By J.M. Opal and Steven M. Opal
October 11, 2019

When Christopher Columbus arrived in the Caribbean in 1492, he brought Spanish visions of gold and glory, as well as new animals and pathogens. Pigs and rats ravaged the island ecosystems while measles, flu and smallpox burned through the native populations, killing millions of people and enabling the Spanish, English, Portuguese and French empires to take root in the New World.

But one Old World disease did not make it across the Atlantic: Yellow fever.

Native to tree-dwelling monkeys in western Africa, this virus could only be passed to people via the Aedes aegypti mosquito, a picky eater that lives just 30 days and rarely flies much more than a football field’s length from where it hatches. An infected monkey could only pass the virus to the mosquito during a certain point in the illness, and the mosquito could only transfer it to a person at a specific moment in the insect’s life cycle. Anyone who was exposed as a child usually survived with lifelong immunity.

When the Portuguese began to ship thousands of enslaved Africans from Angola to Brazil in the early 1600s, infected people and mosquitoes surely made part of the journey. But the mosquitoes must have died or flown away before causing an outbreak. In any case, the virus could not find enough virus-carrying insects and virus-prone people living in close proximity in the Americas.

In the fall of 1647, that all changed on the British colony of Barbados.

Like their counterparts in Virginia, the English settlers who first came to this eastern Caribbean island in 1627 initially relied on white servants, even as small numbers of black slaves arrived via Dutch traders. (The island’s indigenous peoples had been essentially wiped out long before, possibly due to European diseases or slave raids.) In 1642, however, England and Portugal signed a treaty opening Portugal’s slave dungeons on the African coast to London merchants. English slave vessels were soon showing up in Barbados.

When a few mosquitoes flew out of those ghastly ships, they found their own tropical paradise. Unlike other Caribbean islands, Barbados lacked readily available running water, so the settlers had built watering holes to catch the rains—perfect breeding grounds for mosquitoes. After each rainfall, these eggs hatched by the millions, releasing clouds of hungry A. aegypti on the dense population. Once these insects bit someone with the virus, disaster struck.

After suffering flu-like symptoms, the victims of the 1647 outbreak began to vomit a black, grainy discharge. Their eyes and skin turned yellow as the virus consumed their livers, and up to 75% of them fell unconscious and never awoke. “The living were hardly able to bury the dead,” wrote one eyewitness.

Poor men working half-naked in fields were more vulnerable to A. aegypti bites than were women laboring in homes or rich men riding on horseback. More importantly, yellow fever mostly hit the European servants, because many of the African slaves had already survived the virus on the other side of the ocean.

Its arrival a direct result of the slave trade, yellow fever thus helped slavery take over on Barbados. As white servants died by the thousands, the planters replaced them with black slaves. British emigrants now avoided Barbados, making its demographic change even more dramatic.

By the 1660s, Barbados was the first full-blown slave society in the British Empire, a tropical gulag ruled by haughty masters. Their slave code—and their excess slaves—then went to Jamaica, South Carolina and Virginia. In many ways, these places became colonies of Barbados, not of England.

With slavery came yellow fever. Having successfully crossed the Atlantic, the virus and its A. aegypti carriers jumped from Barbados to the rest of the Caribbean by the mid-1650s. From there it took root in monkey populations throughout Brazil and Spanish America.

Carried once more by ships and stowaway insects, yellow fever crippled Philadelphia, then the U.S. capital, in the 1790s. It also devastated European troops in the Caribbean and Gulf Coast regions, convincing Napoleon to sell Louisiana to Thomas Jefferson’s administration in 1803. Later that century, a major outbreak crippled French efforts to build the Panama Canal. Once Dr. Walter Reed (1851-1902) confirmed that yellow fever was a mosquito-borne, viral disease, the U.S. was able to eradicate A. aegypti habitats—and complete the canal in 1914.

The last major outbreak in the United States was in New Orleans in 1905, but yellow fever has remained in Latin America. One began in Brazil in 2017. More will likely follow as climate change and deforestation push monkeys and mosquitoes into greater contact with the region’s teeming cities.

Besides another chapter in the awful saga of American slavery, the story of yellow fever’s arrival in the New World is a grim lesson in humility: no matter how much we try to control our surroundings, we cannot escape the damage we inflict on other people and the natural world.

Historians’ perspectives on how the past informs the present

J.M. Opal is Associate Professor and Chair of the Department of History and Classical Studies at McGill University. Steven M. Opal is Research Scientist and Clinical Professor of Medicine, Alpert Medical School of Brown University.

Contact us at editors@time.com.

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