Detection of Rickettsia in ticks using loop-mediated isothermal amplification (LAMP)

Objectives: The objective of the study was to develop a Loop-mediated Isothermal Amplification (LAMP) assay for screening of Rickettsia species circulating in ticks using the citrate synthase gene (gltA). The LAMP assay employed portable visualisation methods, making the assay more field-suitable. Furthermore, prior methods have not used gltA as the target, despite proven success in Polymerase Chain Reaction (PCR) methods. Methods: Using an alignment of 72 DNA sequences (comprised of 21 Rickettsia species) from GenBank we designed a novel set of gltA LAMP primers. Evaluation used DNA from 12 Rickettsia species as positive controls (extracted from cultures or naturally infected ticks) alongside a panel of negative controls representing different bacterial species. Subsequently this assay was used to screen 295 Ixodes ricinus and 24 I. hexagonus ticks collected from the UK (including northern and southern England and northern Scotland). Results: LAMP successfully detected 11 out of 12 (91.7%) Rickettsia species, excluding Rickettsia akari. Among 319 ticks collected in the UK, three were positive for Rickettsia (0.9%). All three positives were I. ricinus ticks, while none of the 24 I. hexagonus ticks were positive. Results were confirmed using a published PCR method. Sanger sequencing of PCR amplicons generated for each positive tick showed that they were all R. helvetica. Conclusions: This study introduces a novel field-applicable LAMP protocol for efficient Rickettsia screening in ticks to better assess its prevalence and consequent health risks. Furthermore, this assay has proven suitability for rickettsial detection in I. ricinus ticks, which has been reported as unsuccessful in previous European studies.