Lazear, Jesse William (1866-1900), was an American physician and bacteriologist who, as part of a commission on yellow fever, made one of the most significant discoveries in tropical medicine—that the disease was transmitted by the mosquito, of the species now known as Aedes aegypti.

After graduating from Columbia University College of Physicians and Surgeons, Lazear worked for a time in the Pasteur Institute in Paris, before returning to the United States, where he conducted bacteriological research at Johns Hopkins School of Medicine. At that time, scientists knew the symptoms of yellow fever, and ways of controlling it, but did not know its cause. They knew that fomites, articles of clothing and bedding used by those infected, did not transmit the disease. When, in 1900, an outbreak of the disease occurred in the U.S. army garrison located in Havana, Cuba, a medical team of four, the Yellow Fever Commission, was sent there to investigate.

Led by Army surgeon Walter Reed, and including Lazear as an assistant surgeon, the commission studied several victims and soon suspected that the cause of transmission might be the mosquito, although the virulent species had not yet been identified. To test this theory, several volunteers, including Lazear and another team physician, James Carroll, willingly allowed themselves to be bitten by infected mosquitoes. Carroll came down with a severe case of yellow fever but ultimately survived. Lazear was bitten by an infected mosquito and died after seven days of illness.

In 1929, Congress awarded the Congressional Gold Medal to the volunteers of the Yellow Fever Commission. Additionally, a gold plaque exists in Baltimore's Johns Hopkins Hospital naming Lazear for his “courage and devotion,” also noting that “he risked and lost his life to show how a fearful pestilence is communicated and how its ravages may be prevented.”