Dengue NS1 Antigen

 Dengue NS1 Antigen. 

This is a blood test to detect the dengue virus early in the course of an infection. 

Dengue virus contains single strand RNA genome that encodes three structural and seven non-structural proteins (NS).

 The non-structural protein NS1 is considered an important diagnostic marker for acute infection from the first day after onset of infection

NS1 antigen detection ELISA is highly suitable diagnostic tools and it also has great value for use in outbreak and epidemic situation.

The NS1 test should be taken on the very first day of the fever striking. It holds relevance after 24 hours also, but ideally should be taken within 24 hours

NS1 Bioeasy™ ICT in DENV-1 epidemics is a potentially confirmatory test. Invalid results at 15 min should be reread at 30 min. To optimize impact of implementing ICT in the management of false-negatives it should be incorporated into an algorithm according to setting and available specimen.

Overall sensitivity of NS1 Ag detection kit varied widely across the various forms of dengue infection or disease. Sensitivity was highest in patients sampled during the first 3 days after onset of fever, in patients with primary infection, DENV-1 infection, with high level of viremia and in DF rather than DHF/DSS. In asymptomatic patients, RT-PCR assay has proved to be more sensitive than NS1 antigen detection. The NS1 antigen level correlated significantly with viremia and a low NS1 antigen ratio was associated with more severe disease.

The overall sensitivity of dengue NS1 antigen assays within the same period was 81.7%, indicating their potential role as a cost-effective

Antibody tests → these tests are primarily used to help diagnose a current or recent infection. They detect two different classes of antibodies produced by the body in response to a dengue fever infection,IgG and IgM. Diagnosis may require a combination of these tests because the body's immune system produces varying levels of antibodies over the course of the illness. IgM antibodies are produced first and tests for these are most effective when performed at least 7-10 days after exposure. Levels in the blood rise for a few weeks, then gradually decrease. After a few months, IgM antibodies fall below detectable levels. IgG antibodies are produced more slowly in response to an infection. Typically, the level rises with an acute infection, stabilizes, and then persists long-term. Individuals who have been exposed to the virus prior to the current infection maintain a level of IgG antibodies in the blood that can affect the interpretation of diagnostic results.

Immunoglobulin M (IgM)

The first antibody produced by the immune system during a viral infection is IgM. A positive IgM antibody test indicates that the virus may be present and that your body has started the immune response. When IgM is detected you may currently be infected, or you may have recently recovered from a COVID-19 infection

Dengue virus-specific IgM and neutralizing antibodies typically develop toward the end of the first week of illness. IgM levels are variable, but generally are positive starting 4-5 days after onset of symptoms and continuing for approximately 12 weeks post symptom onset, but may persist longer

IgM antibody clearance prevents self-antigen concentrations which could induce an immune response. IgM antibody also binds to misfolded proteins and altered cells, clearing them via dendritic cells, B cells, and macrophages.

approximately at the day 7 of the fever, in the primary infection and persist for a longer time, even up to years. Secondary Dengue infections are characterized by  increases in IgM.

Tests that measure anti-dengue IgM antibodies are useful only for the first 4–6 days of infection

 Immunoglobulin G (IgG) 

In the IgG ELISA assay, the polystyrene microwells are coated with equal proportions of inactivated and purified DENV types 1–4. Diluted serum samples and controls are incubated in the wells to allow specific antibody present in the samples to react with the antigen. Control, calibrator, and patient sera were diluted 1:101 in sample buffer, and 0.1 ml of diluted specimen was added to assigned microtiter wells. Nonspecificreactants are removed by washing and peroxidase-conjugated anti-human IgG isadded and reacts with specific IgG. Excess conjugate is removed by washing. Enzyme substrate and chromogen are added, and the color is allowed to develop. After adding the Stop Reagent, the resultant color change is quantified by a spectrophotometric reading of optical density (OD) which is directly proportional to the amount of antigen-specific IgG present in the sample. Absorbance was measured at 450 nm using an ELISA reader. Sample opticaldensity readings are compared with reference cut-off OD readings to determine results. An index value of > 1.00 is presumptive for the presence of IgG antibodies to DENV

Dengue RNA PCR test.

DENGUE - RNA PCR -

Dengue is a disease caused due to the virus transmitted by mosquitoes. Dengue infection can be observed if the ‘dengue triad’ i.e. fever, rash, and headache can be spotted. The Dengue fever is characterized in two phases namely acute and convalescent. The initial muscle pain and fever symptoms fall in acute phase which lasts for 4-5 days. Once the fever subsides the convalescent phase begins and can last upto 7 days. Dengue Virus (DENV) level is higher in blood during first phase and, therefore, real time PCR test is carried out to detect this virus so that it can be treated in its initial stages itself. 

This test is used for the diagnosis of Dengue fever during the initial stage of infection. Dengue fever is caused by RNA Flavivirus and is transmitted by a mosquito. This test helps in the early detection of the Dengue virus.How to prepare for the test?No special preparation is needed for this test

Molecular testing (polymerase chain reaction, PCR) → this type of test detects the genetic material of the dengue virus in blood up to 5 days after symptom onset (fever).

Molecular testing → a PCR test that detects the presence of the virus itself is generally considered the most reliable means of diagnosis, but the test is not widely available. A positive result from a PCR is considered conclusive. A negative result on a PCR test may indicate that no infection is present or that the level of virus is too low to detect, as may happen if the test was performed after the 5-day window during which the virus is present in the sample collected for this test. If very recent exposure is suspected, repeating the test at a later time may be warranted.

Dengue diagnosis, advances and challenges

Dengue diagnosis was one of the topics discussed at the symposium 'The Global Threat of Dengue - Desperately Seeking Solutions' organized during the 10th International Congress of Infectious Diseases held in Singapore in 2002. In this paper, a review is presented focusing on the main advances, problems and challenges of dengue diagnosis.IgM capture ELISA, virus isolation in mosquito cell lines and live mosquitoes, dengue specific monoclonal antibodies and PCR have all represented major advances in dengue diagnosis. However, an appropriate rapid, early and accessible diagnostic method useful both for epidemiological surveillance and clinical diagnosis is still needed. Also, tools that suggest a prognosis allowing for better management are also needed. Finally, laboratory infrastructure, technical expertise and research capacity must be improved in endemic countries in order to positively influence dengue surveillance, clinical case management and the development of new approaches to dengue control.