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Yellow feverPreventing yellow fever resurgence

Published 20 April 2017

Many people might not have heard of the Aedes aegypti mosquito until this past year, when the mosquito, and the disease it can carry – Zika – began to make headlines. But more than 220 years ago, this same breed of mosquito was spreading a different and deadly epidemic in Philadelphia and just like Zika, this epidemic is seeing a modern resurgence, with Brazil at its epicenter. “The challenge with diseases like yellow fever and Zika is that the conditions that foster an outbreak are not always avoidable, especially in tropical climates, and therefore a vaccine is needed to prevent infection,” says one expert.

Many people might not have heard of the Aedes aegypti mosquito until this past year, when the mosquito, and the disease it can carry – Zika – began to make headlines. But more than 220 years ago, this same breed of mosquito was spreading a different and deadly epidemic in Philadelphia and just like Zika, this epidemic is seeing a modern resurgence, with Brazil at its epicenter.    

It was August of 1793 and Philadelphia – the nation’s capital and the busiest port in the United States – was experiencing a remarkably hot and dry summer. Water levels in streams and wells were low, creating an excellent breeding ground for mosquitos, which seemed to overtake the city. Along with the mosquitos also came an influx of thousands of refugees from the Caribbean seeking to escape political turmoil. But the refugees also brought something else: yellow fever. 

The conditions in Philadelphia created the perfect storm for an outbreak. Symptoms start with head, back, and limb pain and a high fever. Sometimes after a few days, the initial symptoms would subside, giving its victims a false hope of recovery. But within a few days, the disease would return with a vengeance, bringing with it an even higher fever, bleeding, vomiting and eventually turning a person’s skin a ghastly shade of yellow – hence the disease’s name – and ultimately leading to death. 

Philadelphia’s medical community was mystified. Benjamin Rush, MD, the city’s leading physician advised citizens to flee. A large portion of Philadelphia’s citizens, along with members of Congress, President Washington, and his Cabinet, all abandoned the city. By the time the epidemic finally ended in November of that same year, more than 10 percent of the city’s population, approximately 5,000 people, had perished.

Rush, and his protégé, Philip Syng Physick, MD, worked with the few other doctors who stayed behind to try and root out the cause of the outbreak. At that time, little was understood about infectious diseases, especially those that are transmitted via a vector, like a mosquito. Rush and his colleagues tried many unsuccessful techniques that were common at the time, including bloodletting, “purifying” the city’s air with smoke, and finally quarantining the sick. None of it worked.

UPenn says that it took more than a century for physicians and public health experts to discover the true culprit behind yellow fever: the mosquito. Yellow fever is not transmitted by contact