Total 817 cases of tick bite were collected during 21 years from 1980 to 2000 including 261 cases without tick specimens. Tick activity started in late April and finished at the end of October, with maximum activity in June. Distribution of tick bite sites was generally recognized on the body (51.4%), but, the under-10-years-of-age group was predominantly infested in the head region including the auditory canal (81.9%). Two major tick species (Ixodes ovatus and I. persulcatus) prevailed in the low and high lands of Hokkaido. In 1990, we encountered two male cases showing erythema migrans after I. persulcatus biting. The former showed seropositive to antiborrelia antibody, but, the latter gave seronegative result. The author considered that this was a case of seronegative Lyme disease although there was no examination of the isolated agent from the skin. In 1992, erythema on the tick bite skin appeared in two female cases without tick specimens. Therefore, we attempted borrelial isolation from the skin tissues. Small pieces of skin were removed by aseptic surgery and put into BSK medium kept at 32℃. We succeeded in detecting the agents from two cases of skins. Following these cases, all of the skin with tick bite were cultured in BSK medium, especially the cases with appearance erythema case. Total 51 isolates were found from skins with erythema, two Borelia afzelii and the remainder B. garinii. All of these removed the tick by themselves with their fingers within several days, and almost all of them developed erythema except two cases, because the tick was removed from these two victims within a short period (1 or 2 days) of tick infestation. Of the 30 cases where I. persulcatus was removed surgically, the tick and the skin of the patient were checked for the presence of the Lyme disease agent. Although all the ticks were positive for the agent, no agent was found in the skin of the patients. Therefore, I considered that the transmission of agents takes place by regurgitation of spirochetes from the midgut of the tick due to the pressure by fingers. I recommend that the infested tick be removed surgically in a clinic, or by using a pair of tweezers with a firm grip around the mouthpart of the infested tick within 24 hr.
