Tuesday, January 20, 2009 8:51 PM
Flaviviridae It is a spherical enveloped virion with the size of 40-50nm. The inner core contains protein C and the enveloped is made up of glycoprotein peplomers (E).
It is single linear (+) ssRNA which is very infectious.
Dengue is one of the symptoms for flaviviridae. The most important arbovirus is present in the in it and it started from Southeast Asia to Americas to pacific to Africa.
There are 4 different class of Dengue. They are:
- Den-1
- Den-2
- Den-3
- Den-4
Class Den-2 shows the greatest antigenic and genotypic distance from the others. Is has a protective immunity after infection homotypic.
Dengue Life cycle
Symtoms for Dengue Fever
- Many infectious asymptomatic.
- Acute infectious resulting in fever, severe headache, retro-orbital pain, nausea and vomiting
- Severe muscle and bone pain
- Maculopapular rash just before recovery
Severe Dengue fever might lead to DENGUE HAEMORRAHGIC FEVER (DHF) /DENGUE SHOCK SYNDROME (DSS).
DHF/DSS
The properties of DHF/DSS are:
- Prior infection and age key factors
- Seldom occurs in individuals above 15 years
- Similar to yellow fever in biphasic nature:
Initial symptoms similar to DF followed by remission
Sudden deterioration of patent condition
- Severe prostration, hypotension, circulatory collapse, bleeding and shock
- Bleeding
Injection and punction sites
Gastrointestinal bleeding
Petechiae in skin, mucous membranes (mouth)
There are also 4 different classes grading of DHF:
- Grade I: Fever with non-specific, constitutional symptoms and only haemorrhagic manifestations bring positive tourniquet test
- Grade II: As for grade I, but with specific haemorrhagic manifestations
- Grade III: Signs of circulatory failure or hypotension
- Grade IV: Profound shock with pulse and blood pressure undectable
Pathogenesis of DHF/DSS
- Not well understood despite intensive study-2 theories
- Virulent strain theory:
Some strains more virulent than others
Molecular studies show variations in sequences amongst different strains, within serotypes
Early evidence pointed to DEN-2.
- Antibody enhancement:
Main theory for DHF/DSS
Main Cell target of DEN: monocytes/ macrophages
Most cases of DHF/DSS had prior infection or infants below 1 year had maternal Ab
Monkey experiments showed similar enhancement
Cause
- Immune system overreacting
- Sever Acute Respiratory Syndrome
By: Toh Wan Nee