Eastern equine encephalitis in Tennessee: 2002-2008.

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.

Factors associated with Trypanosoma cruzi exposure among domestic canines in Tennessee.

Trypanosoma cruzi , the etiologic agent of Chagas' disease, is enzootic in animal populations of the southeastern United States. In the United States, T. cruzi prevalence has been reported for over 20 different wildlife species, and 7 autochthonous human cases have been documented since 1955. Previous canine (Canis familiaris) serosurveys have been limited either by small sample size or confined geographic reporting areas. In this study, we report a seroprevalence of 6.4% among 860 canines from 31 counties and 5 ecoregions throughout Tennessee, using an indirect immunofluorescent assay (IFA). Statistically significant associations between seropositivity and age, weight, and outdoor living were noted. Differences in seropositivity were not seen based on American Kennel Club (AKC) group, sex, habitat, land cover, and ecoregion. Greater attention should be given to possible T. cruzi transmission in Tennessee and veterinarians should consider Chagas' disease as a differential diagnosis with compatible signs.

Prevalence of Ehrlichia chaffeensis and Ehrlichia ewingii in ticks from Tennessee.

Human ehrlichiosis is the second most common tick-borne disease reported in Tennessee after Rocky Mountain spotted fever. Two closely related ehrlichiae, Ehrlichia chaffeensis and Ehrlichia ewingii, are both causative agents of human disease and are transmitted by Amblyomma americanum, the lone star tick. Prevalence rates and distribution patterns of these pathogens among ticks in Tennessee are currently unknown. To understand prevalence and exposure risk of Ehrlichia spp., we tested 616 ticks (309 Amblyomma americanum (L.), 277 Dermacentor variabilis (Say), 17 Ixodes texanus (Banks), 7 Ixodes cookei Packard, 4 Ixodes scapularis (Say), and 2 Amblyomma maculatum Koch) from 46 counties for E. chaffeensis and 324 ticks (238 A. americanum and 86 D. variabilis) from 29 counties for E. ewingii. Overall, E. chaffeensis was detected in 2.6% (8/309) of A. americanum and E. ewingii in 0.8% (2/238). Ehrlichia spp. DNA was not detected in any tick species other than A. americanum. Although sample sizes were low in many counties, all positive ticks were identified in the Interior Plateau and Southeastern Plains ecoregions which is where the majority of human ehrlichiosis cases are reported from Tennessee (e.g., 66.3% of the human cases in 2008 are from the Interior Plateau ecoregion). The data from this pathogen survey combined with frequent human case reports from certain areas indicate potential "hot spots" for ehrlichiosis infection. Targeted vector control interventions in these areas may help decrease human ehrlichiosis transmission.