9 Types of Worms That Can Harm Dogs

Updated October 12, 2022
A purebred Jack Russell Puppy

Whether you're considering adopting a dog or you're brushing up on your canine knowledge, you need to know about the different types of worms in dogs. It may make you understandably queasy to think your poor puppy's intestines can become infested with parasites, but armed with the right information, you'll be able to fight for your pup's health.

9 Different Types of Worms in Dogs

Depending on your specific location and environment, there are generally nine types of worms that can harm your dog.


Gnathostoma infections in dogs are rare, but under certain circumstances, dogs can be susceptible to this worm, with deadly results. Gnathostoma larvae develop within fish, and when fish are eaten by a larger animal, the larvae are released.

They then burrow through the host animal's body, returning to the stomach as mature worms that attach to the stomach lining of the host. If a nodule forms around the attachment site in the host, and that nodule breaks, the stomach wall will perforate. Stomach contents can leak into the host's body, causing infection and sometimes death.


Hookworms are one of the most common types of worms in dogs. There are four different species of hookworms, but they all cause similar symptoms. Hookworms can infect a dog by burrowing through the host's skin or by being ingested. These worms can also infect newborn puppies through the mother's milk.

Hookworms live in the small intestine and feed off the blood of the host, quickly causing anemia and stunting the growth of puppies. As the disease progresses, your dog may experience vomiting, diarrhea containing digested blood, weight loss, coughing, pneumonia, or even death.


Toxocara canis second stage larvae hatch from eggs

Roundworms are the most common parasitic infection present in dogs and puppies. Experts suggest that 20 percent of adult dogs and a whopping 99 percent of puppies have roundworms. They can infect dogs through the ingestion of an infected animal, like a rodent or bird, through the ingestion of roundworm eggs, or by transmission from a mother to her unborn puppies in utero or during nursing.

Roundworms live in the host's intestine and feed off the nutrients in the host animal's food. Some infections will never progress to the point of detection, but other infections may cause a distended belly, coughing, weight loss, vomiting, diarrhea, or constipation. In severe cases, roundworms can block the intestines of their host animal.

Stomach Worms

Similar in appearance to roundworms, Physaloptera, also known simply as "stomach worms," are transmitted to dogs through the ingestion of an intermediate host insect, typically a beetle, cockroach or cricket. If a dog eats the infected beetle, the larvae have the opportunity to mature within the dog's stomach. Physaloptera don't usually cause severe disease, but if infection occurs, your dog may experience chronic vomiting, diarrhea, loss of appetite, and bleeding in the stomach.

Esophageal Worms

Spirocerca lupi live in the esophagus of their host animal. This type of worm is not very common but can be seen in the southern United States and are transported to dogs through the ingestion of dung beetles or another infected animal, like chickens, rodents, or frogs. The larvae migrate through the cardiac arteries as they mature. In rare but serious cases, the worms can move through the heart's aorta. If this occurs, there is a chance that the aorta could burst and lead to the animal's near-instant death.

The adult worms eventually attach to the esophagus, where they live in nodules that can grow and interfere with the host animal's ability to breathe. Unfortunately, Spirocerca lupi infestations in the esophagus cause so much inflammation they can develop into esophageal cancer with the potential to transport cancer to other areas of the body.


There are a number of different types of tapeworms that use different intermediate hosts, but the "flea tapeworm" is the most common. These tapeworms become present in the host's body through the ingestion of fleas. They then live in the host's intestines, feeding off the nutrients ingested by the host. Tapeworms are recognizable compared to other types of dog worms because they are segmented and shed these segments into their host's stool. You might notice these small rice-like segments in their feces, around your dog's rectum, or even in areas where they sleep.

To help prevent tapeworm infections, use flea preventatives and don't allow your dog to eat common intermediate host animals like wild game, uncooked meat, or fish. In most cases, tapeworm infections are asymptomatic, but if you notice scooting, irritability, lethargy, abdominal discomfort, weight loss, or see dried segments, talk to your vet about possible infection.


Threadworms, or Strongyloides stercoralis, are small, thin worms that look like a strand of thread. Threadworm infections in adult dogs generally cause mild diarrhea and discomfort, but threadworms can be deadly in puppies. Parasitic larvae can enter a host by penetrating the host's skin, ingestion of infected feces, or by entering a puppy's system from the mother during nursing. Symptoms in puppies who contract threadworms include diarrhea, weight loss, loss of appetite, skin rash, and severe dehydration.


Whipworms earned their name from their whip-like shape. Dogs can become infected with whipworms by ingesting infected food or water. Mature whipworms burrow into the lining of the large intestine and feed off the host's blood. In mild infections, no symptoms arise, but in severe infections, the intestinal wall may become inflamed, resulting in anemia, weight loss, and bloody diarrhea.



Heartworms are one of the most prevalent and severe parasites found in dogs. Heartworm larvae enter the dog through mosquito bites. They spend the first few months of infection coursing through the host's body before reaching the blood vessels of the lungs, where they mature into adults.

The growing heartworms inhibit the heart's pumping ability and can damage the blood vessels, leading to heart and lung disease. The most common symptoms of early infection are shortness of breath, low energy, and coughing, although many dogs show no signs at all.

When left untreated, heartworm infections can lead to heart failure and death. The treatment for heartworm infection can be long and arduous and, in some cases, can still result in death. It is better to subscribe to a regular heartworm preventative than risk putting yourself and your dog through the stress of treatment.

Prevent Harmful Worm Infections

In most cases, vets will diagnose a worm infestation by testing your dog's fecal matter. Most worm infections are treatable, but vets often suggest a monthly worm preventative in order to stave off infestations in the first place. It's also wise to keep your dog from eating feces at the park, pick up after your own dog, and thoroughly wash your own hands to help prevent the spread of these harmful parasites.

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9 Types of Worms That Can Harm Dogs