Besides that fact that in this particular case there probably really is 'something' (it would be rare for the brain to spontaneously exhibit CJD symptoms, though it does happen this would most likely not lead to a cluster of cases), you don't need to propose an infectious disease for people that say they have symptoms where there are none, when there is ample proof of people being able to influence each other into believing all kinds of crap to the point that it becomes part of their identity.

I once had a woman and her husband visiting to inquire about buying a house I owned in Northern Groningen, pretty much as far away from anything as you could possibly get in this crowded country. They arrived in a taxi that was blanked for the day (it turned out the man was a cab driver) and after looking the place over and liking it visibly the woman said 'oh, we really like it, but there is one more thing, I am allergic to electromagnetic radiation so let me verify that' (eye roll by the man at this point). She went to the car and came back with a box with a dial on it that she had bought online (a pretty basic field strength meter, set to the most sensitive part of the range) and started walking around muttering to herself and waving the box around like a modern day dowser.

After a while of this she came to me and said she was really sorry but she had to drop her interest because the house was absolutely infested with EM fields. In Amsterdam, where they lived, they had turned their whole apartment into a cage of Faraday with copper mesh nailed against every surface (it turned out they lived right opposite the KPN microwave tower next to the RAI so maybe she even had a point, that thing featured multiple RF links beaming 100's of Watts on tight beam links between other such towers, at some point in the past these carried our long distance phone calls before fiber came along).

I asked if I could see her box for a second and pointed it at the sun: the needle pegged instantly and she was most surprised, so I explained that what she is measuring is real, but so faint that the chances of any kind of interaction with her body are most likely delusional.

Here the conversation abruptly ended...

As for TFA: prions, the agents responsible for CJD are remarkably resilient and annoying and can make it through the foodchain across the digestive barrier and into the brain and even a single one of them can cause CJD.

https://www.nhs.uk/conditions/creutzfeldt-jakob-disease-cjd/