“If you try to build this canal there will not be trees enough on the isthmus to make crosses for the graves of your laborers.” — French resident in Panama to Ferdinand de Lesseps, 1880s

How Did the Americans Control the Mosquitoes?

Thousands of sanitary workers scoured the Canal Zone looking for water sources where mosquitoes could breed. By spraying a thin film of oil on the water’s surface, they smothered any mosquito larvae that might be living there. Using techniques that William Gorgas developed in Havana where he battled yellow fever after the Spanish-American War, workers fumigated buildings, removed standing water, installed door and window screens, and cut grass.

The tropical diseases that killed thousands of workers during the French years threatened to derail the American effort before it even got started. Many people thought yellow fever and malaria were caused and spread by bad air or filth. By the end of the 19th century, however, physicians Ronald Ross of England, Carlos Juan Finlay of Cuba, and Walter Reed of the United States had proved the diseases were transmitted by mosquitoes.

American tropical disease expert William Gorgas used their research and his own experience to rid the isthmus of yellow fever in 18 months. Similar measures to control the mosquito that causes malaria cut those deaths as well. In 1905, with disease in check, construction began with renewed vigor.

Stegomyia fasciata (Aëdes aegypti), commonly known as a house mosquito, was a carrier of yellow fever. It deposited its eggs in the standing water often found around residences. Anopheles, which carried malaria, bred in swamps, along the edges of rivers and streams, and even in puddles.

Although quinine does not cure malaria, it does stop the disease’s progress by interfering with the growth and reproduction of malaria-causing parasites in red blood cells. It also relieves fever and other symptoms. When malaria patients stop taking quinine, however, they relapse. Natural quinine is derived from the bark of the cinchona tree.

No equivalent to quinine existed for yellow fever sufferers. However, those who survived enjoyed lifetime immunity from the disease.

Although medical records, especially those from the French period, are incomplete, as many as 20,000 workers died during the French and U.S. construction periods. The dramatic dip during the 1890s reflects the near standstill in work by the French, not a medical breakthrough. After 1904, deaths increased with the arrival of new, non-immune workers.

Crude oil brought by tanker from California and sprayed on mosquito breeding areas disrupted the insects’ life cycle. Visitors to the Canal Zone often commented on the pervasive smell of petroleum.

Using screens to bar mosquito entry into homes and other buildings also helped limit the spread of yellow fever and malaria.

Working in well-equipped hospitals, Isthmian Canal Commission physicians treated diseases and injuries that were typical at home as well as those more common to the tropics and the construction industry.

Deadly tropical fevers received the most notoriety, but diseases of all types attacked workers, particularly those from the Caribbean who had no natural immunity to some of them. Injuries and deaths from dynamite blasts, drowning, railroad accidents, and other trauma occurred throughout the entire project.