Where did yellow fever get started?
The virus that causes yellow fever probably evolved from an earlier virus that didn’t make people sick. The first cases of yellow fever may have been in East or Central Africa. But people in West Africa were catching yellow fever by 1600 AD. Like most sicknesses, yellow fever slowly became a disease most people caught as children. If you got it when you were a child, it didn’t make you very sick, and then you couldn’t catch it again.
How did yellow fever spread to the Americas?
When slave traders forced people from West Africa to travel to North and South America in the 1600s to work as slaves, apparently some of them had yellow fever. So the virus came to the Americas with them. But in the Americas, people hadn’t had yellow fever when they were children. They caught it as adults, and it made them very sick.
How did you catch yellow fever?
You caught yellow fever when a mosquito bit an infected person and then bit you. If you caught yellow fever, you got a sudden fever and headache. Most people slowly got better, but about a third of the people who caught yellow fever got bad cases.
What happens when you get yellow fever?
If you got a bad case of yellow fever, you became extremely tired and began bleeding into the skin. You got a slow heartbeat, back pains, and vomiting. Then your liver stopped working, and your skin turned yellow with poisons that your liver couldn’t filter out (That’s why it’s called yellow fever). About half the people who got bad cases, or one out of every seven people who caught yellow fever, died.
Yellow fever epidemics in the Americas
When mosquitoes bit these African people, they spread yellow fever to other people. In 1648, yellow fever killed a lot of people in the Maya country. In 1685, it killed a lot of people in Brazil. And in 1793, an epidemic of yellow fever killed a lot of European colonists in Philadelphia. People in Philadelphia thought African-Americans couldn’t catch yellow fever, but really it was only people born in Africa, who had had it as children, who were immune. Black Americans, born in the Americas, did catch yellow fever just like white people, and many died of it.
A vaccination against yellow fever
In 1881, Carlos Finlay, a Cuban doctor, suggested that mosquitoes might be spreading yellow fever, and when Walter Reed’s experiments showed he was right, people began to work hard to get rid of the mosquitoes. This effort stopped most of the yellow fever epidemics.
In 1937, Max Theiler, who was originally from South Africa but was working in New York, invented a vaccination against yellow fever. Because of the vaccination, and programs to control mosquitoes, not very many people catch yellow fever anymore, though there’s still no cure for yellow fever if you do get it.