Introduction

Dengue fever and dengue hemorrhagic fever (DHF) are acute illnesses prevalent in tropical and African regions. They are caused by four closely related virus serotypes belonging to the Flavivirus genus, within the Flaviviridae family. Dengue fever is sometimes referred to as "breakbone fever." It is commonly found in urban areas of tropical countries, including places like Puerto Rico, Singapore, Malaysia, Taiwan, Thailand, Indonesia, the Philippines, India, Brazil, Vietnam, Guyana, Venezuela, and Bangladesh. Each serotype is distinct, providing no cross-protection, which can lead to epidemics caused by multiple serotypes. The transmission of dengue occurs through the Aedes aegypti mosquito (and occasionally Aedes albopictus), which is active during daylight hours.

Signs and Symptoms

Dengue fever typically presents with a sudden onset of severe symptoms, including intense headache, muscle and joint pains (so severe it's sometimes called "break-bone fever" or "bonecrusher disease"), fever, and a characteristic bright red rash. This rash usually starts on the lower limbs and chest, and in some cases, it spreads to cover most of the body. Additional symptoms may include gastritis with abdominal pain, nausea, vomiting, or diarrhea.

Some cases exhibit milder symptoms, which can be misdiagnosed as influenza or other viral infections, especially when there's no rash present. Consequently, travelers from tropical areas might unknowingly transmit dengue in their home countries due to misdiagnosis during the height of their illness. Dengue can only be transmitted to others through mosquitoes or blood products while the individual is still experiencing fever.

The typical dengue fever lasts around six to seven days and often shows a smaller fever peak toward the end (referred to as a "biphasic pattern"). Clinically, the platelet count decreases until the patient's temperature returns to normal.

More severe cases may lead to Dengue Hemorrhagic Fever (DHF), marked by higher fever, bleeding tendencies, reduced platelet count, and increased blood concentration. In a small percentage of cases, this can progress to Dengue Shock Syndrome (DSS), which has a high mortality rate.

Diagnosis

Diagnosing dengue is typically based on clinical observations. The classic presentation includes high fever with no clear local infection source, a petechial rash, thrombocytopenia (low platelet count), and decreased white blood cell count.

The WHO's definition of dengue hemorrhagic fever, in use since 1975, comprises all four criteria:

• Fever, bladder issues, severe headache, dizziness, and loss of appetite.
• Bleeding tendencies (positive tourniquet test, spontaneous bruising, bleeding from mucous membranes, vomiting blood, or bloody diarrhea).
• Thrombocytopenia (less than 100,000 platelets per mm³ or fewer than 3 platelets per high power field).
• Evidence of plasma leakage (elevated hematocrit, a drop of 20% or more in hematocrit following IV fluid, pleural effusion, ascites, hypoproteinemia).

Dengue shock syndrome is defined as dengue hemorrhagic fever plus:

• Rapid, weak pulse.
• Narrow pulse pressure (less than 20 mm Hg).
• Cold, clammy skin and restlessness.

Serology and polymerase chain reaction (PCR) studies are available for confirming the diagnosis of dengue if clinically necessary.