Dengue fever

Dengue fever is a mosquito-borne tropical disease caused by the dengue virus. It is widely prevalent across tropical and subtropical regions, particularly in areas where Aedes mosquitoes thrive. While many infections are mild or asymptomatic, dengue can also manifest as a severe, life-threatening illness. Its global spread continues to increase, partly influenced by climate change and expanding mosquito habitats.
Most symptomatic cases begin three to fourteen days after infection and present with high fever, severe headache, muscle and joint pain, nausea, vomiting and a characteristic itchy rash. Although most people recover within a week, a small proportion may develop severe dengue, involving bleeding, plasma leakage, circulatory shock and organ impairment. This severe form was previously described as dengue haemorrhagic fever or dengue shock syndrome.

Virology and Serotypes

Dengue virus (DENV) belongs to the genus Flavivirus within the family Flaviviridae. It is closely related to viruses that cause yellow fever, West Nile fever and Zika infection. The dengue viral genome contains approximately 11,000 nucleotides encoding three structural proteins—capsid (C), premembrane (prM) and envelope (E)—and seven non-structural proteins essential for viral replication.
There are four antigenically distinct serotypes of the virus: DENV-1, DENV-2, DENV-3 and DENV-4. Infection with one serotype confers lifelong immunity to that specific type but only temporary protection against the others. A subsequent infection with a different serotype increases the risk of severe dengue due to antibody-dependent enhancement, a process in which pre-existing antibodies facilitate viral replication.

Transmission

Dengue spreads primarily through the bite of infected female mosquitoes of the genus Aedes, particularly Aedes aegypti. These mosquitoes prefer to feed at dawn and dusk but can bite at any time of day. Other species such as Aedes albopictus, Aedes polynesiensis and Aedes scutellaris may also transmit the virus. Humans serve as the main reservoir, although non-human primates and some mammals can be infected.
Following a bite from an infected host, the virus replicates in the mosquito’s gut before migrating to the salivary glands, enabling transmission during subsequent feeding. Mosquitoes remain infectious throughout their lifespan.

Signs and Symptoms

Around 80% of dengue infections are asymptomatic or produce only mild illness. Symptomatic cases typically begin abruptly with:

• high fever
• retro-orbital headache
• muscle and joint pain
• swollen glands
• nausea and vomiting
• rash and skin itching

In about 5% of patients, symptoms progress to severe dengue. Warning signs include intense abdominal pain, persistent vomiting, rapid breathing, bleeding from the nose or gums, blood in vomit or stool, pallor, cold skin, exhaustion and restlessness.
Severe dengue involves increased vascular permeability, platelet reduction and plasma leakage, which may result in shock, internal haemorrhage and organ failure.

Clinical Course

Dengue infection progresses through three phases:

• Febrile phase: characterised by high fever, generalised pain, headache, rash, nausea and vomiting; usually lasts two to seven days.
• Critical phase: occurring in a minority of cases, this phase is marked by plasma leakage, hypovolaemia, thrombocytopenia and risk of shock or bleeding.
• Recovery phase: lasting two to three days, this is marked by reabsorption of fluids, improvement of symptoms, itching and occasionally slow heart rate.

Most people recover completely, though some may experience prolonged fatigue or cognitive difficulties.

Complications and Sequelae

Possible complications following severe dengue include:

• persistent fatigue
• somnolence
• headache
• impaired concentration and memory

Pregnant women face increased risks of miscarriage, low birth weight and premature delivery. Children and older adults are more prone to complications and may have more pronounced symptoms. Co-infection with other tropical viruses such as Zika can exacerbate illness and hinder recovery.

Diagnosis

Dengue diagnosis relies on a combination of clinical assessment and laboratory tests. Because its symptoms resemble those of malaria, influenza and Zika virus, confirmation is usually achieved through blood tests detecting viral RNA, viral antigens or immune antibodies. Early diagnosis helps prevent severe complications, especially during the critical phase.

Treatment

There is no antiviral cure for dengue. Treatment is supportive and aims to relieve symptoms and prevent complications. Mild cases are managed with rest, hydration and pain-relieving medicines, avoiding drugs that increase the risk of bleeding. Severe dengue requires hospital care, including careful fluid administration, monitoring for shock and management of bleeding.

Prevention and Control

Prevention focuses on mosquito control and avoiding mosquito bites. Key measures include removing stagnant water, using insecticide-treated materials, installing window screens, wearing protective clothing and applying repellents.
Two vaccines are currently licensed:

• Dengvaxia (2016) – recommended only for individuals previously infected with dengue to prevent reinfection.
• Qdenga (2022) – authorised for adults, adolescents and children aged four and above, regardless of prior infection.

Vaccination strategies complement vector control but do not replace it.

Global Distribution and Epidemiology

Dengue is endemic in more than one hundred countries. Its range is expanding into areas previously unaffected, including parts of southern Europe and the southern United States. Increased travel, urbanisation and climate change contribute to its spread.
In 2023, more than five million infections and over five thousand deaths were reported, though actual numbers are considerably higher due to underreporting and the prevalence of mild, undetected cases. Dengue is categorised as a neglected tropical disease due to its widespread burden and the need for improved healthcare resources in affected regions.
Dengue fever remains a major global health concern. Ongoing research into vaccines, antiviral drugs and vector control continues to shape strategies aimed at reducing transmission, improving clinical outcomes and mitigating future outbreaks.