An outbreak of yellow fever in Brazil has killed 220 people since December, and it might spread further.
Experts fear the virus could be spread by the same mosquitoes that carried the Zika virus and thus bring it to the U.S., The Washington Post reports.
While yellow fever has hit Brazil before, this is a much larger than normal outbreak. And some victims live close to major cities like Rio de Janeiro and Sao Paolo, increasing the odds it could infect a tourist and bring the virus to the U.S.
The good news is, there's a very effective vaccine for yellow fever. Millions of Brazilians have gotten the vaccine since the outbreak started. But the chance of it spreading to a city still remains.
In light of the serious nature of this historically devastating disease, public health awareness and preparedness are critical...
Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, and colleague Catharine Paules, wrote in a report it was "very unlikely" but possible the infected people in Brazil's jungle could make it to the city and have the disease picked up by the Aedes aegypti mosquito.
This is not 'Chicken Little, the sky is falling.' It's a public health heads-up.
Fauci urged colleagues to stay level-headed but cautious.
Worldwide, yellow fever is on the decline. While outbreaks in Africa and Central and South America still kill up to 60,000 people a year, it's still a far cry from centuries past. In Philadelphia in 1793, the disease killed about 10 percent of the city's population.
The disease's symptoms start like an ordinary flu, including headaches, fever (of course), muscle pain, nausea and vomiting. In 15 percent of patients, it gets more serious, with jaundice, organ failure and death all possible.