Yellow fever is a viral infection transmitted by the bite of infected mosquitoes, primarily in tropical regions of Africa and South America. The disease can range from mild flu-like symptoms to severe liver disease with bleeding and jaundice (yellowing of the skin and eyes). Despite being preventable through vaccination, yellow fever remains a serious public health concern in many parts of the world.
What Is Yellow Fever?
Yellow fever is caused by the yellow fever virus (YFV), a Flavivirus transmitted mainly by Aedes aegypti and Haemagogus mosquitoes. The term “yellow” refers to the jaundice that develops in severe cases due to liver involvement.
The infection affects humans and certain species of monkeys, making it a zoonotic disease (transmissible between animals and humans).
How Is Yellow Fever Transmitted?
Yellow fever is spread through the bite of an infected mosquito. The transmission occurs in three main cycles:
- Jungle (Sylvatic) Cycle:
The virus spreads between mosquitoes and monkeys. Humans become infected when bitten while visiting or working in forests. - Intermediate (Savannah) Cycle:
Occurs in rural areas where both humans and monkeys are bitten by infected mosquitoes. - Urban Cycle:
Involves human-to-human transmission through Aedes aegypti mosquitoes in densely populated areas. This is responsible for large outbreaks.
Symptoms of Yellow Fever
Symptoms typically appear 3 to 6 days after infection. The illness has two phases:
1. Early (Acute) Phase
- Sudden onset of fever and chills
- Headache and muscle pain, especially in the back
- Fatigue and weakness
- Loss of appetite
- Nausea or vomiting
Most patients recover after this phase, but about 15–20% progress to the next stage.
2. Toxic Phase (Severe Stage)
- High fever recurrence
- Jaundice (yellowing of skin and eyes)
- Abdominal pain and vomiting, sometimes with blood
- Bleeding from nose, mouth, or eyes
- Liver and kidney failure
The toxic phase can be fatal in 30–60% of severe cases if left untreated.
Diagnosis
Diagnosis is based on clinical symptoms and confirmed through laboratory tests such as:
- Blood tests to detect antibodies (IgM and IgG) against yellow fever virus
- Polymerase Chain Reaction (PCR) for viral RNA detection
- Liver function tests showing elevated bilirubin and liver enzymes in severe cases
Accurate diagnosis is crucial, as symptoms may resemble other infections like malaria, dengue, leptospirosis, or viral hepatitis.
Treatment of Yellow Fever
There is no specific antiviral treatment for yellow fever. Management focuses on supportive care to relieve symptoms and prevent complications.
Supportive Measures Include:
- Adequate hydration to prevent dehydration
- Pain and fever control with paracetamol (avoid aspirin due to bleeding risk)
- Monitoring of liver and kidney function
- Hospitalization for severe cases to manage bleeding and organ failure
In advanced cases, intensive care may be needed to support vital organs.
Prevention of Yellow Fever
The best protection against yellow fever is vaccination and mosquito control.
1. Vaccination
- A single dose of the yellow fever vaccine provides lifelong immunity for most people.
- It is recommended for individuals aged 9 months and older living in or traveling to endemic regions.
- Proof of vaccination (Yellow Card) may be required for international travel to certain countries.
- The vaccine should be given at least 10 days before travel to allow the body to build immunity.
2. Mosquito Bite Prevention
- Use mosquito repellents containing DEET or picaridin.
- Wear long-sleeved clothing and pants.
- Sleep under insecticide-treated nets.
- Avoid areas with high mosquito activity, especially during the day.
- Eliminate stagnant water to reduce mosquito breeding sites.
Complications of Yellow Fever
Severe yellow fever can lead to:
- Liver failure and jaundice
- Kidney failure
- Internal bleeding
- Septic shock
- Death (in about 20–50% of severe cases)
Survivors may experience fatigue and weakness for several weeks after recovery.
Global Distribution and Risk
Yellow fever is endemic in 44 countries across Africa and South America, where climatic conditions favor mosquito breeding.
Outbreaks occur primarily in:
- Sub-Saharan Africa (e.g., Nigeria, Ghana, Sudan)
- South America (e.g., Brazil, Peru, Colombia)
The World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) emphasize vaccination campaigns and vector control as key strategies to eliminate yellow fever epidemics.
When to See a Doctor
Seek immediate medical attention if you develop:
- High fever and jaundice
- Bleeding from gums or nose
- Severe vomiting or abdominal pain
- Recent travel to endemic areas
Early diagnosis and supportive management greatly improve outcomes.
Conclusion
Yellow fever is a preventable yet potentially deadly viral disease transmitted by mosquitoes. Vaccination remains the most effective defense, offering lifelong protection. Travelers to endemic regions should ensure they are vaccinated and take preventive measures to avoid mosquito bites. Awareness, early diagnosis, and global immunization programs play a vital role in controlling and ultimately eliminating yellow fever.
