Conditions · Infectious and tropical diseases

Yellow fever !

Yellow fever is a mosquito-borne viral disease of the tropics. Most cases are mild, but a minority develop jaundice, bleeding and liver and kidney failure.

Updated 2026-11-01

Structures involved

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Microorganisms that cause it

Why it happens

What it is

An acute viral haemorrhagic fever caused by the yellow fever virus (a flavivirus) and spread by mosquitoes. Most infections are mild or silent, but some people progress to a toxic phase with hepatitis, jaundice, bleeding and kidney failure.

Who gets it

Endemic in tropical Africa and South America; Colombia is one of the Latin American countries considered at risk, with sylvatic transmission in forested areas such as the Amazon, Orinoquia and Andean foothills. It is a notifiable disease in Colombia, and vaccination is free in the national programme. Africa carries most of the world burden.

Causes

Yellow fever virus, an RNA flavivirus (same family as dengue and Zika)
Sylvatic cycle: Haemagogus and Sabethes mosquitoes transmit the virus between monkeys and to people who enter the forest
Urban cycle: Aedes aegypti can spread it from person to person in towns

Risk factors

Living in or travelling to endemic areas without vaccination
Forest work: farming, logging, mining, hunting
Unknown or unverifiable vaccination history
Low vaccination coverage in the community

Pathophysiology

After an infected bite the virus replicates in lymph nodes and spreads through the blood. It targets the liver, causing midzonal hepatocyte necrosis with apoptotic hepatocytes (Councilman bodies), which produces jaundice and coagulopathy. Kidney injury, myocardial damage and a cytokine storm with capillary leak lead to bleeding and shock in severe cases.

Classification

Asymptomatic or mild infection
Acute (infection) phase: fever, myalgia, headache
Period of remission lasting hours to a day or two
Toxic (intoxication) phase: jaundice, haemorrhage, liver and kidney failure

Symptoms and signs

Sudden fever, chills, headache and back and muscle pain
Nausea, vomiting and marked weakness
Relative bradycardia despite high fever (Faget sign)
In the toxic phase: jaundice, abdominal pain and recurrent fever
Bleeding from gums, nose or gut (black vomit), and reduced urine output

Diagnosis

Clinical: Fever with jaundice or bleeding in someone with exposure in an endemic area and no verified vaccination. Every suspected case must be notified to the public health surveillance system.
Tests: RT-PCR on blood in the first days; later, IgM ELISA confirmed by neutralisation tests (PRNT) because of cross-reaction with other flaviviruses. Very high transaminases (AST often higher than ALT), raised bilirubin, prolonged clotting times, thrombocytopenia, rising creatinine and proteinuria. Histology (post mortem) shows midzonal necrosis and Councilman bodies.
Imaging: Not diagnostic. Abdominal ultrasound may be used to exclude biliary obstruction.

Differential diagnosis

Dengue (severe dengue)
Severe malaria
Leptospirosis (Weil disease)
Acute viral hepatitis
Other viral haemorrhagic fevers and toxic hepatitis

Goal of treatment

There is no specific antiviral. Care aims to support the patient through the acute illness: keep hydration and perfusion, correct bleeding and coagulopathy, protect liver and kidney function, and treat secondary infections.

Treatment

Acute: Hospital supportive care: fluids, control of fever with paracetamol (avoiding aspirin and NSAIDs because of bleeding risk), blood products for haemorrhage and coagulopathy.
Acute: Intensive care for the toxic phase: vasopressor support, dialysis for acute kidney injury, management of liver failure and encephalopathy.
Medical: Antibiotics for secondary bacterial infections; experimental antivirals only within research protocols.
Follow-up: Close monitoring of vital signs, urine output, bleeding, glucose, liver tests and clotting; mosquito net for the patient during the viraemic phase to avoid further transmission.

Complications

Fulminant hepatitis and liver failure
Acute kidney injury
Haemorrhage and disseminated intravascular coagulation
Myocarditis, arrhythmias and shock
Secondary bacterial infection and death

Prognosis

Most people with the mild form recover fully and gain lifelong immunity. Up to about half of those who enter the toxic phase die, usually within 7 to 10 days.

Prevention

Vaccination with the live attenuated vaccine; one dose gives lifelong protection for most people
Vaccination at least 10 days before travel to risk areas, with the international certificate
Mosquito control and protection from bites (long sleeves, repellent, nets)
Prompt notification of suspected cases to trigger outbreak control

Test yourself

Think of the answer, then tap the question to see it.

Which liver finding is classic in yellow fever?

Midzonal (zone 2) hepatocyte necrosis with apoptotic eosinophilic hepatocytes called Councilman bodies.

What is the Faget sign?

Relative bradycardia: a pulse slower than expected for the height of the fever.

Which mosquitoes transmit sylvatic yellow fever in South America?

Haemagogus and Sabethes species; Aedes aegypti drives the urban cycle.

What is the main measure to prevent yellow fever?

Vaccination with the live attenuated vaccine, which gives long-lasting immunity after a single dose in most people.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Yellow fever (World Health Organization (WHO), 2025); Fiebre Amarilla (Ministerio de Salud y Protección Social de Colombia, 2025).

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Representative model, for educational purposes only.

Liver highlighted on the Durgical 3D model