Dengue Virus and Laboratory diagnosis

 Dengue Virus

There are four serotypes of dengue viruses DEN-1, DEN-2, DEN-3 and DEN-4.1

Pathogenesis: Man gets infection by the bite of infected Aedes aegypti mosquito. Humans are the reservoirs of infection and Aedes acts as vector.

Clinical Features: Incubation period is 5-8 days. Usually older children and adults are affected.

1) Dengue fever is characterized by fever, severe headache, chills, pain behind eye, severe pain in back muscles and joints (break bone fever).

2) Maculopapular rash appears on the trunk after 3-5 days and later on spreads to feet, legs and hands.

3) The illness is usually self limiting and lasts about 10 days.

4) Complications include dengue haemorrhagic fever and dengue shock syndrome.

• Seven nonstructural (NS1, NS2a, NS2b, NS3, NS4a, NS4b, and NS5) proteins are involved in the pathogenesis of severe disease. 
•  NS1 is involved in viral RNA replication. 
• It gets expressed on the surface of infected cells, without forming part of the virion. 
•  Levels of secreted NS1 (sNS1) in plasma positively correlate with viral titers. 
• The higher levels of NS1 in secondary dengue might imply an important role for NS1 in the formation of circulating immune complexes in causing severe dengue.

Before 5 days of illness during the febrile period 

 Dengue infections may be diagnosed by 

• 1)virus isolation in cell culture, 

• 2) detection of viral RNA by nucleic acid amplification tests (NAAT) 

• 3) detection of viral antigens by ELISA or rapid tests. 

Laboratory diagnosis:

(1) Serological methods. Detection of both IgM and IgG antibodies by ELISA as well as rapid tests. 

(2) Culture of virus in cell lines.