If he is showing signs of illness, then you might want to treat--but it doesn't really sound like worms to me. Some sort of respiratory illness--I'm no diagnostician so I can't really help--but I'd keep an eye on it.
DE is diotomaceous earth (and I've almost certainly spelled it wrong). It's available from farm supply stores & catalogs, and gardening stores too. It's the fossil remains of tiny creatures, and it has very sharp edges that tend to make the earth unpleasant for insect critters, and therefore serves a pretty good reducer of insect pests. You simply spread it directly on the earth around the areas you want to de-bug. It is non-toxic to animals.