Despite your best efforts it is almost impossible to keep your dog from getting worms. In the course of his life every dog will contract some kind of worm.
Heartworms roundworms hookworms tapeworms coccidia and whipworms are some of the most common types of worms that dogs can contract.
While heartworms are the most dangerous even those that do not pose a life-threatening threat can cause significant problems. Moreover a dog can get infected so easily.
Worms are typically excreted through feces and even if the poop is removed and disposed of they may stay in the soil.
By killing or paralyzing the worms dewormers allow the body to eliminate them. If you use a broad-spectrum drug to eliminate all worms or medications designed to target specific parasites such as giardia or coccidia the process is basically the same.
There are drugs that show results in as little as 2 hours and others that can take up to 12 hours to kill parasites.
Whenever you deworm your dog you should examine his feces regardless of how unpleasant it might be. Although some parasites are too small to be seen with the naked eye others are large enough to be visible in a dogs feces.
There are some tapeworms that are broken into smaller pieces while others are intact. Even after the paralysis wears off some are still alive. Worms may be found in the dogs stool for 1-2 weeks and there is nothing to worry about. Although its a little gross at least the medicine is working.