Yellow Fever: Causes, Symptoms and Vaccination

What Is Yellow Fever?

Yellow fever is an acute, potentially life-threatening infectious disease caused by the yellow fever virus, a member of the Flavivirus family. The name comes from the characteristic yellowing of the skin and eyes (jaundice/icterus) that occurs in severe cases due to liver damage. The disease is endemic in tropical and subtropical regions of Africa and South America and is classified as a tropical disease.

Causes and Transmission

The yellow fever virus is transmitted exclusively through the bite of infected mosquitoes, primarily of the species Aedes aegypti and Haemagogus. Direct person-to-person transmission does not occur. Three transmission cycles are distinguished:

• Sylvatic (jungle) cycle: The virus circulates between monkeys and mosquitoes in the rainforest. Humans are occasionally infected through mosquito bites.
• Intermediate cycle: Mosquitoes transmit the virus between monkeys and humans in areas bordering rainforests.
• Urban cycle: Urban mosquitoes (Aedes aegypti) transmit the virus between humans in densely populated areas, which can lead to large outbreaks.

Symptoms

The course of the disease is divided into two phases:

Acute Phase (first 3–4 days)

• Sudden onset of high fever
• Chills, headache, and muscle pain
• Nausea and vomiting
• Facial flushing
• Sensitivity to light

Toxic Phase (in severe cases)

Approximately 15% of patients develop a severe form of the disease after a brief period of improvement:

• Jaundice (icterus) due to liver failure
• Dark urine and bloody vomiting
• Hemorrhagic fever with internal bleeding
• Kidney and heart failure
• Delirium and loss of consciousness

The case fatality rate during the toxic phase ranges from 20–50%.

Diagnosis

Diagnosis is based on a combination of clinical examination, travel history, and laboratory tests:

• PCR test (polymerase chain reaction): Direct detection of the virus in the blood during the early phase of illness.
• Serology: Detection of antibodies (IgM and IgG) against the yellow fever virus.
• Blood count and liver function tests: Elevated transaminases, bilirubin, and coagulation disorders indicate a severe course.

Treatment

There is currently no specific antiviral therapy for yellow fever. Treatment is symptomatic and supportive:

• Fever reduction and pain relief (aspirin should be avoided due to bleeding risk)
• Adequate fluid intake and electrolyte replacement
• Intensive care monitoring in severe cases
• Support of liver and kidney function
• Blood transfusions for severe bleeding

Vaccination and Prevention

The most effective prevention is the yellow fever vaccine. The live attenuated vaccine (17D strain) generally provides lifelong protection after a single dose. The World Health Organization (WHO) recommends vaccination for all travelers to endemic areas. Many affected countries require proof of yellow fever vaccination in the form of an International Certificate of Vaccination for entry. Additional preventive measures include:

• Use of mosquito repellents (DEET, icaridin)
• Wearing long, light-colored clothing
• Use of mosquito nets, especially during evening and nighttime hours

References

1. World Health Organization (WHO): Yellow fever – Fact Sheet. Geneva, 2023. Available at: https://www.who.int/news-room/fact-sheets/detail/yellow-fever
2. Robert Koch Institute (RKI): RKI Advisory: Yellow Fever. Berlin, 2022. Available at: https://www.rki.de/DE/Content/Infekt/EpidBull/Merkblaetter/Ratgeber_Gelbfieber.html
3. Monath TP, Vasconcelos PF: Yellow fever. J Clin Virol. 2015;64:160–173. PubMed PMID: 25453327.