Bacterial Pathogens in Ixodid Ticks from a Piedmont County in North Carolina: Prevalence of Rickettsial Organisms

Abstract

In North Carolina, reported human cases of tick-borne illness, specifically Rocky Mountain spotted fever, have escalated over the past decade. To determine the relative abundance of vectors and to estimate the risk of acquiring a tick-borne illness in peri-residential landscapes, ticks were collected in Chatham County, a typical Piedmont county and, samples of the ticks were tested for infection with selected bacterial pathogens using real-time quantitative polymerase chain reaction assays. Ticks (n = 3746) were collected by flagging vegetation at 26 sites from April to July 2006. The predominant questing tick was Amblyomma americanum (98.5%) with significantly fewer Dermacentor variabilis (1.0%) and Ixodes scapularis (0.5%) collected. Spotted fever group (SFG) rickettsiae were detected in 68.2% of 1590 A. americanum with 56.4% of the molecular isolates identified as Rickettsia amblyommii, an informally named member of the SFG rickettsiae. Comparatively, smaller numbers of A. americanum contained Ehrlichia chaffeensis (1.8%) and Borrelia lonestari (0.4%). Of 15 I. scapularis nymphs tested, 6 (40%) were positive for Borrelia burgdorferi sensu lato. Seven (19.4%) of 36 adult D. variabilis tested positive for Rickettsia montanensis, 4 (11.1%) were positive for R. amblyommii, and 5 (13.9%) were infected with unidentified species of SFG rickettsiae. The tick population in Chatham County contains a diverse array of microbes, some of which are known or potential pathogens. Highest attack rates would be expected from A. americanum ticks, and highest potential risk of infection with a tick-transmitted agent would be to rickettsial organisms, particularly R. amblyommii. Accordingly, longitudinal eco-epidemiology investigations are needed to determine the public health importance of A. americanum infected with rickettsial organisms.

Retrospective Case Reports of Two Central North Carolina Residents

“…During the latter years of this report period, in the area where the subjects lived, Smith et al [1] found the predominant questing tick to be the lone star tick, comprising 98.5% of their collection of 3746 ticks, followed by the American dog tick at 1.0%, and the black-legged tick at 0.4%. Rickettsia ssp.…”

“…Exposure to ticks in North Carolina is widespread and some undiagnosed illnesses associated with tick bites could be due to new emerging pathogens [1][2][3]. As studies have documented, ticks and the pathogens they may carry are increasing in numbers and range [3]; it may be time to initiate planning to mitigate this expanding public health problem.…”

“…Several hundred uninhabited acres lay behind the small subdivision where the subjects live. The entire county is known for high deer density and is highly infested with lone star ticks along with occasional dog and black-legged ticks [1]. Acaricides, pesticides that kill ticks and mice, were not used on the property.…”

“…The predominant humanbiting tick in the North Carolina Piedmont is the lone star tick (Amblyomma americanum) while less common species include the American dog tick (Dermacentor variabilis) and the blacklegged (deer) tick (Ixodes scapularis) [1]. All these ticks are known to be potentially infected with a variety of bacterial [1][2][3] and viral human pathogens [2][3][4][5]. Reportable tick-borne illnesses, a considerable source of illness and occasional fatalities in North Carolina [6,7], include Lyme disease, spotted fever rickettsiosis (SFR) (formally Rocky Mountain spotted fever [RMSF]), ehrlichiosis, anaplasmosis, and tularemia.…”

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".…”