How is it Diagnosed?
Dengue Fever
The symptoms of dengue fever are similar to acute fevers of viral origin. These are sudden onset of fever, headache, bodyache, joint pains, and retro – orbital pain. Other common symptoms are anorexia, altered taste sensation, constipation, colicky pain, abdominal tenderness, dragging pains in the inguinal region, sore throat and general depression. Patient may or may not have rash. Some of the patients may also show signs of bleeding from the gum, nose, etc.

Case Definition of Dengue Fever
Suspect Case

• Acute onset
• High fever of less than seven days duration.
• Severe headache, backache
• Joint & muscle pains and pains behind eyes.

Probable Case

• Suspect case of DF.
• High vector density.
• Presence of confirmed case in the area.
• Blood Slide negative for malarial parasite & patient does not respond to anti malarial drugs.

Confirmed Case

• Isolation of virus from blood in early phase.
• Serological test for IgM antibody in single serum samples or 4 fold rise of IgG antibodies in paired serum samples.

Dengue Haemorrhagic Fever: DHF is a severe form of dengue fever. Typically, it begins abruptly with high fever accompaniednby headache, anorexia, vomitting and abdominal pain. During the first few days, the illness resembles classical Dengue Fever (DF), but a maculopapular rash is less common.

Case Definition of Dengue Haemorrhagic Fever
Suspect Case

• Acute onset
• High fever of less than seven days duration.
• Severe headache, backache
• Joint & muscle pains and pains behind eyes.
• Bleeding tendencies.

Probable Case

• Suspect case of DHF.
• Positive tourniquet test.

Confirmed Case

• Probable case.
• Thrombocytopenia <= 1,00,000 / mm
• Haemoconcentration (haematocrit increased by >= 20 % or evidence of increased capillary permeability) (e.g. pleural effusion in X–ray chest.)

Differential Diagnosis of Dengue Haemorrhagic Fever / DSS
Early in febrile illness, the differential diagnosis includes a wide spectrum of viral and bacterial infections. The presence of marked thrombocytopenia with concurrent haemoconcentration differentiates DHF / DSS from other diseases such as endotoxic shock from bacterial or meningicoccaemia. In patients with severe bleeding, evidence of pleural effussion and / or hypoproteinaemia may indicate plasma leakage.

Laboratory Confirmation of Diagnosis

1. The diagnosis of Dengue Fever/Dengue Haemorrhagic Fever can be confirmed by serological tests. The tests include detection of IgM antibodies which appear around the end of first week of onset of symptoms and are detectable for 1–3 months after the acute episode.
2. A rising titre of IgG antibody in paired sera taken at an interval of ten days or more is confirmatory.
3. IgG antibodies indicate previous infection and are useful for conducting sero epidemiological studies to determine the extent of silent infection and immunity levels in the local population.
4. Antigen is produced in limited quantities for operational research and outbreak investigations at the National Institute of Virology (NIV), Pune. With the antigen received from NIV, the National Institute of Communicable diseases (NICD) supports outbreak investigations on the request from the State health authorities. The antigen is also commercially available.
5. Blood for serological studies should be carefully collected taking due universal precautions from suspected DF / DHF cases (a) as soon as possible after hospital admission or attendance at the clinic (S–1) (b) Shortly before discharge from the hospital (S–2) (c) if possible, 14–21 days after disease onset (S–3). Failure to leave an interval of 10–14 days between collection of S–1 and S–2 samples may prevent the serological diagnosis of primary dengue infection. Specimen containers should be clearly labeled.
6. Each specimen should be accompanied with the detailed information about the case as given in the box so that the results could be scientifically interpreted.