One portal of entry for oral spirochetes would be the olfactory tract and bulb. If these spirochetes are involved in AD, the involvement of olfactory system should be one of the earliest events in AD .

Oral spirochetes may invade the CNS via the olfactory system. If oral spirochetes may play a role in AD, (Miklossy, 1993; Riviere et al., 2002) we anticipated that the olfactory system may be affected in early stages of AD. The analysis of 110 autopsy cases showed a close association between the cortical and olfactory AD-type changes and indicated that the involvement of the olfactory bulb and tract is indeed one of the earliest events in the degenerative process of AD (Christen-Zaech et al., 2003).