Parasites used to be ubiquitous before we had medication to kill them. There's even a (not very well supported) theory that these parasites helped with allergies by moderating immune system. They releasing chemicals to lower immune activity in order to protect themselves, so the idea that we had these for thousands of years and basically are made to have them is intriguing. It's called "helminthic therapy" and it's considered alternative medicine but there is some academic interest. Results in clinical trials have been mixed. Perhaps the future is just synthetic hookworm proteins that regulate your immune system as our ancestors once had.

My partner researches one parasite named in this study (a type of whipworm) and they actually get their eggs for in vitro work from another researcher abroad who infected himself with the parasite because he finds it helps with his autoimmune disease. He harvests the eggs and distributes them to other teams.

The average body temperature then was also higher.

Intuitively it wouldn’t be surprising that there’s some symbiosis going on somewhere and that there would be beneficial parasites. In reality I have no idea.

There is a significantly more mainstream but similar-in-the-broad-strokes theory, the Hygiene Hypothesis, which says that the immune system relies on encountering things like this for calibration, but doesn't require them as a continual presence for optimal functioning.

Doesn't seem too off from gut micro biome theories.