Detection of Bacterial Agents inAmblyomma americanum(Acari: Ixodidae) From Georgia, USA, and the Use of a Multiplex Assay to DifferentiateEhrlichia chaffeensisandEhrlichia ewingii

Abstract

Amblyomma americanum, the lone star tick, is the most common and most aggressive human biting tick in the Southeastern United States. It is known to transmit the agents of human ehrlichioses, Ehrlichia chaffeensis and Ehrlichia ewingii. In addition, it carries agents of unspecified pathogenicity to humans, including Rickettsia amblyommii, Borrelia lonestari, and the newly emerging Panola Mountain Ehrlichia (PME). Surveillance of these ticks for recognized or emerging pathogens is necessary for assessing the risk of human infection. From 2005 to 2009, we surveyed A. americanum ticks from four locations in the state of Georgia. Ticks (1,183 adults, 2,954 nymphs, and 99 larval batches) were tested using a multiplex real-time polymerase chain reaction (PCR) assay designed to detect and discriminate DNA from Rickettsia spp., E. chaffeensis, and E. ewingii. This assay was capable of detecting as few as 10 gene copies of the aforementioned agents. Ticks were also tested for PME and B. lonestari by nested PCR. The prevalence of infection ranged from 0 to 2.5% for E. chaffeensis, 0 to 3.9% for E. ewingii, 0 to 2.2% for PME, 17 to 83.1% for R. amblyommii, and 0 to 3.1% for B. lonestari. There were 46 (4.1%) individual adults positive for two agents, and two females that were each positive for three agents. Two larval batches were positive for both B. lonestari and R. amblyommii, indicating the potential for transovarial transmission of both agents from a single female. Although infrequent in occurrence, the dynamics of coinfections in individual ticks should be explored further, given the potential implications for differential diagnosis and severity of human illness.

Increasing Incidence of Ehrlichiosis in the United States: A Summary of National Surveillance of Ehrlichia chaffeensis and Ehrlichia ewingii Infections in the United States, 2008–2012

“…11,13 The primary vector for E. chaffeensis and E. ewingii in the United States is the lone star tick, Amblyomma americanum. 25,26 Transmission to humans is caused almost exclusively by the bites of infected ticks and occurs in areas where the lone star tick is prevalent, most commonly in the southeastern, southcentral, and, recently, northeastern United States. 4,5,10,27 Lone star ticks are aggressive, nonspecific feeders, which bite humans at all stages of their life cycle.…”

Expanding Range of Amblyomma americanum and Simultaneous Changes in the Epidemiology of Spotted Fever Group Rickettsiosis in the United States

“…17,20,[34][35][36][37][38][39][40][41][42][43][44] Because of these large differences in prevalence, exposure to R. rickettsii may be rare relative to exposure to "Ca. Rickettsia amblyommii".…”

Prevalence of Ehrlichia chaffeensis and Ehrlichia ewingii in Amblyomma americanum and Dermacentor variabilis collected from southeastern Virginia, 2010–2011

“…Both E. chaffeensis and E. ewingii were tested for using TaqMan qPCR assays targeting the 16S rRNA gene (Loftis et al, 2003 and Killmaster et al, 2014). A subset of qPCR-positive samples were confirmed by sequencing either the groEL gene of E. chaffeensis (Tabara et al, 2007) or the p28 gene of E. ewingii (Gusa et al, 2001) using a nested PCR assay.…”