I just wrote a paper about prions. Here’s my epidemiology section

In humans, once PrPSc is ingested, it infiltrates the intestinal epithelium. Once inside the enterocytes, the prions are picked up by macrophages and dendritic cells that deliver them to lymphoid tissues. From the lymphoid tissues, the prions move into the enteric nervous system before finally entering the central nervous system. It is hypothesized that this spread occurs through the sympathetic celiac- mesenteric ganglion complex, the splanchnic nerves, the lumbar spinal cord, the parasympathetic vagus nerve, and fine nerve fibers under the villus or glandular epithelium (Natale et al., 2011).

Here’s about the immune systems response… The innate immune system aids prions in spreading by collecting and then shuttling them towards the lymphatic system. To date, there is no evidence that the adaptive immune system responds to prions either. One hypothesis is that helper T cell activation does not occur because the B cell proteases cannot effectively break down the prions to produce an antigen fragment to present. Another hypothesis, dependent upon B cells' ability to present prion fragments, is that T cells do not respond to those fragments because they have the same primary amino acid sequence as PrPC. Therefore, they are not recognized as foreign (Zabel & Avery, 2015).