Diagnosis of dengue virus infection by the visual and simple AuBioDOT immunoglobulin M capture system

Neurological Manifestations of Perinatal Dengue

Dengue viruses (DENVs) are single-stranded RNA viruses belonging to the family Flaviviridae. There are four distinct antigenically related serotypes, DENVs types 1, 2, 3, and 4. These are all mosquito-borne human pathogens. Congenital dengue disease occurs when there is mother-to-fetus transmission of the virus and should be suspected in endemic regions in neonates presenting with fever, maculopapular rash, and thrombocytopenia. Although most of the infected infants remain asymptomatic, some can develop clinical manifestations such as sepsis-like illness, gastric bleeding, circulatory failure, and death. Neurological manifestations include intracerebral hemorrhages, neurological malformations, and acute focal/disseminated encephalitis/encephalomyelitis. Dengue NS1Ag, a highly conserved glycoprotein, can help the detection of cases in the viremic stage. We do not have proven specific therapies yet; management is largely supportive and is focused on close monitoring and maintaining adequate intravascular volume.

Serological Diagnosis of Dengue

A reliable and specific diagnosis is imperative in viral diagnosis, both for clinical management and surveillance, and to ensure that early treatment and control measures are carried out. The number of days of illness is important to choose the most appropriate method to be used and for the correct interpretation of the results obtained. Specific IgM is elicited after that period, indicating an active infection and usually lasts up to 3 months. However, in DENV secondary infections, IgM levels may be significantly lower or undetectable. After 10-12 days, a lifetime specific IgG is produced. Routinely, the laboratory diagnosis of DENV infections can be performed by viral isolation and/or detection of viral nucleic acid, serological assays for the detection of specific antibodies (IgM/IgG), antigen (NS1) and the detection of viral antigens in tissues, which are suitable during certain phases of the disease. For serological diagnosis, serum, plasma, or cerebrospinal fluid (CSF) samples may be investigated. If the test is carried out a few days after collection, the specimens can be stored at 4 °C, since the immunoglobulins are stable in serum or plasma. If the storage period is extended, the material must be kept at -20 °C or -70 °C. In serology, several methods can be used to detect specific viral antigens and/or antibodies, produced by the host in response to DENV infection. Routinely, serological tests include the hemagglutination inhibition (HI) assay, the plaque reduction neutralizing test (PRNT), the gold standard assay for dengue immune response characterization, and ELISAs to detect IgM (MAC-ELISA) and IgG (IgG-ELISA).

DNA-Modified Plasmonic Sensor for the Direct Detection of Virus Biomarkers from the Blood

The rapid spread of viral infections demands early detection strategies to minimize proliferation of the disease. Here, we demonstrate a plasmonic biosensor to detect Dengue virus, which was chosen as a model, via its nonstructural protein NS1 biomarker. The sensor is functionalized with a synthetic single-stranded DNA oligonucleotide and provides high affinity toward NS1 protein present in the virus genome. We demonstrate the detection of NS1 protein at a concentration of 0.1-10 μg/mL in bovine blood using an on-chip microfluidic plasma separator integrated with the plasmonic sensor which covers the clinical threshold of 0.6 μg/mL of high risk of developing Dengue hemorrhagic fever. The conceptual and practical demonstration shows the translation feasibility of these microfluidic optical biosensors for early detection of a wide range of viral infections, providing a rapid clinical diagnosis of infectious diseases directly from minimally processed biological samples at point of care locations.

Development of anti-human IgM nanobodies as universal reagents for general immunodiagnostics

Nanobodies are the smallest antibody fragments which bind to antigens with high affinity and specificity. Due to their outstanding physicochemical stability, simplicity and cost-effective production, nanobodies have become powerful agents in therapeutic and diagnostic applications. In this work, the advantages of nanobodies were exploited to develop generic and standardized anti-human IgM reagents for serology and IgM⁺ B-cell analysis. Selection of anti-IgM nanobodies was carried out by evaluating their yields, stability, binding kinetics and cross-reactivity with other Ig isotypes. High affinity nanobodies were selected with dissociation constants (KDs) in the nM range and high sensitivities for detection of total IgM by ELISA. The nanobodies also proved to be useful for capturing IgM in the serodiagnosis of an acute infection as demonstrated by detection of specific IgM in sera of dengue virus patients. Finally, due to the lack of an Fc region, the selected nanobodies do not require Fc receptor blocking steps, facilitating the immunophenotyping of IgM⁺ cells by flow cytometry, an important means of diagnosis of immunodeficiencies and B-cell lymphoproliferative disorders. This work describes versatile anti-IgM nanobodies that, due to their recombinant nature and ease of reproduction at low cost, may represent an advantageous alternative to conventional anti-IgM antibodies in research and diagnosis.

Cross-Reactivity of Rapid Salmonella Typhi IgM Immunoassay in Dengue Fever Without Co-Existing Infection

INTRODUCTION

Dengue fever is endemic in developing nations worldwide with as many as 500,000 annual cases of dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). A prompt and accurate diagnosis early in the disease course is essential for prompt identification and treatment of severe complications of the dengue virus infection (DVI). We identified cross-reactivity of a rapid IgM test for typhoid fever in patients with febrile illnesses that were determined to be due to dengue virus.

METHODS

All patients with documented DVI during a recent epidemic in Pakistan also underwent diagnostic testing for Salmonella enterica serovar Typhi. The diagnosis of DVI was made based on clinical findings and the positive results for dengue non-structural protein 1 antigen (NS1Ag) and/or dengue IgM antibody (anti-D IgM) during the acute phase of febrile illness. Patients with positive test results for Salmonella typhi (S. Typhi) IgM also had their blood cultures done.

RESULTS

In the group of 322 patients with clinical and serological evidence of DVI, 107 also tested positive for S. Typhi IgM. Blood cultures were negative for S. Typhi bacteria in all patients. Principal disease features included fever, headache, myalgia, retro-orbital pain, and a rash accompanied by thrombocytopenia and leukopenia. Comparisons of clinical and routine laboratory findings between the S. Typhi-positive and negative groups showed no significant differences. Patients testing positive for both NS1Ag and anti-D IgM were significantly more likely to test positive for S. Typhi IgM, even in the absence of typhoid fever. No routine antibiotics were used and all patients survived.

CONCLUSION

One-third of a large group of patients with primary DVI also demonstrated false positive results for typhoid fever. Cross-reactivity of a rapid immunoassay for typhoid fever has not been previously reported in DVI or any other flavivirus infections. Until these findings can be further evaluated, clinicians should be cautious in interpreting S. Typhi rapid immunoassays and have a high index of suspicion of DVI in dengue fever endemic areas.

High pro-inflammatory cytokine secretion and loss of high avidity cross-reactive cytotoxic T-cells during the course of secondary dengue virus infection

BACKGROUND

Dengue is one of the most important human diseases transmitted by an arthropod vector and the incidence of dengue virus infection has been increasing - over half the world's population now live in areas at risk of infection. Most infections are asymptomatic, but a subset of patients experience a potentially fatal shock syndrome characterised by plasma leakage. Severe forms of dengue are epidemiologically associated with repeated infection by more than one of the four dengue virus serotypes. Generally attributed to the phenomenon of antibody-dependent enhancement, recent observations indicate that T-cells may also influence disease phenotype.

METHODS AND FINDINGS

Virus-specific cytotoxic T lymphocytes (CTL) showing high level cross reactivity between dengue serotypes could be expanded from blood samples taken during the acute phase of secondary dengue infection. These could not be detected in convalescence when only CTL populations demonstrating significant serotype specificity were identified. Dengue cross-reactive CTL clones derived from these patients were of higher avidity than serotype-specific clones and produced much higher levels of both type 1 and certain type 2 cytokines, many previously implicated in dengue pathogenesis.

CONCLUSION

Dengue serotype cross-reactive CTL clones showing high avidity for antigen produce higher levels of inflammatory cytokines than serotype-specific clones. That such cells cannot be expanded from convalescent samples suggests that they may be depleted, perhaps as a consequence of activation-induced cell death. Such high avidity cross-reactive memory CTL may produce inflammatory cytokines during the course of secondary infection, contributing to the pathogenesis of vascular leak. These cells appear to be subsequently deleted leaving a more serotype-specific memory CTL pool. Further studies are needed to relate these cellular observations to disease phenotype in a large group of patients. If confirmed they have significant implications for understanding the role of virus-specific CTL in pathogenesis of dengue disease.

Evaluation of immunoglobulin M and G capture enzyme-linked immunosorbent assay Panbio kits for diagnostic dengue infections

BACKGROUND

Serological assays are widely used to confirm dengue virus infections and to differentiate between a primary and a secondary infection.

OBJECTIVE

Two commercial dengue diagnostic kits, Panbio Dengue IgM Capture and Dengue IgG Capture ELISA (Brisbane, Australia) were evaluated.

STUDY DESIGN

Three hundred and seventy-three serum samples were tested. Panel sera included samples from dengue confirmed cases (representing both primary and secondary infections), from non-dengue infectious diseases, and from healthy individuals. The MAC-ELISA/Dengue IPK was used for the detection of anti-dengue virus IgM antibody in the sera and the ELISA inhibition method (EIM/Dengue IPK) was used to differentiate between primary and secondary infections. Both these reference assays, which were previously developed in the Arbovirus Laboratory at the "Pedro Kouri" Tropical Medicine Institute, were employed as the gold standard.

RESULTS

High sensitivity (96.8%) and specificity (99.4%) were found with the commercial diagnostics when compared to the reference methods. Furthermore, high concordance 95.5% in classifying dengue infection types (primary or secondary infections) was observed.

CONCLUSIONS

The Panbio Dengue IgM and IgG assays offer a good alternative for dengue diagnosis. They are easy to perform and results can be obtained in less than 3h.

A multiplexed TaqMan assay for the detection of arthropod-borne flaviviruses

Arboviruses in the genus Flavivirus are major causes of human disease worldwide, and yet they are widely under reported. This is partially due to the classical methods of detection, using virologic or immunologic techniques, which typically lack sensitivity and specificity or require biological containment facilities in order to manipulate infectious cultures. Molecular detection assays based on broadly reactive (degenerate) primers also tend to have differential and lower sensitivity for many flaviviruses. In this study, an assay was designed to test for many flaviviruses using species-specific and group-specific primers in a single reaction. This real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay combines flavivirus species-specific and group-specific TaqMan primers and probes (some previously described) into a single tube and subjected it to a standardized thermocycling conditions. The multiplex assay contains specific detection for St. Louis encephalitis virus, West Nile virus, and consensus sequences for tick-borne encephalitis complex groups: Russian Spring-Summer encephalitis and Central European encephalitis viruses. The assay also contained group-specific primers for Dengue I, II, III and IV viruses. Viral RNA was extracted from infected cell-culture derived stock viruses, field samples, or was synthesized as subgenomic target RNA molecules. All flavivirus species and sample types were detected by the multiplex assay. A sensitivity analysis of the assay suggested that the multiplex was no less able to detect low virus titer samples than the single-virus assay. This technique allows for a collection of specific assays to be used to screen for the presence of many flaviviruses of interest while saving labor and reagents, and without sacrificing sensitivity. The results demonstrated that these viruses can be screened for specifically in multiplex reactions using the rapid and sensitive method of real time qRT-PCR.

Cost-effective real-time reverse transcriptase PCR (RT-PCR) to screen for Dengue virus followed by rapid single-tube multiplex RT-PCR for serotyping of the virus

Virus detection methodology provides detection of dengue virus in the early phase of the disease. PCR, targeting cDNA derived from viral RNA, has been used as a laboratory-based molecular tool for the detection of Dengue virus. We report the development and use of three real-time one-step reverse transcriptase PCR (RT-PCR) assays to detect dengue cases and serotype the virus involved. The first RT-PCR assay uses SYBR green I as the reporting dye for the purpose of cost-effective screening for dengue virus. The detection limit of the SYBR green I assay was 10 PFU/ml (0.01 equivalent PFU per assay) for all four dengue virus serotypes. The second RT-PCR assay is a duplex fluorogenic probe-based real-time RT-PCR for serotyping clinical samples for dengue viruses. The detection threshold of the probe-based RT-PCR format was 0.1 PFU for serotypes Dengue-1 and Dengue-2, 1 PFU for serotype Dengue-3, and 0.01 PFU for serotype Dengue-4. The third is a fourplex assay that detects any of the four serotypes in a single closed tube with comparable sensitivity. Validation of the assays with local clinical samples collected from 2004 to 2006 revealed that there was an 88% positive correlation between virus isolation and RT-PCR with regard to dengue virus detection and a 100% correlation with seroconversion in subsequent samples. The serotyping results derived from duplex and fourplex assays agree fully with each other and with that derived from immunofluorescence assays.

Recombinant truncated nucleocapsid protein as antigen in a novel immunoglobulin M capture enzyme-linked immunosorbent assay for diagnosis of severe acute respiratory syndrome coronavirus infection

We report the development of an immunoglobulin M (IgM) antibody capture enzyme-linked immunosorbent assay (MAC-ELISA) for severe acute respiratory syndrome coronavirus (SARS-CoV) by using recombinant truncated SARS-CoV nucleocapsid protein as the antigen. The newly developed MAC-ELISA had a specificity and sensitivity of 100% as evaluated by using sera from healthy volunteers and patients with laboratory-confirmed SARS. Using serial serum samples collected from SARS patients, the times to seroconversion were determined by IgM antibody detection after SARS-CoV infection. The median time to seroconversion detection was 8 days (range, 5 to 17 days) after disease onset, and the seroconversion rates after the onset of illness were 33% by the first week, 97% by the second week, and 100% by the third week. Compared with the results of our previous report on the detection of IgG, the median seroconversion time by IgM detection was 3 days earlier and the seroconversion rate by the second week after the illness for IgM was significantly higher than by IgG assay. Our results indicating that the IgM response appears earlier than IgG after SARS-CoV infection in consistent with those for other pathogens. Our newly developed MAC-ELISA system offers a new alternative for the confirmation of SARS-CoV infection.

Kinetics of antibodies in sera, saliva, and urine samples from adult patients with primary or secondary dengue 3 virus infections

OBJECTIVES

The kinetics of three serological markers (IgM, IgA, and IgG) in serum, saliva, and urine samples from adult patients with primary or secondary dengue infection were studied.

DESIGN

Serum, saliva, and urine samples were collected from 22 patients with clinical and confirmed dengue 3 virus infection during the outbreak in Havana City in 2001. They were tested by capture IgM (MAC-ELISA), IgA (AAC-ELISA), and IgE (EAC-ELISA) and IgG ELISA inhibition method (EIM) to detect specific dengue antibodies.

RESULTS

Similar kinetics were observed in IgM, IgA, and IgG antibodies in saliva and IgA and IgG in urine samples from secondary cases compared with kinetics in serum samples, although the values were lower. No IgG antibody was detected in saliva and urine samples in primary cases and IgM antibody was not detected in urine samples from either primary or secondary infection. All secondary cases were positive for IgG in saliva and urine samples at day 7. The kinetics of specific IgE antibodies in primary and secondary cases were different.

CONCLUSIONS

The kinetics of three serological markers (IgM, IgA, and IgG) in serum, saliva, and urine samples from adult patients with primary or secondary dengue 3 virus infection were studied for the first time, showing its behavior and usefulness in dengue virus diagnosis. The specific IgE could play a role as a serological marker in secondary infections.

A systematic review and meta-analysis of the diagnostic accuracy of rapid immunochromatographic assays for the detection of dengue virus IgM antibodies during acute infection

A meta-analysis of rapid (</=60 min) dengue diagnostic assays was conducted to determine accuracy and identify causes of between-study heterogeneity. A systematic review identified 302 potentially suitable studies, of which 11 were selected for meta-analysis. All selected studies evaluated the immunochromatographic test (ICT) manufactured by Panbio Pty Ltd. Individual study results for sensitivity ranged from 0.45 to 1.0, specificity 0.57-1.0, diagnostic odds ratio 4.5-1287, and positive:negative likelihood ratios 2.3-59 and 0.01-0.56, respectively. Results indicated that the ICT evaluated in the selected studies can both rule in and rule out disease but is more accurate when samples are collected later in the acute phase of infection. Limitations of this meta-analysis were significant between-study heterogeneity caused by inconsistencies in evaluation methodologies, and the evaluation of only the Panbio ICT. It is recommended that additional, standardized evaluations are required for other dengue ICTs.

Trends in dengue diagnosis

The conventional diagnosis of dengue virus infections includes the detection of the virus in serum or tissue samples, both by isolation in culture or through detection of specific viral molecules (genome RNA or dengue antigens) and detection of specific anti-dengue antibodies (serology). Isolation of dengue virus provides the most direct and conclusive approach to diagnosis, despite the demand for high-level equipment, technical skills and manpower. However, it is useless in early diagnosis because several days are required to isolate and classify the virus. Serology, despite being simpler, is not able to afford an accurate early diagnosis in primary infections because 4-5 days are required for the immune system to produce a sufficient amount of antibodies. Moreover, it leads to misleading results in secondary infections owing to cross-reactivity among serotype-specific antibodies and with other flavivirus antibodies. The RT-PCR and other PCR-based techniques are fast, serotype-discriminating, more sensitive and easier to carry out than conventional nucleic-acid hybridisation, but are handicapped by easy sample contamination and high technological demands. Recently, advances in bioelectronics have generated commercial kits and new techniques for detection of dengue antibodies and RNA, based on biosensor technology. Most of them are rapid, easy to operate, reusable, cheap, sensitive and serotype-specific. Nevertheless, their accuracy is still questionable because most still lack validation and standardisation. This review summarises and describes the techniques currently employed and anticipated in the near future for diagnosis of dengue disease.

Serological markers during dengue 3 primary and secondary infections

BACKGROUND

The detection of the IgM antibody for the dengue virus in serum by ELISA has become one of the most important and useful methods for diagnosis of dengue using a single acute-phase serum sample. Currently, this system is an invaluable tool for the surveillance of dengue fever (DF) and dengue hemorrhagic fever (DHF). The usefulness of other serological markers such as IgA and IgE have been less studied.

OBJECTIVE

To study the IgM, IgA and IgE specific antibody response in dengue 3 infected patients with different clinical picture and type of infection.

STUDY DESIGN

One hundred and twenty-seven serum samples collected on days 5-7 at the onset of fever from clinically and serologically confirmed dengue cases were studied. Forty-two were classified as primary dengue fever cases, 48 as secondary dengue fever cases and 37 as secondary dengue hemorrhagic fever cases. All samples were tested by capture ELISA in order to detect dengue IgM, IgA and IgE antibodies.

RESULTS AND CONCLUSIONS

In this study, significant differences were observed in the IgM, IgA and IgE response between the study groups. High IgA and IgE OD ratios in secondary dengue cases were found. The usefulness of serotype specific IgM antibody detection is also analyzed and discussed. A priority for future dengue research in terms of protection, recovery of infection and immunopathogenesis is to elucidate the role of these immunoglobulins. The cross reactivity response to IgM between dengue virus serotypes in primary and secondary cases should also be more studied.