Carlos Juan Finlay
1833-1915
Cuban Physician, Epidemiologist and Public Health Reformer
Although the American physician Walter Reed (1851-1902) is generally associated with the discovery of the means of transmission of yellow fever, it was the Cuban physician Carlos Juan Finlay who first provided evidence that the Aedes egypti mosquito served as the vector of the disease. Yellow fever was one of the most feared epidemic diseases of the nineteenth century. An understanding of the means of transmission of the disease led to a fairly high level of control over the disease and was instrumental in the successful completion of the Panama Canal.
Finlay was born in Camagüey, Cuba. His father was a Scottish physician and his mother was French. Finlay attended schools in France and Germany before enrolling at Jefferson Medical College in Philadelphia. While a medical student, Finlay became interested in Professor John Kearsly Mitchell's suggestion that an unseen botanical agent was the cause of tropical fevers. After obtaining his M.D. degree in 1855, Finlay continued his training in Paris. He returned to Cuba in 1863, where he established a private practice and pursued his interest in public health medicine.
Yellow fever was one of the most feared epidemic diseases of the nineteenth century. The disease was endemic in the Caribbean islands, but outbreaks also occurred in North America. Almost nothing was known about the cause of the disease or its means of transmission, and preventive measures seemed futile. In 1879 an official U.S. Yellow Fever Commission was sent to Cuba for an investigation. The Spanish government appointed Finlay to serve as the local liaison officer. After his participation in the work of the commission, Finlay developed new ideas about the disease and began his preliminary investigations.
At the International Sanitary Conference held in Washington, D.C., in 1881 Finlay pointed out the futility of the sanitary measures being used to fight the spread of yellow fever. He believed that an intermediate agent transmitted the disease from the sick to the healthy and that effective control measures would require the destruction of this vector. Finlay suspected that a mosquito served as the vector of yellow fever. After considering the characteristics of various species, he decided to investigate the Culex mosquito(Aedes aegypti), a nocturnal insect with a short flight span. Finlay collected eggs, hatched them, and allowed selected mosquitoes to bite patients with yellow fever. To confirm his hypothesis he needed non-immune volunteers who would allow themselves to be bitten by the infected insects.
Finlay obtained permission from the military authorities to inoculate soldiers who had recently arrived from Spain. Finlay eventually inoculated over one hundred volunteers, but the results were not always consistent. In 1894 Finlay presented his results and his recommendations for the control of yellow fever at the Eighth World Congress of Hygiene and Demography. He suggested that patients should be isolated, houses should be fumigated to keep away mosquitoes, and potential mosquito breeding sites should be eliminated.
In 1897 Giuseppe Sanarelli claimed to have discovered a bacterial agent that caused yellow fever. The Surgeon General of the U.S. Army appointed a Board to study the infectious diseases of Cuba. The Board included Major Walter Reed, James Carroll (1854-1907), Jesse Lazear (1866-1900), and Aristides Agramonte (1869-1931). The Board quickly discovered that Sanarelli's alleged causal agent was simply a bacillus frequently found in cadavers.
On August 1, 1900, the members of the Board visited Finlay, who gave them the eggs of the mosquito that seemed to be the vector of yellow fever. Lazear hatched the eggs and allowed the mosquitoes to bite yellow fever victims. Lazear then allowed the mosquitoes to bite several volunteers, including Carroll and himself. Carroll recovered from a severe case of yellow fever, but Lazear died. In October 1900, at a meeting of the American Public Health Association, Reed announced that a mosquito was the intermediate agent of yellow fever.
When he returned to Havana, Reed directed a program of controlled experiments that provided proof for Finlay's hypothesis. Leonard Wood (1860-1927), a physician who was serving as Military Governor of Cuba, called the confirmation of Finlay's doctrine the most important step forward in medicine since the discovery of the smallpox vaccination by Edward Jenner (1749-1823). Major William Gorgas (1854-1920) also praised Finlay and used the methods Finlay had suggested in the battle against yellow fever in Cuba and Panama.
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