Roundworms in Dogs

Written by Small Door's medical experts

Roundworms are common canine parasites that can significantly impact puppy health as well as posing potential risks for humans. The most common type of roundworm in dogs is Toxocara canis, although dogs do occasionally pick up other species of roundworms. Roundworms commonly affect puppies. Being aware of the signs of a roundworm infection in dogs will help you detect a possible infection before the intestinal parasites cause lasting damage or death.

In This Article

What are roundworms in dogs?

Roundworms (or ascarids) are parasites that live freely in the large intestine where they feed off of partially digested contents. Roundworms most commonly infect puppies, but can also infect adult dogs as well. 

Roundworms in dogs are broken down into two species:

  • Toxocara canis 

  • Toxascaris leonina

Toxocara canis is the most common. It’s known for infecting puppies and can also be passed to humans.

Signs & symptoms of roundworms in dogs

The symptoms of roundworms in dogs are similar to the signs of other intestinal worms.

  • Dull haircoat

  • Pot-bellied appearance

  • Secondary cough in young puppies due to pneumonia

  • Poor growth rate

  • Decreased body condition

  • Vomiting

  • Diarrhea

The first thing most owners notice about a puppy or dog with roundworms is a slow growth rate and an overall loss of condition. Although some dogs with roundworms are asymptomatic, they often present with dull coats and a pot-bellied appearance, which may come on gradually. As the infection worsens, you might notice vomiting and diarrhea, and may even see worms, which look like pieces of white spaghetti. Puppies with severe cases can develop pneumonia, which is caused by migrating larvae. Roundworm infections in puppies can be fatal.

How do dogs get roundworms?

Common causes of roundworms in dogs:

  • Contact with contaminated soil or an infected animal’s feces

  • Transmitted from the mother during pregnancy

The most common method of infection for puppies is during gestation, where roundworm larvae pass through the placenta and into the puppy. Puppies are then born already infected with roundworms, which go on to mature in their intestines.

Dogs older than three months become infected with roundworms through their environment, which can occur when dogs come into contact with contaminated soil, like a sandbox used by outdoor cats or soil contaminated by other dog feces. Once ingested, roundworm eggs hatch, penetrate the intestinal mucosa, and make their way to the lungs, where they are coughed up, swallowed, and mature to adulthood in the small intestine. They then lay the eggs that are passed into the environment, completing the life cycle. However, in older dogs, the larvae often migrate to organs, connective tissues, and other types of tissues. These larvae remain dormant, causing few if any symptoms, until something like pregnancy triggers them.

Are roundworms a threat to my dog?

The short answer is, yes, and they’re most dangerous for puppies and those with underlying health conditions. If left untreated, roundworms can be fatal for puppies. Because roundworms feed off partially digested food in the intestinal tract, the most common health problem is stunted growth, also known as a ‘failure to thrive’, as they rob the growing puppy of vital nutrients. Large amounts of roundworms can essentially starve a puppy to death.

Roundworms in puppies can also lead to pneumonia and abdominal fluid buildup, which may require supportive care to resolve, along with antibiotics to prevent secondary infections.

Adult dogs generally aren’t at such a high risk of complications from roundworms as puppies, but it’s nonetheless important to promptly treat infestations in dogs of any age.

Diagnosing roundworms in dogs

Veterinarians diagnose roundworms in dogs based upon clinical signs and a fecal analysis. Your veterinarian will look for evidence of roundworm eggs in the fecal sample, and they will also determine which species of roundworm your dog is infected with to determine if there is a risk that it has been passed to yourself or other humans in the household.

Roundworm eggs are spherical and pitted, and adult worms may show up in samples from dogs with heavy parasite loads. However, eggs do not always appear in fecal samples. This is because sample sizes are small, and eggs may shed intermittently. If your veterinarian suspects that roundworms are the cause of your dog’s condition, or if you have seen evidence of roundworms in your dog’s vomit or feces at home, they may recommend treating for roundworms even without a definitive diagnosis. Repeat fecal testing can lead to a definitive diagnosis in a later visit, and determining the parasite is essential for preventing the spread of the disease to humans.

Roundworm treatment for dogs

Treating roundworms in dogs is relatively straightforward. After making a diagnosis, your veterinarian will most likely prescribe a dewormer, like fenbendazole and pyrantel, or milbemycin. These medicines eliminate worms from your dog’s intestinal tract. Once the initial parasite load is eliminated, it’s important to prevent reinfection by continuing treatment with a monthly preventative that targets roundworms.

Puppies with severe infections may require additional treatment to resolve their symptoms. Because some puppies with roundworms are asymptomatic, routine deworming of puppies is often recommended.

Is there a cure for roundworms in dogs?

Yes. Medications like fenbendazole will cure the initial roundworm infections, and monthly preventatives that contain dewormers can decrease or completely eliminate future infections.

Are roundworms in dogs contagious for humans or other pets?

Toxocara canis is a zoonotic disease, which means it can be transmitted to humans and other dogs in the household. Humans must swallow infective eggs in order to be infected with roundworms, which can happen after handling feces or infected soil. Most cases of roundworms in humans are asymptomatic, but fever, elevated white blood cell levels, and enlarged liver can occur. As the larvae migrate, they can cause a condition called visceral larva migrans. If the larvae migrate to the eye, they can settle in the retina, impairing vision and even causing blindness.

Recently, veterinarians have detected a rise in another type of roundworm found in dogs called the raccoon roundworm (baylisascaris). The raccoon roundworm also has a zoonotic potential, which can lead to visceral and neural larva migrans.

What is the cost of treating roundworms in dogs?

When treating roundworms, you can expect to pay for the cost of the initial office visit and diagnostics, as well as follow-up visits and fecal testing to determine if the medication is working. Deworming medications are relatively inexpensive, and veterinarians recommend continuing treatment with a monthly preventative that targets roundworms. These preventatives should be given for the rest of the dog’s life.

Recovery and management of roundworms in dogs

In most cases, you can expect your dog to recover from a roundworm infection and return to full health. Severe cases, especially in puppies, may require hospitalization and supportive care, and can be fatal if left untreated.

Once the initial infection has been treated, you will need to continue monitoring your dog for signs of infection. Keeping them on a monthly preventative that targets roundworms will help reduce the risk of reinfection, as will picking up poop immediately to avoid environmental contamination.

It is a good idea to take precautions if your dog has been diagnosed with roundworms. Wash your hands after handling feces and potentially contaminated soil, and educate younger members of your household about proper hygiene.

How to prevent roundworms in dogs

Roundworms in dogs are preventable. Talk to your veterinarian about the parasite risks in your area. If roundworms are common, start your dog on a monthly preventative that treats roundworms as a precaution, and deworm breeding and pregnant females to reduce the risk of transplacental infection. Keeping your dog’s living conditions sanitary will also reduce the risk of infection.

What about roundworm eggs shed in the environment?

While eggs themselves are not infective, under the right conditions, eggs will develop into infective larvae — this can take approximately four weeks. Because these larvae can survive in the environment for long periods of time, contamination from your dog’s feces is a concern. 

The best way to prevent the spread and contamination of roundworms for other pets and humans is to make sure you always pick up and throw away your dog’s feces promptly.

Is there a vaccine for roundworms in dogs?

Roundworms are not a viral disease. There is no vaccine for roundworms in dogs, but there are monthly preventatives that can treat and prevent infections.

Summary of roundworms in dogs

Roundworms in dogs are common parasites, but can be particularly dangerous and may even prove fatal to puppies if untreated. Common symptoms include poor growth, loss of condition and a dull coat. You may also see worms in your dog’s feces or vomit. Thankfully, roundworms are easily treatable with deworming medication and can be prevented by providing a monthly preventative medication that protects against roundworms.

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