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destruction on the island. The female
Aedes
mosquito prefers the moist edges of artificial water containers to lay her eggs. The casks of drinking water taken on board slave ships departing from Africa had transported
Aedes
to the Americas. Now ponds, flower vases, old tires, and other water containers were sustaining the disease. Soldiers under Gorgas’s super-vision emptied or smashed water containers and sprayed oil on ponds where
Aedes
might breed. Within five months, these methods had eliminated yellow fever from Cuba. Gorgas was a hero. In 1904, he was dispatched to the American revival of the Panama Canal project. By 1906, using the same methods, Gorgas had eradicated yellow fever there, too.
    It would not be until 1927 that the South African physician Max Theiler and his colleagues would prove that yellow fever was caused by a Flaviviridae virus and eventually develop a successful vaccine. Called 17D, it is still used today. Later, scientists learned where yellow fever hid in between epidemics: the African virus has found a permanent reservoir in the New World tropics among populations of tree-dwelling monkeys and their mosquito parasites. High above humans in the forest canopy, the virus cycles between insect and animal. As long as the forest is undisturbed, yellow fever remains “silent” for years or even decades. But each time a tree is cut to clear more land for habitation or agriculture, yellow fever may crash back to earth, ready to reenter the human population chain.

     
    The Flaviviridae virus
     
    But what about yellow fever’s impact in the white man’s grave? Africans suffered from the disease but were not insensitive to its deadly effects on their colonial masters. While whites saw yellow fever as an obstacle to control, Africans recognized it as an ally in their struggles for freedom and independence. Well into the 1980s, these words were still chanted by many African schoolchildren: “… Only mosquito can save Africa. Only malaria can save Africa. Only yellow fever can save Africa.”

     
    The African Flaviviridae virus has found a permanent reservoir in tree-dwelling New World primates, like these howler monkeys, and their mosquito parasites. When the tropical rain forest is cut down, the pathogens of the canopy may come into contact with people, giving yellow fever a chance to reenter the human infection chain.
     

 

Repeat after me
    You know the drill: wipe, wash, don’t forget to flush. We learn the habits of personal hygiene from our parents, in school, on the job, and from the media. They seem basic, natural, obvious—even scientific. But they didn’t start that way. A little over a century ago, cleanliness and sanitation were still radical notions resisted by just about everyone. It took several global pandemics to change people’s habits.
    In 1817, a new disease swept out of India. It caused a violent, gushing diarrhea and vomiting that within a few hours could turn a healthy human being into a shriveled, blue-tinged corpse. No one knew what caused the illness. No one understood how it was spread. What people
did
know was that it didn’t discriminate: rich or poor, anyone who contracted the disease was likely to die. In seven separate pandemics over 180 years, it traveled to every continent except Antarctica, killing millions of people. Along the way it was given many names: hyperanthraxis, spasmodic cholera, Asiatic cholera, convulsive nervous cholera, cholera asphyxia, malignant cholera, the blue cholera, the blue fever, the blue vomit, the yellow wind, the plague, the pestilence, the black illness.
    Today we call it simply cholera. Simply put, it has been one of the most influential diseases of modern times. Cholera highlighted the desperate poverty and ghastly living conditions of newly industrialized Europe and America. It laid bare the threads connecting poverty to wealth. It settled the argument between two contending theories of disease, miasma and contagion. Most