Roundworms are one of the most common parasites in dogs. In fact, nearly all puppies in the United States are born infected with roundworms¹. That doesn’t mean roundworms are harmless though. You and your pet can be at risk of serious health issues if this parasite is left untreated. 

What Are Roundworms and Why Are They Dangerous?

Roundworms are parasites that live in a dog’s intestines. There are two primary species that affect dogs: Toxocara canis and Toxascaris leonine.

Roundworms can infect dogs of any age, leading to malnutrition if not treated. They can cause serious illness in puppies, leading to stunted growth, weight loss, vomiting, diarrhea, and occasionally intestinal obstruction in young puppies.

While healthy adult dogs may not show signs of infection, they shed roundworm eggs that survive months to years in the environment, even if the area has been disinfected. These eggs can spread to other dogs and pets in the household.

Dogs do not develop any immunity once infected, which means they can become infected many times.

How Dogs Become Infected With Roundworms

One of the most concerning things about roundworms is how easily they can be spread between dogs.

• Mother to puppy. If a mother has roundworms, she can pass the roundworms through the placenta to puppies before birth.
• Eating an infected host of the roundworm. Many animal species, including earthworms, birds, and rodents, are involved in the roundworm lifecycle. If a dog eats one of these animals infected with roundworm larvae, the dog may become infected with roundworms.
• Pets eating feces. Mature roundworms live in the intestines and can produce 200,000 microscopic eggs daily.² This means the eggs can show up in your dog’s poop. The eggs will not be contagious for another one to four weeks, but they can survive in the environment for years and resist many disinfectants.

Since there are so many eggs shed in the poop and they last so long, even when you use a disinfectant to clean the area, it is very important to clean up after your pet every day. They can also spread from dogs to humans. Despite your best efforts, your home and yard may be contaminated with microscopic eggs.

Symptoms of Roundworms in Dogs

Dogs infected with roundworm may show signs like:

• Swelling of the belly
• Dull or scruffy hair
• Difficulty gaining weight
• Stunted growth
• Cough from worms passing through the lungs
• Possible vomiting or diarrhea, occasionally with worms in it

Dogs can get intestinal blockages due to a large number of worms and severe infections may cause death in young puppies.

Diagnosis of Roundworm Infection in Dogs

If you see worms or your dog is showing signs of infection, your veterinarian will do a fecal (poop) test, looking for eggs to help identify the parasite.

Most dogs are screened for parasitic infections during their wellness exams. Since most puppies are born with roundworm infections, they should be dewormed by your veterinarian frequently during their first months of life. Adult dogs should be tested at least once a year. Your veterinarian may recommend testing more often if they are high risk, such as being an outdoor dog or not being on a parasite control regimen.

In addition to the routine wellness fecal screening for parasites, veterinarians typically recommend checking a fecal sample for dogs showing signs of illness.

How To Treat Roundworm in Dogs

There are several very safe anti-parasite medications available. Some are given to a puppy or dog who has an active roundworm infection. The medication is typically given again every few weeks to kill any larvae as they mature. Other anti-parasitic medications are combined with heartworm or heartworm/flea/tick medications as a monthly preventative.

Preventing Roundworm Infection in Your Dog

Thankfully, we have several methods of prevention. The first is to pick up poop as quickly as possible. This removes most eggs before they can cause infection and prevents them from contaminating the area. Keep in mind that when you pick up poop right away, the roundworm eggs that have been shed are not yet contagious to you or your dog  — it takes at least a week. However, it’s always a good idea to use a plastic bag or a hands-free pooper scooper and wash your hands.

The second method is using a broad-spectrum parasite control every month. This type of medication will kill multiple types of parasites in their earliest stages before they can cause signs of illness in your dog. Additionally, it will stop any parasite before it can mature and release eggs or spread infection to other pets.