Yellow fever is caused by the yellow fever virus, transmitted through the bite of infected Aedes or Haemagogus mosquitoes. The virus is endemic in tropical regions of Africa and Latin America.
The yellow fever virus circulates between mosquitoes and primates. Humans become infected when bitten by a mosquito carrying the virus. The virus then replicates in the body, leading to symptoms ranging from mild illness to severe disease with bleeding and organ failure.
There are multiple strains of the yellow fever virus, but they are all part of the same species. The virus is classified within the Flavivirus genus, which also includes other mosquito-borne viruses like dengue, Zika, and West Nile virus.
| Region | Primary Mosquito Vector | Endemic Countries |
|---|---|---|
| Africa | Aedes aegypti | Angola, Burkina Faso, Cameroon, Ethiopia, Ghana, Kenya, Liberia, Nigeria, Sierra Leone, Sudan, Uganda |
| Latin America | Haemagogus spp. | Argentina, Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Panama, Peru, Suriname, Trinidad and Tobago, Venezuela |
Symptoms typically appear 3 to 6 days after infection. Initial symptoms include fever, chills, headache, back pain, muscle aches, nausea, vomiting, fatigue, and weakness. Most people improve after these symptoms, but about 15% develop severe symptoms within 24 hours, including high fever, jaundice, abdominal pain, vomiting (sometimes with blood), dark urine, and bleeding from the nose, mouth, eyes, or stomach.
The most effective protection against yellow fever is vaccination. The vaccine provides immunity for at least 10 years and is safe for children over 9 months and adults. Other preventive measures include using insect repellent, wearing protective clothing, and using mosquito nets.
In areas with outbreaks, public health authorities may implement mosquito control measures, such as spraying insecticides and eliminating standing water where mosquitoes breed. Travelers to endemic areas should get vaccinated at least 10 days before travel.
I once visited a region in Brazil where yellow fever was a concern. The local health authorities had set up vaccination stations at major entry points, and the vaccine was readily available. This proactive approach helped prevent outbreaks among tourists and locals alike.