Toxoplasmosis is an infection caused by a microscopic parasite called Toxoplasma gondii, and cats are the only animals in which this parasite can complete its full life cycle and reproduce. That makes cats central to how the parasite spreads in the environment, which is why the topic comes up so often for cat owners. The good news: most infected cats never show symptoms, and with basic precautions, the risks to both your cat and your family are manageable.
Why Cats Are Uniquely Important
Toxoplasma gondii has a complex two-stage life cycle. It needs a “definitive” host to sexually reproduce and form eggs (called oocysts), and it uses “intermediate” hosts (rodents, birds, livestock, humans) to multiply by cloning itself inside tiny tissue cysts. Wild and domestic cats are the only definitive hosts on the planet. No other animal produces oocysts.
A cat typically picks up the parasite by eating an infected mouse, bird, or other small prey. Once inside the cat’s gut, the parasite reproduces and the cat begins shedding millions of microscopic oocysts in its feces. This shedding starts about 3 to 10 days after the cat eats infected tissue and lasts roughly 10 to 14 days. After that initial window, most healthy cats stop shedding entirely and rarely shed again, even if the parasite remains dormant in their body for life.
How Cats Get Infected
The most common route is hunting. Outdoor cats that catch and eat rodents or birds are at highest risk because these prey animals frequently carry tissue cysts of the parasite. Cats can also become infected by eating raw or undercooked meat, which is why feeding a raw diet without proper safety measures increases the chance of exposure. Indoor-only cats that never hunt and eat only commercial food have a much lower risk, though not zero if they encounter contaminated soil tracked indoors or catch a stray mouse.
Antibody surveys in the United States show that anywhere from 14% to 100% of cats test positive for past exposure, depending on the population studied. Feral and outdoor cats consistently fall at the higher end of that range.
Symptoms in Cats
Most cats that become infected with Toxoplasma never look sick at all. A healthy adult cat’s immune system typically keeps the parasite in check, confining it to dormant cysts in muscle and brain tissue where it causes no obvious harm.
When symptoms do appear, they tend to show up in kittens, elderly cats, or cats with weakened immune systems (such as those also infected with feline immunodeficiency virus or feline leukemia virus). The parasite can affect multiple organs, so the signs vary widely:
- Respiratory signs: labored breathing, coughing, or rapid breathing when the lungs are involved
- Eye problems: inflammation inside the eye, cloudiness, or changes in pupil size
- Neurological signs: seizures, tremors, unsteady walking, or behavior changes when the brain is affected
- General illness: fever, loss of appetite, weight loss, lethargy, or jaundice
Because these symptoms overlap with many other diseases, toxoplasmosis is not something you can diagnose just by looking at your cat. It requires blood testing.
How Vets Diagnose It
Veterinarians rely on blood tests that measure two types of antibodies: IgM and IgG. Each one tells a different part of the story. IgM antibodies appear soon after a new infection and generally fade within about three months. A high IgM level suggests the infection is recent. IgG antibodies take longer to develop, usually appearing by the fourth week, but they can remain elevated for years. A positive IgG result on its own only confirms the cat was infected at some point, not that it’s currently sick.
To distinguish an active infection from old exposure, vets often run paired blood tests three to four weeks apart. A fourfold rise or fall in IgG levels between the two tests points toward an active or recently resolving infection. A single antibody number, on its own, is not enough to make a definitive diagnosis. Vets may also combine blood work with imaging or tissue samples if a cat is showing severe symptoms.
Treatment and Prognosis
When a cat develops clinical toxoplasmosis, treatment typically involves a course of antibiotics lasting several weeks. The goal is to stop the parasite from actively multiplying and give the cat’s immune system a chance to regain control. Most cats with healthy immune systems respond well and recover fully, though the parasite is never completely eliminated from the body. It remains dormant in tissue cysts for life.
Cats with compromised immune systems face a harder path. Those co-infected with feline immunodeficiency virus or feline leukemia virus are more likely to develop severe, widespread disease and may relapse after treatment ends. For these cats, the prognosis depends heavily on how well the underlying immune problem can be managed.
The Human Risk: Cats vs. Other Sources
This is where many cat owners worry most, and where the picture is more nuanced than the headlines suggest. Yes, cats shed the parasite in their feces. But the CDC lists multiple transmission routes for humans, and direct contact with cat litter is only one of them.
The major routes of human infection include:
- Undercooked meat: eating contaminated pork, lamb, venison, or even shellfish like oysters and mussels
- Contaminated produce: eating unwashed fruits or vegetables from soil where infected cats have defecated
- Gardening: handling soil that contains oocysts and then touching your mouth
- Contaminated water: drinking water with oocysts
- Cat feces: accidentally ingesting oocysts while cleaning the litter box
In practical terms, undercooked meat is considered the leading source of human infection in many countries. Owning a cat raises your exposure risk only modestly, especially if you follow basic hygiene around the litter box.
One important detail: oocysts shed in cat feces are not immediately infectious. They need one to five days in the environment to sporulate (mature) before they can infect a person. This means scooping the litter box daily, before the oocysts have time to become dangerous, dramatically cuts your risk. Washing your hands afterward adds another layer of protection.
Keeping Your Cat and Family Safe
Prevention focuses on two goals: reducing your cat’s chance of picking up the parasite, and minimizing your own exposure to oocysts if your cat is infected.
For your cat, the single most effective step is keeping it indoors. An indoor cat that doesn’t hunt and eats only cooked or commercial food has very little opportunity to encounter the parasite. If you feed raw meat, freezing it for several days before serving can reduce (though not completely eliminate) the risk, since the tissue cysts are sensitive to extreme cold.
For yourself, scoop the litter box every day, ideally wearing gloves, and wash your hands thoroughly afterward. If you’re pregnant or immunocompromised, have someone else handle litter duty entirely. Wear gloves while gardening, especially in areas where outdoor cats may defecate, and wash all produce before eating it. Cook meat to safe internal temperatures, and clean cutting boards and utensils that have touched raw meat before using them for other foods.
There is no reason to give up your cat over a toxoplasmosis diagnosis. The shedding window is short, typically just 10 to 14 days in a cat’s entire life, and with daily litter cleaning and hand washing, the chance of transmission from your own cat is low.