Abstract
BackgroundWe performed a nationwide prospective study on the transmission risk for Borrelia to humans, investigating symptoms and serology at enrolment and three months after tick bites, and after standard treatment for erythema migrans (EM). Aiming to quantify the infection risk at point of care by physicians, we explored risk factors such as tick testing for Borrelia and assessment of the duration of the tick's blood meal.Methods and FindingsQuestionnaires, blood samples and ticks from patients who consulted one of 307 general practitioners for tick bites (n = 327) or EM (n = 283) in 2007 and 2008, were collected at enrolment and three months later at follow-up. Borrelia burgdorferi sensu lato DNA was detected in 29.3% of 314 ticks, using PCR/reverse line blot and real-time PCR on the OspA gene. Seroconversion in C6 ELISA, IgM or IgG immunoblots for Borrelia-specific antibodies was observed in 3.2% of tick bite cases. Fourteen tick bite cases had evidence of early Borrelia infection, of which EM developed among seven cases. The risk of developing EM after tick bites was 2.6% (95%CI: 1.1%–5.0%), and the risk of either EM or seroconversion was 5.1% (95%CI: 2.9%–8.2%). Participants with Borrelia-positive ticks had a significantly higher risk of either EM or seroconversion (odds ratio 4.8, 95%CI: 1.1–20.4), and of seroconversion alone (odds ratio 11.1, 95%CI: 1.1–108.9). A third (34%) of the cases enrolled with EM did not recall preceding tick bites. Three EM cases (1%) reported persisting symptoms, three months after standard antibiotic treatment for EM.ConclusionsOne out of forty participants developed EM within three months after tick bites. The infection risk can be assessed by tick testing for Borrelia at point of care by physicians. However, further refining is needed considering sensitivity and specificity of tick tests, accuracy of tick attachment time and engorgement.
Highlights
Lyme borreliosis is caused by different Borrelia species from the Borrelia burgdorferi sensu lato group, which in Europe is transmitted by the tick Ixodes ricinus
The most common clinical manifestation of Lyme borreliosis is erythema migrans (EM), a characteristic rash expanding from the site of the tick bite, which may appear some days to weeks following infection, and is sometimes accompanied by systemic flu-like symptoms
Eighteen ticks (6%) could not be identified, as they had been damaged too much during removal from the patient’s skin. Of these participants who submitted ticks, 278 were cases who consulted their physician for a tick bite, and fifteen were cases who consulted their physician with an EM
Summary
Lyme borreliosis is caused by different Borrelia species from the Borrelia burgdorferi sensu lato group (hereafter referred to as Borrelia), which in Europe is transmitted by the tick Ixodes ricinus. The transmission efficiency increases with the duration of the blood meal, as described for the North American vector Ixodes scapularis infected with Borrelia burgdorferi sensu stricto. We aim to explore to what extent the NNT can be reduced, using tick-screening instruments for general practitioners to predict an individual’s risk of Borrelia infection after each tick bite. Such tick-screening instruments include tick testing for infection with Borrelia, and assessment of the duration of the tick’s blood meal, measured as self-estimated hours of tick attachment time or measured as degree of engorgement of the tick. Aiming to quantify the infection risk at point of care by physicians, we explored risk factors such as tick testing for Borrelia and assessment of the duration of the tick’s blood meal
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