National pandemic-preparedness efforts should include the potential return of yellow fever to the American South, according to authors of a Perspective article. They write: “We need a comprehensive plan for better coordinating mosquito surveillance and control among counties at risk, with steps for rapidly vaccinating the population (possibly including using fractional dosing if the vaccine is not available in sufficient quantities), along with enhanced vector-control efforts and the possible introduction of innovative vector-control technologies, such as wolbachia or gene delivery, which has the potential to reduce mosquito density and virus infectivity rates (vector competence).”
Factors favorable for the spread of this zoonotic disease include outbreaks that have already occurred in Texas and Florida, urbanization, poverty, and larger areas at risk in the Western Hemisphere. “Still another reason for concern about reemergence is the role of climate change and the climate oscillations caused by El Niño,” the authors write. “The 1878 yellow fever epidemic in the U.S. Mississippi Valley occurred during an El Niño event that began the previous year. That event created warmer and wetter conditions in the U.S. South, which may have enhanced the survival of Aedes aegypti mosquitoes and accelerated virus development and replication in mosquito hosts. A warming climate promotes Ae. aegypti–vectored arboviral diseases. With North America facing record-high temperatures and moisture and accelerated warming of its surrounding waters just ahead of an expected El Niño event, the United States could face similar conditions.”