Journal of Medical Society

BRIEF REPORT
Year
: 2012  |  Volume : 26  |  Issue : 3  |  Page : 154--155

Non-structural protein 1 antigen capture kit as an early dengue diagnostic tool


Sheevani Sheemar, Gomty Mahajan, Shashi Chopra, Jaspal Kaur 
 Department of Microbiology, Punjab Institute of Medical Sciences, Jalandhar, India

Correspondence Address:
Sheevani Sheemar
144, Gurjeet Nagar, Garha Road, Jalandhar
India

Abstract

Introduction: Dengue is a major public health problem in tropical and sub-tropical regions of the world. Detection of specific Immunoglobulin M [IgM] antibodies forms the mainstay for diagnosis of dengue infection. However, IgM antibodies develop after 4-5 days of infection and there is an urgent need for an alternative diagnostic tool that can detect dengue infection during this phase. Materials and Methods: We carried out a prospective study with the aim to analyze the utility of a commercial non-structural protein 1 antigen (NS1 Ag) based rapid immunochromatographic test for detection of dengue infection in anti-dengue IgM seronegative serum samples. Results: A total of randomly selected 86 IgM negative samples were tested for the presence of dengue NS1 Ag. Of these, 59.30% (51/86) were positive for NS1 Ag. Conclusions: Our findings, therefore, supplement the findings of other similar studies suggesting NS1 Ag as an early diagnostic marker that is feasible to look for in a routine diagnostic laboratory. Furthermore, NS1 Ag assay may be a useful tool for detecting dengue infection during acute phase of infection when IgM antibodies are not formed to the detectable levels.



How to cite this article:
Sheemar S, Mahajan G, Chopra S, Kaur J. Non-structural protein 1 antigen capture kit as an early dengue diagnostic tool.J Med Soc 2012;26:154-155


How to cite this URL:
Sheemar S, Mahajan G, Chopra S, Kaur J. Non-structural protein 1 antigen capture kit as an early dengue diagnostic tool. J Med Soc [serial online] 2012 [cited 2020 Dec 2 ];26:154-155
Available from: https://www.jmedsoc.org/text.asp?2012/26/3/154/113223


Full Text

 Introduction



Dengue virus (DENV) infection has emerged as a major public-health concern across the globe in terms of mortality, morbidity, and public health cost. It is estimated that annually more than 50 million people are infected with DENV. Early diagnosis during acute infection is critical to clinically manage severe disease and to identify potential outbreaks in a timely manner. [1] Gold standard for the diagnosis of DENV infection is isolation of virus from blood during acute phase of illness or by detecting genomic sequences by using reverse transcriptase Polymerase Chain Reaction [PCR]. However, these procedures are of limited utility in routine clinical use as these are time consuming, technically intensive and expensive procedures. An IgM antibody capture ELISA, which is frequently used for diagnosing dengue infection, shows low-sensitivity in early phase of infection. [2] Non-structural protein 1 (NS1) is a highly conserved non-structural glycoprotein secreted by virus-infected cells during the acute phase of dengue, and it is essential for virus viability. [3] NS1 antigen (Ag) circulates uniformly in all serotypes of DENV and it circulates at high level during the first few days of illness. [4] NS1 Ag levels varies from 0.04 μg/ml to 2 μg/ml in acute-phase serum samples, to only 0.04 μg/ml or even less in convalescent phase serum. [3] This is the reason for its higher detection rate in acute phase sera.

Only few studies are available that have reported the role of rapid tests used for detection of soluble DEN viral NS1 Ag in early DENV infection. [4],[5],[6],[7] Therefore, we undertook this pilot study to evaluate the significance of detection of NS1 Ag using lateral flow immunochromatographic rapid tests in dengue IgM negative sera for early detection of DENV infection without the requirement of paired sera.

 Materials and Methods



This prospective study was carried out at a Tertiary Care Hospital in Jalandhar, India in the Department of Microbiology. Over a period of 3 months (September 2010-November 2010) a total of 1210 samples were received for detection of Anti-dengue IgM and IgG antibodies. Of these 86 randomly selected serum samples, clinically suspected of DENV infection as per WHO criteria, [1] which were found to be seronegative for anti-dengue IgM antibodies using rapid immunochromatographic test by SD Biostandard Diagnostics Pvt. Ltd, Korea and confirmed by ELISA test kit, dengue IgM MicroELISA (J Mitra, New Delhi, India) formed the study group. These 86 anti-dengue IgM seronegative samples were subjected to rapid immunochromatographic test for detection of dengue NS1 Ag (SD Biostandard Diagnostics Pvt. Ltd, Korea).

All tests were performed in strict adherence to the manufacturer's three instructions provided in the kit inserts.

 Results



Out of 1210 samples, 232 (19.17%) tested positive for anti-dengue antibodies, while 978 (80.83%) were negative for the same. Of these 232 positive samples, 155 (66.81%) were positive for IgM anti-DEN antibodies, 44 (18.97%) were positive for IgG anti-DEN antibodies and 33 (14.22%) showed the presence of both IgM and IgG anti-DEN antibodies. Out of 978 seronegative serum samples, 86 samples were randomly selected for detection of DEN NS1 Ag. It was observed that 59.30% (51/86) were positive for the presence of DEN NS1 Ag while 40.70% (35/86) were negative for the same.

 Discussion



Results obtained were analyzed and our study showed high prevalence of DEN NS1 Ag in DEN IgM seronegative samples suggesting restricted scope of detection of IgM antibodies as a routine procedure in the light of absence of paired sera. The requirement of paired sera in these cases would delay the diagnosis. It is an established fact that early diagnosis provides an appropriate management preventing the complications like dengue hemorrhagic fever and dengue shock syndrome. Therefore, need for rapid, inexpensive and simple to perform test for the accurate and early diagnosis of infections like dengue. Fever cannot be argued. High positivity of DEN NS1 Ag in the seronegative samples for IgM antibodies against DENV indicates the high potential of improving dengue diagnosis by use of NS1 Ag capture assays. Other studies have also reported high sensitivity of 70-100% of DEN NS1 Ag detection in contrast to low sensitivity of IgM antibodies detection in acute phase of infection. [4],[5],[6],[7],[8] High specificity of 99-100% of lateral flow rapid test for NS1 Ag detection in early phase of primary DENV infection has also been quoted by various authors in their respective studies. [9],[10]

A limitation of our study was non availability of sample timing, which is important in serological diagnosis of DENV infection and it might be one of the reasons for false-negative dengue anti IgM antibodies tests. In developing countries it is frequently observed that sample timing is often neglected, which makes it all the more important to have a testing algorithm to cover up early acute phase, late acute or early convalescent phase of DENV infection.

 Conclusion



The present pilot study reinforces the findings of other authors suggesting inclusion of rapid tests for detection of DEN NS1 Ag along with antibody assays. It will bridge the diagnostic challenges pointed by the initial period of viremia and the delayed immune response. This testing algorithm would help in determining dengue infection in a timely manner at a reasonable cost, negating the need for paired sera and demanding techniques in performing the test.

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