Definition and epidemiology
Dengue fever is an arboviral disease caused by one of four dengue virus serotypes (DENV-1, DENV-2, DENV-3, DENV-4), members of the Flavivirus genus. The disease ranges from mild febrile illness to life-threatening dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS).
Dengue is the most common mosquito-borne viral disease globally, with an estimated 390 million infections annually across more than 100 countries. Approximately 96 million cases result in clinical manifestations. The disease is endemic in tropical and subtropical regions of Southeast Asia, the Western Pacific, Latin America, the Caribbean, Africa, and parts of the Middle East. Urban and semi-urban areas are most affected.
Incidence has increased 30-fold over the past 50 years due to urbanization, population growth, increased travel, and inadequate vector control. Case fatality rates are less than 1% with appropriate treatment but can exceed 20% in severe dengue without proper medical care. Children under 15 years account for the majority of severe cases in endemic areas, though adults are increasingly affected in epidemic settings.
- Dengue is transmitted by Aedes aegypti (daytime biting); incubation period 4–10 days.
- Classic triad: high fever, severe headache (retro-orbital), thrombocytopenia with leukopenia.
- Biphasic fever (saddleback pattern) is characteristic; critical phase occurs during defervescence (days 3–7).
- Secondary heterotypic infection increases risk of severe dengue via antibody-dependent enhancement.
- Warning signs (abdominal pain, persistent vomiting, fluid accumulation) indicate increased risk of severe disease.
- Hemoconcentration (rising hematocrit >20%) indicates plasma leakage; requires careful IV fluid management.
- Avoid NSAIDs and aspirin due to bleeding risk; use acetaminophen for fever.
- NS1 antigen is positive in first week; IgM appears after day 5; high acute IgG suggests secondary infection.
Etiology and risk factors
Dengue virus is transmitted primarily by Aedes aegypti mosquitoes, which bite during daytime, particularly early morning and before dusk. Aedes albopictus is a secondary vector. The virus is not transmitted person-to-person except in rare cases of vertical transmission, blood transfusion, or organ transplantation.
Risk factors for infection:
- Residence in or travel to endemic areas
- Urban and peri-urban environments with standing water
- Rainy season or warm, humid climates
- Poor sanitation and water storage practices
- Lack of mosquito control measures
Risk factors for severe disease:
- Secondary infection with a different serotype (antibody-dependent enhancement)
- Age extremes (infants, elderly)
- Chronic diseases (diabetes, asthma, cardiovascular disease)
- Pregnancy
- Female sex
- Genetic factors (certain HLA types, ethnicity)
Secondary heterotypic infection is the most important risk factor for DHF/DSS. Pre-existing antibodies from a prior dengue infection can enhance viral entry into monocytes and macrophages, leading to higher viral loads and increased immune activation.
Pathophysiology
After a mosquito bite, the dengue virus replicates in dendritic cells and spreads to lymph nodes, then disseminates via the bloodstream to infect monocytes, macrophages, and hepatocytes. The incubation period is typically 4–10 days.
The disease progresses through three phases:
Febrile phase (days 1–3)
High fever results from viremia and cytokine release. Capillary fragility increases but vascular permeability remains intact.
Critical phase (days 3–7)
Defervescence marks the onset of the critical phase. Plasma leakage occurs due to increased vascular permeability mediated by NS1 viral protein, inflammatory mediators (TNF-α, IL-6), and endothelial dysfunction. Hemoconcentration, pleural effusions, and ascites develop. Thrombocytopenia results from bone marrow suppression, peripheral destruction, and consumption. Hemorrhagic manifestations arise from thrombocytopenia, platelet dysfunction, vasculopathy, and coagulopathy.
Recovery phase (days 7–10)
Reabsorption of extravasated fluid occurs. Hemodynamic stabilization follows if the critical phase is managed appropriately.
In antibody-dependent enhancement (secondary infection), non-neutralizing antibodies from prior infection facilitate viral entry into Fc receptor-bearing cells, amplifying infection and immune activation. This mechanism underlies the increased severity in secondary heterotypic infections.
Clinical features
Clinical manifestations range from asymptomatic infection (75% of cases) to severe life-threatening disease. The 2009 WHO classification divides dengue into dengue without warning signs, dengue with warning signs, and severe dengue.
Dengue without warning signs
Presents with acute onset of high fever (40°C) lasting 2–7 days accompanied by at least two of the following:
- Severe headache (retro-orbital)
- Myalgia and arthralgia (breakbone fever)
- Nausea and vomiting
- Rash (maculopapular, appears 3–5 days after fever onset)
- Leukopenia
- Positive tourniquet test
The classic biphasic fever (saddleback pattern) occurs in some patients, with defervescence around day 3–4 followed by recrudescence.
Dengue with warning signs
Warning signs appear typically during defervescence (days 3–7) and indicate increased risk of progression to severe dengue:
- Abdominal pain or tenderness
- Persistent vomiting
- Clinical fluid accumulation (ascites, pleural effusion)
- Mucosal bleeding
- Lethargy or restlessness
- Liver enlargement >2 cm
- Rising hematocrit with rapid platelet decline
Severe dengue (DHF/DSS)
Defined by the presence of:
- Severe plasma leakage leading to shock or fluid accumulation with respiratory distress
- Severe bleeding (hematemesis, melena, menorrhagia)
- Severe organ impairment (ALT/AST >1000, altered consciousness, myocarditis, acute kidney injury)
Dengue shock syndrome manifests as hypotension, narrow pulse pressure (<20 mmHg), cold clammy extremities, and altered mental status.
Diagnosis
Diagnosis is based on clinical presentation, epidemiological exposure, and laboratory confirmation.
Clinical diagnosis
Suspect dengue in patients with acute fever and compatible symptoms in endemic areas or with travel history. The tourniquet test (positive if ≥20 petechiae per 2.5 cm² area) suggests capillary fragility but has limited sensitivity.
Laboratory diagnosis
Hematological findings:
- Leukopenia (WBC <5,000/μL)
- Thrombocytopenia (platelets <100,000/μL, often <50,000/μL in severe disease)
- Rising hematocrit (>20% increase indicates plasma leakage)
- Prolonged PT/PTT in severe cases
- Transaminitis (ALT/AST elevation, AST typically > ALT)
Virological/serological tests:
- NS1 antigen detection (days 1–7): rapid, high specificity, detects active infection
- RT-PCR (days 1–5): detects viral RNA, confirms diagnosis and identifies serotype
- IgM antibodies (days 5–10): indicates recent infection, may cross-react with other flaviviruses
- IgG antibodies: rise after day 7; high IgG in acute phase suggests secondary infection
Imaging:
Chest X-ray or ultrasound may demonstrate pleural effusion, ascites, or gallbladder wall thickening during the critical phase.
Diagnostic approach
In the first 5 days: NS1 antigen or RT-PCR After day 5: IgM/IgG serology Monitor complete blood count daily during critical phase to detect hemoconcentration and thrombocytopenia.
Differential diagnosis
Dengue presents similarly to other acute febrile illnesses in tropical regions:
- Malaria: consider in overlapping endemic areas; also causes thrombocytopenia; diagnosed by blood smear showing parasites
- Chikungunya: similar presentation, prominent arthralgia; mosquito-borne alphavirus
- Zika virus: milder symptoms, rash, conjunctivitis; same vector
- Influenza: respiratory symptoms more prominent, no thrombocytopenia
- Typhoid fever: prolonged fever, relative bradycardia, positive blood culture
- Leptospirosis: exposure to contaminated water, conjunctival suffusion, renal involvement
- Measles: cough, coryza, Koplik spots, different rash pattern
- Rickettsial infections (scrub typhus): eschar, different geographic distribution
- Viral hemorrhagic fevers (yellow fever, Ebola): consider based on epidemiology
- Acute HIV infection: high-risk exposure, lymphadenopathy
Key distinguishing features of dengue include thrombocytopenia with leukopenia, retro-orbital pain, positive tourniquet test, and biphasic fever pattern in endemic settings.
Management
No specific antiviral therapy exists for dengue. Management is supportive, focused on maintaining fluid balance during the critical phase and preventing complications. Most patients can be managed as outpatients with daily monitoring.
Outpatient management (dengue without warning signs)
- Oral fluid replacement (oral rehydration solution, fruit juices, water)
- Acetaminophen for fever and pain (avoid NSAIDs, aspirin due to bleeding risk)
- Rest
- Daily clinical and laboratory monitoring (platelet count, hematocrit)
- Patient education on warning signs
Indications for hospitalization:
- Warning signs present
- Severe dengue
- Infants, elderly, pregnancy
- Comorbidities
- Social circumstances preventing close follow-up
Inpatient management (dengue with warning signs)
- Isotonic crystalloid IV fluids: careful fluid resuscitation to maintain adequate perfusion without causing fluid overload
- Frequent monitoring of vital signs, urine output, hematocrit
- Serial platelet counts and hematocrit (every 6–12 hours)
- Minimize invasive procedures
Severe dengue/shock management
- Aggressive IV fluid resuscitation: bolus isotonic crystalloids
- Intensive monitoring in ICU setting
- Hematocrit monitoring every 2–4 hours
- Blood transfusion for significant bleeding (packed red cells, platelets, fresh frozen plasma as indicated)
- Inotropic support if shock persists despite adequate fluid resuscitation
- Correct electrolyte and acid-base disturbances
Platelet transfusion is generally reserved for:
- Platelets <10,000/μL with high bleeding risk
- Active significant bleeding regardless of platelet count
- Invasive procedures required
Prophylactic platelet transfusion at higher counts is not routinely recommended.
Prevention
Vector control:
- Eliminate standing water (breeding sites)
- Use insect repellents (DEET, picaridin)
- Wear protective clothing
- Window screens and bed nets
Vaccines:
Dengue vaccines (e.g., Dengvaxia, Qdenga) are available in some countries. Dengvaxia is recommended only for individuals with prior laboratory-confirmed dengue infection due to increased risk of severe disease in seronegative individuals. Qdenga has broader indications but availability varies by region.
Close monitoring during the critical phase (days 3–7) is essential. Most deaths from dengue are preventable with appropriate fluid management and recognition of warning signs.
Complications and prognosis
Complications
Severe plasma leakage:
- Dengue shock syndrome
- Respiratory distress from pleural effusion or pulmonary edema
- Organ hypoperfusion
Hemorrhagic manifestations:
- Gastrointestinal bleeding (hematemesis, melena)
- Intracranial hemorrhage (rare but life-threatening)
- Vaginal bleeding
Organ dysfunction:
- Hepatitis with acute liver failure
- Acute kidney injury
- Myocarditis
- Encephalopathy or encephalitis
- Acute respiratory distress syndrome
Metabolic:
- Hypoglycemia
- Hyponatremia
- Metabolic acidosis
Other:
- Prolonged convalescence with fatigue
- Post-dengue chronic fatigue syndrome
Prognosis
Most dengue infections are self-limited, with recovery in 7–10 days. Prognosis is excellent for dengue without warning signs with appropriate outpatient monitoring.
With early recognition of warning signs and proper fluid management, case fatality rates for severe dengue are less than 1%. Without appropriate care, mortality in severe dengue can exceed 20%.
Poor prognostic indicators:
- Delay in seeking care during critical phase
- Persistent shock despite fluid resuscitation
- Severe bleeding
- Organ failure
- Very young or elderly age
- Comorbidities
Complete recovery without sequelae is typical in survivors. However, infection with one serotype provides lifelong immunity to that serotype only; subsequent infection with a different serotype increases risk of severe disease.
Post-recovery fatigue and weakness may persist for weeks to months in some patients. Rare long-term complications include chronic arthralgia or neurological sequelae following dengue encephalitis.
DENGUE warning signs: Distress (abdominal pain), Enlarged liver, Nausea/vomiting (persistent), Gush of fluid (ascites/effusion), Uneasy (lethargy/restless), Elevated HCT with falling platelets
Practice questions
1. A 28-year-old woman returns from a 2-week trip to Thailand and presents with 4 days of high fever, severe headache, retro-orbital pain, and diffuse myalgia. She reports the fever subsided yesterday but she now has increased fatigue, mild abdominal pain, and three episodes of vomiting. Vital signs: BP 100/70 mmHg, HR 110/min. Physical exam shows mild hepatomegaly. Laboratory results: WBC 3,200/μL, hemoglobin 14.5 g/dL (baseline 13.0 g/dL), platelets 85,000/μL. What is the most appropriate next step in management?
2. A 9-year-old boy in an endemic area presents with 6 days of fever that was initially high but subsided 2 days ago. Today he developed lethargy, cold extremities, and multiple episodes of coffee-ground vomiting. Vital signs: BP 80/60 mmHg, HR 130/min, RR 28/min. Labs show: hemoglobin 16.5 g/dL (baseline 12.0 g/dL), platelets 35,000/μL, NS1 antigen positive. His 5-year-old sibling had confirmed dengue infection 3 weeks ago. Which factor most likely contributed to the severity of this patient's presentation?
3. A 35-year-old traveler presents on day 2 of fever, headache, and body aches after returning from Central America 1 week ago. She wants confirmation of dengue fever. Which diagnostic test is most appropriate at this stage of illness?
Frequently asked questions
What causes dengue fever?
Dengue fever is caused by the dengue virus (DENV), which has four serotypes (DENV-1 through DENV-4), transmitted by Aedes aegypti mosquitoes. These mosquitoes bite primarily during daylight hours, especially in early morning and before dusk. The virus is endemic in tropical and subtropical regions worldwide, and humans are the primary host. Infection with one serotype provides lifelong immunity to that serotype but not to others, and subsequent infection with a different serotype increases the risk of severe disease through antibody-dependent enhancement.
What are the first symptoms of dengue fever?
The first symptoms of dengue fever typically appear 4–10 days after a mosquito bite and begin with sudden onset of high fever (up to 40°C or 104°F). This is accompanied by severe headache, particularly behind the eyes (retro-orbital pain), intense body and joint pain (hence "breakbone fever"), nausea, and fatigue. Some patients develop a faint rash early in the illness. These symptoms usually last 2–7 days, and most people recover without complications if properly hydrated and monitored.
How is dengue fever diagnosed?
Dengue fever is diagnosed through a combination of clinical presentation and laboratory tests. In the first 5 days of illness, NS1 antigen detection or RT-PCR confirms active infection. After day 5, IgM and IgG antibody tests are more useful. Blood tests typically show thrombocytopenia (low platelets), leukopenia (low white blood cells), and rising hematocrit indicating plasma leakage. A positive tourniquet test and compatible symptoms in someone from an endemic area or with recent travel history support the diagnosis. Daily monitoring of blood counts is essential during the critical phase (days 3–7).
Is dengue fever curable?
There is no specific antiviral cure for dengue fever, but the disease is usually self-limited and resolves within 7–10 days with proper supportive care. Treatment focuses on maintaining adequate hydration, managing fever with acetaminophen, rest, and close monitoring for warning signs of severe disease. Most patients recover completely without complications. The key to good outcomes is recognizing warning signs early (especially during days 3–7), maintaining fluid balance, and providing intensive care if severe dengue or shock develops. With appropriate medical management, the case fatality rate is less than 1%.
Dengue vs malaria — what is the difference?
Dengue and malaria are both mosquito-borne diseases common in tropical regions but differ in key ways. Dengue is viral, transmitted by Aedes mosquitoes (daytime biters), causes thrombocytopenia and leukopenia, and is diagnosed by NS1 antigen or serology. Malaria is parasitic (Plasmodium species), transmitted by Anopheles mosquitoes (nighttime biters), causes hemolytic anemia and also frequently presents with thrombocytopenia, and is diagnosed by blood smear or rapid antigen tests. Dengue typically presents with severe body pain and retro-orbital headache, while malaria often shows cyclical fevers with chills and rigors. Both can be severe, but malaria has specific antiparasitic treatment whereas dengue management is supportive.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: A97
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.