Yellow fever is an acute viral disease found in tropical regions of Africa, Central America and South America. The yellow fever virus is transmitted by infected mosquitoes. It can be challenging to distinguish from other viral diseases like arenavirus, hantavirus, or dengue.
Yellow fever occurs in 47 endemic countries in Africa and in Central and South America. Around 90% of cases reported every year occur in Sub-Saharan Africa.
In the Americas, 13 countries and territories (Argentina, Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Panama, Paraguay, Peru, Suriname, Trinidad and Tobago, and Venezuela) are considered at-risk because that is where outbreaks and deaths have been recorded.
Infected travelers from areas where yellow fever occurs can export cases to countries that are free of yellow fever, but the disease can only spread easily if that country has the mosquito species capable of transmitting it, specific climatic conditions, and the animals that allow the virus to continue existing.
Yellow fever is spread by mosquitoes infected with the yellow fever virus.
The mosquitoes that transmit yellow fever belong to the Haemagogus and Sabethes genera (primarily found in tropical rainforests) or the Aedes aegypti species (the same mosquito that spreads Zika, chikungunya, and dengue). All these mosquitoes are part of the Culicidae family.
In tropical rainforests, monkeys can be bitten by wild mosquitoes and get the disease, passing the virus on to other monkeys. Sometimes, people who are working or traveling in the forest can also be bitten by these mosquitoes and catch yellow fever.
In areas close to cities, the same mosquitoes can bite monkeys and then bite people, spreading the virus from monkeys to humans.
Big outbreaks of yellow fever can happen in crowded places where there are lots of Aedes aegypti mosquitoes. No recent outbreaks of urban yellow fever have been reported in the Americas.
Once a person contracts the yellow fever virus, it stays in their body for 3 to 6 days. The most common symptoms are fever, muscle pain with prominent backache, headache, shivers, loss of appetite, and nausea or vomiting. Most patients improve and their symptoms disappear after 3 to 4 days.
However, a small percentage of people enter a more toxic second phase within 24 hours after the initial symptoms disappear. They will experience high fever, jaundice, and abdominal pain with vomiting and deteriorating kidney function. Bleeding can occur from the mouth, nose, eyes, or stomach, with blood appearing in vomit and feces. Half of the patients who enter the toxic phase die within 10 to 14 days, the rest recover without significant organ damage.
There is no specific treatment for yellow fever, but early identification, monitoring for signs of severity, good supportive care, and treatment of complications improves survival rates.
Yellow fever can be prevented through vaccination. The yellow fever vaccine is extremely effective and provides lifelong protection.
Yellow fever confirmation requires laboratory testing because its symptoms can be confused with other common diseases such as malaria, dengue, leptospirosis and Zika virus, as well as with poisoning. Doctors or clinicians who see a sick patient may not be able to tell that they have yellow fever from their symptoms alone, especially if they are in an area where many of these diseases are occurring at the same time.
If you experience yellow fever symptoms, seek medical attention to receive the proper treatment.
Vaccination is the most important way to prevent yellow fever. The yellow fever vaccine is safe and affordable, and a single dose provides life-long immunity against the disease.
Mosquito control can also help to prevent yellow fever transmission in urban settings. To control mosquitoes, it's important to eliminate places where they can breed and use insecticides to kill adult mosquitoes and larvae in areas with lots of mosquitoes. Community efforts, like cleaning out household drains and covering water containers for domestic use are very effective.