Identifying key determinants of Lyme borreliosis distribution in Northern England

Professor Richard Birtles (r.j.birtles@salford.ac.uk)

Lyme borreliosis (LB), caused by infection with spirochaete bacteria belonging to the Borrelia burgdorferi sensu lato complex, is now the most commonly reported vector- borne infection in temperate regions of the world.

In the UK, the incidence of LB has increased by over 500% in the last decade, with over 1500 cases being reported in 2009. The ecology of LB is complicated by the presence of distinct genospecies, each of which is typically associated with a particular reservoir host group. For example, B. afzelii is considered of rodent origin whilst B. garinii and B. valaisiana are associated with birds.

The UK vector of primary epidemiological interest is the sheep tick (Ixodes ricinus) which is widely distributed, particularly in areas of high deer abundance. However, the distribution of B. burgdorferi does not simply correlate with the distribution of I. ricinus. Data from pilot studies in the North of England indicate that in some areas of high tick abundance B.burgdorferi is absent from the tick population. The ecological basis for this variation is currently unknown, and addressing this shortfall is the principle aim of the proposed GTS project.

Utilising sites that have already been identified as having high or low infection prevalence in ticks, the GTS will use a variety of field and laboratory techniques to attempt to quantify those factors that help determine infection prevalence in the tick population. In particular they will: (i) survey questing ticks from sites to determine the dynamics of tick populations and of B. burgdorferi infections (sensu lato and delineated genospecies) in these populations, (ii) optimise and apply molecular blood meal analysis techniques to identify the relative importance of different vertebrate hosts as hosts for ticks and as providers of B. burgdorferi-infected blood meals, thereby to determine correlation between vertebrate host community structure and B. burgdorferi distribution, and (iii) exploit remote sensing data to quantify the importance of the physical environment in B. burgdorferi distribution.

The data from all these sources will then be collated to develop statistical models to enable identification of those factors that play a significant role in determining the distribution of B. burgdorferi. Such information will enhance our understanding the environmental risks associated with the acquisition of LB in the UK, and therefore contribute to control of the disease.

This project is part funded by Merial UK, one of the world’s leading animal health company as part of a growing “One Health” collaboration focused on understanding the epidemiologies of tick-borne diseases of medical and veterinary (livestock and companion animals) importance in the UK.