Yes, coccidia is contagious between cats. An infected cat sheds microscopic egg-like structures called oocysts in its feces, and any other cat that ingests those oocysts can become infected. In multi-cat households and shelters, this makes coccidia one of the most common intestinal parasites passed between cats sharing litter boxes, living spaces, or outdoor areas.
How Coccidia Spreads Between Cats
Coccidia spreads through a fecal-oral route. An infected cat passes oocysts in its stool. Once those oocysts sit in the environment for a day or two, they mature into an infectious form. Another cat picks them up by stepping in contaminated litter or soil and then grooming its paws, or by sniffing and licking surfaces where feces have been. Shared litter boxes are the most obvious transmission point in a home, but any surface contaminated with even a trace of infected stool can be a source.
Cats can also become infected by eating prey animals, like mice, that carry the parasite. This is a common route for outdoor cats, though indoor cats in multi-cat homes are far more likely to catch it directly from a housemate’s stool.
Oocysts Survive a Long Time Outside the Body
One reason coccidia spreads so effectively is that the oocysts are remarkably tough. They have a thick, resistant shell and can survive in the environment for over a year. They persist through winter and are not killed by most standard household cleaners. Temperatures above about 104°F (40°C) or steam cleaning can destroy them, but normal room temperatures allow them to remain infectious for months on floors, bedding, litter boxes, and soil.
This durability means that even after an infected cat is treated or removed from a space, the environment itself can still be a source of infection for other cats unless it’s thoroughly cleaned.
It Only Spreads Between Cats, Not to Dogs or Humans
The species of coccidia that infect cats are host-specific. A cat cannot pass its coccidia to a dog, and a dog’s coccidia cannot infect a cat. Humans also cannot catch the feline species. So if your cat is diagnosed, your dog and your family are not at risk, but every other cat in the household is.
Kittens and Stressed Cats Are Most Vulnerable
Many adult cats can carry coccidia without showing any symptoms at all. Their immune systems keep the parasite in check, though they may still shed oocysts and spread the infection to other cats. The cats most likely to get sick are kittens, especially those under six months old, and cats whose immune systems are weakened by stress, overcrowding, or other illness.
Shelters and foster homes see the highest rates of clinical disease for exactly this reason. Overcrowding and stress are major factors in whether an exposed cat actually develops symptoms. The University of Wisconsin’s shelter medicine program notes that coccidia is an opportunistic pathogen, meaning it takes advantage of a weakened immune system. Reducing stress, for example by fostering kittens out of a shelter environment, gives them a better ability to fight off the infection on their own.
Signs to Watch For
The most common symptom is watery diarrhea, which can sometimes contain mucus or blood. Kittens may also become dehydrated, lose weight, or appear lethargic. In severe cases, particularly in very young kittens, the diarrhea can be dangerous if left untreated simply because small animals dehydrate quickly.
Adult cats that are otherwise healthy often show no symptoms at all. You may not know your cat is carrying coccidia unless a veterinarian runs a fecal exam, which involves looking at a stool sample under a microscope to identify oocysts. If one cat in your household is diagnosed, it’s reasonable to assume the others have been exposed, even if they seem fine.
How Coccidia Is Treated
Treatment is straightforward. The most commonly used medications work by either killing the parasite directly or stopping it from reproducing so the cat’s immune system can clear the infection. A single-dose treatment is sometimes enough, while other protocols call for daily medication over 5 to 21 days depending on the drug and severity. Shelter medicine programs often treat preventively, giving medication to all incoming kittens as early as two to three weeks of age and repeating the dose one to two weeks later.
Your vet will likely recommend a follow-up fecal exam after treatment to confirm the infection has cleared. Cats can continue shedding oocysts for some time after starting medication, so environmental cleanup matters just as much as the medication itself.
Protecting Other Cats in Your Home
If one of your cats has been diagnosed with coccidia, a few practical steps reduce the risk to your other cats significantly.
- Separate litter boxes. Give the infected cat its own box, away from the others. Scoop all boxes at least twice daily to remove stool before oocysts have time to become infectious.
- Clean with heat. Standard disinfectants don’t reliably kill coccidia oocysts. Steam cleaning litter boxes, floors, and bedding is the most effective decontamination method. Boiling water poured over hard surfaces also works.
- Isolate if possible. Keeping the infected cat in a separate room during treatment limits environmental contamination. This is especially important if you have kittens in the home.
- Test your other cats. Even if they’re asymptomatic, a fecal exam can identify carriers before they develop symptoms or spread the parasite further.
- Reduce stress. Keep routines consistent, provide enough resources (food bowls, water stations, resting spots) for each cat, and avoid introducing new animals during an outbreak. A calmer environment helps every cat’s immune system work more effectively.
Because oocysts can persist in the environment for over a year, a single round of cleaning isn’t always enough. Regular steam cleaning of litter boxes and surrounding areas for several weeks after diagnosis helps prevent reinfection, especially in homes with young or immunocompromised cats.