Tick tactics : interactions between habitat characteristics, hosts and microorganisms in relation to the biology of the sheep tick Ixodes ricinus

F. Gassner

Research output: Thesisinternal PhD, WU

Abstract

The sheep tick Ixodes ricinus (L.) is known to transmit a large number of pathogens of medical and veterinary importance, including the bacterium Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis. Ixodes ricinus is found predominantly in woodlands, which provide suitable hosts and microclimates for tick survival. Three blood meals from a wide array of possible hosts are needed to complete the tick life cycle within 2 to 6 years. Ticks can acquire B. burgdorferi s.l. during a blood meal on an infected host and can infect a new host during the next blood meal. In this thesis, interactions between hosts, habitat characteristics, and microorganisms in relation to the biology of I. ricinus were investigated. A longitudinal study that was initiated at 24 sites across The Netherlands revealed that ticks infested with B. burgdorferi s.l. were found at all sites, but with strong spatial and temporal variation. This variation could be partially attributed to habitat characteristics. Substantial variations in the bacterial diversity within I. ricinus nymphs were also observed between habitats. Molecular genetic analyses indicated the presence of several potentially pathogenic and non-pathogenic bacteria. The interactions of these bacteria with hosts, ticks and other micro-organisms that reside in the tick need to be established in the future. It is known that rodent populations can mediate B. burgdorferi s.l. circulation in nature. Therefore, we studied the potential effects of rodents on the spatial variation of Borrelia infections in host-seeking ticks. Wood mice (Apodemus sylvaticus) and bank voles (Myodes glareolus) were abundant at most sites, but had varying tick burdens and Borrelia-infection prevalence between sites. It is argued that the infection prevalence in host-seeking I. ricinus ticks in the vegetation depends on the degree of contact between ticks and mice, which is, in turn regulated by habitat characteristics.
Larger hosts, such as ruminants, are important for tick reproduction. Because domestic cattle is frequently used in the management of forested areas in The Netherlands, the effect of such management on tick populations was addressed. Results from this thesis show that the presence of cattle in a woodland resulted in a locally reduced tick density, whereas Borrelia infection prevalence remained the same compared to ungrazed woodlands. The tick-reducing effect of cattle was attributed to the negative effect of cattle on rodent populations. Effects of other mechanisms such as habitat alteration by the cattle are arguable and require further study. A central issue in the ecology of Lyme borreliosis is the mechanism by which Borrelia species circulate between the life stages of ticks and their hosts. This circulation is strongly affected by the chance that the tick will find a host. It was found that that B. burgdorferi s.l.-infected I. ricinus nymphs displayed increased walking activity and had a greater resistance to desiccation than uninfected ticks. These Borrelia-mediated effects can contribute to increased chances of host finding by the tick, and thereby to an increased transmission of Borrelia species. In conclusion, Borrelia-infected ticks were present at all locations studied, but with a dynamic heterogeneity, which is partly influenced by habitat characteristics and rodent hosts. The introduction of large herbivores could become an advantageous management strategy to help reduce the incidence of Lyme borreliosis, and further experiments confirming the mechanisms underlying this relationship would be valuable. The established B. burgdorferi s.l.-mediated behavioural changes in I. ricinus contribute to the understanding of the ecology of Lyme borreliosis, and create opportunities for future studies on tick-parasite interactions.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Takken, Willem, Promotor
  • Dicke, Marcel, Promotor
  • van Overbeek, Leo, Co-promotor
Award date29 Nov 2010
Place of Publication[S.l.]
Print ISBNs9789085858058
Publication statusPublished - 2010

Keywords

  • ixodes ricinus
  • tickborne diseases
  • metastigmata
  • borrelia burgdorferi
  • host parasite relationships
  • habitats
  • distribution
  • spatial variation
  • temporal variation
  • netherlands

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