Historical Guide to Yellow Fever

In the summer of 1693, a strange disease spread through Boston. Victims suffered from jaundice, high fever and black vomit. For more than two hundred years, yellow fever — as the disease became known — attacked numerous American cities, usually in severe summer outbreaks.

At the dawn of the 20th century, a U.S. Army Yellow Fever Board stationed in Cuba, headed by Major Walter Reed, confirmed a theory of Cuban doctor Carlos Finlay about the role of mosquitoes in the transmission of the disease. This theory was put to the test a few years later during a massive yellow fever outbreak in New Orleans.

Yellow Fever hospital in Cuba | Library of Congres
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HistoryYellow fever was a constant blight for eastern American cities — especially southeastern cities — in the 18th and 19th centuries. Most outbreaks occurred in the summer months, but some summers would pass without incident. Severe outbreaks occurred mostly in the south, especially along the Gulf Coast.

But increased mobility in the period after the Civil War enabled the disease — through infected carriers — to travel farther inland. Health officials offered different theories about the nature of the disease and its transmission, but it wasn't until a Cuban doctor presented his observations on the transmission of the disease by mosquitoes to a board of American Army doctors that an understanding of the disease was mastered.

SymptomsThe first stages of yellow fever are similar to the common flu: headache, fever and muscle aches. This lasts for two to three days and then the victim feels better, even to the point of thinking that their flu has passed.

The second "toxic" phase begins one or two days later, as the virus attacks the internal organs such as the kidneys and liver. Victims become jaundiced and yellowed, hence the name yellow fever. Excessive internal bleeding can cause the victim to vomit blood, which was called the "black vomit."

Death occurs from internal hemorrhaging, usually five to ten days into the second phase.

A female Aedes aegypti mosquito | James Gathany

TransmissionYellow fever is a virus that is transmitted to humans by particular species of mosquitoes — in North American outbreaks, the Aegis Egyptae.

Female mosquitoes with infected parents can be born with the disease, or they can feed on infected humans, acquiring the disease along with the human blood.

The virus replicates in the mosquito's digestive tract, and is then carried through the bloodstream to the salivary glands. This cycle takes between seven and seventeen days, during which the mosquito can not transmit the virus.

The Yellow Fever virus | CDC

After the virus has spread to the salivary glands of the insect, the next time the mosquito feeds, she will transmit the virus into the human skin. From the skin, the virus multiplies and is carried into the lymph nodes, which carries it into the bloodstream. Then symptoms appear.

Patients who survive yellow fever develop immunity from further infections.

Mosquitoes will not survive a frost. However, infected female mosquitoes pass yellow fever to their eggs. These eggs can lie dormant through dry, winter conditions, hatching the next year, releasing new infected mosquitoes; this is the reason the disease returned annually. Areas of standing water are prime breeding grounds and are emblematic of outbreak areas.

Quarantine patient | HSL University of Virginia

Treatment and Prevention"If you get yellow fever today your chances of survival are probably not much different than they were in the 1700s or the 1800. It's still going to be 1 out of every 5 or so who are going to die. There is no treatment, you can prevent it but you can't treat yellow fever." — Jim Writer, author, Yellow Jack: How Yellow Fever Ravaged America and Walter Reed Discovered Its Deadly Scourge

There is no cure for yellow fever.

Before the transmission of yellow fever was understood, yellow fever was thought to be airborne or spread through infected clothing. Urban areas burned tar, blanketing cities in choking smoke, in an effort to purify the air. Infected victims were also subject to strict quarantines in an effort to stop the spread of the disease. Quarantine and isolation, combined with choking smoke, reduced outbreak sites to virtual ghost towns.

Vaccination | CDC

Once mosquitoes were known to transmit the virus, public health officials targeted the insects in their preventive measures. A 1905 yellow fever outbreak in New Orleans was the first large scale test of mosquito control as a means of thwarting yellow fever. Workmen covered cisterns with screens and treated standing water with kerosene. Informed residents burned an estimated three hundred tons of sulphur to fumigate their premises. That year 452 victims died from yellow fever, but the further spread was prevented and future outbreaks did not occur.

In the 1930s, French and American scientists independently developed vaccines against yellow fever. The vaccines are not entirely without risk and are only administered to individuals living or traveling through areas known to be infected with yellow fever.

Vaccination, mosquito control and surveillance for outbreak in high risk areas remain the most effective means of controlling yellow fever.