The doctors also observed that, in an era of frequent global travel, an increase in domestic cases in Brazil has the potential to spread yellow fever to non-endemic areas and could pose serious disease-control challenges. In Brazil specifically, 292 cases have been reported so far, the Pan-American Health Organization (PANO) said, while 920 suspected cases in the country are still being investigated by health officials.
"This proximity raises concern that, for the first time in decades, urban transmission of yellow fever will occur in Brazil", Fauci and Paules wrote.
"In an era of frequent worldwide 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", the team wrote.
US health officials are sounding the alarm over yet another potential mosquito-borne health threat to Americans - yellow fever.
The authors stressed that there's yet no evidence that mosquitoes are transmitting yellow fever between infected people.
Out of a total 1,500 suspected cases, 371 have been confirmed, 966 are still being examined, and the rest ruled out. Yellow fever in the country has now claimed the lives of 220 people and the number could still rise over time. A vaccine was developed in 1937 that is still in use today; it provides lifetime immunity in up to 99 percent of people who get it, according to the World Health Organization (WHO).
Yellow fever is the most severe arbovirus to circulate in the Americas, and Fauci and Paules urged physicians to have a high index of suspicion for the disease, especially in travelers returning from affected regions.
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"In an era of frequent worldwide travel, any marked increase in domestic cases in Brazil raises the possibility of travel-related cases", they wrote.
So far confirmed cases have been reported in three of Brazil's states: Minas Gerais, Espirito Santo, and Sao Paulo.
During the 2015 outbreak in Angola and Congo, health officials were constrained to administer to each infected person only a fifth of the normal dose.
The fearsome disease starts like a common flu, with symptoms of headache, fever, muscle pain, nausea and vomiting.
Top infectious disease experts are warning about a rapidly spreading outbreak of deadly yellow fever in Brazil that could hit parts of the United States. They also warned that yellow fever outbreaks could occur in United States territories.
"As with all potentially reemerging infectious diseases, public health awareness and preparedness are essential to prevent a resurgence of this historical threat", they write. "It's critical that nations have the capacity to quickly detect and control these outbreaks in order to decrease the illness and death and prevent the spread to other locations".
Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, acknowledged that while it was too early to panic, the prospect of "urbanized" yellow fever was one that strikes fear in the hearts of public health officials.