There are several intestinal worms that infest dogs. The most common intestinal worms are: Roundworms, Hookworms, Whipworms, and Tapeworms. However, the one that is most commonly SEEN by the owner is the Tapeworm. It looks like a small grain of rice. The dog is not actually passing the whole worm. It is actually passing an immature worm that breaks off the mature worm. The mature tapeworm can be several inches long and is flat. Occasionally, if the worm burden is high enough, the owner may also see Roundworms. These are long spaghetti shaped worms. Most of the time the dog is only passing the worm eggs which are microscopic.Symptoms of intestinal parasite infestation include: weight loss (or failure to gain weight) and loose stools. Occasionally in small puppies, you will also see vomiting. Hookworms can also cause bloody stools.
Another common intestinal parasite is Giardia. This is not a worm, but is a protozoa organism. Dogs with Giardia infections usually have very loose stools to runny diarrhea.
Puppies will often times have multiple infestations. It is common for them to have Roundworms, Hookworms, Whipworms, and Giardia all at the same time. This is why it is very important to deworm puppies. Typically, your veterinarian will deworm your puppy at the same time that it receives its vaccinations.
Roundworms, Hookworms, Whipworms, and Giardia are all transmitted fecal-orally through the ingestion of the eggs. The infested dog will pass the eggs in their stool and then the next dog usually picks the eggs up on their feet. Then, when they groom themselves, then ingest the eggs. The eggs then mature into adult worms.
Tapeworms are transmitted by the flea. Dogs typically get tapeworms from the biting at the fleas that are biting them. They then accidentally ingest the flea and the immature stages of the tapeworm are released and mature into tapeworms. Cats often become infested with tapeworms by eating a rodent (rat/mouse) that has fleas.
Most Heartworm medications also contain medication that will kill Roundworms and Hookworms. So, you are giving them a monthly heartworm and intestinal worm treatment with each monthly dose.
Tapeworms are not killed by most Heartworm medications. Also, most over-the-counter medications DO NOT kill Tapeworms. It is important if you see evidence of your pet passing Tapeworms to make sure you are using a dewormer that kills them.