Dengue, chikungunya and Zika

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Dengue virus has four serotypes. Infection ranges from asymptomatic disease to an acute febrile syndrome and severe dengue with plasma leakage, shock, haemorrhage or organ impairment. Previous infection with one serotype does not provide reliable protection against the others and can increase the risk of severe disease during a later heterologous infection.

Chikungunya is an alphavirus whose name reflects the stooped posture caused by severe joint pain. Acute fever and polyarthralgia predominate; chronic inflammatory or relapsing musculoskeletal symptoms are the main longer-term burden. Older people, neonates and people with comorbidity are more likely to develop severe complications.

Zika virus usually causes little or no maternal systemic illness. Its importance arises from placental and sexual transmission, congenital brain and eye injury, pregnancy loss and an association with Guillain–Barré syndrome. Advice depends on who travelled, pregnancy status, dates and current country risk classification.

A dated illness timeline guides testing and management. Dengue becomes most dangerous when viraemia and fever decline, whereas direct viral detection is most useful early and antibodies emerge later. The broader assessment of a febrile returned traveller remains necessary, especially urgent exclusion of malaria and epidemiological screening for viral haemorrhagic fever when indicated.

Key points

Dengue, chikungunya and Zika are transmitted by day-biting Aedes mosquitoes and overlap geographically and clinically.
Dengue commonly causes abrupt high fever, severe headache, retro-orbital pain, myalgia, nausea and rash; warning signs cluster near defervescence when capillary permeability rises.
Chikungunya is distinguished by abrupt fever with prominent, often symmetric and disabling polyarthralgia; joint symptoms can persist for months or years.
Zika is often asymptomatic or mild with pruritic rash, non-purulent conjunctivitis and arthralgia, but infection in pregnancy can cause congenital Zika syndrome and pregnancy loss.
First-line acute assessment includes malaria films, FBC and haematocrit, renal and liver profiles, observations, hydration and a dated travel and symptom history.
Confirm acute infection with pathogen-specific PCR or dengue NS1 during the early viraemic window; serology is later and flavivirus cross-reactivity can make interpretation difficult.
Give paracetamol for fever or pain and avoid aspirin, ibuprofen and other NSAIDs until dengue has been excluded and bleeding risk has resolved.
Dengue shock needs small, carefully reassessed isotonic crystalloid steps rather than unmonitored large-volume resuscitation because leaked fluid can produce pulmonary oedema.
After a woman travels alone to a Zika-risk area, avoid conception for two months; if a male partner travelled alone or the couple travelled, use the current three-month precaution.
Mosquito bite avoidance during illness reduces onward transmission where competent vectors occur; UK laboratories report confirmed dengue, chikungunya and Zika organisms under current notification rules.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Aedes mosquito transmission

A. aegypti and A. albopictus acquire virus from viraemic humans and transmit infection during later predominantly daytime blood meals.

Four dengue serotypes

DENV-1 to DENV-4 cause similar acute disease; immunity is serotype-specific, leaving survivors susceptible to infection by the others.

Zika sexual transmission

Zika persists in semen longer than in blood and can pass sexually, creating risk after the travelling partner has recovered.

Vertical transmission

Zika crosses the placenta, chikungunya can transmit around delivery, and dengue in pregnancy can affect both maternal and neonatal outcomes.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Dengue endothelial leak
Immune and viral effects transiently increase capillary permeability, concentrating blood while plasma enters tissues and reduces effective circulating volume.
2
Secondary dengue risk
Non-neutralising antibodies from a previous serotype may facilitate viral entry into immune cells, contributing to severe disease during heterologous infection.
3
Chikungunya synovial inflammation
Viral and persistent immune activation within periarticular tissues drives severe acute pain and, in some people, prolonged inflammatory arthritis.
4
Zika fetal neurotropism
Placental transmission permits infection of developing neural progenitor cells, disrupting brain growth and causing a spectrum of neurological and ocular injury.
5
Post-infectious neuropathy
Immune responses after Zika and occasionally other arboviruses can damage peripheral nerves, producing Guillain–Barré syndrome with ascending weakness.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Classic dengue syndrome

Abrupt fever with severe headache, retro-orbital pain, myalgia, arthralgia, nausea, vomiting and a maculopapular rash follows a compatible journey.

Dengue warning phaseRed flag

Severe abdominal pain, repeated vomiting, mucosal bleeding, lethargy, restlessness, liver enlargement or fluid accumulation emerging near defervescence predicts deterioration.

Compensated dengue shockRed flag

Tachycardia, cool peripheries, delayed refill and narrowing pulse pressure may appear while systolic pressure remains normal; waiting for hypotension is unsafe.

Chikungunya joints

Intense bilateral peripheral polyarthralgia or arthritis involving hands, wrists, ankles and feet can dominate the illness and persist after fever resolves.

Neurological complicationRed flag

Progressive weakness, areflexia, cranial neuropathy, encephalopathy or seizures requires urgent neurological and respiratory assessment for Guillain–Barré syndrome or encephalitis.

Pregnancy exposureRed flag

Possible Zika exposure in a pregnant person or their sexual partner is clinically important even without symptoms and requires a dated specialist pathway.

Red flags requiring action

Deterioration as fever settles, usually during illness days three to seven, is characteristic of the dengue critical phase and must not be mistaken for recovery.
Narrow pulse pressure, delayed capillary refill, cool extremities, tachycardia, oliguria or altered mental state can precede overt hypotension in dengue shock.
A rising haematocrit with rapidly falling platelets suggests plasma leakage; a falling haematocrit in an unstable patient may instead indicate bleeding.
Pregnancy with possible Zika exposure or infection needs prompt fetal-medicine and virology advice because maternal illness may be mild while fetal consequences are substantial.
Encephalopathy, myocarditis, hepatitis, renal injury, major haemorrhage or respiratory compromise warrants monitored specialist care regardless of the presumed arbovirus.
Fever after tropical travel still requires urgent malaria testing; an Aedes exposure history or rash does not safely exclude malaria.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line returning-fever assessmentFirst stepFirst line
Why
Identify malaria, physiological instability and common organ complications before arbovirus confirmation.
Interpretation and limitations
Request urgent malaria films and rapid test, FBC with haematocrit, renal and liver profiles, urinalysis and pregnancy testing when relevant; repeat values according to trajectory.
02
Dengue PCR or NS1 antigen
Why
Demonstrate acute dengue during the early viraemic phase.
Interpretation and limitations
Direct detection is most useful in the first days of illness; record exact onset and send through an accredited or UKHSA reference pathway. A late negative result does not exclude infection.
03
Dengue serology
Why
Support recent infection after the direct-detection window and inform selected pre-travel vaccine decisions.
Interpretation and limitations
IgM develops after several days and may cross-react with other flaviviruses or vaccination; paired samples and reference interpretation may be needed, and NS1 positivity may require later serological confirmation.
04
Chikungunya PCR and serology
Why
Separate chikungunya from dengue, Zika and other causes of febrile polyarthralgia.
Interpretation and limitations
PCR is useful early, while antibody testing becomes informative later; give the laboratory onset date, itinerary, vaccination history and clinical phenotype.
05
Zika reference testing
Why
Assess clinically or obstetrically significant infection using timing-appropriate molecular and serological tests.
Interpretation and limitations
Discuss sampling with virology or RIPL because blood, urine and antibody windows differ and flavivirus serology can be non-specific; routine testing of all asymptomatic returnees is not recommended.
06
Serial haematocrit and platelets
Why
Track dengue plasma leakage, marrow suppression and possible haemorrhage.
Interpretation and limitations
Rising haematocrit with falling platelets supports leakage; after fluids, the direction must be interpreted with perfusion, urine output and bleeding because dilution and haemorrhage can both lower haematocrit.
07
Fetal medicine assessment
Why
Evaluate a pregnancy after significant Zika exposure or confirmed maternal infection.
Interpretation and limitations
Specialists define serial ultrasound, virology and neonatal plans from gestation, exposure dates and results; one normal scan cannot exclude evolving congenital effects.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Malaria

Fever, headache, cytopenias and travel overlap, but urgent blood films reveal parasites; malaria can coexist and remains immediately treatable.

Viral haemorrhagic fever

Compatible place, dates and high-risk contact require immediate isolation assessment before routine handling, particularly with bleeding or severe systemic illness.

Leptospirosis

Freshwater or animal-urine exposure, conjunctival suffusion, jaundice and renal injury favour leptospirosis and prompt blood or urine PCR.

Measles or rubella

Fever and rash with respiratory prodrome, lymphadenopathy, vaccination gaps or contact history require airborne precautions and urgent public-health testing.

Inflammatory arthritis

Rheumatoid, reactive and connective-tissue disease can resemble chronic chikungunya, especially when joint inflammation persists without documented acute infection.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01TRIAGEAssess acute arboviral illnessFirst stepA traveller returns from an Aedes-risk area with fever, rash, arthralgia or conjunctivitis.

1Record destinations, dates, outbreak exposure, mosquito bites, day of illness, pregnancy possibility, sexual partner travel and previous flavivirus infection or vaccination.
2Use ABCDE, obtain urgent malaria testing and baseline haematocrit, platelets, renal and liver profiles; screen separately for high-consequence infection when epidemiology requires it.
3Select early PCR or antigen and later serology according to symptom onset, discussing pregnancy and uncertain results with virology or RIPL.
4Give explicit return instructions for defervescence, abdominal pain, vomiting, bleeding, reduced urine, breathlessness, faintness, weakness or confusion.

02DENGUENavigate the critical phaseDengue is suspected during illness days three to seven or warning signs appear as fever settles.

1Admit patients with warning signs, pregnancy, significant comorbidity, unreliable review or abnormal perfusion and obtain repeated observations, haematocrit and urine output.
2Avoid aspirin, NSAIDs, intramuscular injections and unnecessary invasive procedures; use paracetamol within a safe total daily dose for pain or fever.
3If shock or clinically important leakage develops, give protocolised isotonic crystalloid in a small time-limited step and immediately reassess perfusion, haematocrit and lungs.
4Reduce or stop intravenous fluid as capillary integrity returns; convalescent fluid reabsorption can cause pulmonary oedema if critical-phase rates continue.

03CHIKUNGUNYAControl acute and persistent joint diseaseA compatible illness features prominent arthralgia or arthritis without dengue instability.

1Use rest, oral hydration and paracetamol initially while dengue remains possible; do not introduce an NSAID until dengue and bleeding risk have been reasonably excluded.
2After dengue exclusion, consider a short NSAID course only after checking renal, gastrointestinal, cardiovascular, pregnancy and interaction risks.
3For pain or synovitis beyond the acute phase, arrange rehabilitation and primary-care or rheumatology review rather than repeatedly prescribing unsupervised analgesics.
4Reconsider rheumatoid disease, reactive arthritis and other infection when symptoms are atypical, progressive or accompanied by new systemic findings.

04ZIKAProtect pregnancy and conceptionA pregnant person, someone planning conception or their sexual partner has travelled to a current Zika-risk area.

1Establish exactly who travelled, return dates, symptoms, pregnancy dates and the current UKHSA country risk category; do not infer risk from continent alone.
2If a woman travelled without a male partner, advise avoiding conception for two months after return; if a male partner travelled or both travelled, use three months.
3During an established pregnancy after partner exposure, advise barrier contraception for the remainder of pregnancy and refer according to the UKHSA maternity pathway.
4Discuss indicated virology and serial fetal assessment with specialist teams; avoid indiscriminate asymptomatic testing because negative or cross-reactive results can be misleading.

05PREVENTReduce Aedes exposureA traveller is entering an area with dengue, chikungunya or Zika transmission.

1Check current destination and outbreak pages, including pregnancy-specific Zika advice, and explain that Aedes mosquitoes bite mainly during daylight hours.
2Use effective repellent on exposed skin, cover clothing, screened or air-conditioned rooms and removal of standing water; apply repellent after sunscreen.
3Consider chikungunya vaccination for active-outbreak travel, long or frequent exposure where recent transmission occurred, or laboratory risk; select the product by age and host factors.
4Advise an infected traveller to continue bite avoidance during the viraemic period so local mosquitoes abroad cannot acquire and transmit the virus.

Key medicines and prescribing safety4 treatments · regimens, roles and cautions

Preferred initial antipyretic and analgesic while dengue-related bleeding and renal risk remain possible.

Paracetamol

Give 500 mg to 1 g orally every four to six hours when needed, with at least four hours between doses and no more than 4 g in 24 hours for a suitable adult.

Use a lower maximum or specialist advice in low body weight, liver disease, malnutrition or heavy alcohol use; count all combination products and avoid treating fever alone as a fluid-status marker.

Restores effective circulation during clinically significant dengue plasma leakage while capillary permeability is high.

Isotonic crystalloid for dengue shock

Give a protocolised intravenous crystalloid bolus or infusion matched to shock severity, then reassess perfusion, urine output, haematocrit and respiratory findings before any further fluid.

There is no safe fixed volume divorced from weight and physiology; excessive or prolonged fluid causes pleural effusions and pulmonary oedema, particularly during reabsorption.

Pre-travel prevention for selected people with prior dengue evidence or exceptional risk after an individual benefit-harm assessment.

Qdenga live dengue vaccine

When current UK Green Book criteria are met, give 0.5 mL subcutaneously on day 0 and a second 0.5 mL dose three months later through an authorised travel-vaccine pathway.

Do not give during pregnancy, breastfeeding or clinically significant immunosuppression; serology can be cross-reactive, and vaccination never replaces daytime mosquito-bite precautions.

Prevention for selected outbreak, long-term, frequent or laboratory exposure after current JCVI and NaTHNaC assessment.

Vimkunya or IXCHIQ chikungunya vaccine

Give Vimkunya 0.8 mL intramuscularly once from age 12 years, or IXCHIQ 0.5 mL intramuscularly once in an eligible adult aged 18 to 59 years and at least 30 days before travel.

IXCHIQ is live and must not be used at age 60 or older, with hypertension, cardiovascular disease, diabetes, chronic kidney disease, immunodeficiency including IgA deficiency, or thymus disorder or thymectomy; seek specialist advice for pregnancy or other precautions.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Dengue shock

Capillary leak reduces circulating volume, causing narrow pulse pressure, organ hypoperfusion, metabolic acidosis and ultimately hypotensive collapse.

Severe haemorrhage

Thrombocytopenia, coagulation disturbance, endothelial dysfunction and shock can combine to cause gastrointestinal, mucosal or procedure-related bleeding.

Chronic arthropathy

Chikungunya pain, stiffness and synovitis may relapse or persist for months, limiting mobility, sleep, work and independence.

Congenital Zika syndrome

Fetal infection can cause microcephaly, intracranial calcification, eye abnormalities, contractures, impaired growth and later neurodevelopmental disability.

Neurological and cardiac disease

Guillain–Barré syndrome, encephalitis, myelitis and myocarditis are uncommon but serious complications across these infections and require organ-specific supportive care.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

During possible dengue critical phase, chart pulse, blood pressure including pulse pressure, capillary refill, respiratory rate, oxygen saturation, oral intake and urine output at a frequency matched to risk.
Trend haematocrit and platelets rather than reacting to one value; interpret every change against fluids, bleeding, perfusion and the day of illness.
After intravenous fluid, reassess immediately for warm perfused extremities, improved urine output and new crackles, hypoxaemia, effusions or hepatomegaly.
Review chikungunya joint function after the acute illness; persistent synovitis, disability or neuropathic features needs rehabilitation and sometimes rheumatology assessment.
Use fetal-medicine follow-up after significant Zika exposure or infection, with serial assessment and a documented neonatal plan where indicated.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Defervescence can be dangerous

Dengue vascular leakage often begins as temperature normalises, so improvement in fever alone is not evidence of recovery.

Haematocrit tells a story

A rise suggests concentration from leakage, while a fall with instability suggests bleeding or dilution; context determines the response.

NSAID timing matters

An NSAID may help post-dengue-exclusion chikungunya arthritis but can amplify bleeding and renal injury during undifferentiated acute arboviral disease.

Zika risk is relational

Advice changes with the sex of the traveller, partner travel, conception plans, pregnancy and dates because sexual transmission persists beyond acute symptoms.

Serology can cross-react

Dengue, Zika, yellow-fever infection and flavivirus vaccination can generate overlapping antibody patterns requiring reference interpretation and sometimes paired samples.

11Common pitfallsFrequent interpretation and management errors.

01
Do not call dengue recovered because the fever has settled; ask specifically about warning symptoms and reassess perfusion during days three to seven.
02
Do not give ibuprofen, aspirin or an intramuscular injection before dengue and clinically important bleeding risk have been excluded.
03
Do not treat every thrombocytopenic patient with platelet transfusion; bleeding, procedure need and specialist thresholds matter more than the count alone.
04
Do not continue critical-phase fluid rates into convalescence without repeated reassessment because reabsorbed extravascular fluid can overload the lungs.
05
Do not diagnose chikungunya solely from joint pain in an endemic area; dengue, Zika, malaria and bacterial infection may coexist or mimic it.
06
Do not reassure a pregnant person after Zika exposure on the basis of absent symptoms or one normal ultrasound; follow the dated specialist pathway.
07
Do not offer dengue vaccination without confirming current UK criteria, prior infection evidence and live-vaccine contraindications.