We could change our body's environment by raising our body temperature. The environment would not be as favorable to parasites.
You asked what could be done to fix things. The answer depends of what the problem is--thyroid or adrenals. There is a link inside the link I posted which has a suggested treatment plan.
I thought my problem was thyroid, too. But discovered it's adrenals. The problem has worsened gradually since I've had parasites 3 years now.