The pathway to the brain is a subject of significant research, but currently, no comprehensive answer exists. In TSE linked to consuming TSE-infected material, it is theorized that once prions are ingested, they are taken up by the lymphoid tissue that drains the gastrointestinal tract including Peyer's Patches and other nodes. Prions also have been found in tonsil, spleen and appendix. From the lymphatic system, research suggests that prions replicate, access and move through the autonomic nervous system to the central nervous system.14 Once in the brain, the higher concentration of cellular prion protein speeds up the replication process. Prions also may enter lesions or wounds in the oral cavity and access the vagus nerve as a pathway to the brain.13
Recent laboratory research using fluorescent dye to "brand" scrapie proteins has tracked prions as they invade nerve cells and then travel along wire-like circuits to points of contact with other cells.9 This appears to be the way the prions that cause TSE invade nerve cells and are transported along neural circuits throughout the nervous system.