Factors associated with tick bites and pathogen prevalence in ticks parasitizing humans in Georgia, USA

Abstract

BackgroundThe incidence and emergence of tick-borne diseases has increased dramatically in the United States during the past 30 years, yet few large-scale epidemiological studies have been performed on individuals bitten by ticks. Epidemiological information, including disease development, may provide valuable information regarding effectiveness of tick bite prevention education, pathogen transmission, human-disease dynamics, and potential implications for under reporting of tick-borne diseases.MethodsTicks found attached to Georgia residents were submitted for identification and polymerase chain reaction (PCR) testing for Francisella tularensis, Ehrlichia, Anaplasma, Borrelia, and Rickettsia spp. Tick bite victims were interviewed three weeks after the tick bite to identify various epidemiologic factors associated with infestation and if signs suggestive of a tick-borne disease had developed. Fisher’s exact test of independence was used to evaluate associations between various factors evaluated in the study. A multivariable logistic regression model was used for the prediction of non-specific illness post-tick bite.ResultsFrom April 2005-December 2006, 444 participants submitted 597 ticks (426 Amblyomma americanum, 142 Dermacentor variabilis, 19 A. maculatum, 7 Ixodes scapularis, 3 Amblyomma sp.) which originated from 95 counties. Only 25 (34 %) of 74 interviewed individuals purposely took tick bite prevention measures. Ticks that were PCR positive for bacterial organisms were attached to 136 participants. Of the 77 participants who developed non-specific illness, 50 did not have PCR positive ticks, whereas 27 did have PCR positive tick (s). Of those 27 individuals, 12 fit the criteria for a possible tick-borne illness (i.e., tick attached >6 h [if known], ≥4 day incubation period, and the individual exhibited clinical symptoms typical of a tick-borne illness without exhibiting cough, sore throat, or sinus congestion). Ticks from these individuals were positive for R. amblyommii (n = 8), E. ewingii (n = 1), R. montana (n = 1), R. rhiphicephali (n = 1), and Rickettsia sp. TR-39 (n = 1).ConclusionsAlthough illnesses reported in this study cannot definitively be connected with tick bites, it does provide insight into development, diagnosis, and treatment of possible tick-borne diseases post-tick bite. The study also provided data on pathogen prevalence, and epidemiologic factors associated with tick bites, as well as tick presence by county in Georgia.

Comparative vertical transmission of Rickettsia by Dermacentor variabilis and Amblyomma maculatum

“…In field-collected A. maculatum, R. parkeri infection rates range from 5 to 52% (Hooker et al, 1912; Edwards et al, 2011; Varela-Stokes et al, 2011; Nadolny et al, 2014; Paddock and Goddard, 2015; Gleim et al, 2016). …”

“…Contemporary field studies frequently detect alternative rickettsial species in A. maculatum , including Rickettsia amblyommatis , identified in 5% of ticks, and R. montanensis , a non-pathogenic endosymbiont RickettsiaRickettsia , detected in 14% of ticks (Lee et al, 2014; Gleim et al, 2016). However, whether A. maculatum is a competent host for these additional Rickettsia species remains unknown.…”

Retrospective Case Reports of Two Central North Carolina Residents

“…A recent CDC survey found 25.4% of South Atlantic residents reported tick exposure in their household in the past year; 11.7% sought medical care [11]. A Georgia study examining 597 ticks submitted by 444 participants found 12 individuals fit requirements for possible tick-borne illnesses [12]. We could not find any retrospective reviews of tick bites and illness experience among lay individuals over time anywhere in the United States.…”

“…Thus, 1.7% of the attached ticks were associated with presumed tick-related illness. Interestingly, the Georgia study with 597 ticks from 444 people found 2.7% developed a possible tick-borne illness [12]. The risk of presumed STARI varied considerably between the subjects even though each experienced a similar number of lone star tick bites.…”

“…One report suggested that R. amblyommii could be the cause of STARI, but the description of the rash did not seem consistent with EM; no photograph was included, and only one case was presented [35]. A Georgia study [12] reported EM rashes on two persons bitten by lone star ticks positive for R. amblyommii, but this does not preclude the rashes being caused by another agent. After several papers in the early 2000s looked at whether the then recently discovered Borrelia lonestari was the cause of STARI [19,36], that possibility has been largely dropped [3,19], although more investigation has been suggested [2].…”