Dengue: Properties, Transmission, Clinical features (Signs and Symptoms), Pathogenesis, Breakbone fever, Dengue Haemorrhagic Fever, Lab Diagnosis

Properties of dengue virus:

Dengue Virus

1.   Virus of flavivirus family

2.   RNA, enveloped virus

3.   Has 4 serotypes- DEN- 1,2,3,4

4.   Replication is in cytoplasm

5.   Females Aedes Aegypti mosquito transmit the disease

6.   Viraemia is present at the time of fever

Dengue (disease):

Dengue is a mosquito born infection which is caused by dengue virus

Common feature - fever and acute systemic illness

Incubation Period- 2-7 days

Endemic: in south-east asia, india, Africa, carribean and the Americas

Environmental aedes aegypti: It breeds in

·       Standing water

·       Collection of water in containers

·       Water-based air coolers

·       Tire dumps

Clinical Features and Pathogenesis of Dengue

Mode of transmission of dengue virus:

Female aedes aegypti mosquito transmits the disease

Reservoir: patients are the reservoir

Transmission of Dengue Virus

Clinical feature of dengue:

1.   Prodrom: 2 days of malaise and headache

2.   Acute onset: fever, backache, arthalgia, headache, G.pain (break-bone fever), pain on eye movement, larcimation, anorexia, nausea, vomiting, relative bradycardia, prostration, depression, lymphadenopathy, sclera injection

3.   Fever: Continuous or “saddle back” with break on 4th or 5th days and then recrudescence usually last 7-8 days

4.   Rash: initial flushing faint macular rash in 1st 1-2 days, maculopapular scarlet morbilliform rash from days 3-5 on trunk, spreading centrifugally and sparing the palms and soles. Onset is often with fever effervescence. May desquamate on resolution or give rise to petechiae on extensor surface

5.   Convalescence: Slow

6.   Complication: Minor bleeding from the mucosal sites, hepatitis, cerebral hemorrhage or oedema, rhabdomyolysis

Symptoms of Dengue Fever

Pathogenesis of classical dengue/ 1st exposure dengue/ breakbone fever:

1.   Dengue infection by dengue virus

2.   Ab is formed

3.   Formation of immune complex and activation of complement

Increased vascular permeability and thrombocytopenia

Pathogenesis of dengue haemorrhagic fever:

1.   The patient recovers from classic dengue caused by one of the 4 serotype and Ab against that serotype already produced.

2.   Patient gets infected with another serotype of dengue virus

3.   An anamnestic, heterotypic reaction occurs

4.   Large amount of cross reacting Ab to the 1st serotype are produced

5.   There are two hypotheses about what happens next:

A.  Immune complex composed of virus and Ab are formed and that activates compliments causing increased vascular permeability and thrombocytopenia

B.   The Ab increases the entry of the virus into monocytes with the consequent liberation of large amount of cytokines

6. Resulting in shock and haemorrhage

7. Dengue haemorrhagic fever

Lab Diagnosis of Dengue:

1      Specimen: Blood

2      Isolation of the virus by: Cell culture, Acute phase protein, plasma

3      Demonstration of a rising titer of a specific serum dengue antibodies: by ICT, ELISA, Haemagglutination inhibition test, CFT, Neutralization test

4      Demonstration of a specific viral Ag or RNA in serum or tissue by: PCR, Counter current immunoelectrophoresis, Immuno-chemical staining of peripheral blood mononuclear cells

5      Other tests: CBC, LFT, S. electrolytes, CXR-P/A/V, USG of W/A, S. protein, Blood grouping and Rh typing

That's all for today!
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