What You Need to Know About Parasites in Cats


Editor’s note: This story originally appeared in the March/April 2016 issue of Catster print magazine. Click here to subscribe to Catster magazine.

Sometimes it’s hard to take invisible threats seriously. You read warnings about the bacteria living on your toothbrush or kitchen sponge, and you might resolve to get a new toothbrush or use disposable counter wipes. But those resolutions might not last beyond the next trip to the store. Threats we can see, like an oncoming car or a wildfire, make a much more dramatic impression.

That’s why talking about cat parasites is a little challenging for veterinarians. Even parasites we can see at some phases of a cat’s life cycle are invisible most of the time, lurking in our carpets or our cat’s digestive tract. Mostly invisible parasites and the diseases they carry cannot only make our cats (and us!) sick, but some of them can also kill our feline companions.

Cat scratching by Shutterstock
Cat scratching by Shutterstock

Sound frightening? Probably, but there’s also some good news. The scary stories making headlines about feline parasites are mostly hype, and nearly all parasite risks can be greatly reduced or eliminated with some simple lifestyle changes and modern parasite preventives.

When it comes to familiar parasites such as fleas, roundworm, hookworm, and whipworm, the veterinary community approaches them like the common cold. They’re not harmless, but they are easy to diagnose, treat, and prevent. In fact, many of the topical and oral products recommended by veterinarians to prevent fleas also continuously kill and control those other parasites.


One common parasite that usually isn’t diagnosed until it makes itself visible is the type of tapeworm known as Dipylidium caninum. Transmitted mostly when a cat eats an infected flea, it spends much of its life hiding inside your pet — until it crawls out and makes its wiggling-rice-grain-self known, usually on the fur beneath your cat’s tail. If you spot tape-worm segments on, or a flat worm in the process of exiting, your cat, head for the vet, because you’ll need a prescription medication to kill the parasite.

If your cat has this type of tapeworm, she has also been exposed to fleas. That means you’ll need to treat all the pets in your family for the pesky critters, because while only one pet may be itching, fleas are still present in the home and are undoubtedly biting your other pets — dogs as well as cats.

Cats can also get another type of tapeworm, Taenia taeniaeformis, from eating infected rodents. “If a cat is routinely given flea prevention but still has tapeworm, chances are it is Taenia,” said Dr. Heather Fritz, assistant professor of parasitology at Washington State University College of Veterinary Medicine.


Speaking of worms, did you know that heartworm is actually more dangerous for cats than for canines?

People are far more likely to buy heartworm preventive for their dogs than their cats, especially indoor cats, but mosquitoes do get inside. Far from being a new problem, heartworm disease has been diagnosed in cats since the 1920s. And unlike with dogs, it only takes one or two heartworms to kill them, and there’s no treatment. Do your cat a favor, and reread that last sentence.

Cat and flea shadow by Shutterstock
Cat and flea shadow by Shutterstock

“This is a disease that’s potentially lethal, difficult to diagnose, and with no direct treatment,
but it is easily prevented,” said Dr. Michael Dryden, university distinguished professor of veterinary parasitology at Kansas State University. “I don’t know why these members of our family, our feline friends, aren’t being protected. There are effective oral and topical preventives. I’m not sure why we put our cats at risk when it’s completely needless.”

If I were you, I’d finish this article and then head to your veterinarian to get a parasite control product that also takes care of heartworms.


So, what about the recent headlines about cats and Toxoplasmosis gondii, a disease caused by infection with egg-like structures known as oocysts, which can be spread in cat feces? Is it true this disease can make humans mentally ill?

“No one has ever been able to demonstrate a causal link between toxoplasma infection and mental illness,” Fritz said. While cats can pass oocysts in their feces for a short period after being infected with toxoplasma, Fritz urges people to stop thinking of it as the “kitty litter disease.”

“Most people are likely exposed [in] places other than their cat’s litter box,” she said. “It’s possible for people to be exposed while gardening, eating unwashed fruits and veggies, via water in communities where water is not treated in ways that can remove oocysts, or by eating undercooked meat.”

Can the oocysts be spread in cat litter? And is it of particular risk to pregnant women? Yes, but catching toxoplasma from your cat is not as common as media accounts might suggest. Because of the risk to the unborn baby, Fritz says, “it’s a good idea to have someone else clean the litter box when you’re pregnant. But if the box is cleaned daily, there isn’t enough time for the oocysts to become infective. Wearing gloves, washing hands, and practicing good hygiene is the best protection. Cats who do not hunt do not become infected, so keeping your cat indoors is another way to reduce risk of exposure.”

If you want to go the extra mile, Fritz has one last recommendation. “The other thing people can do is test their cat,” she said. “If the cat already has antibodies and is not currently shedding toxoplasma oocysts in its feces, it’s likely the cat has already been infected and
will not shed oocysts, so that cat is less likely to be a real risk.”


Before we move on to something really scary, let’s touch on giardia, a parasite that causes disease in many species, including humans. Our cats are probably off the hook for this one, however. It turns out giardia is more host-specific than we thought, so it’s not likely the type of giardia your cat has can infect you.

Cat and vet by Shutterstock
Cat and vet by Shutterstock


A new and relatively unknown threat called cytauxzoonosis, which is spread by the Lone Star tick, is
of very high risk to cats. Currently found in the Midwest and Southeast, it appears to be spreading as the range of the Lone Star tick expands. It’s also known as bobcat fever.

“This is a devastating disease to cats,” Dryden said. “It has an incredibly high mortality rate — in some places above 90 percent — even with aggressive combination drug treatments.” In addition to almost never working, he warned, the treatment is very expensive.

“I’m a cat guy. My whole family is a cat family,” Dryden said. “This disease is bad and scary, and even with aggressive, expensive treatment, almost all the cats who get cytauxzoonosis will die. So I recommend people keep their cats indoors, and if the cats do go outdoors at all, use tick preventive.”

In fact, prevention is the word when it comes to most parasites. Most of these problems are preventable if you use the products recommended by your veterinarian. Several of the topical preventives control fleas, internal parasites, and ear mites as well as heartworm.

If you’re not sure if certain parasites are a risk where you live — or you just want to know more about them — your veterinarian is your first, best resource. But you should also take a tip from Dr. Heather Walden, associate professor of parasitology at the University of Florida College of Veterinary Medicine. “One of the best recommendations
I can make for cat owners is to use the website of the Companion Animal Parasite Council (CAPC),” she said. “It was put together by parasitologists and is a site the public can really trust.”

The CAPC site features data compiled by veterinarians across the country, and you can click on a map and see state by state how many of a certain parasite is being reported by veterinarians in that area. It’s full of great information on parasite life cycles, prevalence, whether zoonotic, public concerns, and even what it looks like — guaranteed to give you the willies!

Read more by Dr. Marty Becker:

About the author: Dr. Marty Becker, “America’s Veterinarian,” has spent his life working toward better health for pets and the people who love them. The author of 24 books, Becker was the resident veterinary contributor on Good Morning America for 17 years. He is currently a member of the board of directors of the American Humane Association, as well as its chief veterinary correspondent; a founding member of Core Team Oz for The Dr. Oz Show; and a member of the Dr. Oz Medical Advisory Board. When his schedule allows, he practises at North Idaho Animal Hospital. Connect with him on Facebook, YouTube, Pinterest,Twitter, and Google Plus.

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