F. Gassner

Diversity of Ixodes ricinus tick-associated bacterial communities from different forests

Nymphal Ixodes ricinus ticks (n=180) were collected from three different areas in the Netherlands to investigate the effect of forest composition on tick-associated microbial communities. Sampled habitats differed in thickness of leaf litter and humus layers and vegetation associations and were located near Amsterdam (Beech-Oak), Ede (Birch-Oak) and Veldhoven (Birch-Oak). Analysis of nine 16S rRNA gene clone libraries made from individual ticks showed nearest matches with presumed pathogens Candidatus Neoehrlichia mikurensis and Rickettsia australis and arthropod endosymbionts Wolbachia pipientis and Candidatus Midichloria mitochondrii. Total bacterial species diversity (Shannon index) and Borrelia species infections were determined in I. ricinus by, respectively, PCR-denaturing gradient gel-electrophoresis and PCR-reverse line blot with probes specific for Borrelia burgdorferi sensu stricto, Borrelia afzelii, Borrelia garinii, Borrelia valaisiana, Borrelia lusitaniae and Borrelia ruski. Bacterial diversity differed significantly per area and was lowest in Ede. In contrast, Borrelia species-infected ticks were more abundant in Ede, Candidatus Neoehrlichia mikurensis-infected ticks in Ede and Veldhoven, and R. australis-infected ticks in Amsterdam. Borrelia afzelii was the most common Borrelia species found in all three areas. Bacterial tick diversity was influenced by local differences in forest structure, which is proposed to modulate animal populations that are commonly parasitized by I. ricinus.

Prevalence of Coxiella Burnetii in Ticks After a Large Outbreak of Q Fever

Q fever has emerged as an important human and veterinary public health problem in the Netherlands with major outbreaks in three consecutive years. Goat farms are probably the prime source from which Coxiella burnetii have spread throughout the environment, infecting people living in the vicinity. Coxiella burnetii infection not only spilled over from animal husbandry to humans but could also have spread to neighbouring wildlife and pets forming novel reservoirs and consequently posing another and lingering threat to humans, companion animals and livestock. In these cases, transmission routes other than airborne spread of contaminated aerosols may become significant. Therefore, the role of ticks in the transmission of Coxiella burnetii in the current situation was investigated. A total of 1891 questing Ixodes ricinus ticks and 1086 ticks feeding on pets, wildlife and livestock were tested by a recently developed multiplex Q‐PCR. All ticks were negative, except for a few ticks feeding on a herd of recently vaccinated sheep. Coxiella‐positive ticks were not detected after resampling this particular herd three months later. Based on these data we conclude that the current risk of acquiring Q fever from questing ticks in the Netherlands is negligible. However, for future risk assessments, it might be relevant to sample more ticks in the vicinity of previously C. burnetii infected goat farms and to assess whether C. burnetii can be transmitted transovarially and transstadially in I. ricinus ticks.

Geographic and Temporal Variations in Population Dynamics of Ixodes ricinus and Associated Borrelia Infections in The Netherlands

In a countrywide investigation of the ecological factors that contribute to Lyme borreliosis risk, a longitudinal study on population dynamics of the sheep tick Ixodes ricinus and their infections with Borrelia burgdorferi sensu lato (s.l.) was undertaken at 24 sites in The Netherlands from July 2006 to December 2007. Study sites were mature forests, dune vegetations, or new forests on land reclaimed from the sea. Ticks were sampled monthly and nymphal ticks were investigated for the presence of Borrelia spp. I. ricinus was the only tick species found. Ticks were found in all sites, but with significant spatial and temporal variations in density between sites. Peak densities were found in July and August, with lowest tick numbers collected in December and January. In some sites, questing activities of I. ricinus nymphs and adults were observed in the winter months. Mean monthly Borrelia infections in nymphs varied from 0% to 29.0% (range: 0%-60%), and several sites had significantly higher mean nymphal Borrelia infections than others. Four genospecies of Borrelia burgdorferi s.l. were found, with B. afzelii being dominant at most sites. Borrelia infection rates in nymphal ticks collected in July, September, and November 2006 were significantly higher (23.7%, p<0.01) than those in the corresponding months of 2007 (9.9%). The diversity in Borrelia genospecies between sites was significantly different (p<0.001). Habitat structure (tree cover) was an effective discriminant parameter in the determination of Borrelia infection risk, as measured by the proportion of nymphal ticks infected with B. burgdorferi s.l. Thickness of the litter layer and moss cover were positively related to nymphal and adult tick densities. The study shows that Borrelia-infected ticks are present in many forest and dune areas in The Netherlands and suggests that in such biotopes, which are used for a wide variety of recreational activities, the infection risk is high.

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

BackgroundBetween 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.MethodsHistoric 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.ResultsLong-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.ConclusionsTogether, 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.

Absence of zoonotic Bartonella species in questing ticks: First detection of Bartonella clarridgeiae and Rickettsia felis in cat fleas in the Netherlands

BackgroundAwareness for flea- and tick-borne infections has grown in recent years and the range of microorganisms associated with these ectoparasites is rising. Bartonella henselae, the causative agent of Cat Scratch Disease, and other Bartonella species have been reported in fleas and ticks. The role of Ixodes ricinus ticks in the natural cycle of Bartonella spp. and the transmission of these bacteria to humans is unclear. Rickettsia spp. have also been reported from as well ticks as also from fleas. However, to date no flea-borne Rickettsia spp. were reported from the Netherlands. Here, the presence of Bartonellaceae and Rickettsiae in ectoparasites was investigated using molecular detection and identification on part of the gltA- and 16S rRNA-genes.ResultsThe zoonotic Bartonella clarridgeiae and Rickettsia felis were detected for the first time in Dutch cat fleas. B. henselae was found in cat fleas and B. schoenbuchensis in ticks and keds feeding on deer. Two Bartonella species, previously identified in rodents, were found in wild mice and their fleas. However, none of these microorganisms were found in 1719 questing Ixodes ricinus ticks. Notably, the gltA gene amplified from DNA lysates of approximately 10% of the questing nymph and adult ticks was similar to that of an uncultured Bartonella- related species found in other hard tick species. The gltA gene of this Bartonella- related species was also detected in questing larvae for which a 16S rRNA gene PCR also tested positive for Candidatus Midichloria mitochondrii . The gltA-gene of the Bartonella- related species found in I. ricinus may therefore be from this endosymbiont.ConclusionsWe conclude that the risk of acquiring Cat Scratch Disease or a related bartonellosis from questing ticks in the Netherlands is negligible. On the other hand fleas and deer keds are probable vectors for associated Bartonella species between animals and might also transmit Bartonella spp. to humans.

Rodent species as natural reservoirs of Borrelia burgdorferi sensu lato in different habitats of Ixodes ricinus in The Netherlands

Rodents are natural reservoirs for human pathogenic spirochaetes of the Borrelia burgdorferi complex [B. burgdorferi sensu lato (s.l.)], and the pathogens are transmitted by Ixodes ricinus ticks to humans in The Netherlands. B. burgdorferi s.l. infection prevalence in questing ticks, rodents, and ticks feeding on these rodents, all sampled within the same short time span of five days in three different areas in The Netherlands, were compared in order to establish the relationship between ticks, reservoir hosts, and B. burgdorferi s.l. Questing nymphs were found in all 3 areas and numbers differed per area and even per site within areas. Infection prevalence in questing nymphs ranged between 0 and 20%. Apodemus sylvaticus and Myodes glareolus were the dominant rodents captured, and their numbers differed per area. Infection prevalence, determined by ear biopsies, ranged between 0 and 33.3% for both rodent species. Larvae were most frequently found feeding on these rodents, and their Borrelia infection prevalence ranged between 0 and 6.3% (A. sylvaticus) and between 0 and 29.4% (M. glareolus). The burden of nymphs feeding on rodents was low and varied per area with only 2 of 42 nymphs infected. Comparisons made on the basis of infection prevalence indicated that there was no clear relationship between rodents and questing nymphs when sampled within the same short time span. However, a possible relationship was present when questing ticks were sampled over longer periods in time (months) within or near the same areas (range of infection prevalence between 3.7 and 39.4). Confounding factors thus play a role in the interaction between rodents, ticks, and B. burgdorferi s.l., and it is very likely that other reservoir host species are responsible for the observed fluctuations. It is concluded that the local variations in rodent-Borrelia-tick interactions only partially explain the Lyme borreliosis risk in the sites studied and that other ecological determinants, notably vertebrate hosts and vegetation structure, should be incorporated in future studies of Lyme borreliosis risk.

Variations in Ixodes ricinus Density and Borrelia Infections Associated with Cattle Introduced into a Woodland in The Netherlands

ABSTRACT The effect of introduced large herbivores on the abundance of Ixodes ricinus ticks and their Borrelia infections was studied in a natural woodland in The Netherlands. Oak and pine plots, either ungrazed or grazed by cattle, were selected. Ticks were collected weekly by blanket dragging. Borrelia infections were determined by PCR and restriction fragment length polymorphism. Rodent densities were estimated using mark-release-recapture methods. On occasion, the cattle were inspected for tick infestations. Meteorological data were recorded for each habitat. Significantly more ticks were collected in the ungrazed woodland than in the grazed woodland. The ungrazed oak habitat had higher tick densities than the pine habitat, while in the grazed habitats, tick densities were similar. Borrelia infection rates ranged from zero in larvae to 26% in nymphs to 33% in adult ticks, and B. afzelii, B. burgdorferi sensu stricto, B. garinii, and B. valaisiana were the species involved. Coinfections were found in five ticks. There was no effect of the presence of cattle on Borrelia infections in the ticks. In the ungrazed area, Borrelia infections in nymphs were significantly higher in the oak habitat than in the pine habitat. More mice were captured in the ungrazed area, and these had a significantly higher tick burden than mice from the grazed area. Tick burden on cattle was low. The results suggest that grazing has a negative effect on small rodents as well as on ticks but not on Borrelia infections. Implications of these results for management of woodland reserves and risk of Lyme disease are discussed.

Acarological Risk of Borrelia burgdorferi Sensu Lato Infections Across Space and Time in The Netherlands

A longitudinal investigation on tick populations and their Borrelia infections in the Netherlands was undertaken between 2006 and 2011 with the aim to assess spatial and temporal patterns of the acarological risk in forested sites across the country and to assess variations in Borrelia genospecies diversity. Ticks were collected monthly in 11 sites and nymphs were examined for Borrelia infections. Tick populations expressed strong seasonal variations, with consistent and significant differences in mean tick densities between sites. Borrelia infections were present in all study sites, with a site-specific mean prevalence per month ranging from 7% to 26%. Prevalence was location-dependent and was not associated with tick densities. Mean Borrelia prevalence was lowest in January (4%), gradually increasing to reach a maximum (24%) in August. Borrelia afzelii represented 70% of all infections, with Borrelia burgdorferi sensu stricto, Borrelia garinii, and Borrelia valaisiana represented with 4%, 8%, and 10%, respectively. The density of infected nymphs and the proportional distribution of the four Borrelia genospecies, were significantly different between sites. The results show a consistent and significant spatial and temporal difference in acarological risk across the Netherlands.

Nieuwe richtlijn voor preventie van en omgaan met tekenbeten en lymeziekte tijdens het werk

SamenvattingIedereen kan vroeg of laat tijdens werken in een groene omgeving geconfronteerd worden met tekenbeten. In veruit de meeste gevallen is een tekenbeet onschuldig.

Tick – Borrelia interactions: burden or benefit?

A key factor in the success of parasites is the ability to move between hosts. Some parasites make use of an intermediate arthropod host to move between their primary hosts. Several examples exist where such parasites manipulate their intermediate host to enhance their transmission, but examples for ticks are scarce. In this chapter, we describe how Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis, is associated with changes in the behaviour, physiology and survival of Ixodes ticks. Such changes can lead to more effective host finding for the tick and better colonisation of new hosts by Borrelia. We discuss how these changes may lead to an increased transmission (risk) of Borrelia. A next-generation matrix approach is applied to model potential effects of increased tick survival on the basic reproduction number R 0 of Borrelia. Using this approach, we show that Borrelia-associated increased survival of ticks can have a profound effect on the circulation of spirochaetes, and hence on Lyme borreliosis risk. Future studies would ideally resolve the mechanisms behind the described changes, and establish experimentally whether Borrelia can enhance its circulation between hosts.