Worms In Dogs: Symptoms, Treatment & Prevention

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Heartworm undermicroscope (caption: Worms In Dogs: Symptoms, Treatment & Prevention)There are a wide variety of worms that can infect your dog: heartworms, roundworms, tapeworms, hookworms and whipworms. Although many of the symptoms are similar, each requires a specific type of medication for treatment.

Using inappropriate medication to treat worm infestations can worsen symptoms  and cause additional medical complications.

Article Overview

Non-Intestinal Worms

The biggest problem for dog owners in terms of non-intestinal worms is heartworms.

Heartworm Disease

Heartworms are parasites that dogs contract through bites from infected mosquitoes. As mosquitoes bite dogs, they transmit heartworm larvae into the dog’s bloodstream. The eggs travel to the dog’s heart, where they settle in the right heart ventricle and begin to duplicate.

As the worms increase in number and grow larger, they begin to cause severe damage to the dog’s heart, lungs and other major organs. Heartworms can live as long as 5 years in a dog, but the infestation usually becomes fatal before then.

Veterinarians most commonly diagnose a heartworm infection by taking blood samples and testing them for the presence of heartworm offspring.

Early signs of heartworm infection can be easy to miss, and it’s often not caught until the infection becomes severe.


Heartworm under microscope
Heartworm (Dirofilaria immitis)
  • Hair loss
  • Jaundice
  • Diarrhea
  • Respiratory trouble
  • Wheezing
  • Loss of appetite
  • Blindness
  • Increased heartbeat
  • Vomiting
  • Poor coat
  • Coughing
  • Lethargy
  • Weight loss


Treating a heartworm infestation is dangerous, and since most cases aren’t caught until dogs exhibit symptoms due to organ damage, treatment can often be fatal. Treatment involves injecting toxins that will kill the heartworms into the bloodstream; however, these toxins can also be fatal in weakened dogs.

Numerous treatments are required to eliminate infestations, and the dog must be kept confined and inactive throughout treatments.

In some cases where heartworm infestations are severe and dogs are too disabled from their condition, veterinarians may suggest forgoing treatment and opting for euthanization. Choosing euthanization may be a difficult decision to make, but dogs experience significant discomfort during advanced stages of heartworm infection.

How To Prevent Heartworms In Dogs

Preventing heartworms is easy with a large number of heartworm tablets available for monthly dosage. They vary in price, but all are more affordable than a single heartworm treatment. Some of the most commonly used heartworm preventative medications include:

Pro Tip: Medication Depends On Where You Live

Talk to your vet about the best heartworm preventative for your dog. Depending on where you live, your dog may not need to be on a heartworm preventative all year round. For example, I have my dog on Iverhart Plus from the beginning of spring through the end of fall and don’t give any medication to her during the winter because there are no mosquitoes in Iowa during those months.

Intestinal Worms

Intestinal worms populate the gastrointestinal tract of dogs where they thrive and reproduce, causing a slew of medical side effects. They’re referred to as parasites because they attach to your dog’s intestinal wall and feed by leaching your dog’s nutrients.

If left untreated, infestations of intestinal worms can become deadly by causing intestinal blockage. Your vet should test your dog annually for intestinal parasites through a fecal sample.

All puppies should receive de-wormers to ensure they are not carrying worms or worm larvae. Most of the big-brand heartworm medications also protect against the most common intestinal worm varieties to ensure that fully grown dogs are protected.

Roundworms (Most Commonly Found In Puppies)

Roundworms (also known as Nematodes) are a type of parasitic worm commonly found in young puppies. The majority of puppies have traces of roundworms or roundworm eggs in their tissue at birth as a result of migrating parasites from the mother’s tissue.

Puppies can also contract roundworms from their mother’s milk. This is one of the reasons why puppies are de-wormed as soon as they’re seen by a vet and given their initial “puppy shots.” Many breeders also administer de-wormers to ensure that their puppies remain healthy.

Once within the dog’s body, roundworms travel to the intestinal tract, where they attach to the intestinal wall and continue to grow. Some roundworms can grow as large as 5 inches long. Once roundworms reach sexual maturity, they begin shedding eggs within the dog’s small intestine. Infected dogs will pass roundworm eggs in their feces, and the eggs go on to infect other dogs exposed to the infected feces.

Once dogs ingest the roundworm eggs (these eggs can survive in soil for years), the eggs will hatch, and young roundworms will travel to the lungs. Eventually, the dog coughs the small larvae out of the lungs and swallows them. The larvae then travel to the small intestine to grow to full-sized worms.

It’s easy to see how an untreated infection of roundworms can create a cycle of infection among a neighborhood or kennel of dogs.


Roundworm under microscope
Roundworm (Nematoda or Nemathelminthes)
  • Bloated stomach
  • Poor growth
  • Vomiting
  • Diarrhea
  • Cough
  • Pneumonia
  • Anemia
  • Worms in vomit or feces
  • Bloody stool


Veterinarians treat roundworms with a de-wormer, but it should be noted: this treatment is only effective for fully grown worms living in a dog’s intestinal tract, not for eggs. It’s important to administer a full course of de-wormer prescribed for roundworms to ensure that you completely eradicate the infestation.

The most commonly prescribed medications for roundworm infestations include:

How To Prevent Roundworms

Preventing roundworms in most dogs is as easy as keeping dogs away from other dog feces and administering a heartworm preventative that also protects against roundworms.

Learn More About Roundworms


Tapeworms live within the dog’s intestines and absorb nutrients from the digestive tract through their skin. Like most other intestinal worms, tapeworms attach to the intestinal wall with their heads, though these worms utilize “suckers” to attach to the tissue. Tapeworms are segmented and can have as many as 90 different attached segments and reach as long as 6 inches.

Dogs usually contract tapeworms by eating animals that are infected with tapeworms or by eating fleas that feed on tapeworm eggs.

Each section of the tapeworm can reproduce and contains eggs. As the eggs are released, they’re passed in the dog’s feces. This is often where fleas ingest tapeworm eggs, and the cycle begins again when another (or the same) dog ingest that flea.

As the tapeworm grows, the end segments of the worm’s body will detach, and the containing eggs and sections are excreted. Most pet owners can identify the presence of tapeworms by spotting these small rice-like segments (which are often still moving) in their dog’s fur near their anus. Tapeworms can be spread from dogs to humans.


Tapeworm under microscope
Tapeworm (Cestoda, Platyhelminthes)

Dogs with a tapeworm infestation may have no symptoms at all, or they may have several general intestinal-type symptoms.

  • Itching around the anus
  • Vomiting
  • Upset stomach
  • Diarrhea
  • Abdominal discomfort
  • Convulsions (in extreme cases)


How To Prevent Tapeworms

Unlike many other worms, tapeworms are not treated with heartworm medications that also cover parasitic worms. Tapeworms can be prevented by applying a flea preventative regularly.

Rodent populations should also be controlled since they can lead to an increase in fleas that feed on tapeworm eggs.

Learn More About Tapeworms


Hookworms are very small worms named because of their hook-like teeth they use to attach to the intestinal lining. They feed upon the host animal’s blood and are the most common parasitic worm found in dogs.

Dogs can contract hookworms in the same way as roundworms, particularly during the puppy life stage. Humans can contract hookworms from their dogs.

Hookworms are much like other parasitic worms in that they lay eggs in the intestinal tract of dogs, and those eggs are then expelled in feces or through a mother dog’s tissues during pregnancy. Hookworm infestations are particularly devastating to young and elderly dogs and should be treated as soon as a vet identifies hookworm eggs (pictured) in a fecal sample.


Hookworm egg under microscope
Hookworm (Ancylostoma caninum)
  • Poor stamina
  • Poor weight maintenance
  • Progressive overall weakness
  • Anemia
  • Bloody diarrhea
  • Unwillingness to eat


Common hookworm medications for dogs include:

How To Prevent Hookworms

You can prevent hookworms with many heartworm preventative medications that also treat parasites and by keeping your dog’s environment clean.

Learn More About Hookworms


Whipworms look like a whip with one end thicker than the other. The thinner end resembles a piece of thread. This type of parasitic worm lives in the first section of the dog’s large intestines (the cecum).

Whipworms can be transmitted to humans from dogs, but it is extremely rare.

Whipworms bury their heads into the dog’s large intestine and feed on the dog’s blood. Once established in the dog’s intestines, whipworms lay their eggs, which get excreted in the dog’s feces. Whipworm eggs are extremely difficult to eradicate from the soil and can only effectively be destroyed by replacing soil. Even picking up feces can leave traces of whipworm eggs behind, leaving other dogs susceptible to infection.

While roundworm females can produce up to 200,000 eggs in a single day, whipworms produce much fewer eggs making detection of an infection much more difficult. Even with the examination of a fecal sample, a veterinarian may miss an infection.

In cases where dogs exhibit clear symptoms of whipworm infestation yet a fecal test comes up negative, additional fecal samples may be required. Whipworms rarely cause fatal infections in dogs, but they can lead to complications.


Whipworm under microscope
Whipworm (Trichocephalus trichiuris or Trichuris trichiura)
  • Anemia
  • Diarrhea
  • Hemorrhaging
  • Weight loss
  • Upset stomach


You should pick up all feces and replace the soil to avoid re-infection. Common medications for whipworm infections include:

How To Prevent Whipworms

You can use a preventative oral medication to stave off whipworms. Interceptor is currently one of the few heartworm preventative medications that treats whipworms as well as heartworms.

Learn More About Whipworms

Other Intestinal Parasites To Consider

Many other intestinal parasites can affect dogs. They’re commonly confused with the various worms already mentioned due to a similarity in symptoms.

Coccidia Parasitic Infection (Coccidiosis)

Coccidiosis is a parasitic infection caused by coccidium bacteria. This bacterium spreads through the feces of infected dogs and is most commonly found in puppies that have developed the disease after exposure to an infected adult dog’s feces.

Like many intestinal parasites, coccidiosis can be particularly dangerous to young puppies with under-developed immune systems. Adult dogs can also contract this infection, particularly when undergoing periods of stress such as traveling, moving and even weather changes.


Coccidia under microscope
Coccidia (Coccidiasina)
  • Watery and mucus-like diarrhea
  • Bloody diarrhea (in severe cases)
  • Dehydration
  • Overall weakness
  • Lethargy

Whenever you notice any of these symptoms, it’s crucial to get your dog to the vet, regardless of their age, because symptoms can escalate quickly.


The most common test to detect coccidiosis is a fecal examination. The coccidium parasite is easily visible under the microscope — it resembles an eye with a pupil.

After confirming coccidiosis, your veterinarian will assess your dog’s overall health. If your dog is experiencing significant distress due to dehydration and weakness, they will keep your dog for inpatient treatment to administer fluids as well as medications to kill the parasite.

If your dog is in overall good health, your vet will send you home with medication to treat the parasite and suggest administering unflavored Pedialyte and plenty of water to keep your dog hydrated.

Two weeks following completion of medication, your vet will request a follow up fecal test to ensure that the parasite is no longer present.

The most commonly prescribed medications for coccidiosis infestations include:

How To Prevent Coccidiosis

The best way to prevent the spread of coccidiosis is to keep infected animals apart from other animals and to ensure infected animals get treatment. It’s also important to test the feces of pregnant dogs to ensure that newborn puppies are protected from infection. Many people will also test young puppies to ensure they are not infected with coccidiosis after their birth.

Learn More About Coccidia

Giardia Infection In Dogs

Giardia is a protozoan parasite that dogs ingest when infectious cysts are shed in infected dog’s feces. Infection with the guardian parasite is referred to as giardiasis.

Dogs can ingest these cysts through both direct and indirect contact with them, and once swallowed, they travel down to the dog’s intestinal tract. Many dogs ingest Giardia cysts through water contamination, which is why new puppy owners are advised against letting their dogs near local lakes and water bodies that could house the parasite.

It is important to note that Giardia is the most common intestinal parasite found in the human digestive tract. It is possible for Giardia to be passed from dogs to humans, so proper handling of infected dogs and infected feces is crucial.

Approximately 50% of puppies will develop a case of giardiasis, and close to 100% of dogs that are confined in a kennel environment will contract the parasite. The reason for such a high incidence is the proximity of dogs and the ease of exposure.


Giardia under microscope (illustration)
Giardia (Giardia intestinalis, Giardia lamblia or Giardia duodenalis)

Spotting Giardia in adult dogs can be trickier than with younger dogs since the disease tends to accelerate rather rapidly in younger dogs with less developed immune systems.

  • Diarrhea that may be greasy or frothy in appearance
  • Diarrhea with mucus in it
  • Feces with a strong odor

If your dog exhibits any of these symptoms, it’s crucial to get them veterinary care to avoid dehydration, particularly in the case of very young puppies.


Your vet will take a fecal sample to confirm the presence of the Giardia parasite as well as rule out any other potential causes for symptoms, such as maldigestion and malabsorption.

After confirming Giardia parasites, your veterinarian will decide whether or not to keep your dog for observation or whether they can be released for treatment. Your vet may also opt to administer fluids and then send you home to administer medication at home.

In addition to prescription medication, veterinarians recommend bathing infected dogs to prevent any recontamination from remaining parasites on the dog’s coat. Once you complete medication, vets will request a second fecal exam to confirm the parasite’s eradication. This step is particularly crucial since an ongoing Giardia infection can have devastating effects on a dog and can even result in the death of young puppies in a relatively short time.

The most commonly prescribed medications for Giardia include:

How To Prevent Giardia

Don’t take young dogs to water bodies where the parasite could be present and ensure that no dog drinks from the water or licks their paws after stepping in the water. Also, ensure that whenever boarding your dog, you pick a kennel that offers individual spaces for dogs rather than communal kennel areas where the parasite can quickly spread.

Learn More About Giardia

How To Prevent Worms In Dogs

First, you should speak with your vet about getting your dog on a worm preventative. Most vets offer medicine for you to take home with you, but you can also purchase inexpensive worm preventative medications online.

Second, always pick up after your dog since leaving infected feces can pass the disease to other dogs. You can find the best pooper scooper and poop bags here. Additionally, keep your dog away from other dogs’ feces, especially if they are interested in eating poop! This may mean you need to shorten the leash when you go for walks to keep your dog from sniffing around too much.

Has your dog been diagnosed with a parasite before?

About The Author:

Kimberly received her Bachelor of Arts in multimedia journalism from Simpson College. She has been writing about dogs since 2014, covering subjects such as dog insurance, training, health, accessories, and more. Her work has appeared in many notable brands, including The New York Times' Wirecutter, Reader's Digest, Forbes, People, Woman's World, and Huffington Post.

Kimberly's natural curiosity helps her research as she seeks the truth when learning about, comparing, and personally testing canine products and services. With every piece she writes, her goal is to help our readers find the best fit for their unique needs. Kimberly grew up in a family that loved Labrador Retrievers and remembers running and playing in the yard with them as a child.

In 2017, she and her husband adopted their Coonhound mix, Sally, from a local shelter. Kimberly’s research was put to good use since Sally faced some aggression issues with other dogs and needed some training to be an inside dog. She worked daily with Sally and sought help from professionals to help Sally become the happy pup she is today. One of Kimberly’s favorite pastimes is spoiling Sally with new toys, comfy beds, and yummy treats (she even makes homemade goodies for her). She tries to purchase the safest products for Sally and knows that each canine has their own specific likes and dislikes. Kimberly is passionate about dogs and knows the bond between humans and canines is like no other.

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Tiffany Givens
August 4, 2016 10:48 am

My 11 week old blue gator pit is being treated for round worm and hook worm and I also gave him a monthly dose of heartworm meds he goes back in 2 weeks for his second dose of worm meds. First two nights I saw one or two worms in his poop, I have four kids and have kept him confined in a room that I bleach mop every time he has an accident, since there isn’t any of the worms in his poop now should I keep him confined until his next dose in two weeks or is it safe now?

Michelle B.
November 23, 2013 12:27 pm

I recently acquired two hound puppies about eight weeks old. They immediately showed signs of mucous and bloody stools and the shelter gave us a three-day worm treatment designed to kill three types of worms. It worked immediately and within hours they were passing round worms but it has now been six days and they got the three full doses but they still have runny, bloody stool. They are eating and drinking and playing but the blood really concerns me. How long should it take to clear up? Is there some home remedy that can be helpful while they complete the treatment and recovery? They still have another three day treatment to follow up in another week.

July 23, 2013 11:11 pm

Rufus was dropped off at our farm so we really do not know anything about him except I think he may have a lot of Pembroke Welch corgi in him. He is a very smart little dog and seems to understand what you say and minds fairly well. At first he would start gaging and then would either regurgitate just grass and foamy liquid, or just the foamy liquid by itself. Now, the past couple of days, every time he eats or drinks he regurgitates whatever. He has a cough/gag he goes into giving me a warning, but often we do not make it outside in time. Living in the country it is very hard to keep the fleas off him and I have tried everything I know of on the market, but the fleas are driving him crazy. After reading about all the worms and flea interaction I am getting concerned. Again, as I said he was a drop off and we do not have the money to take him to a veterinarian so I am hoping you have some advice for me. Thanking you in advance…

February 20, 2013 4:22 pm

My dog has recently been diagnosed with worms. My question is that we live in an apartment, and although she does her business anywhere during regular walks, when we pop out for a quick one, she will head to the same spots in our parking lot or on our front walk. Seeing as they are concrete it is easier to pick up the feces, unless it is wet. I know in this article it says to replace soil in soiled areas, but should I scrub the concrete/brick with bleach water occasionally to keep it clean and prevent re-infestation?

Guest Author
February 20, 2013 4:25 pm
Reply to  Anonymous

Great question! We agree that the same logic applies here as it does to soil. If your dog has worms and is going to the bathroom on concrete rather than soil, bleaching the area is a great idea to decrease the future infections of your pet or others who live in your apartment complex.

Another tip in case of future illness expenses, would be to invest in Pet Insurance. You can read more about how insurance for your pet works, a comparison of the various companies as well as our pick for best Pet Insurance company. 

Hope your dog is feeling better and stays well.

July 7, 2012 8:05 am

One of the most common problems in dogs are worms. There are a wide variety of worms can infect your dog, including heart worms, round worms and hook worms (there are many more as well). If your dog becomes infected with any type of worm, it can be a long and difficult process to get rid of them. The better option is to help protect them from contracting these in the first place.

Another thing to consider is that while these worms are usually more common in dogs, they can also infect other animals and even people. The best ways to avoid contracting worms include avoiding contact with other animals known (or suspected) to be infected already. Keep your home clean, especially the areas where your pet frequents. It is important to pick up dog feces as soon as you can, since this is a prime method of spreading worms.

It is also important to keep your pets on regular preventative medications. There are a small number of medicines which are effective for a wide range of things, including worms. It is also important to keep your pets on flea and tick prevention as well.

July 3, 2012 10:45 am

As most dog owners are certainly aware, there are a wide variety of worms which dogs can develop. Some of these can be particularly nasty and dangerous for your dog, causing a lot of discomfort, pain, illness and even death in certain cases. It is very important for a dog owner to have a good understanding of several different types of worms.

Whipworms get their name because of their appearance. These varmints live in the first section of the canine large intestine and are not easy to detect because they do not produce a large amount of eggs. They bury their heads into the intestinal wall and then feed on the dog’s blood. Fortunately, there are a number of medications which can be used for treatment, including Sentinel and Interceptor.

Hookworms are probably the most common types of worms found in dogs. They also attach to the intestinal wall and feed on the blood of their host. Dogs with this type of infection may display poor stamina, poor weight maintenance, bloody diarrhea and even an unwillingness to eat. 

July 3, 2012 4:40 am

I am glad I am not the only one who is overly concerned about their pets. I am so concerned for them that I really do not even want them around anyone else's animals. It is not just about things like fleas or anything like that either, though that is a concern. It is about larger fears, like worms and Parvo.

In fact, just the other day my brother brought his dog over here and I was wondering what in God's name he was thinking. It was a male dog, which made mine go nuts. And then my cats were not really happy about it either. And that was just the annoying part! My real fear is that my dog will catch something from some other animal. I don't know about anyone else, but I don't have the time to watch every single thing my dog does, so if he eats another animal's feces, I would not even know it.

That's also why I don't take my dog to anyone's house. I like it that he is safe at home with me and I don't have to put him or any other animal at risk. I wish people would think about things like that more.

June 24, 2012 4:48 am

I have a few pets that make me worry about worms. I sometimes imagine little worms in their hearts or something and ask myself what I would do if that happened. I cannot imagine that would a pleasant thing for any animal to experience. And for some reason, the fact that those worms are so small just kind of freaks me out completely. I can bait a hook, but I cannot allow myself to have a visual of my animals with little worms in them.

Hopefully, I never have to worry about it. I try to make sure all of my animals are up to date on all their pills and shots. The pills to prevent worms really are not that expensive at all. And when you compare the cost of the pills to the cost of a vet or worse, the cost of your pet's life, the pills really start to look affordable.

The only thing is, I am bad about taking my own pills, so I have a hard time remembering to give our dog his. That's why I passed that job on to my son. He gives him his pills the same week he gives him his flea bath. It has become almost a ritual here.

June 17, 2012 7:24 am

As any dog owner or lover can say for sure, one of the most common problems or issues that we will face with our dogs is worms. There are a number of different types of worms which can develop either on or within your dog. If your dog exhibits any behavior or eating habits which seem unusual, you may want to have them checked out by a qualified veterinarian.

Heartworms are parasites that infect a dog through mosquito bites. The larvae is deposited into their blood stream and the worms eventually travel to and settle in the heart. If not treated this can become fatal. Typical signs include hair loss, jaundice, loss of appetite and even increased heart rate.

Intestinal worms are parasites which attach to the insides of a dog's intestines. They feed by basically stealing the nutrients from the food a dog eats. If left untreated they will eventually cause death due to intestinal blockage.

Round worms are a particular type of intestinal worm. They are found most often in puppies, which is why puppies should be dewormed as soon as possible.

June 12, 2012 5:15 am

I did not know that the same worms that infect dogs could also infect humans. I know that humans can get ring worm, but I think that is actually a fungal infection and not actually a worm. There are so many out there. How can we protect our animals against them all?

I know you can buy different pills for heart worms, but there really should just be a start up package for people who just got a dog. What would be really cool for people like me who are on the computer all the time is if there was a start up package that came from a company that would send reminders to people enrolled in a program. You know, like a monthly reminder to give your dog the pill? It could vary with the pills that a person got. For instance, if someone bought pills they gave their dogs once a month, they would get a monthly reminder. If you gave it to them once every six months you get a bi-annual reminder and so on.

In fact, it would also be nice if you could have a list of everything you need to get your dog because every time I turn around I find that there is some other pill or something I should get him.

June 8, 2012 6:25 am

I'm leery about giving vaccinations to my loved ones. I don't go to the doctor unless I have to and I don't want to start to rely on them more. I worry about vaccinations not only because it makes me inject my dog and possibly change his DNA wouldn't even knowing it. But I also wonder about the bigger picture.

I think a lot about evolution. I believe that everything we do has an impact on the world. We make evolution happen. We change the environment. In response, since every species has the one task of perpetuating the species, they change to survive the environment. Those who have lost the ability to do this will be a short-lived species.

So, these worms we vaccinate against are simple creatures. There's not even anything near as complicated in them as there is in us. It seems to me that they would easily mutate. When a species changes, they start to establish their own status as a species. So, has there been evidence of worm changing and being resistant to the medication?