Hill, Verity, Koch, Robert T., Bialosuknia, Sean M., Ngo, Kiet, Zink, Steven D., Koetzner, Cheri A., Maffei, Joseph G., Dupuis, Alan P., Backenson, P. Bryon, Oliver, JoAnne, Bransfield, Angela B., Misencik, Michael J., Petruff, Tanya A., Shepard, John J., Warren, Joshua L., Gill, Mandev S., Baele, Guy, Vogels, Chantal B.F., Gallagher, Glen, and Burns, Paul
Eastern equine encephalitis virus (EEEV) causes a rare but severe disease in horses and humans and is maintained in an enzootic transmission cycle between songbirds and Culiseta melanura mosquitoes. In 2019, the largest EEEV outbreak in the United States for more than 50 years occurred, centered in the Northeast. To explore the dynamics of the outbreak, we sequenced 80 isolates of EEEV and combined them with existing genomic data. We found that, similar to previous years, cases were driven by multiple independent but short-lived virus introductions into the Northeast from Florida. Once in the Northeast, we found that Massachusetts was important for regional spread. We found no evidence of any changes in viral, human, or bird factors which would explain the increase in cases in 2019, although the ecology of EEEV is complex and further data is required to explore these in more detail. By using detailed mosquito surveillance data collected by Massachusetts and Connecticut, however, we found that the abundance of Cs. melanura was exceptionally high in 2019, as was the EEEV infection rate. We employed these mosquito data to build a negative binomial regression model and applied it to estimate early season risks of human or horse cases. We found that the month of first detection of EEEV in mosquito surveillance data and vector index (abundance multiplied by infection rate) were predictive of cases later in the season. We therefore highlight the importance of mosquito surveillance programs as an integral part of public health and disease control. • Genomic sequencing from a large outbreak of EEEV in the Northeast US in 2019 • Outbreak caused by several independent, short-lived virus introductions from Florida • Mosquito abundance and infection rate are predictive of human and horse cases • High-quality mosquito surveillance is vital for controlling outbreaks Hill et al. investigate the drivers behind outbreaks of eastern equine encephalitis virus in the Northeast US, including a large one in 2019. Using virus genome sequencing and mosquito surveillance data, they show it was caused by several small virus introductions from Florida and could be predicted by mosquito abundance and infection rates. [ABSTRACT FROM AUTHOR]