Dengue virus: structure, serotypes and mode of transmission
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.