Diagnosis of dengue

BY- DR. ANNOY MALLICK

DIAGNOSIS OF DENGUE FEVER

HISTORY:

• Date of onset of fever/illness

• Quantity of oral intake

• Warning signs• Diarrhoea• Change in mental

state, seizure, dizziness

• Urine output• Co-existing

conditions

EXAMINATION:

• Mental state• Hydration status• Haemodynamic

status• Tachypnoea• Acidotic breathing• Pleural effusion• Abdominal

tenderness, hepatomegaly, ascites

• Rash and bleeding manifestations

• Torniquet test

INVESTIGATION:

• Full blood count• Haematocrit (in

early febrile phase, establishes baseline hematocrit),decreasing WBC makes dengue very likely, rapid decrease in platelet count in parallel with a rising haematocrit compared to baseline suggestive of progress to plasma leakage/critical phase of the disease

OVERALL ASSESSMENT

Acute febrile illness with 2 or more of the following:1. Headache2. Retro-orbital pain3. Myalgia4. Arthralgia/bone pain5. Rash6. Haemorrhagic manifestations7. Leucopenia(WBC<5000/mm38. Thrombocytopenia(platelet count<150000/mm3)9. Rising haematocrit (5 to 10%) And atleast one of following:1. Supportive serology on single serum sample: titre>1280

with haemagglutination inhibition test, comparable IgG titre with ELISA or testing positive in IgM antibody test

2. Occurrence at the same location and time as confirmed cases of dengue fever

PROBABLE DIAGNOSIS

Probable case with at least one of the following:1. Isolation of dengue virus from serum, CSF or

autopsy samples2. Fourfold or greater increase in serum IgG(by

haemagglutination inhibition test) or increase in IgM antibody specific to dengue virus

3. Detection of dengue virus or antigen in tissue, serum or CSF by immunohistochemistry, immunofluorescence or ELISA

4. Detection of dengue virus genomic sequences by RT-PCR

CONFIRMED DIAGNOSIS

All of following:

1. Acute onset of fever of 2-7 days duration2. Haemorrhagic manifestations; shown by any of the

following; positive torniquet test; petechiae; ecchymoses or purpura or bleeding from mucosa, GIT, injection sites or other locations

3. Platelet count<100000/mm34. Objective evidence of plasma leakage due to

increased vascular permeability shown by any of the following:

Rising haematocrit/haemoconcentration>20% from baseline or evidence of plasma leakage such as pleural effusion, ascites or hypoproteinaemia/albuminaemia

Dengue haemorrhagic fever

Criteria for dengue haemorrhagic fever as above with signs of shock including:

1. Tachycardia, cool extremities, delayed capillary refill, weak pulse, lethargy or restlessness, which may be a sign of reduced brain perfusion

2. Pulse pressure<20mmHg with increased diastolic pressure

3. Hypotension by age, defined as systolic pressure<80mmHg for those aged <5years or 80 to 90 mmHg for older children and adults

Dengue shock syndrome

Rapid and accurate dengue diagnosis is of a paramount importance for: clinical management, epidemiological surveillance, research and vaccine trials.1. Virus isolation- isolation of dengue virus from clinical specimens is

possible provided the specimen is taken during the first 6days of illness and processed without delay. Specimen that are suitable for virus isolation are- acute phase serum, plasma washed buffy coat from the patient, autopsy tissue from fatal case and mosquitoes collected from the affected areas.

2. Viral nucleic acid detection- dengue viral genome, which consists of RNA, can be detected by RT-PCR assay and real time RT-PCR. (better than viral isolation)

3. Immunological response and serological tests: Haemagglutination–inhibition assay Complement fixation Neutralization test IgM capture enzyme-linked immunosorbent assay Indirect IgG-ELISA IgG/IgG ratio

Laboratory diagnosis

4. Viral antigen detection- ELISA and dot blot assays directed against the envelop/membrane antigens and nonstructural protein can be detected in both patients with primary and secondary dengue infection up to 6 days after the onset of the illness. Commercial kits for the detection of NS1 antigens are now available.

5. Rapid diagnostic tests- a number of commercial rapid format serological test-kits for anti-dengue IgM and IgG antibodies have become available in the past few years (results within 15 mins)

6. Analysis of haematological parameters: TLC, Platelet count and Heamatocrit

Laboratory diagnosis

THANK YOU