Parasites and Worms in Dogs and Cats Internal Parasites that Can Infect Pets

Parasites and Worms in Dogs and Cats
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There are many types of intestinal parasites that can infect pets, sometimes in different ways. Find out about common parasites and how to protect your pet.

Several different types of parasites can make cats and dogs their home. From biting insects like fleas and ticks to internal worms, all of these pests are unpleasant, dangerous, and can cause serious complications.

The good news is that they’re all largely preventable, through monthly oral medications, spot-ons, and good old-fashioned grooming and cleaning of your pet's space. 

Internal parasites that can attack cats and dogs include heartworm, tapeworm, whipworm, roundworm, and hookworm. Depending on the type, these parasites can enter the pet’s body through transfer of infected soil and stool or through the bite of a carrier, like a mosquito. Hookworms can even enter through your pet’s foot as they walk outside, by burrowing into their body.

These worms grow from the larval stage to adulthood inside the pet’s body, and some migrate between organs, causing internal damage along the way. Most latch onto an organ and feed off your pet's blood.

Here’s what you need to know about common worms in pets and how to get rid of them. 


Heartworms are the most common internal parasite for pets, and are more likely to infect dogs than cats. They're transferred to pets through mosquito bites and while they're most common in the country's warm, southern states, more and more incidents in northern states are being reported.


Tapeworms can be carried by fleas and transferred to pets through a flea bite. Pets can also get tapeworm from eating a rodent or other mammal that was infected. Once inside a pet, tapeworms attach to the small intestine wall and block the digestive tract.


Whipworms feed off a pet's blood in the cecum, which is part of the digestive tract where the small and large intestines meet.


Roundworms complete their life cycle in an animal's intestines, but they can also move throughout a pet's body, infecting the throat and lungs.


Hookworms can enter your pet's body a number of ways, and can infect the lungs before moving on to the intestines.

Whipworms, roundworms, and hookworms are all "zoonotic," meaning they can be transferred to people. It's always a good idea to have your pet on a dewormer, and many monthly heartworm preventatives like Heartgard, Trifexis, Interceptor Plus chewables for Dogs, Iverhart Plus, and Tri Heart Plus will protect against other types of worms as well. To get rid of these worms, medications like Panacur can be highly effective. Other medications like the Sentinel Spectrum chewable medication works on fleas, heartworms, and common intestinal worms.

Another type of “worm," ringworm: Ringworm is actually not a parasite, despite it’s name. The name comes from the ring-shaped rash that develops on human skin when people are infected, though ringworm is caused by fungus. On pets, the rash develops as a scaly patch of skin.

More on Pet Health

Heartworm Medication Comparison Chart
Flea and Tick Medication Comparison Chart
Sure Signs of Heartworm

This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.

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