Havana, Cuba, 1881.
Yellow fever was a terrible disease. It came with a high fever and pain, and sometimes the patients' skin turned yellow. In Havana many people died of it every year, and no one knew how it spread.
Many doctors thought the disease traveled in dirty air, or in the clothes and beds of the sick. So they burned clothes and cleaned houses. But the disease kept spreading.
The problem was not only Cuba's. Yellow fever also struck other ports in the Americas, such as New Orleans, in the United States.
Carlos Finlay was a Cuban doctor. He had been born in Cuba, the son of a Scottish doctor and a French mother, and he had studied medicine in Philadelphia, in the United States. He was calm, patient and very observant. He studied his patients carefully and wrote everything down in his notebooks. When he was not seeing patients, he watched insects for hours.
Finlay began to suspect a small insect that was everywhere: the mosquito. What if the mosquito bit a sick person and then a healthy one? What if the mosquito was the culprit?
In February 1881 he traveled to Washington, to an international health conference. There he explained that yellow fever needed an "agent" to pass from one person to another. According to his biographers, when he finished, no one asked a single question. For Finlay it was a hard moment: he had traveled a long way to present his idea, and no one seemed interested.
In August of that year he presented his work in Havana, with a very long title: "The Mosquito Hypothetically Considered as the Transmitting Agent of Yellow Fever."
Some people made fun of him. A mosquito? What an absurd idea! For many doctors, such a tiny insect could not cause so many deaths.
But Finlay did not stop investigating. For almost twenty years he kept studying mosquitoes and writing about his theory, even though almost no one listened to him.
In 1900 everything changed. The United States Army was in Cuba, and yellow fever was killing many soldiers. Washington sent a group of doctors led by Dr. Walter Reed. The doctors visited Finlay, and he explained his theory to them.
Reed's group carried out experiments with volunteers. Some slept for twenty nights in beds and clothes used by sick people, but with no mosquitoes. They did not get sick. Others were bitten by mosquitoes. Many of them did get sick.
It was dangerous work. One doctor in the group, Jesse Lazear, died of yellow fever in 1900.
But the experiments confirmed that Finlay was right: the mosquito was the culprit.
With that information, the authorities got rid of the places where mosquitoes bred, such as still water in barrels and puddles. Yellow fever almost disappeared from Havana. And a few years later, in Panama, the same method helped achieve something enormous: building the canal. Without mosquitoes, thousands of workers could live and work in the jungle.
But in many books, the most famous name was Walter Reed's, even though the idea was Finlay's. Many people forgot Finlay. Reed, however, acknowledged in his writings that the idea had been Finlay's.
Finlay was nominated for the Nobel Prize seven times. He never won it. He died in Havana in 1915, at the age of eighty-one. Today, every December 3, the day he was born, several Latin American countries celebrate Doctor's Day in his honor.
Today, every campaign against mosquitoes follows his idea. Carlos Finlay was right… even though almost no one believed him.