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.
Immunity
Infection with one serotype provides life long homologous immunity but does not provide protection against other serotypes, and instead may exacerbate subsequent infection.

Important Instructions for Treatment of Dengue hemorrhagic Fever

• Cases of DHF should be observed every hour.
• Serial platelet and haematocrit determinations, drop in platelets and rise in haematocrits are essential for early diagnosis of DHF.
• Timely intravenous therapy – isotonic crystalloid solution can prevent shock and / or lessen its severity.
• If the patient’s condition becomes worse despite giving 20 ml / Kg / hr for one hour, replace crystalloid solution with colloid solution such as dextran or plasma. As soon as improvement occurs replace with crystalloid.
• If improvement occurs, reduce the speed from 20 ml to 10 ml then to 6 ml, and finally to 3 ml / kg.
• If haematocrit falls, give blood transfusion 10 ml / kg and then give crystalloid IV fluids at the rate of 10 ml / kg / hr.
• In case of severe bleeding, give fresh blood transfusion about 20 ml / kg for 2 hours. Then give crystalloid at 10 ml / kg for a short time (30–60 min) & later reduce the speed.
• In case of shock, give oxygen.
• For correction of acidosis (sign: deep breathing), use sodium bi carbonate. (One third of the total fluids should consist of 0.167 mol / litre of sodium bicarbonate i.e. three quarters of crystalloid solution plus glucose plus one quarter sodium bicarbonate).
• For more details on management of DHF / DSS cases, the physician is advised to consult other appropriate references on their treatment. A list of references is given as under:
  1. Suchitra Nimmannitya, “Clinical Manifestation of DF / DHF” is WHO Regional Publication No. 22–monograph of Dengue / DHF – pp 48 n–n 54, WHO / SEARO, New Delhi.
  2. Suchitra Nimmannitya, “Management of DF / DHF” is WHO Regional Publication No. 22 – monograph of Dengue / DHF – pp 55–61, WHO / SEARO, New Delhi.
  3. Suchitra Nimmannitya, Dengue Haemorrhagic Fever diagnosis and management, pp 133–145, in “Dengue and Dengue Haemorrhagic Fever” edited by D. J. Gubler and G. Kuno, Published by CAB International, 1997.
  4. “Dengue Haemorrohagic fever – diagnosis, treatment, prevention and control” 2nd Edition, WHO, Geneva, 1997.
  5. “Regional Guidelines for Prevention and Control of Dengue / DHF”, WHO / SEARO, New Delhi, 1998.
• What not to do
  1. Do not give Aspirin or Brufen for treatment of fever.
  2. Avoid giving intravenous therapy before there is evidence of haemorrhage and bleeding.
  3. Avoid giving blood transfusion unless indicated, reduction in haematocrit or severe bleeding.
  4. Avoid giving steroids. They do not show any benefit.
  5. Do not use antibiotics.
  6. Do not change the speed of fluid rapidly, i.e. avoid rapidly increasing or rapidly slowing the speed of fluids.
• Insertion of Nasogastric Tube to determine concealed bleeding or to stop bleeding (by cold lavage) is not recommended since it is hazardous.

Signs of Recovery from Dengue

• Stable pulse, blood pressure & breathing rate.
• Normal temperature.
• No evidence of external or internal bleeding.
• Return of appetite.
• No vomitting.
• Good Urinary output.
• Stable haematocrit.
• Convalescent confluent petechiae rash.

Criteria for Discharging Patients

• Absence of fever for at least 24 hours without the use of anti fever therapy.
• Return of appetite.
• Visible Clinical improvement.
• Good Urine Output.
• Minimum of three days after recovery from shock.
• No respiratory distress from pleural effussion and no ascites.
• Platelet count of more than 50,000 mm3