Geographical expansion of the mosquito has been aided by international commercial trade particularly in used tyres which easily accumulate rainwater. Increased air travel and breakdown of vector control measures have also contributed greatly to the global burden of dengue and DHF. Many other countries in Asia and the Pacific are already facing an unprecedented increase in dengue.

Sequence surveillance of dengue virus genotypes has suggested that some subtypes are more commonly associated with severe dengue. For example, DEN-2 and DEN-3 with Asian origins have been associate with epidemics of severe dengue.

Dengue fever (DF) is the most commonly diagnosed form of dengue infection, usually occurs in older children or adults. It is an acute febrile viral disease similar to the flu characterized by acute high fever, with two or more of the following manifestations : headache, retro-orbital pain, muscle, bone and joint pain, rash, hemorrhagic manifestations (e.g., petechiae). Severe bone and muscle pain may occur in adults (break-bone fever) which recovery may be associated with prolonged fatigue and depression. M aculopapular rash or petechiae may be noticed, with a positive tourniquet test. In adults, during dengue epidemics, hemorrhagic complications may also appear, such as bleeding from the gums, nosebleeds, and bruising. It is very important to distinguish between DF with hemorrhagic symptoms and DHF so that appropriate therapy can be initiated in the case of DHF. Case fatality due to DF is very low.

The most significant changes in laboratory findings include leucopenia and thrombocytopenia, for some cases . There is no specific treatment for DF beyond symptomatic treatment, rest, and rehydration.

Dengue haemorrhagic fever (DHF) is a potentially deadly complication though represents a small proportion of all dengue illnesses. The illness often begins with a sudden rise in temperature accompanied by facial flush, often with enlargement of the liver, and other flu-like symptoms. The fever usually continues for two to seven days and can be as high as 41°C, possibly with convulsions and other complications.

Cases of DHF are characterized by four clinical manifestations, all of which must be present: (1) fever or recent history of acute fever, (2) hemorrhagic phenomena (presence of at least one of the following: positive tourniquet test; petechiae,ecchymoses, or purpura; or bleeding from mucosa, gastrointestinal tract, injection sites, or others), (3) thrombocytopenia (100,000 mm 3 or less), and (4) plasma leakage due to increased capillary permeability. Moderate to marked thrombocytopenia with concurrent hemoconcentration is a distinctive clinical laboratory finding of DHF. However, the major pathophysiological change that determines the severity of disease in DHF, and differentiates it from DF, is plasma leakage manifested by a rising hematocrit value (i.e., hemoconcentration).

In moderate DHF cases, all signs and symptoms abate after the fever subsides. The normal course of DHF lasts between seven and ten days, and with appropriate intensive supportive therapy-maintenance of the circulating fluid volume is the central feature of DHF case management-mortality may be reduced to less than 1%.

Dengue shock syndrome(DSS) In severe cases of DHF, the patient’s condition may suddenly deteriorate after a few days of fever; the temperature will drop, followed by signs of circulatory failure; and the patient may rapidly go into a critical state of shock (dengue shock syndrome) and die within 12-24 hours, or quickly recover following appropriate volume replacement therapy.

Patients who are dehydrated, poor feeding, vomiting or near/within critical phase of DHF grade III/IV or complications such as bleeding, or CNS manifestations, should be promptly admitted to hospital.

Symptomatic treatment
For DHF, medical care by physicians and nurses experienced with the effects and progression of the complicating haemorrhagic fever can frequently save lives- decreasing mortality rates from more than 20% to less than 1%. Maintenance of the patient's circulating fluid volume is the central feature of DHF care.

Volume replacement
In the febrile stage, fluid volume is maintained at a level low enough to maintain adequate circulation. Oral replacement therapy is recommended, while parenteral fluid therapy is needed if fluid intake is less than required.

With the earliest suspicion that the patient may be developing a severe illness, an intravenous line should be placed so fluids can be provided. It is important to monitor blood pressure, hematocrit, platelet count, the occurrence of hemorrhagic manifestations, urinary output, and the level of consciousness.

Plasma leakage in DHF is very rapid, so the hematocrit may continue to rise even while IV fluids are administered, but the “leaky capillary” period is short; the need for IV fluids is usually only one to two days. There is great variability from patient to patient, and the physician must carefully adjust treatment using serial hematocrits, blood pressure, and urinary output. Insufficient volume replacement will allow worsening shock, acidosis, and disseminated intravascular coagulation, while fluid overload will produce massive effusions, respiratory compromise, and congestive heart failure.

The recommended amount of total fluid replacement in 24 hours is approximately the volume required for maintenance, plus replacement of 5% of body weight deficit, but this volume is not administered uniformly throughout the 24 hours. In the critical stage, immediate volume replacement with isotonic solution such as normal saline (NSS), 5% D/NSS, Ringer’s lactate solution (RLS) or Ringer’s acetate solution (RAS), at a rate of 10-20 ml/kg/h in 1-2 hours, should be administered until circulation improves and an adequate urinary output is obtained. Vital signs should be measured every 30 to 60 minutes, and hematocrit every two to four hours, then less often as the patient’s condition becomes stable. If hematocrit increases or remains stable, colloidal fluid, such as dextran 40, plasma, or other plasma expander, should be given. Colloidal fluid is indicated in massive leakage, in which a large volume of crystalloid fluid has been given. The use of steroids in the treatment of DSS has shown no benefit.

Platelet transfusion
In general, low platelet counts in dengue cases do not require treatment with transfusions. When patients are diagnosed and treated promptly and appropriately with intravenous fluids, hemorrhages are prevented and requests for blood transfusions are reduced markedly. Platelet transfusion should be considered for the patient with severe bleeding and a platelet count < 50,000/cu.mm.

Oxygen therapy should be administered to all patients with shock.
If the shock does not improve, hematocrit level should be monitored; decreased hematocrit indicates bleeding, and a blood transfusion should be considered. If the patient has improved (hematocrit decreases slowly and vital signs are stable), the rate of fluid replacement should be reduced slowly and adjusted according to hematocrit, vital signs, and urine output. Intravenous fluid should be discontinued when plasma leakage has stopped, not > 48 hours after onset of leakage or shock.

Careful monitoring and appropriate volume replacement during the critical phase, within 24-48 hours after defervescence, are crucial for the lowest mortality rates among DHF patients.