Helically shaped microorganisms were observed in the cerebrospinal fluid (CSF), blood and cerebral cortex in 14 AD cases that were absent in 13 controls (Miklossy, 1993, 1994a). 

Illustration of spirochetes in the cerebrospinal fluid (A, B) and isolated from the cerebral cortex (D, E) compared to reference spirochete (C)(Borrelia burgdorferi B 31 strain) in patients suffering from neuropathologically confirmed Alzheimer's disease. (Miklossy, 1993, Fig. 1)

In three of these 14 AD cases, spirochetes were grown in a medium selective for Borrelia burgdorferi.

Illustration of spirochetes cultivated from the brain of a neuropathologically confirmed AD patient in BSK II medium, shown in dark field illumination (Miklossy, 1993).

Based on these observations it was proposed that AD may correspond to late stages of neurospirochetoses caused by various types of spirochetes, including oral spirochetes, Borrelia burgdorferi and various other spirochetes.