Deworming Puppies: What To Expect

What are the common parasites inside puppies, what are the signs a puppy has them, and how are these prevented or treated?

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If a puppy is infected, his feces or urine might contain parasites that could be passed on to you. alexsokolov/iStock/Thinkstock
If a puppy is infected, his feces or urine might contain parasites that could be passed on to you. alexsokolov/iStock/Thinkstock
Dr. Brian Roberts

Have you ever watched some of those veterinary shows on the Animal Planet network? My son, who is 8, loves the show called “Monsters Inside Me,” which focuses on people who get infections, notably those caused by parasites. During an episode, he asked me if animals get parasites like people, and I replied, “Well, of course and a matter of fact, many animals harbor parasites that can then get transmitted to other animals and people.” The fact that a TV series can focus on parasitic infections exemplifies their importance and interest to veterinarians and medical doctors.

This article focuses on parasites and puppies. Puppies are immature dogs, and the word “puppy” describes dogs from birth to sexual maturity, which is around 4 to 6 months of age. It varies depending on the breed. You may have heard the term “deworm” which is, basically, treating for parasites using drugs called anthelmintics. Given the term deworm, people seem to mainly think about worms, but a couple of other categories of parasites are worth mentioning.

Common Parasites That Affect Puppies

There are five main groups of parasites that commonly infect puppies:

  • Ascarids (roundworms)
  • Nematodes (hookworms, heartworms, whipworms)
  • Cestodes (tapeworms)
  • Coccidia (Isospora, Cryptosporidium)
  • Protozoa (Toxoplasma and Giardia)

Only a few of these parasites can be easily seen: tapeworms, whipworms and roundworms. The rest are microscopic, and they are identified in body fluids, primarily in the feces. So, if your puppy has diarrhea but you don’t see any “worms” that doesn’t mean parasites are not the cause! The most important being roundworms, hookworms, coccidia and tapeworms.

What Parasites Are Most Common In Puppies?

While parasites can infect dogs at any life stage, puppies are a concern because they don’t have a mature immune system, they don’t have a lot of fat stores to use for energy and they have higher fluid intake demands than adults. Because most of the common parasites cause inappetance, diarrhea and vomiting, loss of fluid is more harmful to puppies than adult dogs. Some parasites are spread to puppies through their mother via the placenta or through mother’s milk — roundworms are a key example of this. The following table gives you an idea of how common these parasites are:


So, in puppies, the greatest concern is infection with roundworms and hookworms because they are very common and cause serious illness. Tapeworms and whipworms, while sometimes found as frequently or more often, don’t cause as serious of disease in puppies.

Symptoms And More Of Specific Parasites


Diagnosis Of Worms And Other Parasites In Puppies

Some puppy parasites are large enough to see and can be found in the feces or on the areas around the anus. I would say the most common is the tapeworm. Tapeworms are made up of segments (proglottids) where their eggs are contained. They shed these segments in the stool, and many puppy owners see these segments in the stool, on their puppy’s fur or on the ground. They look like small maggots or cooked rice grains that move — YUCK!

Even if you see parasites in your puppy’s stool, a veterinarian should still examine him to determine exactly what is infecting your puppy. Choosing the treatment, knowing if the parasite is a danger to you, other pets or your family, and the need for environmental/home cleaning all depend on the type of parasite causing the infection.

Have you ever been asked by your veterinarian to “bring in a stool sample”? Well, that’s what we examine to search for parasite eggs and microscopic parasites. This is the most common method to diagnose roundworms, hookworms, whipworms and coccidia. Other parasites, namely whipworms and Toxoplasma, don’t shed their eggs routinely in the stool. There are other tests of the blood and serum for those parasites whose eggs are not readily found in feces; these are mostly used for Giardia.

Treating Worms And Other Parasites In Puppies

Many treatments are available for control of parasitic infections, and these come in many formulations: pills, chewable treats, liquid, granules added to food, pastes and injections. The benzimidazoles are most popular and include drugs like fenbendazole, mebendazole and albendazole. This class of anthelmintics (anti-parasite drugs) are used to treat roundworms, tapeworms, hookworms and whipworms. A typical treatment protocol would be to give the product for one to three days and then repeat the dosing in two to three weeks. The repeat dosing is used to kill the parasites that were not adults (eggs, larvae) during the first treatment but have now “grown up.” Most life cycles of puppy parasites are around three weeks long.

Other parasite treatments include praziquantel, used for flukes and tapeworms; pyrantel pamoate for roundworms and other nematodes; and macrocyclic lactones like ivermectin and milbemycin found in heartworm preventives. So, by using most monthly heartworm preventives, you can also treat for intestinal parasites.

Side Effects Of Deworming Puppies

For the most part, the major classes of anti-parasite drugs (avermectins/benzimadizoles) have a very high margin of safety, meaning that giving too much will rarely cause problems. That being said, always follow your veterinarian’s recommendations for deworming.

Puppies with a large number of parasites (high worm burden) may become ill after treatment. Imagine all of the parasites in the intestines all dying at once, the lining of the intestines become inflamed, causing diarrhea, vomiting and lack of appetite. This is usually a self-limiting problem, and puppies are back to normal within a day or so.

Use of heartworm preventive in higher doses (ivermectin) is very effective against most parasites; however, some breeds cannot tolerate the higher dose. This relates to a mutation in a gene called MDR-1, which codes for proteins that protect the brain (blood-brain barrier). When dogs with MDR-1 mutation get drugs like ivermectin, opiates (morphine-like painkillers) and chemotherapy, they can have serious problems like lapsing into a coma, tremors and death.

Prevention: Puppy Worming Schedule And The Environment

Using many of the same drugs for treating parasitic infections will also prevent them. Current recommendations from the CDC and the American Association of Veterinary Parasitologists are to provide deworming medications against roundworms and hookworms at 2 weeks of age, repeating the dewormer every 2 weeks until the pups are 2 months old. Ideally, treat monthly from 2 months to 6 months of age to eliminate different developing stages of the intestinal parasites.

Puppies should be dewormed using the above protocol despite fecal exam results. Puppies may have prepatent infections with minimal to no parasite eggs being shed in their feces.

Pregnant dogs should also be treated to try to prevent transplacental infection to the fetal pups and to prevent transmission through nursing. Your veterinarian will provide a plan for you, because there are a few regimens available.

Housing conditions and location are important factors related to parasitic infection. Puppies housed together, with frequent exposure to new dogs and puppies, are more likely to become infected. Unclean conditions, exposure to other animals’ feces, and transmission from other creatures — like fleas, mosquitoes and cockroaches — increase the chance of infection, too.

Natural Dewormers

As with any medical product, there are persons who search for more “natural” ingredients. The problem is that there is little scientific data proving or disproving their effectiveness. Many products have multiple ingredients like sage leaf, fennel seed and papaya leaf. Although individual ingredients can have some degree of anti-parasite activity, the exact dose and combination needed to kill and prevent parasites is largely unknown to the scientific community.

Some naturalistic and holistic health care providers recommend products like diatomaceous earth and garlic to prevent parasites from infecting the GI tract. I could find little peer-reviewed, scientific information on whether that combination truly is effective in puppies. However, there was one paper that stated garlic and papaya do not control parasites in goats and lambs.

In my opinion, because the more modern dewormers (fenbendazole, praziquantel, pyrantel) are so safe, proven and relatively inexpensive, there is no need to experiment with herbs and plants on your puppy to treat his or her worms.

Puppy Parasite Danger To Humans

Not only do many of these parasites cause illness in puppies, but some can infect people and other species like cats. Contagious agents that infect multiple species and spread from animals to humans are called “zoonotic.” Hookworms and roundworms can invade broken skin, causing “larva migrans,” which are parasites that migrate through an unsuitable host. Parasites need their hosts to not only get food, but also to complete their life cycle and reproduce.

When puppy parasites like hookworms, roundworms and Toxoplasma infect people, those parasites cannot complete their life cycle. However, they will cause problems! For example, say you are playing catch in the dog park and bend down to tie your shoelace. Then you wipe your brow, unsuspectingly infecting your eye with a dog roundworm. Well, that worm can cause ocular larva migrans. It will actually grow and move around inside your eye, and could cause blindness. Visceral migrans occurs when roundworms migrate through the inside of the abdomen, causing damage to internal organs. Canine roundworms are the leading cause of visceral and ocular larva migrans. Hookworms cause cutaneous larva migrans; they penetrate the skin and live under the surface, creating red, irritated marks. I tell my kids that they are never to run around a sandbox or playground without their shoes on because stray dogs and cats frequent those areas to find food from trash bins. It’s likely that they’ll also urinate and defecate in those same areas, infecting the ground with parasites.

If you have children, then you’ve probably heard about toxoplasmosis, which is caused by Toxoplasma gondii, a very common parasite found in cats. Toxoplasmosis can cause birth defects and death of the fetus, in dogs and in humans. This protozoan needs a feline host and most cats never become ill from it. They shed Toxoplasma oocysts in their feces. This parasite is not a major problem for puppies.

Coccidia and Giardia are also zoonotic and many dogs will have a few of these parasites but not have illness associated with them. Some experts believe that all dogs have coccidia and Giardia as commensal organisms, like the bacteria that live in your mouth. Most recommend only treating for these parasites if symptoms of vomiting, diarrhea and such are present.

Cryptosporidium is a major problem in cows and other ruminants. Dogs are rarely affected, but puppies and dogs with compromised immune systems can get sick, typically with vomiting and diarrhea. Luckily the strain that infects cows and people rarely is found in puppies. That strain led to a major outbreak of illness in Milwaukee back in 1993. It was the largest waterborne outbreak of disease in U.S. history!

In The Know About Parasites In Puppies

I hope that you now have plenty of information about parasites affecting puppies. Remember, all puppies should be treated from 2 weeks of age to 8 weeks of age, minimum. Products like fenbendazole are very safe and effective. Many parasites that your puppy may have can infect you and your family, like roundworms and hookworms. Please speak to your family veterinarian about parasite control and stay away from “Dr. Google,” where you’ll find thousands of testimonials on how a homemade brew of herbs and such cured a puppy’s whipworm infection.

Article Categories:
Dogs · Health and Care · Puppies


  • I wormed my puppy he’s probly almost 11weeks, I think I gave him to much. Now he won’t eat and he sleeps alot but he does drink some water. It also been a few days what do I do? And I also don’t have a lot of money for the vet.

    Samantha May 17, 2016 10:38 pm Reply
    • What happened to your dog now samantha? Because my pup is experiencing the same now.

      Jean June 3, 2016 9:55 am Reply
  • What happened to your dog now samantha? Because my pup is experiencing the same now.

    Jean June 3, 2016 9:54 am Reply
  • Thank you for this article! It was very educational.
    However, I don’t think your mockery of natural medicine was very mature or professional. Those who are researched in such medicines, like myself, are aware of the effectiveness of diatomaceous earth and recognize the truth of it’s nature as a cure.
    I bought a neglected, malnourished, potbellied pup with a bad case of parasites out of compassion, and after a few days of diatomaceous earth she lost the wormy belly and is now simply skinny, and so I’m using healthy fattening supplements to bring her to the proper weight.
    In these natural treatments, I saw no signs of an undeveloped hick band-aid solution, but rather of an effective, well-evidenced alternative to the medicines supported by the veterinary community.
    Thank you for your effort in writing the article.

    Marilyn October 18, 2016 8:20 am Reply
    • The author most certainly did not mock naturopathic / natural remedies. But given that roundworms and other worms can cause serious problems in immune-compromised adults and children… I agree that you should stick to proven remedies such as the medications mentioned in the article. Improving, I mean that there is valid scientific research to show that they either work or do not work for their intended purpose. And they are not at all expensive. So do yourself and your dog a favor and you’ve proven treatment. To do otherwise, in my humble opinion, is animal neglect and cruelty.

      DDr Will November 6, 2016 11:58 am Reply
    • As stated in the article, there is little peer-reviewed scientific research regarding natural remedies. It would be “malpractice” for me, the author, to recommend unproven therapies which may not be effective, which may do harm and which may increase the risk of zoonosis because they didn’t work. If you want to use them, it’s your choice, but I cannot recommend them until the research proves their efficacy

      Bkr Bkr November 6, 2016 12:19 pm Reply
  • My puppy is approximately 2-2 1/2 months old. When I first got her she was pitiful!! (We have all 3 pups that were left basically to die&i wasn’t about to let that happen!!!) But my fiancé and I got them some dewormer.. They got waaaay better within the first week and a half but worms keep showing up in only ones feces. Also I have found a few on her tail while she was asleep. I really love my baby girl and I really need to know if I need to do more than just give her the medicine! She eats and drinks good but she has whined more than usual in the past couple days. I’m just worried about my girls! Help please! Thank you!

    Shiann October 27, 2016 10:35 am Reply
  • My baby boy is going on 3 months this Friday he’s had his first 2 sets of shots but hasn’t been wormed is it ok to do it know once a week or what ????

    EMMA November 1, 2016 5:56 pm Reply
    • You refer to a baby boy. If this is a human infant, consult your pediatrician. If you are only referencing a canine, fall of the information in this article, or contacted veterinarian.

      For the record, some of us are deeply offended when people refer to pets as their children. I have a real child and don’t like him being compared to a dog. We also have a dog which we do not call our child. Agree or disagree with me, but please respect my right to have a different opinion.

      Dr Will November 6, 2016 12:01 pm Reply
  • Thank you Dr. Roberts for one of the most complete and insightful articles regarding this problem that I have found on the internet. We recently purchased a Cocker Spaniel puppy at 10 weeks of age. At 4 months of age, we saw obvious roundworm in his stool and immediately traded with deworming medication. We have an autistic child, so we’re somewhat concerned about him getting worms from the puppies. You have largely put my fears to rest.

    Prophylactic deworming during the puppy stage is a reasonable strategy given the relatively low cost of the medication.

    I have seen worms in children. It can cause a variety of problems including loss of weight. If the position doesn’t look for worms, often their parents are investigated for neglect. It’s an area that Physicians need to be better trained in also.

    If you do revise this article, I would ask that you talk about regions of the country where certain words are more prevalent. And what times of the year they are more prevalent. Also talking about the different flea / tick products out there would be helpful. We use an advantage / top spot flea and tick medication once a month. And of course we attend regular vet visits for immunizations.

    Our puppy (American Cocker Spaniel) is a very expensive purchase, and our son is forming an emotional bond with him. So is my wife. I cannot look at him as anything other than an animal, so I don’t become emotionally attached. Although I would like to take him hunting with me, as he appears to have all the natural skill for being a good bird dog.

    Dr Will November 6, 2016 12:08 pm Reply

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