Human tick infestation pattern, tick-bite rate, and associated Borrelia burgdorferi s.l. infection risk during occupational tick exposure at the Seedorf military training area, northwestern Germany

The human tick infestation pattern, tick bite rate, and associated Borrelia burgdorferi s.l.-infection risk were investigated during occupational tick exposure of military personnel at the Seedorf military training area, northwestern Germany, from January to December 2009. Borrelia burgdorferi s.l. seroconversion rates were monitored from April to September 2009. Continuous occupational health surveillance and education were established. Feeding ticks were mostly removed by medical personnel, transferred to 70% ethanol, identified, and tested for B. burgdorferi s.l. Pre- and post-exposure sera were screened for B. burgdorferi s.l. antibodies. A total of 710 feeding ticks was removed, 704 (99.2%) of which were I. ricinus, 5 were I. hexagonus (0.7%), and one was H. concinna (0.1%). Of the I. ricinus specimens, 63.9% were nymphs, 24.7% larvae, 10.9% adult females, and 0.5% adult males. The tick bite rate among occupationally exposed personnel was 42.2% from April to September 2009. Up to 18 simultaneously feeding ticks per person per exposure incident were detected. The mean number of attached ticks was 2.0 ± 2.2 per person per exposure incident. Overall, 86.4% of all feeding ticks were removed from patients within less than 24 h after attachment. Borrelia burgdorferi s.l. DNA could be detected in 3.5% of larval, 4.4% of nymphal, 13% of adult female, and 33.3% of adult male ticks, indicating a mean prevalence of 5.3%. Among the genospecies detected, B. afzelii accounted for 84%, B. burgdorferi s.s. for 11%, B. garinii for 3%, and B. spielmanii for 3%. The overall seroconversion rate in 566 personnel exposed from April to September was 1.7%, and 0.7% acquired clinical Lyme borreliosis. Experiences reported herein indicate the need to further improve personal protection measures, health education, and medical staff training in order to minimize exposure to ticks and optimize diagnosis of tick-borne diseases.