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Human and equine outbreaks caused by eastern equine encephalomyelitis virus (EEEV) typically occur in North America adjacent to coastal wetlands associated with the presence of Culiseta melanura (Coquillet) mosquitoes. Eastern equine encephalomyelitis (EEE) is an emerging disease in Tennessee, as the first records of equine disease began in 2002. In 2006 we trapped and tested mosquitoes for EEEV at hardwood swamps in western Tennessee that were at the epicenter of a multi-equine outbreak in fall of 2005. Additionally, the Tennessee Valley Authority tested mosquito pools collected in Tennessee swamps from 2000 to 2007 for the presence of arboviruses. Two pools of EEEV positive Culex erraticus (Dyer and Knab) mosquitoes were found (one each in 2003 and 2004) in a county adjacent to where the 2005 outbreak occurred. In 2008, another EEE outbreak involving multiple horses occurred in West Tennessee. A brain specimen was collected from a horse during this outbreak and the first isolate of EEEV from Tennessee was obtained. In total, 74,531 mosquitoes collected from 2000 to 2008 were tested via polymerase chain reaction and VecTest for EEEV. The traditional enzootic vector, Cs. melanura, was found in low numbers at all collection sites. Cx. erraticus, however, was consistently found in high numbers and was the only mosquito species in which EEEV was detected. We suggest that EEE transmission may be maintained by Cx. erraticus in a nontraditional cycle. We discuss the importance of a nontraditional cycle from the perspective of EEEV adaptation and emergence.

In 2006, 2,817 blood-fed mosquitoes were collected from the site of a 2005 eastern equine encephalitis outbreak in Chester County, TN. Using a polymerase chain reaction-based assay, 264 vertebrate hosts were identified from seven mosquito species. Culex erraticus and Cx. nigripalpus fed on a diversity of mammalian, avian, and reptilian hosts, whereas Anopheles quadrimaculatus and An. punctipennis were predominantly mammalophagic. Overall, 27% of Cx. nigripalpus, 16% of Cx. erraticus, and 7% of An. quadrimaculatus blood meals were acquired from avian hosts. No avian-derived blood meals were identified from An. punctipennis. The house finch, Carolina wren, and mourning dove were the most commonly identified avian host species. By incorporating this study with flight range, vector competence, and virus field isolation data, we assessed certain aspects of the enzootic and epizootic vectorial capacity of the mosquito species present at this outbreak site.