Clinically, the diagnosis of DF is suggested by the presence of fever, severe headache, maculopapular skin rash, and myalgias associated with either the isolation or identification of DENV from either serum, plasma, or tissue specimens, or by demonstration of a 4-fold increase of DENV antibodies in paired serum samples. The diagnosis of DHF is based on similar clinical features associated with a bleeding diathesis and/or thrombocytopenia. In some patients, a shock syndrome (dengue shock syndrome) may be observed.

The principal symptoms of dengue fever are high fever, severe headache, severe pain behind the eyes, joint pain, muscle and bone pain, rash, and mild bleeding (e.g., nose or gums bleed, easy bruising). Generally, younger children and those with their first dengue infection have a milder illness than older children and adults.

Dengue hemorrhagic fever (DHF) is characterized by a fever that lasts from 2 to 7 days, with general signs and symptoms consistent with dengue fever. When the fever declines, warning signs may develop. This marks the beginning of a 24 to 48 hour period when the smallest blood vessels (capillaries) become excessively permeable (“leaky”), allowing the fluid component to escape from the blood vessels into the peritoneum (causing ascites) and pleural cavity (leading to pleural effusions). This may lead to failure of the circulatory system and shock, and possibly death without prompt, appropriate treatment. In addition, the patient with DHF has a low platelet count and hemorrhagic manifestations, tendency to bruise easily or have other types of skin hemorrhages, bleeding nose or gums, and possibly internal bleeding.