Prevalence ofEhrlichia chaffeensisandEhrlichia ewingiiin Ticks from Tennessee

Abstract

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.

Molecular identification of Ehrlichia species and host bloodmeal source in Amblyomma americanum L. from two locations in Tennessee, United States

“…This is the first confirmation of Panola Mountain Ehrlichia in A. americanum from the state of Tennessee. Cohen et al (2010) did not identify any PME-infected ticks in Tennessee, however the 16S rRNA PCR employed in that study is not expected to detect PME (A. Loftis, pers.…”

“…We documented low-prevalence E. chaffeensis, E. ewingii, and PME infection among A. americanum from both of our study areas. Cohen et al (2010) tested small numbers of A. americanum (mean sample size ∼10/county) from numerous Tennessee counties in 2007-08 and found E. chaffeensis in 2.6% of 309 ticks and E. ewingii in 0.8% of 238 ticks. Combining E. chaffeensis and E. ewingii, prevalence did not differ significantly between their study (3.2%) and ours (4.0%; P = 0.57).…”

“…The presence of these three pathogenic Ehrlichia species in A. americanum represents a significant public health risk in Tennessee and other southeastern states. In 2008, 74 'human monocyctic ehrlichiosis' cases were reported to the Tennessee Department of Health (Cohen et al, 2010). Official reporting since 2008 has made a distinction between 'E.…”

Infection Prevalences of Common Tick-borne Pathogens in Adult Lone Star Ticks (Amblyomma americanum) and American Dog Ticks (Dermacentor variabilis) in Kentucky

“…Human monocytotrophic ehrlichiosis is most commonly reported from the southeastern and south central United States. 34 The A. americanum tick is also a vector for Ehrlichia ewingii , 35,36 the cause of granulocytic ehrlichiosis in humans. [37][38][39] Thirteen cases of ehrlichiosis were reported in Kentucky in 2008, a 325% increase over 2007.…”

“…13 In Tennessee, 2.6% of A. americanum ticks were found to be infected with E. chaffeensis , and 0.8% were infected with E. ewingii , and no other Amblyommma , Ixodes , or Dermacentor ticks tested were positive for any Ehrlichia spp. 36 In a study conducted during 1996-2001, whitetailed deer from eight states were tested for E. ewingii by PCR. It was found that 5.5% were positive for E. ewingii infection, including one deer from Kentucky.…”