Clinical course

The characteristic symptoms of dengue are sudden-onset fever, headache (typically located behind the eyes), muscle and joint pains, and a rash. The alternative name for dengue, "break-bone fever", comes from the associated muscle and joint pains.[1][7] The course of infection is divided into three phases: febrile, critical, and recovery.[8]

The febrile phase involves high fever, often over 40 °C (104 °F), and is associated with generalized pain and a headache; this usually lasts two to seven days.[7][8] At this stage, a rash occurs in approximately 50–80% of those with symptoms.[7][9] It occurs in the first or second day of symptoms as flushed skin, or later in the course of illness (days 4–7), as a measles-like rash.[9][10] Some petechiae (small red spots that do not disappear when the skin is pressed, which are caused by broken capillaries) can appear at this point,[8] as may some mild bleeding from the mucous membranes of the mouth and nose.[5][7] The fever itself is classically biphasic in nature, breaking and then returning for one or two days, although there is wide variation in how often this pattern actually happens.[10][11]

In some people, the disease proceeds to a critical phase, which follows the resolution of the high fever and typically lasts one to two days.[8] During this phase there may be significant fluid accumulation in the chest and abdominal cavity due to increased capillary permeability and leakage. This leads to depletion of fluid from the circulation and decreased blood supply to vital organs.[8] During this phase, organ dysfunction and severe bleeding, typically from the gastrointestinal tract, may occur.[5][8] Shock (dengue shock syndrome) and hemorrhage (dengue hemorrhagic fever) occur in less than 5% of all cases of dengue,[5] however those who have previously been infected with other serotypes of dengue virus ("secondary infection") are at an increased risk.[5][12]

The recovery phase occurs next, with resorption of the leaked fluid into the bloodstream.[8] This usually lasts two to three days.[5] The improvement is often striking, but there may be severe itching and a slow heart rate.[5][8] During this stage, a fluid overload state may occur; if it affects the brain, it may cause a reduced level of consciousness or seizures.