Ixodes ricinus density, Borrelia prevalence and the density of infected nymphs along an urban-rural gradient in southern England

Abstract

Ticks are found across a range of habitats, with woodland being particularly important for high densities and prevalence of Borrelia infection. Assessments of risk in urban woodland can be difficult if there are low densities and small sample sizes for Borrelia prevalence estimates. This study targeted six urban woodlands with established tick populations, as well as six woodlands in peri-urban zones and six woodlands in rural zones in and around the cities of Bath and Southampton, in the South of England. Nymph densities were estimated, and 100 nymphs were tested from each of the 18 woodlands studied. Ixodes ricinus ticks were found in all woodlands surveyed, and overall density of nymphs (DON) per 100 m2 was 18.17 in urban woodlands, 26.0 in peri-urban woodlands and 17.67 in rural woodlands. Out of 600 nymphs tested across urban woodlands, 10.3% were infected with Borrelia. The same proportion of nymphs collected in rural woodlands were positive for Borrelia. In peri-urban woodlands, 10.8% of nymphs tested positive. Across both cities combined, density of infected nymphs (DIN) was 2.73 per 100 m2 in peri-urban woodland, 1.87 per 100 m2 in urban woodland and 1.82 per 100 m2 in rural woodland. Overall, DON, Borrelia prevalence and DIN did not differ significantly along an urban-rural gradient. This suggests the risk of Lyme borreliosis transmission could be similar, or perhaps even elevated in urban woodland if there is higher public footfall, subsequent contact with ticks and less awareness of the risks. This is particularly important from a public health perspective, as Borrelia garinii dominated across the gradient and this genospecies is linked to neuroborreliosis.