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Open Access Research

Circumstantial evidence for an increase in the total number and activity of borrelia-infected ixodes ricinus in the Netherlands

Hein Sprong1*, Agnetha Hofhuis1, Fedor Gassner12, Willem Takken2, Frans Jacobs2, Arnold JH van Vliet3, Marijn van Ballegooijen1, Joke van der Giessen1 and Katsuhisa Takumi1

Author Affiliations

1 Centre for Infectious Disease Control, National Institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands

2 Laboratory of Entomology, Wageningen University, Wageningen, The Netherlands

3 Environmental Systems Analyses Group, Wageningen University, Wageningen, The Netherlands

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Parasites & Vectors 2012, 5:294  doi:10.1186/1756-3305-5-294

Published: 17 December 2012

Abstract

Background

Between 1994 and 2009, a threefold increase has been observed in consultations of general practitioners for tick bites and Lyme disease in The Netherlands. The objective of this study was to determine whether an increase in the number of questing ticks infected with B. burgdorferi sensu lato is a potential cause of the rise in Lyme disease incidence.

Methods

Historic data on land usage, temperature and wildlife populations were collected and analyzed together with data from two longitudinal field studies on density of questing ticks. Effective population sizes of Borrelia burgdorferi s.l. were calculated.

Results

Long-term trend analyses indicated that the length of the annual tick questing season increased as well as the surface area of tick-suitable habitats in The Netherlands. The overall abundances of feeding and reproductive hosts also increased. Mathematical analysis of the data from the field studies demonstrated an increase in mean densities/activities of questing ticks, particularly of larvae between 2006 and 2009. No increase in infection rate of ticks with Borrelia burgdorferi sensu lato was found. Population genetic analysis of the collected Borrelia species points to an increase in B. afzelii and B. garinii populations.

Conclusions

Together, these findings indicate an increase in the total number of Borrelia-infected ticks, providing circumstantial evidence for an increase in the risk of acquiring a bite of a tick infected with B. burgdorferi s.l. Due to the high spatiotemporal variation of tick densities/activities, long-term longitudinal studies on population dynamics of I. ricinus are necessary to observe significant trends.

Keywords:
Borrelia burgdorferi sensu lato; Ixodes ricinus; Population dynamics; Lyme disease; The Netherlands