The first outbreak of eastern equine encephalitis in Vermont: outbreak description and phylogenetic relationships of the virus isolate.
Authors: Saxton-Shaw Kali D, Ledermann Jeremy P, Kenney Joan L, Berl Erica, Graham Alan C, Russo Joel M, Powers Ann M, Mutebi John-Paul
Journal: PloS one
Summary
# Eastern Equine Encephalitis in Vermont: First Outbreak and Epidemiological Mystery Vermont experienced its first documented eastern equine encephalitis (EEE) outbreak in 2011 on an emu farm in Rutland County, prompting researchers to characterise the virus isolate and investigate its origins and transmission route. Using phylogenetic analysis and molecular sequencing, the team established that the Vermont strain (VT11) clustered most closely with a Florida isolate from 2001, suggesting either a decade-long circulation in undetected populations or reintroduction from a geographically distant source—an unexpected finding that complicates understanding of EEEV epidemiology. Despite testing 3,905 mosquito specimens collected during the outbreak, the researchers found no EEEV RNA, leaving the vector species and transmission mechanism unidentified, which represents a significant gap in outbreak response. For equine professionals, this study highlights that EEE can emerge in regions previously considered low-risk and underscores the limitations of vector surveillance in determining disease source; heightened awareness during summer months, rapid diagnostic capability, and vaccination protocols remain critical, particularly as climate change and mosquito range expansion may alter disease distribution. The phylogenetic disconnect between the Vermont strain and contemporary circulating viruses warrants continued monitoring of EEE in regions bordering infected areas and investigation into whether cryptic transmission cycles sustain the virus in unexpected locations.
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Practical Takeaways
- •EEE can emerge in previously unaffected regions; monitor for neurological disease in equids and other species even in areas without prior outbreak history
- •Outbreak investigation and phylogenetic analysis are critical for understanding disease emergence patterns and potential geographic spread mechanisms
- •Vector identification remains challenging; work with veterinary authorities to report suspected EEE cases for investigation and control measures
Key Findings
- •First documented outbreak of EEE in Vermont occurred on an emu farm in Rutland County in 2011
- •Vermont EEEV isolate (VT11) was phylogenetically most closely related to a Florida strain from 2001 despite geographic and temporal distance
- •EEEV RNA was not detected in any of 3,905 mosquito specimens tested, leaving vector identification undetermined