Pet Parasites: How to Protect Your Dog or Cat

Written by Diana Bocco
Updated October 12, 2016
dog on a couch
Regular heartworm, flea and tick prevention can keep parasites from infesting your pet. (Photo by Brandon Smith)

Learn about what parasites can attack your pets and the harm that can result, plus preventing troubles and how to treat your pet if it's infected.

Two types of pests can affect your pet: external ones live on the skin or hair follicles; internal ones live in the gastrointestinal system and can attack organs.

Here’s a look at both:

External parasites

Fleas, mites and ticks: Besides causing itchiness and being incredibly annoying, they can cause health problems.

Fleas can cause anemia, plus transmit tapeworm infection and lead to flea allergy dermatitis.

Mites cause demodectic and sarcoptic mange, two skin conditions that lead to hair loss, intense itching and scabs. Sarcoptic mange (known as scabies) is highly contagious to humans and other animals.

Ticks can transmit Lyme disease, which can cause severe anemia or death in dogs. It’s rare in cats.

Video: External and Internal Pet Parasites

Internal parasites

Heartworms: Adult heartworms set up in the heart and lungs, reproducing quickly until they cause kidney and liver damage, internal bleeding and congestive heart failure. Heartworms are transmitted through mosquito bites and are deadly if untreated.

Intestinal worms: There are more than a dozen types of intestinal worms and parasites, depending on where you live.

Four types of worms are especially common and troublesome: hookworms, roundworms, tapeworms and whipworms. Hookworms and roundworms can be passed on to people. Hookworms can be deadly if untreated, especially in puppies.

Keeping your pet healthy

A clean environment helps your pet. If no fleas, ticks or sick animals are around, the chances your pet will become ill drop considerably. If you have a flea or tick infestation, you'll need to treat your pet plus wash linens, pillows and pet beds in hot water to kill any parasites or eggs on them.

Preventing and treating parasites

Heartworms: To prevent heartworms, pets need a monthly dose of one of three chemicals: ivermectin (sold as Heartgard, Iverhart Max or Ivomec), selamectin (sold as Revolution) or milbemycin oxime (sold as Interceptor, which Elanco plans to bring back to the market in 2015).

Which one’s best for your pet depends on its breed (some dogs, like collies, are sensitive to ivermectin) and whether you have a dog or a cat.

Other worms: First, check that your pet’s heartworm medication doesn’t already protect from worms.

Ivermectin also protects against hookworms; milbemycin oxime is effective against some hookworms plus roundworms and whipworms. Selamectin protects against fleas, sarcoptic mange and ear mites.

If your pet needs deworming, check with your veterinarian about which option would be best for your pet.

External parasites: Topical and oral preventives are the safer and most effective treatment option. Also, some topical treatments control both ticks and fleas.

Flea and tick collars, on the other hand, can be highly toxic, according to the Natural Resources Defense Council, which in 2009 filed a lawsuit claiming that the collars left residue up to 1,000 times the dose of chemicals allowed by the U.S. Environmental Protection Agency and posed a threat to humans.

Signs of parasites

External: In most cases, external parasites cause itchiness, skin redness and hair loss. You also can see fleas and ticks attached to the skin. Mange causes scaly bald patches, sores and a foul smell on the skin.

Internal: Most intestinal parasites cause some abdominal pain, sometimes diarrhea and general discomfort and weakness. Large infestations can cause the belly to swell. Heartworm has no early symptoms; by the time the infestation is severe, pets will start having difficulty breathing and tire quickly.

Internal parasites can sometimes be seen in feces, so check for signs of worms, especially if you notice your pet has other symptoms.

When to go to the vet

The best time to address problems is before they appear. Every parasite that can affect your pet can be prevented through medication and general care. This is especially important for heartworm, which is easily prevented but very difficult to treat.

If you notice any change in your pet's behavior – loss of appetite, diarrhea, vomiting or intense itching – head to the vet for a consult.

Editor's note; This is an updated version of a story originally posted Sept. 13, 2015