The National Institute of Allergy and Infectious Diseases published an essay writing that yellow fever can spread through traveling, especially along the Gulf Coast.
"In an era of frequent global travel, any marked increase in domestic cases in Brazil raises the possibility of travel related cases and local transmission in regions where yellow fever is not endemic", they write.
Doctors are anxious Brazil's yellow fever outbreak could be as devastating an epidemic as the Zika virus, the New England Journal of Medicine reported.
Brazil's Health Ministry said Tuesday that since December, when the yellow fever outbreak was first detected, there have been 127 confirmed deaths, with another 106 under investigation.
In the virtual absence of stockpiled vaccine, wrote Fauci and Dr. Catharine I. Paules, "early identification of cases and rapid implementation of public health management and prevention strategies, such as mosquito control and appropriate vaccination, are critical" to preventing an explosion of yellow fever. They warn that the virus may spread to warmer regions of the USA because of the same mosquito that carries Zika.
"This proximity raises concern that, for the first time in decades, urban transmission of yellow fever will occur in Brazil", Fauci and Paules wrote.
While the likelihood of yellow fever outbreaks in the USA is low, "travel-related cases of yellow fever could occur, with brief periods of local transmission in warmer regions such as the Gulf Coast states", wrote Dr. Anthony Fauci, director of National Institute of Allergy and Infectious Diseases and colleague Dr. Catharine Paules.
The entire state of Espirito Santo is now considered at risk for transmission of the virus, the World Health Organization (WHO) claims.
The United States also had the worst Zika outbreak with Florida being the most affected. It's taking place primarily in jungle areas, where forest-dwelling mosquitoes are spreading the virus mainly to monkeys.
"It's a public health heads-up".
An uncommon spike in the number of yellow fever cases in the country has raised concerns that it could also increase travel-related cases.
"This isn't 'chicken little, the sky is falling, '" Dr. Fauci told the Washington Post.
Worryingly, the number of suspected and confirmed cases is Brazil's highest since 2000.
Awareness and preparedness may just be what it takes to prevent the next outbreak of yellow fever.
A yellow fever outbreak in Angola and the Democratic Republic of Congo in 2016 exhausted the world's emergency vaccine stockpile. The Philadelphia epidemic of 1793, for example, killed approximately 10 percent of the city's population and prompted the federal government to flee the city, the authors noted.
Yellow fever symptoms include fever, chills, severe headache, back pain, general body aches, nausea and vomiting.
In the Brazilian outbreak, 80 people have died from the 234 documented cases.