On 25 September 1900, a 34 year old American physician died in Cuba after developing yellow fever. His name was Jesse William Lazear and his death helped confirm how one of history’s deadliest epidemics spreads.
Lazear was part of a United States Army research team investigating yellow fever after the Spanish American War, when more soldiers were dying from disease than combat. He left behind his wife in Maryland, a one year old son and a newborn daughter he would never meet.
He had been bitten by a mosquito that had previously fed on a yellow fever patient. Soon after, he fell ill and died. His infection became the crucial proof that yellow fever is transmitted by mosquitoes, transforming public health worldwide.
Before arriving in Cuba, Lazear was already studying mosquito borne disease. He earned his medical degree in 1892 from the College of Physicians and Surgeons of Columbia University and later trained in Europe. He then worked at Johns Hopkins Hospital in Baltimore, where he studied the structure of the malarial parasite.
At a time when insect transmission of disease was still debated, this background made him uniquely prepared to investigate yellow fever.
Yellow fever originated in African rainforests and spread to the Americas through colonial trade routes. Outbreaks devastated tropical regions and major port cities across the Caribbean and the Americas.
After a three to six day incubation period, patients developed high fever, chills, headache, back pain and vomiting. About one in five progressed to liver failure, jaundice and internal bleeding, which was often fatal.
For centuries, scientists blamed contaminated objects or bad air. In 1881, Cuban physician Carlos Finlay proposed that mosquitoes spread the disease, but his idea was widely dismissed.
In June 1900, the United States Army formed a research team in Cuba consisting of Walter Reed, James Carroll, Aristides Agramonte and Jesse Lazear.
Initially they investigated a bacterial cause and proved it incorrect. Meanwhile malaria research had already shown insects could transmit disease, making Finlay’s mosquito theory plausible.
Lazear began breeding Aedes mosquitoes and feeding them on infected patients. The team discovered the mosquito required several days before it could infect another person, now known as the extrinsic incubation period.
Researcher James Carroll first allowed himself to be bitten and nearly died but survived. A healthy soldier was later bitten under controlled conditions and developed yellow fever before recovering.
Soon after, Lazear himself was exposed to an infected mosquito around 13 September 1900. Whether intentional or accidental remains debated, though his notebook suggested deliberate self experimentation.
Within days he developed fever and deteriorated rapidly. He died twelve days later.
After his death, the team intensified experiments at a research station outside Havana later named Camp Lazear.
Volunteers slept in bedding contaminated with body fluids from yellow fever patients and none became ill. However volunteers exposed to infected mosquitoes developed yellow fever, while protected volunteers sharing the same air did not.
The results proved mosquitoes transmit the disease. In 1901, the findings were published in the Journal of the American Medical Association.
Following the discovery, sanitation officer William C Gorgas launched mosquito control campaigns including draining standing water, screening patients and destroying larvae.
Havana eliminated yellow fever within ninety days. The discovery later enabled construction of the Panama Canal by making the tropics safer for workers.