If your kitty recently developed a case of diarrhea, this common parasite may be the cause.
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If your cat developed a sudden, foul-smelling diarrhea, it could be caused by a tiny parasite called Giardia that is commonly spread through the poop of infected animals. A Giardia infection in cats is typically treated with oral medication and a deep cleaning of their environment to completely remove the parasite. Luckily, the risk of severe illness is low, and it's simple to protect your kitty from infection.

What is Giardia?

Giardia duodenalis (also called Giardia intestinalis and Giardia lamblia) is a small parasite that can infect the intestines of humans and animals. In people, Giardia is one of many infectious agents that can cause "Traveler's Diarrhea" after eating or drinking contaminated food or water. This parasite can also infect dogs and, less commonly, cats.

According to the Companion Animal Parasite Council (CAPC), animals infected with Giardia shed the parasite through cysts in their poop, which contaminates things the poop comes in contact with, like litter, cat beds, fur, and water. When another cat accidentally eats or drinks one of these cysts, they become infected and the cycle continues.

"This is commonly seen in kittens in unclean environments, or in cat shelters," says Sara Ochoa, DVM, a veterinarian at Senior Tail Waggers with over 6 years of experience working as a veterinarian for Whitehouse Veterinary Hospital in Whitehouse, Texas. 

"Most cats and kittens do not get Giardia since most people keep their cats clean and make sure that they have fresh drinking water," Ochoa says. However, if your cat spends a lot of time outdoors near a water source, they're more likely to contract the parasite.

Signs and Symptoms of Giardia in Cats

Many cats infected with Giardia don't show any symptoms. When the infection does cause signs seen by a pet parent, it's known as clinical giardiasis. In cats, diarrhea is a common sign of giardiasis; they may have unformed/soft, and/or pale, foul-smelling stool. Other potential signs include lethargy, abdominal discomfort, gas, and poor coat condition. Nausea and vomiting are uncommon in cats by may develop. Left untreated, weight loss or even death may occur in very young, or older, debilitated animals. 

"Giardia can cause your cat to not want to eat and drink and eventually cause them to be very sick," Ochoa says.

The disease is more likely to be serious in kittens or older cats with damaged immune systems from Feline Immunodeficiency Virus (FIV), Feline Leukemia Virus (FeLV) or other illnesses.

How to Treat Giardia in Cats 

It can be difficult to diagnose giardiasis in cats, so your veterinarian may need to perform several tests. After your cat is diagnosed by their vet, she'll likely be prescribed an anti-parasitic medication to help clear the infection.

There is no approved medication for this condition, however "metronidazole and fenbendazole are two commonly prescribed medications for the treatment of Giardia. Usually these are very effective at treating Giardia infection," Ochoa says.

At the end of her treatment, you'll want to prevent reinfection by keeping your cat and her environment clean. Make sure to clean her fur (bathing the back-end with shampoo to remove fecal material is very helpful) to remove any remaining cysts that may be hanging around and give her litter box a deep clean once her treatment is complete. You'll also want to disinfect your home—including bedding, carpet, carriers, and furniture your kitty lounges on most. If your cat spends time outdoors, make sure she has a clean water source and keep her away from ones that may be infected.

Is It Possible to Prevent Giardia in Cats?

While there aren't any preventative medications for Giardia in cats, the risk of infection can be reduced with a clean environment. Make sure to clean your cat's litter box regularly, especially if you have multiple cats. If your kitty spends time outdoors, watch them to ensure they're not drinking from potentially contaminated water.

Can Cats Spread Giardia to Humans and Other Pets?

Unfortunately, yes. Giardia is a zoonotic parasite, meaning it can be spread from animals to humans. However, the CAPC says there's little evidence for direct transmission between pets and people, and humans are more likely to contract it from other humans. However, it's important to be extra cautious with immune-compromised household members.

If your cat has Giardia, other pets in your household may also get infected. The easiest way to prevent infection is to make sure your pets can't get to the infected cat's fecal matter—especially if your dog is notorious for eating poop or if the cats in your home like to help each other clean. This may mean keeping them in separate rooms while your kitty completes treatment and ensuring everything they've touched is disinfected.