Incubation Period of Dengue
Infected person with Dengue becomes infective to mosquitoes 6 to 12 hours before the onset of the disease and remains so upto 3 to 5 days.

The incubation period of Dengue fever is usually 5 to 6 days but may vary from 3 to 10 days.

Management of Dengue Fever
The management of Dengue Fever is Symptomatic and Supportive and Comprises of

• Bed rest is advisable during the acute febrile phase.
• Antipyretics or sponging are required to keep body temperature below 39°C. Salicylates should be avoided. paracetamol may be prescribed.
• Analgesic or a mild sedative may be required for those with severe pain.
• Home available fluids and Oral Rehydration Salt (ORS) solution are recommended for patients with excessive sweating, nausea, vomitting or diarrhea to prevent dehydration.

Management of Dengue Haemorrohagic Fever

• Management during febrile phase is similar to that of DF.
• Antipyretics may be indicated but salicylates should be avoided.
• Increased fluid intake.
• Fluid and electrolyte replacement by IV fluids, isotonics etc.
• Plasma expanders if clinically indicated.
• Fresh frozen plasma may be indicated in some cases.
• Blood transfusion.

As thrombocytopenia and concurrent haemoconcentration usually occurs well before the onset of shock, the use of these criteria can enable the clinician to make early diagnosis at the time the plasma leakage starts and hence early fluid replacement for plasma loss can be administered and disease severity can be modified. Prolonged shock is often complicated be severe massive bleeding indicating grave prognosis.

Judicious volume replacement is mandatory as the plasma loss is only for 24 to 48 hours and is more rapid around the time of defervescence and/or shock. Haematocrit determination is essential for monitoring the rate of IV fluid infusion and to check overload (which has been recognised as a common problem).

Isotonic solution (0.9% sodium chloride, also known as normal saline) or a compound solution of sodium lactate is preferred. Saline with or without glucose can be used depending upon availability. Glucose solution without saline do not provide the salt required to restore electrolyte balance and is not recommended.

Transfusion of platelets does not change the course of the illness and is not recommended. Blood transfusion may be indicated in patients with severe shock, massive bleeding and disseminated intravascular coagulation (DIC).

Amount of fluid given should be constantly monitored. Any evidence of swelling, shortness of breath or puffiness may indicate fluid overload.

Pathogenesis and Pathophysiology
The pathogenic mechanism of Dengue hemorrhagic fever is not clear, but two main pathophysiologic changes occur.

1. Vascular permeability increases which results in plasma leakage, leading to hypovolaemia and shock.
2. Abnormal haemostasis, due to vasculopathy, thrombocytopenia and coagulapathy, leading to various haemorrhagic manifestations.

The severity of DHF as compared with dengue fever may be explained by the enhancement of virus multiplication in macrophages by heterotypic antibodies resulting from a previous dengue infection. There are evidences suggesting that cell mediated immune response may also be involved in the pathogenesis of DHF.