Carlos Finlay: Cuban Physician Who Identified Carrier of Yellow Fever

The method by which yellow fever spread was proposed by Dr. Carlos Finlay (1833-1915), a Cuban physician. It took twenty more years for the Reed Board (Army Surgeon Walter Reed) to definitively prove Finlay’s theory that the disease was carried by the mosquito. Once scientists understood this, they could move forward to reduce the incidence of yellow fever in tropical climates.

In the United States, this was important in the southern states where the weather was often subtropical. The discovery was also crucial in Panama where the U.S. invested heavily to build a canal to reduce the shipping time of goods from the East to California and the West.

About Yellow Fever

Yellow fever was a terrifying disease in the 17^th, 18^th and 19th centuries. The illness was devastating—killing many and sickening even more. Because so many people got sick, economic disruption inevitably followed. Communities were terrified of outbreaks.

Yellow fever predominated in tropical areas of Africa and Central and South America, but it sometimes spread to parts of the United States.

Today there is an effective vaccine, but the search for a way to prevent it or treat it took on more urgency in the late 1800s and early 1900s. People were moving into regions where yellow fever outbreaks occurred.

The spread of disease frequently interrupted construction of the badly-wanted Panama Canal.  After 22,000 deaths, the French company attempting to build it pulled out.

Studying the Illness

Scientists saw that they could not prevent the illness unless they learned how it traveled from person to person. Belief in germ theory was still relatively new, so while some doctors felt better sanitation would help reduce spread of the disease, others returned to an old theory that illness traveled by miasma (bad air). As late as 1898, a Marine Hospital Service Report wrote that better management of “railway travel” would help reduce the incidence of the disease. Among their recommendations were that rail cars should have cane seats instead of upholstery. This fell under the belief that inanimate objects could spread the disease.

About Carlos Finlay

Finlay was born in 1833 in Puerto Principe (now Camagüey), Cuba. His mother was French and his father, a doctor, was Scottish. The couple relocated to Cuba before his birth and embraced the country as their own, but as their son became old enough for school, they sent him to Europe for his education.

Twice he returned to Cuba for a prolonged period because of illness. When he eventually finished the equivalent of secondary education in Europe, he attended Jefferson Medical College in Philadelphia for his medical degree.

In 1855 he returned to Havana to establish a medical practice. Finlay was known as a kindly man who would not turn away patients even when they could not pay.

Finlay was also a devoted scientific researcher and was fascinated by epidemiology. Cuba often had outbreaks of yellow fever and malaria, and Finlay spent his spare time trying to find the cause. His focus was on yellow fever.

Focus on Yellow Fever

During the 1870s, Finlay noticed that yellow fever cases spiked in areas where the mosquito population was high. He theorized that perhaps a mosquito was the carrier (vector) of the disease.

In 1881, he was invited to present a paper to the International Sanitary Commission that was meeting in Washington, D.C.  His talk put forward his belief that the vector for yellow fever was the mosquito. Finlay identified the Culex (now Aedes aegypti) mosquito as the specific carrier. While some took his report under consideration, many were derisive in their comments.  One reason for skepticism was likely because at that time, only one relatively rare illness– filariasis, caused by the parasitic roundworm–was thought to be spread by mosquito.

Though he was disappointed that no one stepped in to do more research, he stayed in Havana to continue his medical practice and progress on his scientific research. He ultimately contributed at least 40 articles on the disease. 

Americans Take More Interest

Yellow fever outbreaks had occurred in the United States in New Orleans, Mississippi and even Philadelphia. The United States became more interested in understanding yellow fever after many Americans fighting in the Spanish-American War became ill with yellow fever. (The Spanish, too, suffered greatly.)  The United States also wanted the Panama Canal to be finished. Thus far, disease kept halting progress.

Since the 1850s, America and parts of Europe wanted a faster trade route through Central America to avoid the long voyage by ship around Cape Horn. In 1881, the French attempted to span Panama with a canal which would greatly speed the trip. They brought with them the experience of having built the Suez Canal, but they found the engineering challenges in Panama to be far greater than those they had addressed in Egypt.

But it was tropical disease that ultimately halted progress. Both the French engineers and the local labor force suffered mightily from various tropical diseases, particularly yellow fever and malaria.  From 1881-1889 (the duration that France spent trying to build the canal), it is estimated that over 22,000 people died.  Finally the French abandoned their efforts.

Study Needed

At this point, the U.S. medical establishment decided to put some heft behind the need to better understand yellow fever. Army doctors heard Finlay’s theory of the mosquito as vector, but they wanted a doctor or scientist of their own to study the matter.

In 1900, the U.S. Army asked Major Walter Reed (1851-1902) to head a board to study the issue. Reed included assistant surgeons James Carroll, Jesse W.Lazear, and Aristides Agramonte. Reed and James Carroll traveled to Cuba to meet up with doctors Agramonte and Lazear who were already there.

Initially, Reed’s board discounted Finlay’s theory and focused on trying to identify the orgaanism that caused the disease. But they were still without answers. Finally, the doctors turned to Finlay’s research. By this time he had almost 30 years of scientific information.

While Reed was back in Washington on official business, Lazear began mosquito experiments on human volunteers, but Lazear became ill with yellow feer and died. It was believed by those present that he experimented on himself. On Dr. Reed’s return, he went through all of Lazear’s materials and continued the trials with human volunteers.

Dr. Walter Reed is often given credit for this initial break-through, but Dr. Reed was always first to say that they could not have accomplish what they did if it hadn’t been for Carlos Finlay’s work.

The next task was to apply this theory and reduce the mosquito population to halt spread of the disease. This was quickly accomplished in Havana by Army physician William Crawford Gorgas.

The United States Takes Over

When the United States took over the Panama project (1901-1902), they were well aware that 22,000 people died working on the canal in the 1880s, and that 12,000 more people died while working through the same terrain building the Panama Railway (1850s). But now the United States had knowledge on their side.

The Walter Reed Board confirmed what Dr. Finlay had long been telling everyone. Reduce the mosquito population to cut the incident rate of disease.

The Americans now knew that additional preparation and planning were necessary to finish the canal.  U.S. Army physician Dr. William Gorgas (1854-1920) was brought in to implement a sanitation program so that the area would be habitable for humans. A full-scale effort was made to eliminate as many mosquito breeding locations as possible.

Reducing Swamps and Wetlands

Swamps and wetlands around the Canal Zone were filled in, and Gorgas divided Panama into multiple districts so that inspectors could check regularly for stagnant water. In addition, he ordered that sleeping quarters be built with screens so that the workers were protected during the night when the mosquito population is most active.

He also experimented with fumigating buildings where people with yellow fever had been housed. Pans of sulfur or pyrethrum were placed in areas where yellow fever had taken root and the powder in the pans was set on fire. The smoke proved effective at reducing the mosquito population within buildings.

The final measure implemented under Dr. Gorgas involved quarantine of an individual if someone did become sick.  The patient was transported to screened structures that prevented future mosquito bites so that the disease could not be spread from an infected individual.

Finlay’s knowledge, Reed’s successful trials, and Gorgas’s work made the building of the Panama Canal possible. This was to change the course of American transport and greatly speed access to the West.

Finlay Finally Recognized

Carlos Finlay was viewed as a hero in Cuba, but recognition elsewhere came later—fortunately still within his lifetime.  Finlay was nominated seven times for the Nobel Prize in Physiology, though he never was awarded it. However in 1908 he received the Legion of Honour from France.

There is a memorial to him in Havana and a statue of him in Panama City near the canal, the canal he made possible.

But best of all was certainly the statement made by General Leonard Wood, the U.S. military governor of Cuba from 1898 to 1902: “The confirmation of Dr. Finlay’s doctrine is the greatest step forward made in medical science since Jenner’s discovery of the vaccination.”

Finlay concluded his career as the Chief Sanitary Officer of Cuba, a position he held for eight years before retiring in 1909.

****A special thank you to Army physician John R. Pierce, M.D., who took the time to point out some issues in my original article about Finlay and then didn’t give up on me! Thank you, John.

To read about a young American girl and her family who traveled across the Isthmus of Panama before there was a canal and before the railroad was finished, click on Traveling West in 1854.

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