Dengue Fever: Symptoms, Causes & Treatment Guide

What Is Dengue Fever?

Dengue fever is a mosquito-borne viral infection caused by the dengue virus (DENV), which belongs to the Flavivirus family. The disease causes flu-like symptoms and can range from mild illness to severe, potentially life-threatening complications. An estimated 390 million people are infected globally each year, with about 96 million developing clinical disease.

Dengue fever represents one of the most significant mosquito-borne viral diseases affecting humans worldwide. The infection is caused by four distinct but closely related virus serotypes (DENV-1, DENV-2, DENV-3, and DENV-4), all of which can cause the full spectrum of disease from asymptomatic infection to severe dengue with organ impairment. Understanding this diversity is crucial because infection with one serotype provides lifelong immunity only to that specific type, while subsequent infections with different serotypes actually increase the risk of severe disease through a mechanism called antibody-dependent enhancement.

The global burden of dengue has increased dramatically over the past 50 years. According to the World Health Organization, the number of reported cases increased from 505,430 in 2000 to over 5.2 million in 2019. This dramatic rise is attributed to urbanization, population growth, international travel, and climate change, which has expanded the geographic range of the Aedes mosquito vectors. The disease is now endemic in more than 100 countries across Africa, the Americas, the Eastern Mediterranean, South-East Asia, and the Western Pacific, with the latter two regions being the most seriously affected.

The disease derives its alternative name "breakbone fever" from the characteristic severe muscle and joint pain that patients experience. This intense pain, combined with high fever and other symptoms, can be extremely debilitating, although the vast majority of patients make a full recovery within one to two weeks. However, approximately 500,000 people develop severe dengue each year, requiring hospitalization, with about 25,000 deaths annually despite the availability of effective supportive treatment.

The Dengue Virus and Its Transmission

The dengue virus belongs to the genus Flavivirus, which also includes the viruses causing yellow fever, Zika, and Japanese encephalitis. All four dengue serotypes are transmitted to humans through the bite of infected female Aedes mosquitoes, primarily Aedes aegypti and, to a lesser extent, Aedes albopictus (the Asian tiger mosquito). These mosquitoes are well-adapted to urban environments and breed in small collections of standing water commonly found around homes, such as flower pot saucers, discarded tires, water storage containers, and blocked gutters.

Unlike many other disease-carrying mosquitoes that bite at night, Aedes mosquitoes are daytime feeders, with peak biting periods occurring during early morning hours after sunrise and in the late afternoon before sunset. This behavioral pattern has important implications for prevention strategies, as bed nets alone are insufficient protection. The mosquitoes are also "sip feeders," meaning they often bite multiple people during a single blood meal, which enhances their efficiency as disease vectors.

Understanding Serotypes and Immunity

One of the most important aspects of dengue epidemiology is the existence of four distinct serotypes. When a person is infected with one serotype, they develop lifelong immunity to that specific serotype. However, this immunity does not extend to the other three serotypes, and cross-protection is only temporary (lasting approximately 2-3 months). This means an individual can potentially be infected with dengue up to four times during their lifetime.

What makes secondary infections particularly concerning is the phenomenon of antibody-dependent enhancement (ADE). During a second infection with a different serotype, antibodies from the first infection can actually enhance viral entry into cells, leading to higher viral loads and more severe disease. This is why dengue control programs and vaccination strategies must consider all four serotypes simultaneously, and why the WHO recommends certain vaccines only for individuals who have already had one dengue infection.

What Are the Symptoms of Dengue Fever?

Dengue fever symptoms typically begin 4-10 days after a mosquito bite and include sudden high fever (up to 40°C/104°F), severe headache, pain behind the eyes, muscle and joint pain, nausea, vomiting, swollen glands, and skin rash. Most people recover within a week, but severe dengue can cause dangerous bleeding, plasma leakage, and organ damage.

The clinical presentation of dengue fever can vary considerably, ranging from asymptomatic infection to severe, life-threatening disease. Understanding the typical symptom progression is essential for early recognition and appropriate management, particularly for identifying warning signs that indicate progression to severe dengue.

Dengue infection follows a characteristic three-phase clinical course: the febrile phase, the critical phase, and the recovery phase. Each phase has distinct features that help healthcare providers assess disease severity and guide treatment decisions. Recognition of these phases is particularly important because the critical phase, when severe complications typically develop, often begins as the fever subsides, which can mislead patients into thinking they are improving.

Many infected individuals, particularly children experiencing their first infection, may have minimal or no symptoms at all. This is known as asymptomatic or inapparent dengue infection. While these individuals do not become ill, they can still transmit the virus to mosquitoes that bite them, contributing to ongoing disease transmission in the community. Studies suggest that up to 75% of dengue infections may be asymptomatic.

Febrile Phase (Days 1-7)

The febrile phase marks the onset of symptomatic disease and is characterized by the sudden development of high fever, typically reaching 39-40°C (102-104°F). This fever often has a distinctive "saddleback" or biphasic pattern, where it drops for a day or two before rising again. The fever is usually accompanied by severe symptoms that can be extremely debilitating.

During this phase, patients typically experience intense headache, particularly in the frontal region, along with characteristic retro-orbital pain (pain behind the eyes) that worsens with eye movement. The muscle pain (myalgia) and joint pain (arthralgia) can be so severe that dengue has earned the nickname "breakbone fever." These musculoskeletal symptoms are often accompanied by general malaise and profound fatigue.

• High fever: Sudden onset, often reaching 40°C (104°F), may have biphasic pattern
• Severe headache: Intense pain, typically frontal, lasting throughout the febrile period
• Retro-orbital pain: Pain behind the eyes that worsens with eye movement
• Muscle and joint pain: Severe myalgia and arthralgia affecting multiple body areas
• Nausea and vomiting: Gastrointestinal symptoms that may limit oral intake
• Skin rash: Maculopapular or morbilliform rash appearing 2-5 days after fever onset
• Facial flushing: Red coloration of the face in the first 24-48 hours
• Swollen lymph nodes: Generalized lymphadenopathy
• Mild bleeding: Easy bruising, bleeding gums, or nosebleeds in some cases

Critical Phase (Days 3-7)

The critical phase typically occurs around the time of defervescence (when fever subsides), usually between days 3-7 of illness. This is paradoxically when patients may feel their fever breaking and assume they are improving, but it is actually the period of greatest risk for developing severe dengue. During this phase, increased capillary permeability can lead to plasma leakage, which may progress to shock if not properly managed.

Not all patients progress to the critical phase, but those who do require careful monitoring and often hospitalization. The key is to identify warning signs early so that appropriate supportive care can be initiated before severe complications develop. Patients who progress through this phase without developing severe plasma leakage typically enter the recovery phase and make a full recovery.

Recovery Phase (Days 7-10)

Following the critical phase, patients who have weathered the illness enter the recovery phase. During this period, plasma leakage stops and is reabsorbed, vital signs stabilize, and the patient's condition gradually improves. The rash may become more prominent and itchy during this phase, and patients often experience a characteristic "islands of white in a sea of red" skin appearance.

While patients generally feel much better during recovery, profound fatigue is common and may persist for several weeks to months. Some patients experience depression or other mood changes during the recovery period. Full recovery of energy levels and sense of wellbeing may take 2-3 months in some individuals.

What Is Severe Dengue?

Severe dengue (formerly called dengue hemorrhagic fever or dengue shock syndrome) is a potentially fatal complication characterized by plasma leakage, severe bleeding, and organ damage. It typically develops 24-48 hours after fever subsides and requires immediate hospitalization with intensive supportive care including intravenous fluids.

Severe dengue represents the most serious form of the disease and is a leading cause of serious illness and death in some Asian and Latin American countries. The condition typically develops after the initial fever begins to subside, when patients and their families often expect improvement. This timing makes recognition of warning signs critically important, as early intervention with fluid management can be life-saving.

The pathophysiology of severe dengue centers on increased vascular permeability, which leads to plasma leakage from blood vessels into surrounding tissues and body cavities. This plasma leakage can cause a dangerous drop in blood volume (hypovolemia) that, if not corrected with careful fluid replacement, can progress to dengue shock syndrome. The condition also affects platelet function and the clotting cascade, increasing the risk of significant bleeding complications.

Several risk factors increase the likelihood of developing severe dengue. The most significant is previous infection with a different dengue serotype, which through antibody-dependent enhancement can amplify viral replication and disease severity. Other risk factors include younger age (particularly infants under 1 year), pregnancy, obesity, chronic diseases such as diabetes and asthma, and certain genetic factors that affect immune response.

Severe Plasma Leakage

Plasma leakage is the hallmark of severe dengue and results from dysfunction of the vascular endothelium (the cells lining blood vessels). When plasma leaks from the intravascular space, it accumulates in body cavities such as the pleural space (around the lungs) and the peritoneal cavity (abdomen). This can be detected through clinical examination, ultrasound, or chest X-ray showing pleural effusion or ascites.

If plasma leakage is severe and not compensated by appropriate fluid therapy, it leads to hypovolemic shock - dengue shock syndrome. Signs of shock include a rapid, weak pulse, narrowing of pulse pressure (the difference between systolic and diastolic blood pressure), cold extremities, delayed capillary refill, and altered mental status. Without prompt treatment, dengue shock syndrome has a mortality rate of up to 20%, but with appropriate fluid management, this can be reduced to less than 1%.

Severe Bleeding

While minor bleeding manifestations such as petechiae (tiny red spots), easy bruising, and bleeding gums are common in dengue, severe bleeding is a feature of severe dengue. This can manifest as gastrointestinal bleeding (vomiting blood or bloody/black stools), heavy menstrual bleeding, or bleeding from other sites. Severe bleeding typically occurs in the context of prolonged shock and is associated with poor prognosis.

Organ Impairment

Severe dengue can affect multiple organs beyond the vascular system. Liver involvement is common, with elevated liver enzymes and, in severe cases, acute liver failure. The heart may develop myocarditis, and the central nervous system can be affected, leading to encephalopathy or encephalitis. Acute kidney injury can occur, particularly in the setting of prolonged shock. These organ complications require specialized management in an intensive care setting.

How Does Dengue Fever Spread?

Dengue fever spreads through the bite of infected Aedes mosquitoes, primarily Aedes aegypti. These mosquitoes bite mainly during daytime hours, especially in early morning and late afternoon. The virus does not spread directly from person to person, but an infected person can transmit the virus to mosquitoes that bite them.

Understanding the transmission cycle of dengue is essential for implementing effective prevention strategies. The virus circulates between humans and mosquitoes in a cycle that requires both hosts to maintain transmission in a community. When a mosquito bites an infected person during the viremic phase (when the virus is present in the blood), the mosquito becomes infected. After an incubation period of 8-12 days in the mosquito, the virus reaches the mosquito's salivary glands, and the mosquito becomes capable of transmitting the virus to another human during subsequent blood meals.

The Aedes aegypti mosquito is the primary vector for dengue transmission worldwide. This species is highly adapted to urban environments and demonstrates a strong preference for human blood. Unlike many mosquito species that breed in natural water bodies, Aedes aegypti thrives in artificial containers commonly found around homes, making urban and peri-urban areas hotspots for dengue transmission. The mosquito's ability to breed in very small amounts of water - even a bottle cap can suffice - makes source reduction challenging.

Female Aedes mosquitoes are "nervous feeders," meaning they are easily disturbed during feeding and may bite multiple people during a single feeding session. This behavior significantly enhances their efficiency as disease vectors. Additionally, these mosquitoes can remain infectious for their entire lifespan (typically 2-4 weeks), during which they may bite dozens of people.

Geographic Distribution

Dengue is endemic in tropical and subtropical regions worldwide, with the highest burden in Asia and the Americas. The disease has expanded dramatically in recent decades, with new countries reporting their first outbreaks and previously affected areas experiencing more frequent and larger epidemics. Climate change is expected to further expand the geographic range of Aedes mosquitoes and increase transmission intensity in already-affected areas.

High-risk regions include Southeast Asia (particularly Thailand, Vietnam, Philippines, Indonesia, and Malaysia), South Asia (India, Bangladesh, Sri Lanka, Pakistan), the Pacific Islands, Central and South America (especially Brazil, Colombia, and Mexico), the Caribbean, and parts of Africa. Travelers to these regions should take precautions against mosquito bites, and healthcare providers should consider dengue in the differential diagnosis of fever in returned travelers.

Seasonal Patterns

Dengue transmission follows seasonal patterns closely linked to rainfall and temperature. In most endemic areas, transmission peaks during and shortly after the rainy season when mosquito breeding sites are abundant. However, in areas with year-round rainfall or irrigation, transmission may occur throughout the year. Temperature also plays a crucial role, as the virus replicates more efficiently in mosquitoes at higher temperatures, shortening the extrinsic incubation period and increasing transmission potential.

How Is Dengue Fever Diagnosed?

Dengue fever is diagnosed through laboratory tests including the NS1 antigen test (effective in the first week), PCR testing (detects viral RNA), and IgM/IgG antibody tests (detect immune response). Clinical diagnosis is based on symptoms combined with epidemiological factors such as travel to endemic areas or local outbreak status.

Accurate and timely diagnosis of dengue is important for appropriate clinical management and public health response. The clinical presentation of dengue overlaps significantly with many other febrile illnesses, including other mosquito-borne diseases (malaria, chikungunya, Zika), viral infections (influenza, COVID-19), and bacterial infections. Laboratory confirmation is therefore essential, particularly in non-endemic areas where healthcare providers may be less familiar with the disease.

The choice of diagnostic test depends on the timing of presentation relative to symptom onset. During the first week of illness (the acute phase), the virus is present in the blood, and tests that detect viral components are most useful. After about day 5 of illness, the immune response develops, and antibody-based tests become more reliable. Understanding this timing helps ensure appropriate test selection and interpretation.

NS1 Antigen Test

The NS1 (nonstructural protein 1) antigen test detects a protein produced during dengue virus replication. This test is most useful during the first 1-7 days of illness when viral antigen levels are highest. The NS1 test is available as a rapid diagnostic test that can provide results within minutes, making it valuable for point-of-care testing. Sensitivity is highest in the first 3 days of illness and declines thereafter.

PCR Testing

Polymerase chain reaction (PCR) testing detects dengue viral RNA and is the most specific method for confirming acute dengue infection. PCR can also identify the specific serotype causing infection, which is valuable for epidemiological surveillance. Like the NS1 test, PCR is most useful during the acute viremic phase (first 5-7 days). While highly accurate, PCR testing is more complex and expensive than rapid tests and may not be available in all settings.

Antibody Tests (IgM/IgG)

Antibody tests detect the immune response to dengue infection. IgM antibodies typically become detectable around day 4-5 of illness and remain positive for 2-3 months. IgG antibodies appear later and persist for years. The pattern of IgM and IgG response can help distinguish between primary and secondary infections, which has implications for severe disease risk. However, antibody tests can cross-react with other flaviviruses, potentially leading to false positives in areas where multiple flaviviruses circulate.

Supporting Laboratory Findings

In addition to specific dengue tests, routine blood tests can support the diagnosis and help monitor disease severity. Characteristic findings in dengue include:

• Thrombocytopenia: Low platelet count, often dropping significantly during the critical phase
• Leukopenia: Low white blood cell count, particularly lymphocytes
• Elevated hematocrit: Indicates hemoconcentration due to plasma leakage
• Elevated liver enzymes: AST and ALT are commonly elevated
• Abnormal coagulation studies: May be seen in severe cases

How Is Dengue Fever Treated?

There is no specific antiviral treatment for dengue fever. Management focuses on supportive care including rest, adequate fluid intake, and paracetamol (acetaminophen) for fever and pain. Aspirin and ibuprofen must be avoided as they increase bleeding risk. Severe dengue requires hospitalization with careful intravenous fluid management.

The management of dengue fever is entirely supportive, as no specific antiviral medication has proven effective against the dengue virus. The goals of treatment are to maintain adequate hydration, control symptoms, and monitor for warning signs that indicate progression to severe disease. With appropriate supportive care, the vast majority of dengue patients make a full recovery.

Treatment recommendations differ based on disease severity, which is typically classified into three categories: dengue without warning signs, dengue with warning signs, and severe dengue. Patients without warning signs can usually be managed at home with close monitoring, while those with warning signs or severe dengue require hospitalization for more intensive management.

Early recognition of warning signs and prompt initiation of appropriate fluid therapy are the keys to preventing dengue-related deaths. Healthcare systems in endemic areas have developed triage protocols to identify high-risk patients and ensure they receive appropriate levels of care. In non-endemic areas, awareness of dengue among healthcare providers is crucial for appropriate management of imported cases.

Home Management for Mild Dengue

Patients with dengue fever who do not have warning signs can typically be managed at home, provided they have access to healthcare if their condition worsens. The cornerstone of home management is adequate hydration. Patients should drink plenty of fluids, including water, oral rehydration solutions, fresh fruit juices, and clear soups. The goal is to maintain good urine output as an indicator of adequate hydration.

For fever and pain, paracetamol (acetaminophen) is the only recommended medication. The standard adult dose is 500-1000mg every 4-6 hours, not exceeding 4 grams per day. It is critically important to avoid aspirin, ibuprofen, and other non-steroidal anti-inflammatory drugs (NSAIDs) because these medications interfere with platelet function and can significantly increase the risk of bleeding complications.

Rest is important during the acute illness, and patients should avoid strenuous activity until fully recovered. Tepid sponging can help reduce fever and improve comfort. Patients and caregivers should be educated about warning signs that indicate the need for immediate medical attention.

Hospital Management

Patients with warning signs or evidence of severe dengue require hospitalization for close monitoring and treatment. The primary intervention for severe dengue is careful intravenous fluid therapy. The goal is to maintain effective circulation while avoiding fluid overload, which can lead to pulmonary edema and respiratory distress. This requires frequent reassessment and adjustment of fluid rates based on clinical response.

Monitoring in the hospital typically includes regular vital signs (pulse, blood pressure, respiratory rate), serial hematocrit measurements (to assess plasma leakage), urine output monitoring, and assessment for warning signs and complications. Blood transfusion may be needed for patients with severe bleeding, and platelet transfusion may be considered in specific circumstances, though routine platelet transfusion is not recommended.

Patients with severe dengue, particularly those with shock, require management in an intensive care unit where more aggressive fluid resuscitation, vasopressor support if needed, and organ support can be provided. With appropriate intensive care, mortality from severe dengue can be reduced to less than 1%.

How Can You Prevent Dengue Fever?

Preventing dengue fever involves protecting yourself from mosquito bites and reducing mosquito breeding sites. Use DEET-based insect repellent, wear long-sleeved clothing, stay in air-conditioned spaces with screens, and eliminate standing water around your home. Vaccination is available for eligible individuals in endemic areas.

Prevention of dengue operates at two levels: individual protection from mosquito bites and community-level vector control to reduce mosquito populations. Both approaches are important, and their combined implementation offers the best protection against dengue transmission. For travelers to endemic areas, personal protective measures are essential, while for residents of endemic areas, sustained community efforts to control mosquitoes are crucial.

The challenge of dengue prevention is compounded by the daytime biting habits of Aedes mosquitoes, which makes bed nets less effective than for malaria prevention, and by the ability of these mosquitoes to breed in very small amounts of water in and around homes. Successful dengue control requires sustained effort and community engagement to identify and eliminate breeding sites.

Personal Protection from Mosquito Bites

Protecting yourself from mosquito bites is the most important individual-level prevention measure. Insect repellents containing DEET (20-30% concentration), picaridin (20%), IR3535 (20%), or oil of lemon eucalyptus (OLE/PMD) are effective at repelling Aedes mosquitoes. Repellent should be applied to all exposed skin and reapplied according to product instructions, typically every 4-6 hours.

Wearing long-sleeved shirts and long pants provides an additional physical barrier against mosquito bites. Light-colored clothing is preferable as mosquitoes are attracted to dark colors. Treating clothing with permethrin (an insecticide) provides additional protection, particularly for travelers to high-risk areas. Permethrin-treated clothing remains effective through multiple washings.

Environmental measures include staying in air-conditioned accommodations when possible, as the cool air deters mosquitoes and windows remain closed. When air conditioning is not available, window and door screens provide protection. Mosquito nets can be useful when sleeping during daytime hours or outdoors. Using mosquito coils or plug-in vaporizers indoors can provide additional protection.

• Use insect repellent: Apply DEET, picaridin, or IR3535-based repellent to exposed skin every 4-6 hours
• Wear protective clothing: Long sleeves, long pants, and light-colored fabrics
• Stay in screened or air-conditioned areas: Especially during peak biting hours (early morning and late afternoon)
• Use mosquito nets: Particularly for daytime sleep or outdoor activities
• Treat clothing with permethrin: For enhanced protection during travel

Eliminating Mosquito Breeding Sites

Aedes mosquitoes breed in stagnant water, and eliminating these breeding sites is crucial for reducing mosquito populations. Because these mosquitoes prefer small, artificial containers rather than natural water bodies, source reduction focuses on the domestic environment. Regular inspection and treatment or removal of potential breeding sites can significantly reduce local mosquito populations.

Common breeding sites include flowerpot saucers, unused plant pots, blocked gutters, discarded tires, buckets, water storage containers, animal water bowls, birdbaths, and any container that can hold even a small amount of water. Weekly inspection and emptying or treating of these containers is recommended. For water storage containers that cannot be emptied, tight-fitting lids or mesh covers prevent mosquitoes from laying eggs.

Dengue Vaccination

Dengue vaccines represent an important advancement in prevention, though their use requires careful consideration of individual circumstances. Two vaccines are currently licensed: Dengvaxia (CYD-TDV) and Qdenga (TAK-003). These vaccines differ in their recommendations and target populations.

Dengvaxia is approved for individuals aged 9-45 years who have documented previous dengue infection and live in endemic areas. The requirement for prior infection is crucial because the vaccine can increase the risk of severe dengue in individuals who have never been infected before. Qdenga is approved for individuals 4 years and older regardless of prior dengue status and may be considered for travelers to endemic areas. Both vaccines require multiple doses for full protection.

The decision to vaccinate should be made in consultation with a healthcare provider who can assess individual risk factors, travel plans, and local dengue epidemiology. Vaccination does not replace the need for mosquito bite prevention measures, as no vaccine provides 100% protection.

When Should You See a Doctor for Dengue?

Seek immediate medical attention if you have fever after traveling to a dengue-endemic area. Seek emergency care immediately if you develop warning signs such as severe abdominal pain, persistent vomiting, bleeding, rapid breathing, fatigue or restlessness, or pale/cold skin. These signs indicate possible severe dengue requiring urgent treatment.

Knowing when to seek medical care is crucial for anyone who may have dengue fever. While most cases are mild and can be managed at home with supportive care, identifying those who need more intensive management can be life-saving. The timing of seeking care depends on the clinical situation and the resources available in your location.

Any fever developing within two weeks of travel to a dengue-endemic area should prompt medical evaluation. Healthcare providers can assess for dengue and other travel-related infections, perform appropriate diagnostic tests, and provide guidance on management and monitoring. Early evaluation is particularly important for individuals at higher risk of severe disease, including those who have had dengue before, young children, pregnant women, and those with chronic medical conditions.

For individuals already diagnosed with dengue or managing symptoms at home, close monitoring for warning signs is essential. The critical period typically occurs around days 3-7 of illness, often coinciding with defervescence (when fever begins to subside). This is when plasma leakage and progression to severe dengue most commonly occur. Patients and caregivers should be vigilant for warning signs during this period.

Warning Signs Requiring Emergency Care

The following warning signs indicate possible progression to severe dengue and require immediate medical attention. Do not wait to seek care if any of these develop:

• Severe abdominal pain: Intense, persistent pain in the abdomen
• Persistent vomiting: Three or more episodes in 24 hours, or inability to tolerate fluids
• Bleeding: Blood in vomit, stool, or urine; bleeding gums; heavy menstrual bleeding
• Rapid or difficult breathing: May indicate fluid accumulation in the lungs
• Extreme fatigue or restlessness: Especially lethargy or irritability in children
• Skin changes: Pale, cold, or clammy skin indicating poor circulation
• Decreased urination: May indicate dehydration or shock
• Altered consciousness: Confusion, drowsiness, or difficulty staying awake