Hektoen International

A Journal of Medical Humanities

Carlos J. Finlay: The mosquito man

Enrique Chaves-Carballo
Kansas City, Kansas, United States

Portrait Dr. Carlos J. Finlay
Portrait Dr. Carlos J. Finlay. From Images History of Medicine (IHM), National Library of Medicine.

Carlos Juan Finlay was born in Puerto Príncipe (now Camagüey), Cuba, on December 3, 1833. He was sent to Europe to complete his secondary education but was forced to return to Cuba after suffering a neurological illness (Sydenham’s chorea) and later a severe bout of typhoid fever. Finlay completed his medical studies at the Jefferson Medical College in Philadelphia in 1855 and trained in ophthalmology and internal medicine in Paris. Finally, he obtained authorization to practice medicine in Cuba in 1857.1

Yellow fever first arrived from Panama into Havana in 1620. Havana became a permanent endemic area and, according to William Gorgas, more than 20,000 persons died in the city during the thirty-year period from 1871 to 1900. By the end of the nineteenth century, Havana had secured its reputation as one of the pestholes of the New World.2

Finlay, despite his busy clinical practice, became interested in the dreaded yellow scourge. In 1865, he presented to the Royal Academy of Medical, Physical and Natural Sciences in Havana a lengthy report on “The Etiology of Yellow Fever” based on his meticulous daily observations of atmospheric alkalinity over a period of thirteen years. This supported the prevailing miasmatic theory of malignant vapors emanating from nearby swamps as the cause of diseases.3

In 1879, the United States sent the First Yellow Fever Commission to Havana.4 Finlay followed closely the work of the commission and examined microscopically the tissues of affected victims. Noting the characteristic hemorrhagic lesions seen in yellow fever, he reasoned that the causative agent must have been deposited within vessels and that the mosquito was admirably suited for that purpose. He studied the many varieties of mosquitoes found in Havana and concluded that one of these, Culex or Stegomyia fasciata (later named Aedes egyptii) was responsible for the transmission of yellow fever in humans, based on its preferred habitat and feeding habits.5 Finlay then proceeded with proper authorization from the military to inoculate twenty volunteers using infected mosquitoes.6 Some of the volunteers developed fever, jaundice, and albuminuria. Convinced that he was on the right track, Finlay presented on August 14, 1881, to the Royal Academy a paper entitled “The Mosquito Hypothetically Considered as the Agent of Transmission of Yellow Fever.”7 The audience responded with incredulity and ridicule. His colleagues called him derisively “the mosquito man.” Unfortunately, Finlay was unaware that mosquitoes could only become infected by biting a human within the first three days of the disease and that an incubation period of ten to fourteen days must elapse before the mosquito can transmit the disease after she has bitten an infected person.8 Therefore, Finlay was unable to reproduce a full-fledged case of yellow fever despite inoculations in more than 100 experimental subjects, including himself. Finlay was aided in this endeavor by his unfaltering colleague and disciple, Claudio Delgado, a Spaniard physician who was trained in hematology and bacteriology.

In 1900, Surgeon General George Sternberg sent a Fourth Yellow Fever Commission to Cuba consisting of Major Walter Reed and contract surgeons James Carroll, Arístides Agramonte, and Jesse Lazear.9 The commission decided to test Finlay’s mosquito hypothesis and conducted human experiments using for the first time an informed consent from volunteers. Using infected mosquitoes provided by Finlay, the first nine inoculations were unsuccessful. However, members of the commission agreed to participate themselves in these experiments. Carroll, who did not believe in the mosquito theory, developed a severe case but survived despite a chronic heart ailment. Lazear, who was bitten by a stray mosquito at Las Animas Hospital (where all yellow fever patients in Havana were hospitalized), succumbed to the disease. Additional experiments proved the crucial role of mosquitoes in the transmission of yellow fever. Reed announced the historic results on October 23, 1900, to worldwide acclaim at the annual meeting of the American Public Health Association in Indianapolis, acknowledging the invaluable contribution Finlay had made to this enterprise.10

Finlay received numerous honors for his patience and persistence despite adversity. His vast knowledge and likeable personality won him many friends and admirers. He was fluent in English, German, and French and could read the classics in Latin and Greek. Yet he was humble and his manners were those of a true gentleman. Gorgas praised Finlay in these terms: “Dr. Finlay is a most lovable man in character and personality, and no one could be constantly with him as I was daily for several years without becoming attached to him and forming the highest estimate of his scientific honesty and straightforwardedness.”11 Gorgas, however, did not subscribe to the mosquito vector theory and believed yellow fever resulted from filth and poor ventilation. He implemented an ambitious plan to thoroughly clean Havana, but despite his efforts an epidemic of yellow fever ravaged the city in 1900. Once the mosquito was identified as the culprit, Gorgas was able to sanitate Havana and the city became free of yellow fever for the first time in 150 years.

Leonard Wood, governor general of Cuba, recognized Finlay for his seminal contribution at a dinner at Delmonico’s in Havana in December 1900. He presented a bronze bust and boasted that “the confirmation of Dr. Finlay’s doctrine is the greatest step forward made by the medical sciences since Jenner’s discovery of the vaccination.”12 This was followed by numerous honors and monuments bestowed in Finlay’s name. France decorated him with the Legion of Honor. He received an honorary degree from Jefferson Medical College and became an honorary member of the College of Physicians of Philadelphia. He was awarded the Mary Kingsley Medal from the Liverpool School of Tropical Medicine and was nominated for the Nobel Prize in Physiology and Medicine by both Alphonse Laveran and Ronald Ross, independently.13 His Cuban colleagues, who once ridiculed and criticized him for his revolutionary ideas, eventually acknowledged his great contributions and awarded him the Cuban National Decoration and inaugurated a museum in Havana exhibiting his effigy and many publications.

Gorgas departed Cuba in 1902 after his successful campaign to sanitate Havana. Theodore Roosevelt then charged him with the unenviable task of ridding Panama of yellow fever to assure the successful completion of the Panama Canal. Finlay was named his successor as chief of the Cuban Sanitary Department. Following a gradual decline in his customary energetic and inquisitive character, Finlay died on August 20, 1915, at the age of eighty-two.

Finlay never faltered in his convictions. He met obstacles frequently throughout his life but overcame these with patience and tenacity. The “mosquito man” was the moniker given to him by his ridiculing colleagues but one that he probably held proudly as a just reward for his untiring efforts to conquer yellow fever.


  1. Finlay CE. Carlos Finlay and Yellow Fever. New York: Oxford University Press, 1940, 11-45.
  2. Gorgas WC. Sanitation in Panama. New York, D. Appleton & Co., 2015, 27.
  3. Finlay CJ. Alcalinidad atmosférica observada en la Habana. [Atmospheric alkalinity observed in Havana.] Annals of the Royal Academy of Medical, Physical and Natural Sciences of Havana. 1872;9:183-192.
  4. Finlay CE, op. cit., 56.
  5. Ibid., 58-75
  6. DelRegato JA. Carlos Juan Finlay (1883-1915). J Public Health Policy 2001;22:98-104.
  7. Finlay CJ. The mosquito hypothetically considered as the agent of transmission of yellow fever. Presented to the Royal Academy of Medical, Physical and Natural Sciences of Havana on August 14, 1881. Translated and reprinted in abridged form in Military Medicine 2001;166 (Suppl 1):6-10.
  8. Gorgas, Sanitation, 27.
  9. Kelly HA. Walter Reed and yellow fever. New York: McClure, Phillips & Co., 1906:120-153.
  10. Reed W, Carroll J, Agramonte A, Lazear JW. The etiology of yellow fever—A preliminary note. Presented to the American Public Health Association Annual Meeting in Indianapolis on October 22-26, 1900. Military Medicine 2001;166 (Suppl 1):29-37.
  11. Gorgas WC. Sanitation in Panama. New York: D. Appleton and Company, 1916, 15.
  12. Bean WB. Walter Reed. A Biography. Charlottesville: University Press of Virginia, 1982, 156-7.
  13. Chaves-Carballo E. Carlos Finlay and yellow fever. Mil Med 2005;170:881-885.

ENRIQUE CHAVES-CARBALLO, MD, is a pediatric neurologist and clinical professor emeritus, Department of History and Philosophy of Medicine, Kansas University Medical Center. He received his medical degree from the University of Oklahoma and trained in pediatrics and neurology at Mayo Clinic, Rochester, MN. His main research interest is the medical history of the Panama Canal and he has published several articles and books on tropical diseases, yellow fever, malaria, and Darling.

Highlighted in Frontispiece Volume 13, Issue 1 – Winter 2021

Fall 2020 |  Sections  |  Infectious Diseases

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