Dengue is the most common mosquito-borne viral disease of humans that in recent years has become a major international public health concern. Globally, 2.5 billion people live in areas where dengue viruses can be transmitted. The geographical spread of both the mosquito vectors and the viruses has led to the global resurgence of epidemic dengue fever and emergence of dengue hemorrhagic fever (dengue/DHF) in the past 25 years with the development of hyperendemicity in many urban centers of the tropics.

Transmitted by the main vector, the Aedes aegytpi mosquito, there are four distinct, but closely related, viruses that cause dengue. Recovery from infection by one provides lifelong immunity against that serotype but confers only partial and transient protection against subsequent infection by the other three. There is good evidence that sequential infection increases the risk of more serious disease resulting in DHF.

Infection with dengue virus causes a broad spectrum of illnesses, ranging from asymptomatic infection, undifferentiated fever and classical dengue fever (DF), to the more severe forms, dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) with high rates of morbidity and

mortality. DF is characterised by fever lasting 3-5 days, headache, muscle and joint pain, rash, but usually patient recovery. DHF or DSS, which mainly occur in patient previously infected with the virus, present similar symptoms to DF, but are followed by increased vascular permeability and hemorrhagic signs leading to reduce blood pressure, hypovolemia, vascular collapsus and death.

The most challenging problem associated with infected patient management is rapid and specific detection of dengue virus during acute phase in order to implement timely clinical treatment. Isolation and identification of the virus or detection of viral nucleic acid allow early diagnostic during febrile phase, but both methods need a specialized laboratory and results are not immediate. Detection of dengue virusspecific antibodies are commonly used for routine diagnostic. However, antibodies appear after symptoms onset. In primary infection, IgM and IgG arise approximatively 5 and 14 days respectively after symptom onset. In secondary infection, IgM levels are low or undetectable while IgG rise 1-2 days after symptom onset with higher levels than in primary infection.

Flaviviruses are enveloped, single-stranded, positive-sense RNA viruses. The genomic RNA is about 11 kb long and contains 10 genes encoding three structural proteins (capsid [C], envelope [E], and membrane [M]), and seven nonstructural proteins (NS1, NS2a, NS2b, NS3, NS4a, NS4b, and NS5). The polycistronic coding region is flanked by non-coding regions at its 5′ and 3′ ends. The nonstructural protein, NS1, is a highly conserved glycoprotein, but its biological activity has not been established. During in vitro infection, the flavivirus NS1 protein is expressed as an intracellular membrane-associated form essential for viral replication or as a cell surface-associated form that may be involved in signal transduction. In solution, secreted NS1 protein behaves as a hexamer; it circulates and accumulates in the sera of dengue virus-infected patients throughout the clinical phase of the disease. A recent study demonstrated that soluble NS1 protein binds to endothelial cells and, following recognition by anti-NS1 antibodies, could contribute to plasma leakage during severe dengue virus infection.

In 2006, Bio-Rad Laboratories had launched the first commercial EIA test kit for NS1 Antigen detection during the acute phase of Dengue detection. Since then, Dengue NS1 Antigen testing has taken a new approach in early dengue detection throughout the world.

With the detection as early as the first day of fever until the fifth day, Dengue NS1 Antigen has sensitivity between 88% to 95% and specificity of 100% to detect dengue infection in patient in the early stage of fever. All of the studies in journal and publication confirm that the detection of dengue virus NS1 antigen in Dengue NS1 Antigen tests is useful for the rapid, early biological diagnosis of dengue disease.

The Platelia Dengue NS1 Ag assay is a one-step microplate enzyme immunoassay. It is simple, rapid, subject to quality assurance, and robust, based on strong discrimination between positive and negative samples. It would be easy to implement this test in any clinical diagnostic laboratory equipped with an incubator and an ELISA reader. Automation should facilitate the testing of large numbers of samples over periods of time useful for physicians.

In order to improve the practicability of NS1 detection, in 2007 Bio-Rad Laboratories has developed the Dengue NS1 Ag STRIP, the first immunochromatography test for qualitative detection of Dengue virus NS1 antigen in human serum or plasma. Dengue NS1 Ag STRIP is the first rapid lateral-flow assay designed for screening of acute dengue infection. Dengue NS1 Ag STRIP is an individual and easy-to-use test which do not require specialized materials and is perfectly adapted to non experimented laboratories.

Physicians using this proposed acute and early convalescence diagnostic strategy on inpatients and outpatients should be able to obtain rapid, specific dengue diagnosis within a few hours for acute-phase samples, but such diagnoses should also be possible for patients presenting at a late stage of the disease. With the expansion of the geographic range of dengue fever and the increasing number and severity of reported cases, this strategy could allow clinical diagnostic laboratories to identify dengue virus infections early enough to adjust patient management, reducing the time between detection of the first cases, based on NS1 antigen detection, and the notification of public health authorities, including vector control teams.

In conclusion, all of the evaluation being done on the new dengue diagnostic tool Platelia Dengue NS1 Ag test indicates that this test is highly appropriate to field testing conditions, particularly for early-acute-phase samples, as its sensitivity and specificity far exceed those of the MAC-ELISA for such samples. NS1 antigen detection has great potential value for use in epidemic situations, as it could facilitate the early screening of patients and limit disease expansion.