I rescued a goose a couple months ago. She was very undernourished, and took her to the vet for a health check. She looked terrible, but her fecal sample was clean. I've heard geese can get worms, and I'd have thought the way she looked she had something!
Their body temps are very high, naturally, and this prevents a lot of parasites from finding a home in them. So if they have a reasonably clean environment, a reasonable diet and mostly fresh water, they probably won't get parasites at all, not like chickens and turkeys.
