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9 Common Parasites Found in Cats & Dogs & How to Spot Them


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At some point in your dog or cat’s life, they are bound to become infected with an internal or external parasite.

Monitoring for any changes in behavior or appearance, as well as regular veterinary examinations, can help you keep ahead of an infestation, ensuring the safety and wellness of not only your pet, but your family.

Below are the most common parasites found in cats and dogs, and how to spot them:

Internal Parasites


Heartworm is very common in dogs across the U.S., but cats get them too!

They are transmitted by mosquitoes and, once mature, live in the heart and large blood vessels in the lungs. Once they have reached the heart, they can affect blood flow throughout the body.

Heartworms are extremely damaging but completely preventable with medication. Your veterinarian may suspect a heartworm infection if a normally active animal tires easily, has shortness of breath, or is coughing.

Diagnosis is confirmed by blood test, and occasionally an x-ray of chest and/or ultrasound of heart.


Roundworm is the most common parasite in dogs and cats.

Many are born with the larvae already in their system because it was passed to them by their infected mother. It can also be transferred through the mother’s milk or contact with infected feces.

You may find roundworms in your dog or cat’s vomit or stool, and your pet may become pot-bellied or have diarrhea.

Roundworms can be passed to humans through skin contact with infected stool or soil where dogs frequently go to the bathroom. It can migrate beyond the skin and cause issues to the liver, eyes, and central nervous system if left untreated.

Dogs and cats should be treated at 2, 4, 6, and 8 weeks of age, followed by a monthly preventative treatment.


More commonly found in dogs than cats, hookworm is another intestinal parasite that attaches to the lining of the intestinal wall and feeds on blood.

Hookworm eggs are then excreted into the digestive tract and pass through the feces, infecting the soil. The larvae thrive in the soil and can infect your pet through ingesting the dirt or daily cleaning (licking).

Hookworms cause internal blood loss, which can be especially fatal for a young pup without transfusions. Older dogs may experience diarrhea and weight loss.

Puppies should be treated at 2, 4, 6, and 8 weeks of age with deworming medication.

Hookworms can infect humans by penetrating the skin, most likely from contact with infected soil (walking barefoot where dogs may deposit feces). This usually results in an itching sensation and even visible tracks from the hookworms. While extremely uncomfortable, it is completely treatable in humans


Whipworms typically make their home in the area where the small and large intestine meet. They are contracted by swallowing eggs in contaminated soil or other areas containing fecal matter.

Your pet may not show any sign of infection, but more serious infections may result in bloody diarrhea.

Left untreated, whipworm infection causes serious disease and even death.

Clean up your pet’s feces regularly from your yard to prevent contamination.


Tapeworm is most commonly transmitted by swallowing fleas infested with tapeworm eggs.

The tapeworm then sheds part of its tail and it may be visible in feces, or the fur under the tail

Symptoms include general anal itchiness, scooting, weight loss without change in appetite, or increased appetite without weight gain.


Unlike the other parasites, giardia is not a worm. It is a single-celled parasite that lives in the intestine. It is usually contracted by swallowing giardia present in water or ingesting anything contaminated by feces.

Giardiasis, the disease caused by giardia, results in vomiting and diarrhea and can be confirmed by your veterinarian by testing a stool sample.

If your pet is experiencing any of the symptoms outlined above, you should contact your veterinarian immediately to schedule a visit.

External Parasites


Fleas are the most common external parasite in both cats and dogs. If your pet has fleas you may notice that they are itching frequently. You may even see tiny brown fleas moving throughout your pet’s coat.

Fleas can transmit other diseases, such as tapeworm.

Luckily, there are many different types of treatments and preventative measures for fleas. Talk to your veterinarian about the best option for your pet.


Ticks attach themselves to your pet by inserting mouth parts into skin and then feeding on their blood. They are responsible for transmitting diseases such as Lyme and Rocky Mountain spotted fever, both of which can result in lameness.

It is very difficult to prevent exposure to ticks, so your best bet is to use tick-control products. If your yard has a tick problem, you may need to look into treatments for that as well. Be sure to do your research to ensure your method of choice is safe for your pet and your yard.

If you do plan to go out into a wooded area with your pet, check their coat thoroughly for signs of ticks as soon as you get home.

Ear Mites

Ear mites are tiny mites that live on the surface skin of the ear canal. They are transmitted through social interaction with infected animals.

All pets should be checked fairly regularly for ear mites. This is easy to do while you are petting your dog or cat.

If you have multiple animals in your home and one is infected with ear mites, then all of your pets should be treated since they are so easily passed along.

Preventative & Wellness Care for Your Pet in Potomac, MD

Regular preventative care and wellness examinations are key in keeping ahead of health problems, such as parasites.

At Falls Road Veterinary Hospital, we recommend that all pets receive a comprehensive physical examination at least once a year. Our preventative care and wellness services include laboratory screening, parasite control, disease prevention, and so much more. Keep your furry companion feeling their best. 


Contact Us

Falls Road Veterinary Hospital


10229 Falls Road Potomac, MD 20854

Clinic Hours

Mon-Wed: 8:00am - 8:00pm
Thur & Fri : 8:00am - 6:00pm
Sat: 8:00am - 1:00pm
Sun: Closed