DENGUE FEVER

                                                           DENGUE FEVER

Dengue is a mosquito born viral disease

Occurs in tropical areas

Vector- Aedes aegypti mosquito

Cause: dengue virus

4 distinct type of dengue virus- type 1,2,3and 4.

Clinical presentation: 3 broad patterns.

1.       Classical dengue

2.       Dengue hemorrhagic fever

3.       Mild atypical form.

Classic Dengue

Incubation period about 1 week

Prodromal symptoms like mild conjunctivitis,cold

Abrupt onset of fever with splitting headache, retro orbitl pain,back ache,joint pain.

Insomnia,anorexia, loss of taste weakness.

PHYSICAL EXAMINATION

conjunctival congestion,

Tenderness upon pressure on eyeball

Lymph adenopathy,

Skin rash

2-3 days after the onset ,temperature may decrease to  near normal  and other symptoms may disappear.This remission typically lasts 2 days

Following this there is return of fever and symptoms

This is called saddle back fever

Lab findings:

Neutropenia,leuko penia

Virus can be isolated from blood,

Viral antibody titre rises.

TREATMENT: only symptomatic with analgesics and antipyretics.

HEMORRHAGIC FEVER/Dengue shock syndrome

Can be caused by all 4 viral sero types.

WHO clinical classification of Dengue fever

Grade1:                Fever,constitutional symptoms, positive tourniquet test

Grade 2:               Grade1 Plus spontaneous bleeding

Grade3:                  Grade 2 plus circulatory failure plus agitation

Grade4;                    Grade2 plus  profound shock.

All 4 grades are associated with thrombocytopenia and hemoconcentration

TREATMENT

Fluid replacement,

Platelet/blood transfusion

Corticosteroids

Symptomatic treatment.

WHO criteria for diagnosis of Dengue Hemorrhagic fever

Acute onset high continuous fever lasting for 2-7 days

Hemorrhagic manifestations:  petichea/purpura/ecchymoses/epistaxis/bleeding gums

Hemetemisis,melena

Hepatomegaly

Thrombocytopenia ≤ 100000/cubic mm

Hemoconcentration , hematocrit increased by≥ 20%

Dengue Shock syndrome:

Rapid, thready pulse with narrow pulse pressure less than 20mm /hypotension

Cold clammy skin and restlessness.

LAB tests:

Important lab tests  at present available

1.viral culture

2.viral RNA detection by reverse transcriptase(RT-PCR)

3.serological tests-immunoglobulinM

ELISA-enzyme linked immunoabsorbant assay (MAC-ELISA)

All these diagnostic assays have their own snags.

Also  diagnosis at the early stage of illness is very difficult.

Gold standard test is viral culture - disadvantage –time consuming procedure-cannot be used as a routine.

RT-PCR useful in early stage-but trained staff ,cost and sophisticated equipment ‘s need-disadvantage.

MAC-ELISA-commonly used-but sensitivity is low  in first 4 days

 

New approach

ELISA against non structural glycoproteins( NSI antigen)- very useful in early phase

Early diagnosis and treatment reduces mortality

But it may not predict severity of dengue infection early.

Molecular virology- the basis of lab diagnosis

 

The viral poly proteins are classified into 2 types

1.structural polyproteins: 3 in number:- C,PrM and E

2.Non structural poly proteins.:NS proteins: seven in number

Of these NS1 is important.;It  has a role in viral RNA replication

NS1 antigen

This antigen, a glycoprotein, is found in abundance in patient’s serum in early stages

It is useful for the diagnosis in early and acute stage

ELISA based assay of  this antigen- non structural glycoproteins( NSI antigen)- very useful in early phase diagnosis,in the viremic stage

Summarizing,

current therapy is symptomatic consists mainly of fluid  replacement

Selective therapy is not available.

Vaccine

No vaccine is available.

Finding a vaccine agaist all 4 sero types is being problematic.

 A Japenese firm is expected to market a  dengue vaccine soon.

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