Recombinant envelope protein-based enzyme immunoassay for IgG antibodies is comparable to neutralization tests for epidemiological studies of dengue infection

Reactivity of DENV-positive sera against recombinant envelope proteins produced in bacteria and eukaryotic cells

Dengue is a mosquito-borne disease endemic in many tropical and subtropical countries. It is caused by the dengue virus (DENV) that can be classified into 4 different serotypes (DENV-1-4). Early diagnosis and management can reduce morbidity and mortality rates of severe forms of the disease, as well as decrease the risk of larger outbreaks. Hiperendemicity in some regions of the world and the possibility that some people develop a more severe form of disease after a secondary infection caused by antibody-dependent enhancement justify the need to understand more thoroughly the antibody response induced against the virus. Here, we successfully produced a recombinant DENV-2 envelope (E) protein and its domains (EDI/II and EDIII) in two distinct expression systems: the Drosophila S2 insect cell system and the BL21 (DE3) pLySs bacterial system. We then evaluated the reactivity of sera from patients previously infected with DENV to each recombinant protein and to each domain separately. Our results show that the E protein produced in Drosophila S2 cells is recognized more frequently than the protein produced in bacteria. However, the recognition of E protein produced in bacteria correlates better with the DENV-2 sera neutralization capacity. The results described here emphasize the differences observed when antigens produced in bacteria or eukaryotic cells are used and may be useful to gain more insight into the humoral immune responses induced by dengue infection.

The Seroprevalence of Dengue Virus Infection and Its Association With Iron (Fe) Level in Pregnant Women in Guangzhou, China

Dengue fever is regarded as the most prevalent mosquito-borne viral disease in humans. However, information of dengue virus (DENV) infection in pregnant women and the influence factors remain unclear. In this study, we extracted information of 2,076 pregnant women from the Prenatal Environment and Offspring Health (PEOH) birth cohort conducted since 2016 in Guangzhou, China. Peripheral blood and clean midstream urine samples of participants were collected during their hospitalization for childbirth. Indirect enzyme-linked immunosorbent assay (ELISA) was used to detect immunoglobulin G (IgG) antibodies of DENV in serum samples, and inductively coupled plasma mass spectrometry (ICP-MS) was applied to determine the Fe concentrations in the urine samples, which were then adjusted for by urine creatinine and transformed by natural logarithm (ln-Fe). The seroprevalence of DENV IgG antibody in all included participants was 2.22% (46/2,076). We observed higher seroprevalence of IgG antibody in women aged ≥35 years (2.9%), education ≤ 12 years (2.5%), yearly income per capita <100,000 yuan (2.4%), no use of air-conditioner (2.4%), no use of mosquito coils (2.3%), and no exercise during pregnancy (4.1%). A U-shaped relationship was found between ln-Fe concentration and the risk of positive IgG antibody. Compared with women with ln-Fe concentration of 2.0–2.9 μg/g creatinine, slightly higher risks of positive IgG antibody were found among women with ≤2.0 (RR = 4.16, 95% CI: 0.78, 19.91), 3.0–3.9 (RR = 1.93, 95% CI: 0.65, 7.08), 4.0–4.9 (RR = 2.19, 95% CI: 0.65, 8.51), and ≥5.0 μg/g creatinine of ln-Fe (RR = 2.42, 95% CI: 0.46, 11.33). Our findings suggested that the seroprevalence of dengue IgG antibody in pregnant women was comparable to the general population in Guangzhou, China. The risk of DENV infection may be associated with maternal demographic characteristics and behaviors. Both maternal low and high Fe concentrations may be positively associated with the risk of DENV infection.

A graphene-based dengue immunosensor using plant-derived envelope glycoprotein domain III (EDIII) as the novel probe antigen

The envelope glycoprotein domain III (EDIII) of dengue virus (DENV) has been recognised as the antigenic region responsible for receptor binding. In the present work, we have proposed a novel immunosensor constructed on a graphene-coated screen-printed carbon electrode (SPCE) using plant-derived EDIII as the probe antigen to target DENV IgG antibodies. The developed immunosensor demonstrated high sensitivity towards DENV IgG within a wide linear working range (125-2000 ng mL^-1) under the optimised sensing conditions. The limit of detection was determined to be 22.5 ng mL^-1. The immunosensor also showed high specificity towards DENV IgG, capable of differentiating DENV IgG from the antibodies of other infectious diseases including the similarly structured Zika virus (ZIKV). The ability of the immunosensor to detect dengue antibodies in serum samples was also verified by conducting tests on mouse serum samples. The proposed immunosensor was able to provide a binary (positive/negative) response towards the serum samples comparable to the conventional enzyme-linked immunosorbent assay (ELISA), indicating promising potential for realistic applications.

Highly sensitive and specific graphene/TiO2 impedimetric immunosensor based on plant-derived tetravalent envelope glycoprotein domain III (EDIII) probe antigen for dengue diagnosis

This study reports on the development of a novel impedimetric immunosensor design using plant-derived antigenic glycoprotein for the detection of dengue virus (DENV) IgG antibodies. The electrochemical immunosensor platform was constructed using screen-printed carbon electrode (SPCE) modified with graphene/titanium dioxide (G/TiO₂) nanocomposite to improve the electrode in terms electrochemical performance and specific surface area. A plant-derived dengue envelope domain III (EDIII) protein was used as the antigenic probe protein in this immunosensing strategy. Under optimised sensing conditions, the immunosensor demonstrated high sensitivity towards DENV IgG in a wide linear working range (62.5-2000 ng/mL), with a limit of detection of 2.81 ng/mL. The immunosensor showed high specificity for discriminating DENV IgG against antibodies of other infectious disease, including the closely related Zika virus (ZIKV). The reliability of the immunosensor in serological diagnosis was verified by challenging the immunosensor against serum samples, compared to conventional enzyme-linked immunosorbent assay (ELISA). As shown by its remarkable performance throughout the study, the devised immunosensor is proposed as a reliable and practical diagnostic tool for the serological detection of dengue in realistic applications.

Production of Proteins prM/M and E of Dengue Virus-3 in Pichia pastoris: Simplified Purification and Evaluation of Their Use as Antigens in Serological Diagnosis of Dengue

Dengue is a major arbovirus affecting humans today. With the growing number of cases, it is essential to have large-scale production of antigens for the development of diagnostic kits for the rapid detection of patients infected by the virus and consequent proper medical intervention for them. In this work, we express the prM/M and E proteins of dengue virus-3 in yeast Pichia pastoris KM71H. The proteins were produced in soluble form in the supernatant of the culture and were purified by precipitation with ammonium sulfate. The fraction of 80% of ammonium sulfate was used as an antigen in an indirect enzyme-linked immunosorbent assay (ELISA), providing a sensitivity of 82.61% and a specificity of 89.25%. Thus, the methodology proposed here showed promise for obtaining antigens of dengue viruses and creating quick and inexpensive diagnostic tests, which is of great value since large portions of the areas affected by this disease are economically neglected.

Nanosensors based on LSPR are able to serologically differentiate dengue from Zika infections

The Flaviviridae virus family was named after the Yellow-fever virus, and the latin term flavi means “of golden color”. Dengue, caused by Dengue virus (DENV), is one of the most important infectious diseases worldwide. A sensitive and differential diagnosis is crucial for patient management, especially due to the occurrence of serological cross-reactivity to other co-circulating flaviviruses. This became particularly important with the emergence of Zika virus (ZIKV) in areas were DENV seroprevalence was already high. We developed a sensitive and specific diagnostic test based on gold nanorods (GNR) functionalized with DENV proteins as nanosensors. These were able to detect as little as one picogram of anti-DENV monoclonal antibodies and highly diluted DENV-positive human sera. The nanosensors could differentiate DENV-positive sera from other flavivirus-infected patients, including ZIKV, and were even able to distinguish which DENV serotype infected individual patients. Readouts are obtained in ELISA-plate spectrophotometers without the need of specific devices.

Design and production of dengue virus chimeric proteins useful for developing tetravalent vaccines

Dengue virus (DENV) is a Flavivirus estimated to cause 390 million infections/year. Currently, there is no anti-viral specific treatment for dengue, and efficient DENV vector control is still unfeasible. Here, we designed and produced chimeric proteins containing potential immunogenic epitopes from the four DENV serotypes in an attempt to further compose safer, balanced tetravalent dengue vaccines. For this, South American DENV isolate sequences were downloaded from the NCBI/Virus Variation/Dengue virus databases and intraserotype-aligned to generate four consensuses. Four homologous DENV sequences were retrieved using BLAST and then interserotype-aligned. In parallel, sequences were subjected to linear B epitope prediction analysis. Regions of the envelope and NS1 proteins that are highly homologous among the four DENV serotypes, non-conserved antigenic regions and the most antigenic epitopes found in the C, prM, E and NS1 DENV proteins were used to construct 11 chimeric peptides. Genes encoding the chimeric proteins were commercially synthesized, and proteins were expressed, purified by affinity chromatography and further subjected to ELISA assays using sera from individuals infected with DENVs 1, 2, 3 or 4. As a proof-of-concept, the chimeric EnvEpII protein was selected to immunize BALB/c and C57BL/6 mice strains. The immunization with EnvEpII protein associated with aluminum induced an increased number of T CD4⁺ and CD8⁺ cells, high production of IgG₁ and IgG₂ antibodies, and increased levels of IL-2 and IL-17 cytokines, in both mouse strains. Because the EnvEpII protein associated with aluminum induced an efficient cellular response by stimulating the production of IL-2, IL-4, IL-17 and induced a robust humoral response in mice, we conclude that it resembles an efficient specific response against DENV infection. Although further experiments are required, our results indicate that epitope selection by bioinformatic tools is efficient to create recombinant proteins that can be used as candidates for the development of vaccines against infectious diseases.

Seroprevalence of severe fever with thrombocytopenia syndrome virus antibodies among inhabitants of Dachen Island, eastern China

Severe fever with thrombocytopenia syndrome virus (SFTSV) has been emerging and has caused many human cases in China, Japan and Korea. Some studies speculated that SFTSV was transmitted with bird migration among these countries. Notably, SFTS cases have been identified in a Chinese island named Dachen which is situated southwest of Japan and Korea. In this study, we conducted a serum survey of SFTSV antibodies among inhabitants of the island. A total of 439 serum specimens were collected in June 2018. All serum samples were tested for total antibodies and IgM antibody with double-antigen sandwich ELISA method. The rates of seropositivity for SFTSV total antibodies and IgM antibody were 3.0% (95% CI 1.4-4.6) and 0.5% (2/439), respectively. The median age of all participants was 61 years and all seropositive samples were all from inhabitants aged >50 years. The differences of seroprevalence between different gender groups and different age groups were not significant. However, seroprevalence varied significantly among different villages (P = 0.033). Our results showed that some inhabitants of Dachen Island had been infected with SFTSV, and some ticks and host animals of the island carry SFTSV. Comprehensive measures should be conducted to prevent the occurrence of SFTS cases in the island.

High seroprevalence of dengue virus indicates that dengue virus infections are frequent in central and eastern Sudan

OBJECTIVES

To determine the seroprevalence of dengue in central and eastern Sudan and the breadth of neutralising antibody responses.

METHODS

Blood was drawn from 483 patients with fever who visited outpatient clinics in Port Sudan, Red Sea state, in three towns in Kassala state and in El Obeid, North Kordofan, in December 2012 and January 2013. Sera were tested for dengue virus IgG and IgM by ELISA (Panbio) and sera without serologic evidence of acute infection (IgM negative) were used for the analysis of the seroprevalence. DENV neutralisation tests were performed to determine the specificity of the ELISA and to examine the degree of cross-neutralisation of multiple DENV serotypes.

RESULTS

Sixty-seven per cent (302 of 448) of the sera were dengue virus IgG-positive. The seroprevalence in Port Sudan was 89% (106 of 119 sera), in Kassala 61% (128 of 209) and in North Kordofan 56.7% (68 of 120). Thirty-one of 32 ELISA-positive sera neutralised dengue viruses indicating that the ELISA was highly specific. The majority of the sera broadly neutralised all four dengue virus serotypes indicating multiple infections.

CONCLUSIONS

The majority of the population in central and eastern Sudan has been infected with dengue viruses, many people repeatedly. The high seroprevalence underscores the need for extended dengue surveillance in Sudan, broad disease awareness in medical institutions and in the population and diagnostic capacity building for severe dengue infections.

Low Seroprevalence of Severe Fever with Thrombocytopenia Syndrome Virus Antibodies in Individuals Living in an Endemic Area in Japan

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infection with a high mortality rate. It is caused by the SFTS virus (SFTSV) and is endemic in some areas in western Japan, including the Kagoshima prefecture. In the present study, healthy individuals living in this prefecture were examined to assess for anti-SFTSV seroprevalence. An initial study was performed using the serum samples collected from a total of 646 individuals living in Kagoshima. At the same time, a questionnaire was used to collect information (such as occupation and a history of tick bite). Enzyme-linked immunosorbent assay and indirect immunofluorescence assay were used for the screening. Finally, the seroprevalence of anti-SFTSV antibodies was confirmed using a neutralization assay. Only 2 (0.3%) out of 646 study participants were positive for anti-SFTSV antibodies. No significant difference was observed between individuals who are at a high or low risk of tick bite in terms of seropositivity. Next, a total of 1,000 serum samples collected from general blood donors by the Japanese Red Cross Kyushu Block Blood Center were tested. None of these samples tested positive for anti-SFTSV antibodies. These results suggest a low seroprevalence of anti-SFTSV antibodies in healthy individuals living in an endemic area in Japan.

Multi-walled carbon nanotubes functionalized with recombinant Dengue virus 3 envelope proteins induce significant and specific immune responses in mice

BACKGROUND

Dengue is the most prevalent arthropod-borne viral disease in the world. In this article we present results on the development, characterization and immunogenic evaluation of an alternative vaccine candidate against Dengue.

METHODS

The MWNT-DENV3E nanoconjugate was developed by covalent functionalization of carboxylated multi-walled carbon nanotubes (MWNT) with recombinant dengue envelope (DENV3E) proteins. The recombinant antigens were bound to the MWNT using a diimide-activated amidation process and the immunogen was characterized by TEM, AFM and Raman Spectroscopy. Furthermore, the immunogenicity of this vaccine candidate was evaluated in a murine model.

RESULTS

Immunization with MWNT-DENV3E induced comparable IgG responses in relation to the immunization with non-conjugated proteins; however, the inoculation of the nanoconjugate into mice generated higher titers of neutralizing antibodies. Cell-mediated responses were also evaluated, and higher dengue-specific splenocyte proliferation was observed in cell cultures derived from mice immunized with MWNT-DENV3E when compared to animals immunized with the non-conjugated DENV3E.

CONCLUSIONS

Despite the recent licensure of the CYD-TDV dengue vaccine in some countries, results from the vaccine's phase III trial have cast doubts about its overall efficacy and global applicability. While questions about the effectiveness of the CYD-TDV vaccine still lingers, it is wise to keep at hand an array of vaccine candidates, including alternative non-classical approaches like the one presented here.

Evaluation of the effectiveness of mass trapping with BG-sentinel traps for dengue vector control: a cluster randomized controlled trial in Manaus, Brazil

The objective of this study was to assess the effectiveness of BG-Sentinel (BGS) traps for mass trapping at the household level to control the dengue vector, Aedes aegypti (L.), in Manaus (Brazil) by performing a cluster randomized controlled trial. After an initial questionnaire and baseline monitoring, 6 out of 12 clusters were randomly allocated to the intervention arm, where participating premises received one BGS trap for mass trapping. The other six clusters did not receive traps and were considered as the control arm. Biweekly monitoring with BGS in both arms assessed the impact of mass trapping. At the end of the study, a serological survey was conducted and a second questionnaire was conducted in the intervention arm. Entomological monitoring indicated that mass trapping with BGS traps significantly reduced the abundance of adult female Ae. aegypti during the first five rainy months. In the subsequent dry season when the mosquito population was lower, no effect of mass trapping was observed. Fewer Ae. aegypti females were measured in the intervention arm during the next rainy period, but no significant difference between arms was observed. The serological survey revealed that in participating houses of mass trapping areas recent dengue infections were less common than in control areas, although this effect was not statistically significant. The majority of participants responded positively to questions concerning user satisfaction. Our results suggest that BGS traps are a promising tool which might be deployed as part of dengue control programs; however, further investigations and larger scale studies are necessary.