Abstract
We estimated the probability of exposure of people to questing ticks, infected with bacterial agents of the tick—borne zoonoses—in Aosta Valley, western Alps, Italy. We collected ticks by dragging, and from collectors’ clothes in three hiking trails, which were divided into an internal path, with short vegetation, and an external part with taller grass. Dragging yielded 285 Ixodes ricinus nymphs and 31 adults, and two Dermacentor marginatus adults. Eleven I. ricinus nymphs and 9 adults were collected from collectors’ clothes. Borrelia burgdorferi s.l. was identified by PCR in 12 out of 30 I. ricinus nymphs (prevalence = 40.0%, 95% confidence interval = 22.5, 57.5). The prevalence of infection by Rickettsia spp. was 13.3% (95% CI = 1.2, 25.5). The probability of encountering at least one questing I. ricinus infected by each bacterial agent (probability of exposure, E) in 100 m2 was obtained by combining the number of collected nymphs, the prevalence of infection by each bacterial agent, the frequency of passage by visitors, and the probability of tick attachment to people. The mean number of nymphs collected by dragging was greatest in the internal part of hiking trails (mean = 7.9). Conversely, E was greater in the external part (up to 0.14 for B. burgdorferi s.l., and 0.07 for Rickettsia spp.), due to a greater probability of tick attachment to people in relatively tall vegetation.
Highlights
The hard tick Ixodes ricinus is the vector of zoonotic viruses, bacteria, and protozoa, across a wide geographic range, from southern Spain, to northern Scandinavia [1,2,3]
We collected questing ticks in three hiking trails in a municipality of Aosta Valley, and estimated the prevalence of infection by Borrelia burgdorferi sensu lato (s.l.) and Rickettsia spp.—the agents of tick—borne zoonoses, which are most frequently detected in I. ricinus in Europe [13]
We adapted the terminology of the World Organisation for Animal Health (OIE) [14] to our case study: hazard characterization included the study of ticks and transmitted agents; release assessment was the estimation of the probability of finding infected, questing ticks in 100 m2 of land; exposure assessment was the estimation of the probability of people’s contact with infected ticks
Summary
The hard tick Ixodes ricinus is the vector of zoonotic viruses, bacteria, and protozoa, across a wide geographic range, from southern Spain, to northern Scandinavia [1,2,3]. I. ricinus and transmitted agents have been reported in mountains in northwestern Italy, at altitudes greater than. In Aosta Valley, tick bites have been reported by Parini. We collected questing ticks in three hiking trails in a municipality of Aosta Valley, and estimated the prevalence of infection by Borrelia burgdorferi sensu lato (s.l.) and Rickettsia spp.—the agents of tick—borne zoonoses, which are most frequently detected in I. ricinus in Europe [13]. We applied a risk assessment approach to estimate the probability of exposure of people to infected ticks, to provide suggestions to avoid tick bites, and to set the basis for further studies of a larger scale.
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