Int.J.Curr.Microbiol.App.Sci (2015) 4(11): 289-294

International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 4 Number 11 (2015) pp. 289-294 http://www.ijcmas.com

Original Research Article

Evaluation of NS1 Antigen Detection as Point of Care Test against Other Dengue Markers

C.S. VinodKumar1*, B.S. Prasad2, Satish Patil1, N.K. Kalappanavar2, S.G. Jayaraj3, K.G. Basavarajappa1, Rithesh Kumar1 and S. Chethan Kumar1

1Department of Microbiology, S. S. Institute of Medical Sciences & Research Centre, NH-4, Bypass Road, Davangere, Karnataka, India 2Department of Pediatrics, S. S. Institute of Medical Sciences & Research Centre, NH-4, Bypass Road, Davangere, Karnataka, India 3Department of Medicine, S. S. Institute of Medical Sciences & Research Centre, NH-4, Bypass Road, Davangere, Karnataka, India *Corresponding author

ABSTRACT

Early and accurate diagnosis is need for hour in cases of dengue virus . The present study was conducted to evaluate the usefulness of the dengue NS1

antigen with other dengue biomarkers. A total of 306 samples collected from the fever of unknown origin (FUO) during the period July 2014 to March 2015 were K eywo rd s tested for parameters such as dengue NS1 antigen, dengue antibody tests (IgM, IgG) by rapid immunochromatography, RT-PCR for the presence of

Dengue fever, dengue virus RNA and CBC. Out of 306, 47(15%) were positive for dengue virus NS1 antigen, infection by RT PCR, among them 89.4% were infected with single DENV RT- PCR, serotype and 10.6% had concurrent infection. 45 samples were positive for NS1 Dengue antigen test, of which 43 were positive in samples which were positive for RT PCR antibodies and 2 samples were positive in RT PCR negative samples. The sensitivity and

specificity of NS1 antigen detection was 91.5% and 99.2% and positive predictive value was 95.6% and negative predictive value was 98.5%. Platelet count less than 3 100,000/mm was observed in 42 (89.6%) patients and a platelet count of >100,000/mm3 were observed in 5 (10.6%). NS1 has the sensitivity and specificity

of 91.5% and 99.2% in the early diagnosis of dengue fever. It doesn’t require any special instruments and it is easy to perform and to interpret. It can be used easily in the peripheral laboratories for the early diagnosis of dengue fever where the facilities are minimal

Introduction

Dengue has become a major cause of human people live in areas where there are risks of morbidity and mortality in International exposure to dengue virus infection and Public Health. Globally, more than 2.5 billion worldwide WHO estimates about 50 million

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Int.J.Curr.Microbiol.App.Sci (2015) 4(11): 289-294 people are infected with dengue virus every during the period of July 2014 to March year (WHO, 2000). Controlling and the 2015. These patients were selected based on rapid diagnosis of dengue is the a clinical diagnosis of dengue infection and major challenge faced by the stakeholders. fulfilled the WHO case definition for dengue Dengue virus infection with any one of four fever. Dengue NS1, IgM and IgG was serotypes produces a spectrum of clinical performed by using Immuno- illness ranging from asymptomatic to its chromatographic kit (J Mitra diagnostics). most severe form like dengue hemorrhagic The manufacturer’s instructions were fever and dengue shock syndrome. followed in the procedure and results were interpreted as reactive and nonreactive. In view of high mortality and morbidity rates, it is imperative to have rapid and Viral RNA was extracted from serum sensitive laboratory assay for early detection samples using the QIAamp Viral RNA mini of the disease. For a diagnosis of ―confirmed kit (Qiagen, Germany) according to the dengue,‖ dengue virus should be identified manufacturers’ instructions. Extracted RNA by isolation or there should be a 4-fold rise was stored at −70°C or immediately used for in paired serum antibody titer. Several RT-PCR. RT and PCR were performed in methods have been applied for laboratory one tube using a universal primer and a one- diagnosis of dengue virus infections. These step RT kit (QIAGEN, GmbH, Hilden, approaches include detection of the virus, Germany); the reaction was then placed in a detection of virus antigen, and detection of thermal cycler (Eppendorf). The preliminary anti-dengue virus antibody by product was further used for nested PCR in hemagglutination inhibition, complement another reaction tube (Yamada, 1999). fixation test, neutralization test, or ELISA, Nested PCR was performed with a thermal and detection of virus nucleic acids by cycler. The secondary PCR product was reverse transcription PCR or real-time RT- subjected to agarose gel electrophoresis PCR (Huhtamo, 2010). Recently, using a 2% agarose gel (Bangalore Gene) in commercially available kits for the detection Tris—borate buffer, followed by staining of dengue virus NS1 antigen have been with ethidium bromide and visualization on developed, and studies have shown that a UV transilluminator at 302 nm (Eles dengue virus NS1 antigen could be useful 2005). for the detection of early stages of dengue virus infections (WHO, 2000; Chippaux, Statistical analysis 1991; Guzman, 2004; Alcon, 2002; Blackshell, 2008). Assessment of efficiency, sensitivity, specificity, positive and negative predictive In this study, we describe the evaluation of values of NS1 antigen was calculated using Immunochromatographic technique that is SPSS software version 16. designed to detect the presence of dengue virus NS1 antigen and dengue virus Results and Discussion antibodies in samples from patients with dengue virus infection Median age of the study population was 10 years and the sex ratio (male/female) was Materials and Methods 1.4.

A total of 306 sera were collected from Out of 306 samples subjected to RT-PCR, patients with suspected dengue infection 47 tested positive for dengue virus, among 290

Int.J.Curr.Microbiol.App.Sci (2015) 4(11): 289-294 them 89.4% were infected with single 13 (27.7%) and a platelet count of DENV serotype and 10.6% had concurrent >100,000/mm3 was observed in 5 (10.6%) infection. DENV 2 dominated the outbreak (Table 3). Hematocrit value greater than 20 among the single DENV serotype and was observed in 20 RT-PCR positive cases. among the concurrent infection DENV 2 and Liver function tests were derailed in 51.1% DENV 3 combination was more prevalent. and renal function test showed higher value in 31.9% of dengue cases. 45 samples were positive for NS1 antigen test, of which 43 were positive in samples The sensitivity and specificity of NS1 which were positive for RT PCR and 2 antigen detection was 91.5% and 99.2% and samples were positive in RT PCR negative positive predictive value was 95.6% and samples (Table 1). negative predictive value was 98.5%.

The results of dengue NS1 antigen detection Efficient and accurate diagnosis of dengue is were also compared to the results of dengue of primary importance for clinical care i.e. antibody tests (IgM and /or IgG). A total of early detection of severe case, case 45 samples positive for NS1 antigen, 30 confirmation and differential diagnosis with cases were positive along with dengue other infectious diseases. As the initial antibody tests (Table 2). symptoms of dengue mimic those of , typhoid and leptospirosis which are Sensitivity of NS1 antigen in detecting endemic in the country, availability of a dengue fever was 91.5%, specificity 99.2%, rapid and differential diagnosis at an early positive predictive value is 95.6%, and stage of infection is utmost importance for negative predictive value is 98.5%. better patient management (Wiwanitikit, 2010). For long time detection of dengue Platelet count less than 40,000 was observed specific antibody has been main stay of in 29 (61.7%) patient and a platelet count diagnosis of dengue infection (Hu, 2011; between 40,000 to 80,000 was observed in Guzman, 2010).

Table.1 Correlation of Dengue NS1 antigen test compared to RT-PCR

RT-PCR Positive Negative Total Positive 43 02 45 Dengue NS1 Negative 04 257 261 Total 47 259 306  Sensitivity: 91.5%  Specificity: 99.2%  Positive Predictive value: 95.6%  Negative Predictive value: 98.5%

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Table.2 Correlation of Dengue NS1 antigen test compared to dengue antibody tests

Antibody test (IgM and /or IgG) Positive Negative Total Positive 30 15 45 Dengue NS1 Negative 04 257 261 Total 34 272 306

Table.3 Laboratory Investigations in patient with dengue fever

Investigations Numbers (%) Hematocrit ≥ 20% 22 (46.8) Platelet Count ≤40,000/mm3 29 (61.7) Platelet Count 40,000 – 80,000/ mm3 13 (27.7) Platelet Count >100,000/ mm3 5 (10.6.) Aspartate Aminotransferase >40 U/L 24 (51.1) Alanine Aminotransferase >40 U/L 24 (51.1) Creatinine Kinase >175 U/L 15 (31.9) Partial thromboplastin time >2 fold 16 (34.0)

Serological IgM-ELISA and IgG-ELISA are isolation is carried out only by reference currently widely used for dengue fever laboratories and is a time consuming and diagnosis in routine laboratories (Young, expensive technique. The use of dengue RT- 2002; Dussart, 2006). The tests are user PCR in most laboratories is currently friendly and robust; however, the sensitivity difficult due to the cumbersome procedure, of these tests does not become acceptable difficult interpretation and the time taken until five days after the onset of fever. (Conceicao, 2010). Accuracy of these tests is dependent on the timing of their sample collection. Moreover, Recently, an up-to-date test for early a single serological detection of IgM is diagnosis of dengue infection is dengue NS1 merely indicative of recent dengue virus antigen detection. This is possible due to the infection and a paired second serum sample presence of antigens in the early phase of is required for confirmation (Kumarswamy, infection. in DENV infection 2007). Additionally, IgM detection is not generally lasts from 4 to 5 days and DENV always conclusive because of cross antigens remain detected in patients with reactivity with other flaviviruses. Therefore, both primary and secondary dengue early laboratory diagnosis (within 1–2 days infection up to 9 days. There are both of illness) will be more important. Virus ELISA and immunochromatographic test

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(rapid test) formats available in the market combination of tests definitely increases the for the detection of NS1 antigens (Ramirez, sensitivity and the specificity for the early 2009; Zainah, 2009; Datta, 2010). These diagnosis of DENV infection. diagnostic test kits, especially the immunochromatographic strip kits, can help Acknowledgement early diagnosis and shorten the turnaround time (Watthanaworawit, 2011). NS1 protein Authors acknowledge M/s. J Mitra & Co Pvt is highly conserved for all dengue serotypes, Ltd and Vision Group of Science and circulating in high levels during the first few Technology, Government of Karnataka for days of illness. There is no cross reaction of their support dengue NS1 protein with those of other related flaviviruses (Guzman, 2010). Plasma References viremia levels would associate with the detection of plasma NS1; since NS1 like Alcon, S., Talarmin, A., Debruyne, M., virions is product of infected cells. Falconar, A., Deubel, V., Flamand, M. Srivastava et al. (2011) have reported that 2002. Enzyme-linked immunosorbent viremia levels significantly higher in assay specific to dengue virus type-1 patients who were NS1 positive versus those nonstructural protein NS1 reveals who were NS1 negative. circulation of the antigen in the blood during acute phase of disease in In the present study evaluation of the NS1 patients experiencing primary or assay indicated moderately high sensitivity secondary infections. J. Clin. and very high specificity to dengue Microbiol., 40: 376–81. infection. Out of 45 NS1 positive cases, 15 Blacksell, S.D., Mammen, M.P. Jr., cases were detected on the day 2 of the Thongpaseuth, S., et al. 2008. dengue fever and all these 15 cases were Evaluation of the Panbio dengue virus negative for dengue antibodies. While nonstructural 1 antigen detection and correlating various dengue specific immunoglobulin M antibody enzyme- parameters with thrombocytopenia, we linked immunosorbent assays for found that out of 47 RT-PCR positive cases, diagnosis of acute infections in Laos. 42 cases had the platelet count less than Diagn. Microbiol. Infect. Dis., 60: 43– 100,000/ml. Out of 45 exclusive NS1 9. positive cases, thrombocytopenia was Chippaux, A., Deubel, V. 1991. Application evident in 39 cases. of the polymerase chain reaction to diagnosis in virology. Bull. Soc. Pathol. The results obtained from this study allow Exot., 84(5): 704–11. the laboratory to consider a combination of Conceicao, T.M., Da Poian, A.T., Sorgine, tests that are suitable to increase the M.H. 2010. A real-time PCR procedure sensitivity. Since it is not possible to set up a for detection of dengue virus serotypes PCR laboratory in the rural settings, it is 1, 2, and 3, and their quantitation in advisable to use the NS1 antigen detection clinical and laboratory samples. J. as an alternative method for the speedy Virol. Methods, 163(1): 1–9. diagnosis of dengue fever. This study Datta, S., Wattal, C. 2010. Dengue NS1 doesn’t advocate replacing the current antigen detection: A useful tool in early antibody test used in the laboratory, but NS1 diagnosis of dengue virus infection. could be used as complement. The Indian J. Med. Microbiol., 28: 107– 110. 293

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