Modern concern about the spread of virulent diseases like Ebola is nothing new. People of every era understood that diseases could spread from place to place, even though how they spread was poorly understood. In the colonial period, a different African disease, yellow fever, struck fear in the hearts of men and women throughout the colonies, particularly along the coasts. One of the worst yellow fever epidemics in the colonial period took place in Philadelphia in 1793, when more than 4000 people, almost 1/10th of the city, perished in just three months.

Yellow fever “season” in the northern American colonies was from mid to late summer into fall. No one understood why, they simply knew when to be on the lookout. The yellow fever epidemics of this period predate the understanding of germ theory, and it wouldn’t be until over one hundred years after the signing of the Constitution that the transmission vector of yellow fever, the Aedes Aegypti mosquito, would be discovered. Unknown to everyone in the 18th century, the life and reproductive cycle of the yellow fever mosquito determined the spread of this dangerous disease.

Aedes Aegypti is a hardy little insect. While the mosquito is native to Africa, it can survive in a wide range of temperatures and environments. Both the male and female mosquitos can sustain themselves on fruit and nectar, but the female requires a blood meal in order to lay her eggs. Once she gets blood, she can lay several hundred eggs. Unlike other types of mosquitoes, she will not lay them all in one place, nor will she lay them directly in water. Aedes Aegypti prefers to lay eggs in damp places prone to flooding. The eggs develop a thick black shell for protection, and can survive for months without water.

The yellow fever mosquito migrated from Africa to the New World because of the way sailing ships of the time operated. Wooden ships had to be prepared to spend months at sea, which required large supplies of fresh water. Water was stored in reusable wooden casks. Empty casks would be moved up to the top deck in a rainstorm for refilling, helping extend the range of ships at sea.

This turned out to be ideal for Aedes Aegypti. A slave ship visiting West African ports took on large numbers of water casks to ensure their valuable cargo would survive the passage to the Caribbean. The water was likely infested with mosquito eggs or larvae. More mosquitos, attracted to the huge number of potential meals, might fly into the hold as well. Once fed, the females would find a convenient wet place to lay eggs. The water casks were perfect. As the water was used, the wood stayed damp, and the eggs would remain there, waiting to be submerged. And at the next rainstorm, the crew would bring the empty casks up to the open decks for refilling, reflooding the eggs.

This provided a perfect life cycle for the insects to make the passage. A typical yellow fever mosquito only lives about two weeks. But the regular filling and emptying of water casks, combined with ready access to blood, ensured the mosquitoes’ survival.

Yellow fever was firmly established in the Caribbean by the middle of the 17th century. The mosquitoes had no problem surviving in the climate of the East Indies, and yellow fever epidemics became common. A major epidemic on Barbados, believed to be the first large-scale outbreak in the New World, killed six thousand settlers between 1647-1650. White settlers suffered much more than their African-born slaves, most of whom acquired immunity to yellow fever while young. Once established in the Caribbean, the mosquito continued to spread via ships and water casks throughout the southern colonies of Britain and Spain.

By the end of the 18th century, yellow fever was a well-known disease throughout the New World, and periodic epidemics were common. Northern ports weren’t exempt, as the same mode of transportation that brought the mosquitoes from Africa to the Caribbean worked just as well for the shorter journey from the islands to the American colonies. The most famous epidemic during the colonial period struck Philadelphia in 1793. Then the capital of the young country, Philadelphia was one of the busiest ports in America, home of 40-50,000 inhabitants. At the height of the panic, an estimated 20,000 people fled to the countryside, bringing the local and federal government nearly to a standstill. Approximately 8000 people contracted the disease, and the death toll reached 4044 before frost finally killed the mosquitoes and ended the epidemic. A ship carrying refugees from a slave revolt in Haiti was the likely source of the plague.

To put this in perspective, imagine yellow fever hitting the twenty million people in the New York City area today with one-fifth of the city falling ill to a disease that killed one out of every two victims, and which no one knew how to stop. Imagine four million sick and desperate people converging on the city’s hospitals, with half of them dying. Imagine millions of displaced New Yorkers fleeing for their lives. Imagine what would happen to those left behind when truckers and ships refused to bring them food and other supplies out of fear of infection.

Luckily for us, there is no modern equivalent to yellow fever. As dangerous as Ebola can be, it pales in comparison to the diseases of the past. As of writing this, the number of people that have been married to Kim Kardashian is greater than the number of Americans that have died in the current outbreak of Ebola.