Severe dengue fever is a life-threatening complication with the onset of shock or bleeding complications. Usually after the resurgence of the proud, the infection resumes and can progress in rare cases (1% of cases in people with symptoms of dengue fever) towards severe dengue. Clinical vigilance should be maximal around the 4th day.

In the hemorrhagic form, blood collects in the skin vessels, the rash becomes hemorrhagic and petechiae are observed (small red to purplish skin spots, related to the infiltration of blood under the skin), bruises (bruises), sometimes accompanied by mucous or internal bleeding, digestive or cerebral in particular.

The unfavorable evolution can also be towards a state of shock: body fluids exit the vessels, accumulating in various organs, causing edema, pleural effusions, pericardium (membrane around the heart), or peritoneum (membrane in the abdomen) and a drop in blood pressure. This leads to a risk of circulatory failure, a drop in body temperature.

In endemic areas, these serious forms mainly concern children; in the event of imported dengue, they can occur at any age and in any individual, but will be all the more severe in the most vulnerable subjects. The management of these severe forms is done in the intensive care unit in order to compensate for the various failures. Thus, the mortality of these severe dengues is very low in countries where health structures are developed, but can reach 10% in countries that do not have adequate resuscitation facilities.