The first known outbreak of eastern equine encephalitis (EEE) in Vermont occurred on an emu farm in Rutland County in 2011. The first isolation of EEE virus (EEEV) in Vermont (VT11) was during this outbreak. Phylogenetic analysis revealed that VT11 was most closely related to FL01, a strain from Florida isolated in 2001, which is both geographically and temporally distinct from VT11. EEEV RNA was not detected in any of the 3,905 mosquito specimens tested, and the specific vectors associated with this outbreak are undetermined.

O'nyong nyong virus (ONNV) and Chikungunya virus (CHIKV) are two closely related alphaviruses with very different infection patterns in the mosquito, Anopheles gambiae. ONNV is the only alphavirus transmitted by anopheline mosquitoes, but specific molecular determinants of infection of this unique vector specificity remain unidentified. Fifteen distinct chimeric viruses were constructed to evaluate both structural and non-structural regions of the genome and infection patterns were determined through artificial infectious feeds in An. gambiae with each of these chimeras. Only one region, non-structural protein 3 (nsP3), was sufficient to up-regulate infection to rates similar to those seen with parental ONNV. When ONNV non-structural protein 3 (nsP3) replaced nsP3 from CHIKV virus in one of the chimeric viruses, infection rates in An. gambiae went from 0% to 63.5%. No other single gene or viral region addition was able to restore infection rates. Thus, we have shown that a non-structural genome element involved in viral replication is a major element involved in ONNV's unique vector specificity.

Serum samples from 489 free-ranging white-tailed deer (Odocoileus virginianus) were screened for antibodies against the Eastern equine encephalitis virus (EEEV) using plaque reduction neutralization tests (PRNTs). EEEV antibodies were detected in 10.2% of serum samples. This evidence is the first evidence that EEEV is present in Vermont. Serum was collected from deer in all 14 counties in the state, and positive EEEV sera were found in 12 (85%) of 14 counties, suggesting statewide EEEV activity in Vermont. Analysis of the spatial distribution of PRNT-positive samples revealed a random distribution of EEEV throughout the state. Results indicate widespread EEEV activity in Vermont, and they suggest that EEEV is not a recent introduction in the state but that EEEV activity has not been detected until now.

During fall 2010, 21 moose (Alces americanus) sera collected in northeastern Vermont were screened for eastern equine encephalitis virus (EEEV) antibodies using plaque reduction neutralization tests. Six (29%) were antibody positive. This is the first evidence of EEEV activity in Vermont, and the second report of EEEV antibodies in moose.