Of all the parasites a dog can catch, worms take home first prize for Most Disgusting. Nobody wants to imagine little worms crawling around in their dog's digestive system, but it's a fairly common ailment that's easily passed from dog to dog. So if he does happen to contract them, tell your furry fella not to feel ashamed of his worms! They're easily prevented and controlled with medication that your vet routinely prescribes to hundreds of pooches just like him.