Limited occurrence of Borrelia burgdorferi sensu lato in the European hedgehog (Erinaceus europaeus) and Ixodes hexagonus in Great Britain

Abstract

Borrelia burgdorferi sensu lato (Bbsl) are multi-host bacteria and the causative agents of the zoonotic disease, Lyme borreliosis, for which Ixodes spp. are the vectors. In Great Britain (GB), research to date has primarily focussed on Ixodes ricinus as the main tick transmitting this pathogen, while the role that the European hedgehog (Erinaceus europaeus) and the hedgehog tick (Ixodes hexagonus) might have in the transmission cycle requires investigation. This study aimed to examine the occurrence of Bbsl infection in hedgehogs and I. hexagonus in GB; to characterise the species if present; and to better inform our understanding of these species as potential hosts or vectors. Post-mortem examinations have been conducted on hedgehogs found dead from across GB over the period 2013–2022 inclusive. We collated the available convenience sample archive from 96 hedgehogs for which both frozen ear tissue and Ixodes spp. (comprising 563 I. hexagonus, 18 I. ricinus and one Ixodes frontalis) in 70 % ethanol were available. Supplementary tissue samples were analysed from the hedgehogs where either ear tissue or ticks tested Borrelia DNA-positive, to investigate whether the infection was localised or disseminated. An additional 86 I. hexagonus collected from 14 hedgehogs with no ear tissue available were included to increase the sample size. DNA from tissue and tick samples was tested using a pan-Borrelia qPCR assay. Only 4.2 % (4/96) of hedgehogs and 1.2 % (4/335 total: 0.6 %, 2/329 I. hexagonus; 40 %, 2/5 I. ricinus) of tick pools were qPCR-positive suggesting that Bbsl infrequently circulate in hedgehog and I. hexagonus in GB. Therefore, both species may play a limited role in wider transmission cycles in this country. Borrelia afzelii was the sole species characterised by subsequent sequence analysis in both hedgehogs and ticks, providing some evidence of host-vector interaction at larval and nymph life stages, as all the positive ticks were collected from B. afzelii DNA-positive hedgehogs. Histopathological examination of hedgehog tissues found no evidence of borreliosis and therefore no clinical significance of B. afzelii infection to hedgehog health. The low occurrence of B. afzelii detected in I. hexagonus, combined with the lower frequency of human biting behaviour of I. hexagonus when compared with I. ricinus, suggests that the public health risk of infection from I. hexagonus bites is lower than for I. ricinus. Notably, our dataset found minimal co-feeding of these tick species on hedgehog hosts in contrast to studies in mainland Europe, which could influence pathogen dynamics in GB.