Distribution ofBorrelia burgdorferisensu lato inIxodes ricinusPopulations Across Central Britain

Abstract

Lyme borreliosis is rapidly emerging in the United Kingdom, with over 1000 cases per annum now reported. Lyme borreliosis is caused by the Borrelia burgdorferi sensu lato (s.l.) group of spirochetes, which are transmitted by ixodid ticks. In the United Kingdom, Ixodes ricinus is recognized as the principal vector of the spirochetes, and this tick species is widely distributed across the country. However, as yet, it is unclear whether the distribution of B. burgdorferi essentially mirrors that of its vector, or if there are marked differences between the 2. The aim of this survey was to investigate the prevalence of B. burgdorferi in I. ricinus populations across northern England, north Wales, and the Scottish Border region. We surveyed for questing I. ricinus nymphs and adults at 17 sites, encountering ticks at 12. At 8 sites, large numbers (>160) ticks were collected, and at 3 of these sites B. burgdorferi infection prevalence was significantly higher (>7.5%) than the other 5 (<1.0%). Habitat type was associated with B. burgdorferi prevalence, with ticks from deciduous and mixed woodland being significantly more likely to be infected than those from other habitat types. Identification of infecting Borrelia species indicated that Borrelia valaisiana was the most common and widespread species encountered. B. garinii was common at sites where infection prevalence was high, and B. afzelii was also occasionally encountered at these sites. The survey revealed a surprisingly uneven distribution of B. burgdorferi s.l. across the region, thereby indicating that the presence of ticks does not necessarily mean the presence of the pathogen. Indeed, the spirochete appears to be absent or very rare at some sites where ticks are abundant.

Borrelia miyamotoiin host-seekingIxodes ricinusticks in England

“…Although low numbers of infected ticks were sequenced (but within the expected levels for the molecular method used), this finding is in contrast to a previous study in northern England where B. valaisiana (58%) and B. garinii (33%) were reported as the most commonly detected genotypes [33] and also to a study in Scotland which reported B. afzelii (48%) and B. garinii (36%) as the most common [35]. B. burgdorferi s.l.-infected ticks were found in all survey sites except Richmond Park; however, infected ticks have been reported here previously [36].…”

“…Forty ticks tested positive for B. burgdorferi s.l. (4·2%, 95% CI 3·01-5·7), which is similar to overall prevalence rates found in other studies in the UK [33][34][35] which reported 3·3%, 5-7·7% and 5·6%, respectively. However, direct comparisons between prevalence rates need to be made with caution due to differences in sample sizes, stages of ticks tested and molecular methods used.…”

Heterogeneity in the abundance and distribution of Ixodes ricinus and Borrelia burgdorferi (sensu lato) in Scotland: implications for risk prediction

“…were found at lower prevalences. Consistent with previous reports [9, 36], B. valaisiana was detected only in seminatural mixed woodland and B. burgdorferi ( s.s .) was detected only in coniferous woodland.…”

“…in the UK have indicated broad scale patterns in genospecies distribution. Bird-associated genospecies B. garinii and B. valaisiana appear to dominate in England [6, 35, 36], with some reports of rodent associated B. afzelii [37, 38]. In Scotland, B. afzelii appears to be the most common genospecies [8].…”

“…in I. ricinus nymphs collected at higher altitudes [8] and a higher prevalence of infection associated with semi-natural mixed woodlands compared to coniferous forest [8, 9]. A study from northern England also found a higher prevalence of infection in I. ricinus nymphs sampled from semi-natural mixed woodlands compared to coniferous forests [36]. It has been suggested that the higher prevalence of infection detected in semi-natural mixed woodlands may be due to higher densities of competent reservoir hosts.…”