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Dengue

(Breakbone Fever; Dandy Fever)

by Craig R. Pringle, BSc, PhD

Dengue is a mosquito-borne disease caused by a flavivirus. Dengue fever usually results in abrupt onset of high fever, headache, myalgias, arthralgias, and lymphadenopathy, followed by a rash that appears with a 2nd temperature rise after an afebrile period. Respiratory symptoms, such as cough, sore throat, and rhinorrhea, can occur. Dengue can also cause potentially fatal hemorrhagic fever with a bleeding tendency and shock. Diagnosis involves serologic testing and PCR. Treatment is symptomatic and, for dengue hemorrhagic fever, includes meticulously adjusted intravascular volume replacement.

Dengue is endemic to the tropical regions of the world in latitudes from about 35° north to 35° south. Outbreaks are most prevalent in Southeast Asia but also occur in the Caribbean, including Puerto Rico and the US Virgin Islands, Oceania, and the Indian subcontinent; more recently, dengue incidence has increased in Central and South America. Each year, only about 100 to 200 cases are imported to the US by returning tourists, but an estimated 50 to 100 million cases occur worldwide, with about 20,000 deaths.

The causative agent, a flavivirus with 4 serogroups, is transmitted by the bite of Aedes mosquitoes. The virus circulates in the blood of infected humans for 2 to 7 days; Aedes mosquitoes may acquire the virus when they feed on humans during this period.

Symptoms and Signs

After an incubation period of 3 to 15 days, fever, chills, headache, retro-orbital pain with eye movement, lumbar backache, and severe prostration begin abruptly. Extreme aching in the legs and joints occurs during the first hours, accounting for the traditional name of breakbone fever. The temperature rises rapidly to up to 40° C, with relative bradycardia. Bulbar and palpebral conjunctival injection and a transient flushing or pale pink macular rash (particularly of the face) may occur. Cervical, epitrochlear, and inguinal lymph nodes are often enlarged.

Fever and other symptoms persist 48 to 96 h, followed by rapid defervescence with profuse sweating. Patients then feel well for about 24 h, after which fever may occur again (saddleback pattern), typically with a lower peak temperature than the first. Simultaneously, a blanching maculopapular rash spreads from the trunk to the extremities and face.

Mild cases of dengue, usually lacking lymphadenopathy, remit in < 72 h. In more severe disease, asthenia may last several weeks. Death is rare. Immunity to the infecting strain is long-lasting, whereas broader immunity to other strains lasts only 2 to 12 mo.

Diagnosis

  • Acute and convalescent serologic testing

Dengue fever is suspected in patients who live in or have traveled to endemic areas if they develop sudden fever, headache, myalgias, and adenopathy, particularly with the characteristic rash or recurrent fever. Evaluation should rule out alternative diagnoses, especially malaria and leptospirosis.

Diagnostic studies include serologic testing, antigen detection, and PCR of blood. Serologic testing involves hemagglutination inhibiting or complement fixation tests using paired sera, but cross-reactions with other flavivirus antibodies are possible. Antigen detection is available in some parts of the world (not in the US), and PCR is usually done only in laboratories with special expertise. Although rarely done and difficult, cultures can be done using mosquitoes or specialized cell lines in specialized laboratories.

CBC may show leukopenia by the 2nd day of fever; by the 4th or 5th day, the WBC count may be 2000 to 4000/μL with only 20 to 40% granulocytes. Urinalysis may show moderate albuminuria and a few casts. Thrombocytopenia may also be present.

Treatment

  • Supportive care

Treatment is symptomatic. Acetaminophen can be used, but NSAIDs, including aspirin, should be avoided because bleeding is a risk. Aspirin increases the risk of Reye syndrome in children and should be avoided for that reason.

Prevention

People in endemic areas should try to prevent mosquito bites. To prevent further transmission by mosquitoes, patients with dengue should be kept under mosquito netting until the 2nd bout of fever has resolved. Vaccines are being evaluated.

Dengue Hemorrhagic Fever

(Philippine, Thai, or Southeast Asian Hemorrhagic Fever; Dengue Shock Syndrome)

Dengue hemorrhagic fever (DHF) is a variant presentation that occurs primarily in children < 10 yr living in areas where dengue is endemic. DHF requires prior infection with the dengue virus. It is an immunopathologic disease; dengue virus–antibody immune complexes trigger release of vasoactive mediators by macrophages. The mediators increase vascular permeability, causing vascular leakage, hemorrhagic manifestations, hemoconcentration, and serous effusions, which lead to circulatory collapse (ie, dengue shock syndrome).

Symptoms and Signs

In adults, DHF begins with abrupt fever and headache and is initially indistinguishable from classic dengue. Warning signs that predict possible progression to severe dengue include

  • Abdominal pain and tenderness

  • Edema

  • Lethargy or restlessness

  • Hepatomegaly

Shock and increasing illness may develop rapidly 2 to 6 days after onset. Bleeding tendencies occur, usually as purpura, petechiae, or ecchymoses at injection sites; sometimes as hematemesis, melena, or epistaxis; and occasionally as subarachnoid hemorrhage. Bronchopneumonia with or without bilateral pleural effusions is common. Myocarditis can occur. Mortality is usually< 1% in experienced centers but otherwise can range to up 30%.

Diagnosis

  • Clinical and laboratory criteria

DHF is suspected in children with WHO-defined clinical criteria for the diagnosis: sudden fever that stays high for 2 to 7 days, hemorrhagic manifestations, and hepatomegaly. Hemorrhagic manifestations include at least a positive tourniquet test and petechiae, purpura, ecchymoses, bleeding gums, hematemesis, or melena. The tourniquet test is done by inflating a BP cuff to midway between the systolic and diastolic BP for 15 min. The number of petechiae that form within a 2.5-cm diameter circle are counted; > 20 petechiae suggests capillary fragility.

CBC, coagulation tests, urinalysis, liver function tests, and dengue serologic tests should be done. Thrombocytopenia ( l00,000 platelets/μL) and a prolonged PT characterize the coagulation abnormalities. There may be mild proteinuria and increases in AST levels. Complement fixation antibody titers against flaviviruses are usually high.

Patients with WHO-defined clinical criteria plus thrombocytopenia ( 100,000/μL) or hemoconcentration (Hct increased by 20%) are presumed to have the disease.

Treatment

  • Supportive care

Patients require intensive treatment to maintain euvolemia. Both hypovolemia (which can cause shock) and overhydration (which can cause acute respiratory distress syndrome) should be avoided. Urine output and the degree of hemoconcentration can be used to monitor intravascular volume.

No antivirals have been shown to improve outcome.

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