Introduction

• Dengue is an arthropod borne virus belongs to family Flaviviridae and genus Flavivirus.
• Dengue virus is transmitted between people by female mosquitoes Ades aegypti and Ades albopidus, which are found throughout the tropical and sub-tropical regions.

Structure of Dengue virus:

• Dengue virus is spherical enveloped viruses with approximately 40-60 nm in diameter.
• Dengue virus has single-stranded Positive-sense RNA genome of about 11 Kbp long, surrounded by a nucleocapsid and covered by a lipid envelope that contains the viral glycoproteins.

I. Genome:

• Dengue has + SS RNA as genome which contains 3 structural gene and 7 non-structural gene.
• The RNA genome lack poly A tail at 3’end
• Genome contains a single open reading frame (ORF) flanked by two untranslated regions (5’ and 3’UTRs).
• The 5’ and 3’ terminal RNA sequences of the genome form large stem loop structures known as stem loop A (SLA) and 3’ stem loop (3’ SL) respectively, both essential for viral replication.
• Structural gene codes for core protein (capsid), membrane associated protein and envelope protein.
• Non-structural gene codes for non-structural proteins such as NS1, NS2a, NS2b, NS3, NS4a, NS4b and NS5 which helps in viral replication.
• NS5 is the RNA dependent RNA polymerase.

II. Capsid:

• Icosahedral capsid, 20-30 nm in diameter
• Spherical shape

III. Envelope:

• Envelope contains glycoprotein spike which has haemagglutinin activity.

Serotypes of Dengue

• There are 4 serotype of Dengue designated as DEN-1, DEN-2, DEN-3 and DEN-4
• All 4 serotypes have +ss RNA as genome of 11 Kbp length.
• DENV-5 is a new serotype which has recently been described from Malaysia

Mode of transmission:

• Dengue is transmitted by female Ades aegypti and Ades albopidus
• In order to transmit dengue between person, Mosquitoes must feed blood of patient during 5 days period when large amount of virus are present in blood.
• Inside mosquito, virus requires additional 8-12 days incubation period before it can be transmitted to healthy person.
• The dengue virus mixed with saliva of mosquito and transmitted intradermally during biting.
• In rare cases dengue is transmitted through blood transfusion, organ transplant and from infected mother to foetus.

Dengue virus: structure, serotypes and mode of transmission

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