the diagnosis. An early identification of Lassa fever is crucial for maximizing the benefit of available antiviral therapy, as treatment efficacy rapidly decreases following the clinical onset of the disease. This minireview provides an overview of the currently available diagnostic tests for Lassa fever and their strengths and weaknesses.

Retrospective survey of severe fever with thrombocytopenia syndrome in patients with suspected rickettsiosis in Japan

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by the SFTS virus (SFTSV). The aim of this study was to clarify whether SFTS is potentially mis-diagnosed as rickettsioses, including spotted fever, typhus fever, and scrub typhus, which are also tick-borne disease. A total of 464 serum samples collected from 222 patients with clinically suspected rickettsiosis between 1999 and 2012 were tested for antibodies against the SFTSV. Of the 464 serum samples, one was positive for antibodies against the virus in an enzyme-linked immunosorbent assay and indirect immunofluorescence assay. The patient of SFTSV antibody-positive sample (15 days after disease onset) was positive for SFTSV genome in the acute phase sample (3 days after disease onset) as determined via reverse transcription-quantitative polymerase chain reaction. This patient, who was a resident of the Yamaguchi prefecture in Western Japan, was in his 40s when he showed symptoms in 2011. As the result, 1 of 222 patients, who was clinically suspected of rickettsiosis, was retrospectively diagnosed with SFTS. In this case, both the C-reactive protein and white blood cell count levels were lower than the ranges of these parameters for patients diagnosed with rickettsiosis. Therefore, SFTS should be considered in the differential diagnosis for rickettsiosis in Japan.

Family Cluster Analysis of Severe Fever with Thrombocytopenia Syndrome Virus Infection in Korea

Severe fever with thrombocytopenia syndrome (SFTS) is tick-borne viral disease that was first suspected in China in 2009. The causative virus (SFTSV) was isolated in 2009 and reported in 2011, and SFTSV expanded its geographic distribution in 2012–2013, from China to South Korea and Japan. Most SFTSV infections occur through Haemaphysalis longicornis. However, SFTSV infection can also occur between family members, and nosocomial transmission of SFTSV is also possible through close contact with a patient. In this study, we first analyzed clinical, epidemiological, and laboratory data for SFTS patients and family members of an index patient in Korea. The S segment of SFTSV was amplified from the sera of three patients, and the S segment of SFTSV and IgG specific to SFTSV were detected in the serum from one family member; although this individual had no history of exposure to H. longicornis, she frequently had close contact with the index patient. In Korea, SFTSV infection among family members does not have to be reported, and we suggest that person-to-person transmission of SFTSV among family members is possible in Korea.

Severe Fever with Thrombocytopenia Syndrome Virus Antigen Detection Using Monoclonal Antibodies to the Nucleocapsid Protein

Background

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infectious disease with a high case fatality rate, and is caused by the SFTS virus (SFTSV). SFTS is endemic to China, South Korea, and Japan. The viral RNA level in sera of patients with SFTS is known to be strongly associated with outcomes. Virological SFTS diagnosis with high sensitivity and specificity are required in disease endemic areas.

Methodology/Principal Findings

We generated novel monoclonal antibodies (MAbs) against the SFTSV nucleocapsid (N) protein and developed a sandwich antigen (Ag)-capture enzyme-linked immunosorbent assay (ELISA) for the detection of N protein of SFTSV using MAb and polyclonal antibody as capture and detection antibodies, respectively. The Ag-capture system was capable of detecting at least 350–1220 TCID₅₀/100 μl/well from the culture supernatants of various SFTSV strains. The efficacy of the Ag-capture ELISA in SFTS diagnosis was evaluated using serum samples collected from patients suspected of having SFTS in Japan. All 24 serum samples (100%) containing high copy numbers of viral RNA (>10⁵ copies/ml) showed a positive reaction in the Ag-capture ELISA, whereas 12 out of 15 serum samples (80%) containing low copy numbers of viral RNA (<10⁵ copies/ml) showed a negative reaction in the Ag-capture ELISA. Among these Ag-capture ELISA-negative 12 samples, 9 (75%) were positive for IgG antibodies against SFTSV.

Conclusions

The newly developed Ag-capture ELISA is useful for SFTS diagnosis in acute phase patients with high levels of viremia.

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne emerging infectious disease caused by a novel bunyavirus, SFTS virus (SFTSV). Since first discovered in China in 2011, SFTSV has been detected from SFTS patients and ticks with expanding geographic ranges from China to Japan and South Korea. The potential for SFTS spread to other warm or sub-tropical regions makes it a serious concern to the public health. It is of great importance to detect SFTSV rapidly and specifically for the effective control of the disease. For the diagnosis of viral infections, a sandwich antigen (Ag)-capture ELISA detecting viral nucleoprotein (N) in viremic serum samples has been widely applied to detect the agents, since it is the most abundant viral antigen and has highly conserved amino acid sequence. In this study, using the novel monoclonal antibodies raised against SFSTV-N, an Ag-capture ELISA system was developed, and the validation of this system was performed using sera collected from SFTS-suspected patients. Our data show that the Ag-capture ELISA was useful for the diagnosis of SFTS patients in the acute phase of the disease. This study shows a novel methodology for the diagnosis of SFTS, which may provide helpful information for the effective control of the disease.

Non Susceptibility of Neonatal and Adult Rats against the Middle East Respiratory Syndrome Coronavirus

The present study examined the susceptibility of rats to the Middle East respiratory syndrome coronavirus (MERS-CoV) and determined whether this animal is a suitable model for MERS-CoV infection. Immunohistochemical analysis identified dipeptidyl peptidase 4 (DPP4), a known receptor for MERS-CoV on type I pneumocytes from infected rats. Whereas adult rats developed antibodies against MERS-CoV spike protein after intranasal inoculation, there was no evidence of viral replication in the lungs of adult, young, or neonatal rats after intranasal inoculation with MERS-CoV. In addition, human DPP4-expressing rat kidney fibroblasts, but not rat DPP4-expressing cells, were susceptible to MERS-CoV. Taken together, these results suggest that the rat is not a useful animal model for studying MERS-CoV infection.

Research efforts to control highly pathogenic arenaviruses: a summary of the progress and gaps

Significant progress has been made in the past 10 years in unraveling the molecular biology of highly pathogenic arenaviruses that are endemic in several West African countries (Lassa fever virus) and in some regions of South America (Argentine and Bolivian hemorrhagic fever viruses). While this has resulted in proof-of-concept studies of novel vaccine candidates in non-human primates and in the discovery of several novel antiviral small molecule drug candidates, none of them has been tested in the clinic to date. The recent Ebola outbreak in West Africa has demonstrated very clearly that there is an urgent need to develop the prophylactic and therapeutic armamentarium against viral hemorrhagic fever viruses as part of a global preparedness for future epidemics. As it pertains to this goal, the present article summarizes the current knowledge of highly pathogenic arenaviruses and identifies opportunities for translational research.

Development and validation of serological assays for viral hemorrhagic fevers and determination of the prevalence of Rift Valley fever in Borno State, Nigeria

Background

Rift Valley fever (RVF) is endemic to the tropical regions of eastern and southern Africa. The seroprevalence of RVF was investigated among the human population in Borno State, Nigeria to determine the occurrence of the disease in the study area in comparison with that of Lassa fever and Crimean-Congo Hemorrhagic fever.

Methods

Recombinant nucleoprotein (rNP)-based IgG-ELISAs for the detection of serum antibodies against RVF virus (RVFV), Lassa fever virus (LASV), and Crimean-Congo hemorrhagic fever virus (CCHFV) were used to test human sera in Borno State, Nigeria. The presence of neutralizing antibody against the RVFV-glycoprotein-bearing vesicular stomatitis virus pseudotype (RVFVpv) was also determined in the human sera.

Results

Of the 297 serum samples tested, 42 (14.1%) were positive for the presence of RVFV-IgG and 22 (7.4%) and 7 (2.4%) of the serum samples were positive for antibodies against LASV and CCHFV, respectively. There was a positive correlation between the titers of neutralizing antibodies obtained using RVFVpv and those obtained using the conventional neutralization assay with the attenuated RVFV-MP12 strain.

Conclusions

The seroprevalence of RVF was significantly higher than that of LASV and CCHF in Borno State, Nigeria. The RVFVpv-based neutralization assay developed in this study has the potential to replace the traditional assays based on live viruses for the diagnosis and seroepidemiological studies of RVF.

Generation and characterization of monoclonal antibodies against Rift Valley fever virus nucleoprotein

Due to the unpredictable and explosive nature of Rift Valley fever (RVF) outbreaks, rapid and accurate diagnostic assays for low-resource settings are urgently needed. To improve existing diagnostic assays, monoclonal antibodies (MAbs) specific for the nucleocapsid protein of RVF virus (RVFV) were produced and characterized. Four IgG2a MAbs showed specific binding to denatured nucleocapsid protein, both from a recombinant source and from inactivated RVFV, in Western blot analysis and in an enzyme-linked immunosorbent assay (ELISA). Cross-reactivity with genetically related and non-related arboviruses including Bunyamwera and Calovo viruses (Bunyaviridae family), West Nile and Dengue-2 viruses (Flaviviridae family), and Sindbis and Chikungunya viruses (Togaviridae family) was not detected. These MAbs represent a useful tool for the development of rapid diagnostic assays for early recognition of RVF.

Validation of a commercially available indirect ELISA using a nucleocapside recombinant protein for detection of Schmallenberg virus antibodies

A newly developed Enzym Like Immuno Sorbant Assay (ELISA) based on the recombinant nucleocapsid protein (N) of Schmallenberg virus (SBV) was evaluated and validated for the detection of SBV-specific IgG antibodies in ruminant sera by three European Reference Laboratories. Validation data sets derived from sheep, goat and bovine sera collected in France and Germany (n = 1515) in 2011 and 2012 were categorized according to the results of a virus neutralization test (VNT) or an indirect immuno-flurorescence assay (IFA). The specificity was evaluated with 1364 sera from sheep, goat and bovine collected in France and Belgium before 2009. Overall agreement between VNT and ELISA was 98.9% and 98.3% between VNT and IFA, indicating a very good concordance between the different techniques. Although cross-reactions with other Orthobunyavirus from the Simbu serogroup viruses might occur, it is a highly sensitive, specific and robust ELISA-test validated to detect anti-SBV antibodies. This test can be applied for SBV sero-diagnostics and disease-surveillance studies in ruminant species in Europe.

Serological assays based on recombinant viral proteins for the diagnosis of arenavirus hemorrhagic fevers

The family Arenaviridae, genus Arenavirus, consists of two phylogenetically independent groups: Old World (OW) and New World (NW) complexes. The Lassa and Lujo viruses in the OW complex and the Guanarito, Junin, Machupo, Sabia, and Chapare viruses in the NW complex cause viral hemorrhagic fever (VHF) in humans, leading to serious public health concerns. These viruses are also considered potential bioterrorism agents. Therefore, it is of great importance to detect these pathogens rapidly and specifically in order to minimize the risk and scale of arenavirus outbreaks. However, these arenaviruses are classified as BSL-4 pathogens, thus making it difficult to develop diagnostic techniques for these virus infections in institutes without BSL-4 facilities. To overcome these difficulties, antibody detection systems in the form of an enzyme-linked immunosorbent assay (ELISA) and an indirect immunofluorescence assay were developed using recombinant nucleoproteins (rNPs) derived from these viruses. Furthermore, several antigen-detection assays were developed. For example, novel monoclonal antibodies (mAbs) to the rNPs of Lassa and Junin viruses were generated. Sandwich antigen-capture (Ag-capture) ELISAs using these mAbs as capture antibodies were developed and confirmed to be sensitive and specific for detecting the respective arenavirus NPs. These rNP-based assays were proposed to be useful not only for an etiological diagnosis of VHFs, but also for seroepidemiological studies on VHFs. We recently developed arenavirus neutralization assays using vesicular stomatitis virus (VSV)-based pseudotypes bearing arenavirus recombinant glycoproteins. The goal of this article is to review the recent advances in developing laboratory diagnostic assays based on recombinant viral proteins for the diagnosis of VHFs and epidemiological studies on the VHFs caused by arenaviruses.

[Arenavirus infections]

Arenaviruses are the collective name for viruses, which belong to the family Arenaviridae. They replicate in the cytoplasm of cells, and were named after the sandy (Latin, arenosus) appearance of the ribosomes often seen in thin sections of virions under electron microscope. Several arenaviruses, such as Lassa virus in West Africa, and Junin, Guanarito, Sabia, Machupo, and Chapare viruses in South America, cause sever viral hemorrhagic fevers (VHF) in humans and represent a serious public health problem. These viruses are categorized as category 1 pathogens thus should be handles in a BSL4 laboratory. Recently, Lujo virus was isolated as a newly discovered novel arenavirus associated with a VHF outbreak in southern Africa in 2008. Although, we have no VHF patients caused by arenaviruses in Japan, except for a single imported Lassa fever case in 1987, it is possible that VHF patients occur as imported cases as for other VHF in the future. Therefore, it is necessary to develop the diagnostics and therapeutics in consideration of patient's severe symptoms and high mortality even in the disease-free countries. In this review, we will broadly discuss the current knowledge from the basic researches to diagnostics and vaccine developments for arenavirus diseases.

Characterization of monoclonal antibodies to Junin virus nucleocapsid protein and application to the diagnosis of hemorrhagic fever caused by South American arenaviruses

Junin virus (JUNV), Machupo virus, Guanarito virus, Sabia virus, and Chapare virus are members of New World arenavirus clade B and are the etiological agents of viral hemorrhagic fevers that occur in South America. In this study, we produced three monoclonal antibodies (MAbs) to the recombinant nucleocapsid protein of JUNV, designated C6-9, C11-12, and E4-2. The specificity of these MAbs was examined by enzyme-linked immunosorbent assay (ELISA), indirect immunofluorescence assay, and an epitope-mapping method. Using these MAbs, we developed antigen (Ag) capture ELISA systems. We showed that by using MAb C6-9, JUNV Ag was specifically detected. On the other hand, by using MAb C11-12 or E-4-2, the Ags of all human pathogenic South American arenaviruses were detected. The combined use of these Ag capture ELISA systems in the present study may be useful for the diagnosis of acute-phase viral hemorrhagic fever due to infection by a South American arenavirus.

Argentine hemorrhagic fever diagnostic test based on recombinant Junín virus N protein

Junín arenavirus is the etiologic agent of Argentine hemorrhagic fever. Due to its morbidity and high mortality rate in untreated cases, this endemic disease is of mandatory report in Argentina. Secure and accurate diagnostic methods are needed for the epidemiological surveillance of the disease. Current assays rely on antigens prepared from lysates of virus infected mammalian cells. The bio-safety issue related to the manipulation of large quantities of virus restricts such antigen production to laboratories with the appropriate containment facilities. In this report, we describe the development of an enzyme linked immunosorbent assay for the etiologic confirmation of the disease, based on recombinant antigens expressed in insect cells. Eight different variables of the assay were optimized with the Taguchi approach for experimental design (L18 design, seven three-level factors and one two-level factor). The area under the receiver operating characteristics (ROC) curve was 0.966, showing the high accuracy of the test discriminating positive from negative samples. Taking into account the biosafety benefits, the high yields of antigen in cell culture, and the general performance of the assay, it is expected that it will be a useful alternative to the current ELISA for the detection of antibodies in sera from convalescent patients.