Yellow fever
Yellow fever is a vaccine-preventable viral disease spread by mosquitoes that can range from a mild fever to severe liver disease, bleeding, shock, and death.
What yellow fever is
Yellow fever is an acute viral disease that circulates in parts of Africa and South America. Many infections are mild or go unnoticed, but some people develop severe disease after an initial fever improves. Severe yellow fever can damage the liver and kidneys, cause bleeding, and progress quickly.
How mosquitoes spread it
The virus spreads when infected mosquitoes bite people or other primates. Transmission can follow different patterns: forest cycles involving monkeys and wild mosquitoes, intermediate cycles near forest edges or savannas, and urban cycles where Aedes aegypti mosquitoes spread the virus among people. Urban spread is especially dangerous because it can move fast in places with low vaccination coverage.
Symptoms
Early symptoms can include fever, chills, severe headache, back pain, body aches, nausea, vomiting, fatigue, and weakness. Some people recover after this phase. Others enter a more toxic phase with high fever, jaundice, abdominal pain, vomiting, bleeding, kidney problems, shock, or organ failure.
Diagnosis
Yellow fever can resemble malaria, dengue, leptospirosis, viral hepatitis, and other hemorrhagic fevers. Diagnosis depends on symptoms, travel or residence history, vaccination history, and laboratory testing. Because the disease can be serious and outbreaks have public-health consequences, suspected cases need prompt medical and public-health attention.
Treatment
There is no widely used specific antiviral treatment for yellow fever. Care focuses on supporting the body while the illness runs its course: fluids, fever control, treatment of complications, and hospital care for severe disease. People with suspected yellow fever should avoid mosquito bites for several days after symptoms begin so local mosquitoes do not pick up and spread the virus.
Vaccination
Yellow fever vaccine is a live attenuated vaccine used for personal protection and outbreak control. A single dose provides long-lasting protection for most people, though some travelers and people with certain medical conditions need individualized advice. Because the vaccine is live, clinicians screen for age, immune status, allergies, pregnancy, and other factors before giving it.
Travel and certificates
Some countries require proof of yellow fever vaccination for entry, especially for travelers arriving from places with transmission risk. The International Certificate of Vaccination or Prophylaxis is often called the yellow card. Entry requirements can change, so travelers should check destination-specific guidance before departure rather than relying on old advice.
Why it matters
Yellow fever has shaped public health, urban planning, military history, and travel medicine. The vaccine is highly effective, yet outbreaks still occur when vaccination gaps, mosquito exposure, forest spillover, and delayed detection line up. That makes yellow fever a reminder that prevention systems need maintenance even when a disease is familiar.
What public health teams watch
Surveillance looks for human cases, unusual monkey deaths, mosquito activity, vaccination coverage, and travel-related risk. Outbreak response can include emergency vaccination campaigns, mosquito control, risk communication, and cross-border coordination. Climate, land use, urban growth, and vaccine supply all influence future risk.