Dengue NS1 Antigen – A New Rapid Test
We all remember the mad rush of patients and doctors alike for repeated platelet counts during the dengue season and despite efforts by the authorities to control the mosquito menace dengue fever did grip Delhi and its neighboring areas. With an aim to establish an accurate diagnosis of acute dengue virus infection early, in order to provide timely information for the management of patients and early public health control of dengue outbreak Dr Lal Path labs added a new rapid test Dengue NS1 antigen to its test menu.
Dengue is the most important arbovirosis in terms morbidity and mortality.
Early laboratory diagnosis of acute dengue virus infection still remains a problem. At present, the three basic methods used by most laboratories for the diagnosis of dengue virus infection are:
- Viral isolation and identification
- Detection of viral genomic sequence by a nucleic acid amplification technology assay (rt-pcr)
- Detection of dengue virus-specific igm antibodies by the igm-capture enzyme-linked immunosorbent assay (MAC-ELISA) and/or the rapid dengue immunochromatographic test (DIT).
Though virus isolation and characterisation are considered as the gold standard of laboratory diagnosis for acute dengue virus infection, it is expensive and it takes at least 6–10 days for the virus to replicate in tissue cell culture or laboratory mosquitoes.
Detection of viral genomic sequence by RT-PCR is also an expensive method and is not widely available in most hospital diagnostic laboratories.
The third method, assay of antidengue specific IgM, depends on the time taken for an infected person’s immunological response to produce IgM antibodies against dengue virus antigens.
Thus, both DIT (often considered as the rapid test for diagnosis of dengue infection) and MAC-ELISA do not provide early diagnosis of acute dengue infection, as in most cases, the first detectable IgM only appears on Days 4–5 of the illness. Moreover, a single serological detection of IgM is merely indicative of a recent dengue virus infection, and should not be interpreted as a diagnosis of acute infection without a paired second serum sample.
Recent studies have shown DENGUE NS1 AG test gives an:
- Overall higher sensitivity rate than the current three established diagnostic test methods for laboratory diagnosis of acute dengue infection.
- Compared to dengue virus isolation and molecular detection of viral rna, the ns1 antigen-capture elisa gave a higher positive detection within the first four days of illness.
- Also, the ns1 antigen-capture elisa has the added advantage of continuing to give good detection rates up to seven days of the illness.
- Ithas also been evaluated in some studies that, the NS1 antigen-capture ELISA gave a significantly higher detection rate in acute primary dengue than in acute secondary dengue. Despite the lower detection rate for serum samples from patients with acute secondary dengue, this was still higher than the other dengue diagnostic methods.
Dengue NS1 antigen test is an easy to perform, rapid and specific test is needed to confirm infection during the acute phase of the infection in order to implement appropriate treatment during the early course of the disease. NS1 antigen is a non structural protein recognized as a marker of acute phase of dengue infection, a period for which traditional serological antibodies based methods are of limited value. NS1 antigen has been found circulating in the sample of infected patients from the first day and up to 9 days after onset of fever.
Advantages:
- The test can be performed in human serum or plasma.
- It is a disposable test using lateral flow immunochromatographic technique.
- Rapid test ; result can be read within 15- 30 minutes.
- It has a high sensitivity of 92.3% and a specificity of 100%.
Take home message
Thus, antigen-capture ELISA should be considered as the test of choice for patients suspected of acute dengue illness, especially those with fever lasting five days or less. For those patients with a history of fever for more than six days and are suspected to have acute dengue infection, the test could also be considered concurrently with an assay of dengue specifi c IgM.
