Eastern equine encephalitis in Tennessee: 2002-2008.

This research article discusses the outbreaks of the Eastern equine encephalomyelitis (EEE) disease in Tennessee between 2002 and 2008. The researchers highlight that the EEE disease is an emerging concern in the region and they present a potential new transmission cycle involving insects other than the traditionally implicated ones.

Background of EEE disease and its Importance in Tennessee

• Eastern equine encephalitis (EEE) is a disease caused by the Eastern equine encephalomyelitis virus (EEEV). It generally breaks out in areas near coastal wetlands in North America.
• EEEV is transmitted mainly through a mosquito species called Culiseta melanura.
• EEE is recognised as an emerging disease in Tennessee. The first records of this disease affecting horses in the region began in 2002.

Investigation on EEE occurrences

• In response to a multi-horse EEE outbreak that occurred in 2005, the research team carried out an investigation in 2006, trapping and testing mosquitoes in several hardwood swamps located in Western Tennessee, the epicenter of the outbreak.
• Furthermore, the Tennessee Valley Authority subjected mosquito pools gathered from Tennessee swamps between 2000 and 2007, to tests for arboviruses, a group of viruses that are transmitted by insects.

Results of the Investigation

• Two instances of EEEV positive mosquitoes of the Culex erraticus species were identified, one in 2003 and the other in 2004. Notably, these were found in regions neighboring the location of the 2005 EEE outbreak.
• By 2008, another EEE outbreak emerged in West Tennessee, involving multiple horses. The researchers managed to obtain a brain specimen from one of the affected horses, which led to the first isolation of EEEV in Tennessee.
• In total, there were 74,531 mosquitoes subjected to testing via polymerase chain reaction and VecTest for EEEV from 2000 to 2008.

Key Findings and Discussion

• Interestingly, they found that the mosquito species traditionally implicated in EEEV transmission, Cs. melanura, was present in low numbers at all the collection sites.
• Meanwhile, the mosquito species Cx. erraticus was consistently found in high numbers and it was the only mosquito species that tested positive for EEEV. This suggested that EEEV might be transmitted through a nontraditional cycle involving Cx. erraticus.
• The researchers emphasize the importance of understanding this possible nontraditional cycle, as it could significantly impact the adaptation and emergence of EEEV.