But like I said, the most likely culprit is tapeworms, because if you get your
dog wormed at vet visits, and you keep your
dog on a monthly heartworm preventative like Heartgard, then intestinal worms are generally not a problem, except for tapeworms. Heartgard takes care of all worms except tapeworms. Tapeworms have to be treated with another wormer (like Panacur).
Tapeworms are caused by fleas.