Risk of Lyme disease development after a tick bite

Abstract

Background/Aim. Despite numerous research of Lyme disease (LD), there are still many concerns about environmental of infectious agent of LD, as well as its prophylaxis, diagnosis and treatment. The aim of this work was to determine the risk of LD in relation to the way of removing ticks and duration of tick attachment. Methods. In the period from 2000 to 2007 a prospective study was conducted including persons with tick bite referred to the Institute of Epidemiology, Military Medical Academy, and followed for the occurrence of early Lyme disease up to six months after a tick bite. Epidemiological questionnaire was used to collect relevant information about the place and time of tick bites, the way of a removing tick, duration of tick attachment, remnants of a tick left in the skin (parts of the mouth device) and the signs of clinical manifestations of LD. Duration of tick attachment was determined on the basis of size of engorged tick and epidemiological data. Removed ticks were determined by the key of Pomerancev. Professional removing of attached tick was considered to be removing of tick with mechanical means by healthcare personnel. Fisher's exact test, Chi squares test and calculation of the relative risk (RR) were used for data analysis. Results. Of 3 126 patients with tick bite, clinical manifestations of LD were demonstrated in 19 (0.61%). In the group of subjects (n = 829) in which a tick was not removed professionally there were 17 (2.05%) cases with LD, while in the group of respondents (n=2 297) in who a tick was removed professionally there were 2 (0.09%) cases with LD after tick bite (RR, 23.55; p < 0.0001). The disease was most frequent in the group of respondents with incompletely and unprofessionally removed ticks (2.46%). In the groups of patients with unprofessionally but completely removed ticks LD occurred in 0.89%, while in the group of subjects with a tick removed by an expert, but incompletely in 0.78% cases. The disease occurred rarely in the group with a tick removed completely and professionally (0.05%). There was no case of LD in the group of patients with a tick removed within 24 hours. The longer time of exposure after 24 hours, the higher absolute risk of disease was reported. Conclusion. In prevention of Lyme disease it is important to urgent remove a tick, to use a correct procedure of removing and to remove the whole tick without any remnants.