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Microbiology and the Panama Canal

Although the economic and political advantages were immeasurable, the French had given up in defeat. Panama had simply claimed too many lives. Too many of the engineers sent there had developed fever and muscle pains, begin vomiting, and died within a week. There was no treatment and no known means of prevention. The waterway connecting the oceans would have to wait until yellow fever, known in many areas as the black vomit, could be conquered.
In the late, 1890’s the United States began where the French had quit. A yellow fever commission led by Major Walter Reed was dispatched to Havana, Cuba where the disease had killed more American War. The commission’s major task was to determine how yellow fever was transmitted. Most researcher’s believed that yellow was a” filth disease” similar to typhoid fever-a disease spread by human feces. Improving sanitary conditions, however failed to reduce its incidence in Cuba. Clean Havana was as disease-ridden as filthy Havana. The disease spread in a curious pattern, something striking one side of a street but not the other. It was more prevalent in low wetlands than nearby highlands and usually spread in the direction of the prevailing wind. The disease flourished in hot weather and disappeared with cold and frost.
These observations led Reed to investigate an unpopular theory proposed 20 years earlier by the ridiculed “mosquito doctor”. Carlos Finlay. Finlay believed that the disease was acquired by inoculation with a “living miniature hypodermic needle” an infected mosquito. But because he was unable to demonstrate mosquito-borne transfer of the disease, his proposal was not considered seriously by his contemporaries. Reed’s group discovered the reason for Finlay’s failures. Finlay had mosquitoes bite yellow fever patients and then let these freshly charged insects bite healthy persons. Unfortunately for his hypothesis, these persons remained healthy. With carefully timed experiments and a handful of courageous volunteers, Reed showed that mosquitoes become infected only when they draw blood from a person during the first 4 days of the fever. In addition, the infected mosquito’s bite can transmit the disease only after the pathogen has incubated in the insect for 7 to 10 days.
Reed also ruled out other possible modes of transmission. Health volunteers were confined for 3 weeks in special mosquito-proof houses where they slept on bed sheets and blankets taken from yellow fever wards and wore pajamas removed from the bodies of yellow fever victims. All these volunteers remained healthy. Reed wrote, “The bubble of the belief that clotting can transmit yellow fever was picked by the first touch of human experimentation”. To show that these men were not immune to the disease, two of them volunteered to be intentionally exposed to infected mosquitoes and both contracted the disease.
With experiments like these, Walter Reed conclusively proved that the mosquito Aedes aegypti is the vector of yellow fever. This discovery provided the first successful tactic for controlling the disease. Mosquito-reduction programs allowed construction of the Panama Canal to begin in 1904, 4 years after Walter Reed’s yellow fever team arrived in Havana.
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