Dengue Fever

Philadelphia, where 'breakbone fever' was described in 1780

Overview
Pathogen Biology
Transmission & Epidemiology
Symptoms by Phase
Diagnosis
Treatment
Home & Supportive Care
Complications
Prevention & Vaccines
Key Research Papers
Connections
Featured Videos

1. Overview

Dengue fever is the world's most prevalent mosquito-borne viral illness, with an estimated 390 million infections each year (a 2013 modelling estimate) and posing a risk to roughly half the global population. Caused by any of four antigenically distinct dengue virus serotypes (DENV-1 through DENV-4), dengue ranges from a self-limiting febrile illness to the potentially life-threatening dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS).

The disease is caused by flaviviruses transmitted primarily by Aedes aegypti mosquitoes and, to a lesser extent, Aedes albopictus. First clearly described in the 18th century, dengue has expanded dramatically over the past 50 years with urbanization, global travel, and mosquito range expansion. It is endemic in more than 100 countries across tropical and subtropical regions of the Americas, Southeast Asia, the Western Pacific, Africa, and the Eastern Mediterranean.

There is no specific antiviral therapy for dengue; management is supportive. Early recognition of warning signs — abdominal pain, persistent vomiting, rapid breathing, bleeding, fatigue, liver enlargement, and rising hematocrit with rapid fall in platelet count — is critical to preventing death, which occurs in fewer than 1% of detected cases when appropriate care is provided but can exceed 20% in severe dengue without treatment.

2. Pathogen Biology

Dengue virus (DENV) is a positive-sense single-stranded RNA virus belonging to the family Flaviviridae, genus Flavivirus. Its ~10.7 kb genome encodes three structural proteins — capsid (C), pre-membrane (prM), and envelope (E) — and seven nonstructural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, NS5).

Four Serotypes and Cross-Immunity

DENV-1, -2, -3, and -4 are genetically and antigenically distinct enough that infection with one serotype confers lifelong homotypic immunity but only transient (2–3 months) heterotypic protection. A second infection with a different serotype is associated with substantially higher risk of severe dengue, driven by antibody-dependent enhancement (ADE): pre-existing cross-reactive antibodies from the first infection bind the new serotype virus but fail to neutralize it; instead, they facilitate Fc receptor-mediated entry into monocytes and macrophages, amplifying viral replication 100-fold.

Envelope Protein and Cell Entry

The envelope (E) protein mediates receptor binding and fusion with host cell membranes following endocytosis. DENV infects dendritic cells, macrophages, monocytes, and endothelial cells. NS1 is secreted into the bloodstream and plays a central role in pathogenesis by disrupting endothelial tight junctions and activating complement, contributing to the capillary leak that defines severe dengue.

Cytokine Storm and Vascular Permeability

Severe dengue is characterized by a rapid cytokine storm involving tumor necrosis factor-alpha, interleukin-6 (IL-6), IL-8, CXCL10, and vascular endothelial growth factor (VEGF). This drives increased vascular permeability, plasma leakage into serous cavities (pleural effusion, ascites), and hemoconcentration. Thrombocytopenia results from virus-induced megakaryocyte suppression, platelet destruction by immune mechanisms, and consumption during coagulopathy.

3. Transmission & Epidemiology

Dengue is transmitted exclusively by mosquito bite — it is not contagious person-to-person (except rarely via blood transfusion, organ transplant, or vertical mother-to-infant transmission).

Vector Biology

Aedes aegypti is the primary vector: a day-biting, highly domesticated mosquito that breeds in small, clean, stagnant water containers (flower pots, discarded tires, water storage drums, buckets). It is abundant in tropical and subtropical urban environments. Aedes albopictus (tiger mosquito) is a secondary vector with a wider geographic range including temperate regions of Europe, North America, and East Asia.

The extrinsic incubation period in the mosquito is 8–12 days at temperatures above 25°C. A single infectious blood meal makes the mosquito capable of transmitting dengue for its entire lifespan. Temperature-sensitive vector competence means climate change is expanding dengue's geographic range.

Global Burden

A 2013 modelling study (Bhatt and colleagues) estimated 390 million dengue infections a year, of which about 96 million cause symptoms — more than three times the burden estimate of the World Health Organization (WHO) at that time. The Americas, Southeast Asia, and Western Pacific are the most heavily affected. Brazil, the Philippines, Vietnam, Indonesia, and Bangladesh together account for a large proportion of global cases. Dengue causes roughly 40,000 deaths per year, though this figure is likely an underestimate. Dengue is the leading cause of acute febrile illness in returning travelers from endemic regions.

Seasonality and Outbreaks

Dengue transmission correlates with rainy season when mosquito breeding sites proliferate. Major epidemic cycles occur every 3–5 years as dominant circulating serotypes shift. All four serotypes can co-circulate; introduction of a new serotype into a partially immune population is a predictor of severe disease outbreaks.

4. Symptoms by Phase

The World Health Organization 2009 classification recognizes dengue without warning signs, dengue with warning signs, and severe dengue. In 2025 WHO published combined clinical guidelines for dengue, chikungunya, Zika and yellow fever, because these infections often look alike in their early stages and several can circulate in the same region at once; WHO states that over 5.6 billion people are at risk of these mosquito-borne infections. Disease progresses through three overlapping clinical phases:

Febrile Phase (Days 1–3)

Abrupt onset of high fever (39–40°C), often called "breakbone fever" for its severe myalgia and arthralgia. Other features: frontal headache, retro-orbital pain (pain behind the eyes, worsened by eye movement), facial flushing, diffuse erythema, nausea, vomiting, and a positive tourniquet test (capillary fragility). The fever may be biphasic — defervescing then returning ("saddleback" pattern) — though this is less reliable diagnostically than formerly thought.

Critical Phase (Days 4–6)

Fever defervesces around days 3–7. This is the period of greatest danger. Plasma leakage peaks during the 24–48 hours around defervescence. In patients who will develop severe dengue, rapid platelet fall (often <100,000/mm³) and rising hematocrit (>20% above baseline) signal plasma leak. Warning signs that hospitals treat as urgent:

Abdominal pain or tenderness
Persistent vomiting (≥3 episodes in 1 hour)
Clinical fluid accumulation (ascites, pleural effusion)
Mucosal bleeding (gum bleeding, nosebleeds)
Lethargy or restlessness
Liver enlargement >2 cm
Laboratory: rising hematocrit with rapid platelet decline

Recovery Phase (Days 7–10)

Reabsorption of leaked plasma back into the intravascular space. Pulse slows, blood pressure improves, diuresis resumes. A second rash — described as "islands of white in a sea of red" — may appear. Bradycardia is common. Fluid overload becomes a concern if excessive intravenous (IV) fluids were given during the critical phase. Recovery is usually complete within 2–4 weeks; persistent fatigue and depression are reported in a minority of patients.

5. Diagnosis

Diagnosis integrates clinical suspicion (fever + relevant travel/residence history + classic symptoms) with laboratory confirmation. Dengue mimics many other febrile illnesses including malaria, chikungunya, Zika, leptospirosis, typhoid, and influenza.

NS1 Antigen Test

Dengue NS1 antigen is detectable in blood during the febrile phase (days 1–5). Rapid NS1 immunochromatographic tests have sensitivity of 70–95% and high specificity; false negatives increase after day 5. NS1 is the preferred test for early-phase dengue.

Dengue Immunoglobulin M/Immunoglobulin G Serology

Immunoglobulin M (IgM) antibodies rise after day 4–5 and peak at 2 weeks; immunoglobulin G (IgG) rises later. In primary infection, immunoglobulin M predominates. In secondary infection, immunoglobulin G rises rapidly (anamnestic response). A single sample with immunoglobulin M/immunoglobulin G ratio or a paired sample showing fourfold immunoglobulin G rise confirms the diagnosis. Serology is the method of choice after day 5 of illness.

RT-PCR

Reverse transcriptase-PCR detects dengue RNA during the febrile phase (days 1–5) with high sensitivity and specificity and can serotype the infecting strain. It is the gold standard for early confirmation and epidemiologic surveillance but requires laboratory infrastructure not universally available in endemic settings.

Full Blood Count

Leukopenia (WBC <5,000) is typical during dengue fever; it helps distinguish dengue from bacterial infection. Thrombocytopenia and rising hematocrit are the key laboratory warning signs. Serial complete blood count (CBC) every 24 hours (or more frequently in patients with warning signs) guides fluid management decisions.

6. Treatment

There is no approved antiviral therapy for dengue. Treatment is supportive and stratified by severity.

Dengue Without Warning Signs (Home Management)

Rest and generous oral fluid intake (oral rehydration solution, fruit juice, water — 2–3 liters per day for adults).
Paracetamol (acetaminophen) is the medicine used for fever and pain, with the aim of keeping temperature below 39°C.
Nonsteroidal anti-inflammatory drugs (NSAIDs) and aspirin are left out of dengue care — ibuprofen, naproxen, and aspirin inhibit platelet function and increase bleeding risk; aspirin specifically can cause Reye's syndrome in children.
The warning signs listed under the critical phase are signs hospitals treat as urgent.

Dengue with Warning Signs (Hospital Monitoring)

Intravenous crystalloid fluid replacement (isotonic saline or Ringer's lactate) titrated to clinical response — start 5–7 mL/kg/hour and titrate based on hematocrit, urine output, and clinical signs.
Serial monitoring of hematocrit, platelet count, and vital signs.
Platelet transfusion is generally not indicated unless platelet count falls below 10,000/mm³ with active bleeding.
Careful fluid management to prevent both under-resuscitation (shock) and over-hydration (fluid overload during recovery).

Severe Dengue (Intensive Care Unit Care)

Dengue shock syndrome requires aggressive intravenous fluid resuscitation (10–20 mL/kg intravenous bolus of isotonic crystalloid), colloids for refractory shock. Severe hemorrhage may require fresh whole blood or packed red cells. Dengue with severe organ impairment (liver failure, encephalitis, myocarditis, acute kidney injury) is managed with organ-specific supportive care. Mortality with appropriate intensive care unit (ICU) care is below 1%.

7. Home & Supportive Care

For the majority of dengue patients managed at home, practical supportive measures significantly reduce discomfort and aid recovery:

Hydration: Frequent small sips, for example every 30 minutes, are a common approach. Oral rehydration solution (ORS), coconut water, and clear soups are the fluids commonly listed. Caffeinated drinks and alcohol are dehydrating.
Fever management: Sponging with lukewarm (not cold) water is used to bring fever down. Paracetamol is taken every 6 hours, up to 4 g a day for adults, the standard adult daily maximum; going above it adds strain on the liver, which dengue can already inflame (mild hepatitis).
Rest: Complete rest during the febrile phase reduces metabolic demand and aids immune response.
Monitoring at home: Home monitoring means checking temperature twice daily, looking for bleeding signs (gum bleeding, nosebleeds, blood in urine or stool, skin bruising), and tracking fluid intake and urine output.
Nutrition: Foods commonly listed during recovery are light and easy to digest — bananas, toast, boiled vegetables. Nausea often reduces appetite; small frequent meals are better tolerated.
Mosquito protection during illness: Mosquito nets and repellent matter while a person is sick, because a viremic patient can infect a mosquito that then infects others.

8. Complications

Dengue hemorrhagic fever (DHF): Defined by fever lasting 2–7 days, hemorrhagic manifestations, thrombocytopenia (platelet count ≤100,000/mm³), and evidence of plasma leakage. Most frequently occurs in secondary dengue infection or in infants with maternal antibodies.
Dengue shock syndrome (DSS): DHF with circulatory failure — rapid weak pulse, narrowing pulse pressure (≤20 mmHg) or hypotension. Fatal in up to 40% of cases if untreated; <1% with appropriate intravenous fluid management.
Expanded dengue syndrome: Unusual clinical manifestations including dengue encephalitis, myocarditis, hepatitis (alanine aminotransferase (ALT)/aspartate aminotransferase (AST) 10x normal), nephritis, and acute respiratory distress. More common in elderly, obese, pregnant, or immunocompromised patients.
Congenital dengue: Maternal dengue near delivery can cause perinatal dengue in neonates with thrombocytopenia and hemorrhage.
Post-dengue fatigue syndrome: Weeks to months of persistent fatigue, cognitive difficulty, and depression following acute infection, particularly after severe disease.

9. Prevention & Vaccines

Vector Control

Eliminating Aedes breeding sites is the most effective community intervention: removing standing water from containers, covering water storage, using larvicides (Bacillus thuringiensis israelensis, temephos) in water that cannot be emptied, and adult mosquito control via insecticide fogging during outbreaks. Sterile insect technique (SIT) and Wolbachia-infected mosquito releases are emerging biologic control strategies.

Personal Protection

DEET (30–50%) or picaridin-based repellents applied to exposed skin; permethrin-treated clothing; long sleeves and pants during peak biting hours (dawn and dusk, though Ae. aegypti also bites during the day); window screens and air conditioning.

CYD-TDV Vaccine

The first licensed dengue vaccine, a live recombinant (attenuated chimeric) tetravalent vaccine. Its use was recommended only for individuals aged 9–45 years with documented prior dengue infection (seropositive). A 2026 review reports that manufacturing of CYD-TDV has been discontinued. In seronegative individuals, the vaccine acts like a first dengue infection, paradoxically increasing severe dengue risk upon subsequent natural infection. Pre-vaccination screening for serostatus was required where CYD-TDV was used.

TAK-003 Vaccine

A live attenuated tetravalent dengue vaccine (two doses, 3 months apart) approved in the European Union (2022), Indonesia, Brazil, and other countries for individuals aged 4–60 years; a 2026 review reports it is authorized in more than 40 countries. In the 4.5-year results of the TIDES phase 3 trial (20,099 children and teenagers aged 4–16 in eight countries), protection was 61.2% against confirmed dengue and 84.1% against hospital admission for dengue. In children with no earlier dengue infection, the figures were 53.5% and 79.3%; in these children protection was shown against DENV-1 and DENV-2 but not against DENV-3, and DENV-4 cases were too few to judge. The trial did not require pre-vaccination seroscreening, a key logistical difference from CYD-TDV.

Butantan-DV Vaccine

A third live attenuated tetravalent vaccine, the Butantan dengue vaccine (Butantan-DV), is given as a single dose and is licensed in Brazil. In a phase 3 trial in Brazil, 16,235 people aged 2–59 received the vaccine or a placebo. Over 5 years of follow-up, protection against symptomatic dengue was 65.0% overall, 77.1% in people who had had dengue before and 58.9% in people who had not, and 80.5% against dengue with warning signs or severe dengue. Only DENV-1 and DENV-2 cases occurred during the trial, so protection against DENV-3 and DENV-4 is not known. In June 2026, Brazil's National Immunization Program and Anvisa temporarily suspended vaccination with Butantan-DV while 42 dengue-like illnesses with warning signs and three severe cases, including two deaths, among more than 500,000 people vaccinated were investigated. The Ministry of Health said there was not yet enough evidence that the vaccine caused them (SBIm statement, 11 June 2026; see Dengue Vaccines).

Key Research Papers

Bhatt S, Gething PW, Brady OJ, et al. The global distribution and burden of dengue. Nature. 2013;496:504–507. — PubMed PMID: 23563266 · doi:10.1038/nature12060
Halstead SB. Dengue antibody-dependent enhancement: knowns and unknowns. Microbiol Spectr. 2014. — Search PubMed · doi:10.1128/microbiolspec.aid-0022-2014
WHO. Dengue: Guidelines for Diagnosis, Treatment, Prevention and Control (2009 revision). Geneva: World Health Organization, 2009. — PubMed PMID: 23762963
Simmons CP, Farrar JJ, Nguyen VVC, Wills B. Dengue. N Engl J Med. 2012;366:1423–1432. — PubMed PMID: 22494122 · doi:10.1056/NEJMra1110265
Screaton G, Mongkolsapaya J, Yacoub S, Roberts C. New insights into the immunopathology and control of dengue virus infection. Nat Rev Immunol. 2015;15:745–759. — PubMed PMID: 26603900 · doi:10.1038/nri3916
Katzelnick LC, Gresh L, Halloran ME, et al. Antibody-dependent enhancement of severe dengue disease in humans. Science. 2017;358:929–932. — PubMed PMID: 29097492 · doi:10.1126/science.aan6836
Biswal S, Reynales H, Saez-Llorens X, et al. Efficacy of a tetravalent dengue vaccine in healthy children and adolescents. N Engl J Med. 2019;381:2009–2019. — PubMed PMID: 31693803 · doi:10.1056/NEJMoa1903869
Capeding MR, Tran NH, Hadinegoro SRS, et al. Clinical efficacy and safety of a novel tetravalent dengue vaccine in healthy children in Asia. Lancet. 2014;384:1358–1365. — PubMed PMID: 25018116 · doi:10.1016/S0140-6736(14)61060-6
Anders KL, Nguyet NM, Chau NV, et al. Epidemiological factors associated with dengue shock syndrome and mortality in hospitalized dengue patients in Ho Chi Minh City, Vietnam. Am J Trop Med Hyg. 2011;84:127–134. — Search PubMed · doi:10.4269/ajtmh.2011.10-0476
Duong V, Lambrechts L, Paul RE, et al. Asymptomatic humans transmit dengue virus to mosquitoes. Proc Natl Acad Sci USA. 2015;112:14688–14693. — PubMed PMID: 26553981 · doi:10.1073/pnas.1508114112
Hoffmann AA, Montgomery BL, Popovici J, et al. Successful establishment of Wolbachia in Aedes populations to suppress dengue transmission. Nature. 2011;476:454–457. — PubMed PMID: 21866160 · doi:10.1038/nature10356
Wilder-Smith A, Ooi EE, Horstick O, Wills B. Dengue. Lancet. 2019;393:350–363. — PubMed PMID: 30696575 · doi:10.1016/S0140-6736(18)32560-1
Tricou V, Yu D, Reynales H, et al. Long-term efficacy and safety of a tetravalent dengue vaccine (TAK-003): 4·5-year results from a phase 3, randomised, double-blind, placebo-controlled trial. Lancet Glob Health. 2024;12(2):e257–e270. — PubMed PMID: 38245116
Kallás EG, Moreira JA, Patiño EG, et al. Long-term efficacy and safety of the single-dose tetravalent Butantan dengue vaccine. Nat Med. 2026;32(4):1393–1400. — PubMed PMID: 41781546
Norman FF, McGuinness SL, Chen LH. Dengue and chikungunya vaccines past, present and future: implications for travelers. Curr Opin Infect Dis. 2026;39(5):404–414. — PubMed PMID: 42296464
WHO. WHO guidelines for clinical management of arboviral diseases: dengue, chikungunya, Zika and yellow fever. Geneva: World Health Organization, 2025. — PubMed PMID: 40690567

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