Toxoplasmosis in Cats: Shedding, Risks, and the Truth About Indoor Cats
Toxoplasmosis is one of those topics that tends to generate more alarm than understanding. The parasite behind it — Toxoplasma gondii — has been sensationalised in popular media to the point where some people rehome their cats upon becoming pregnant, or avoid cat ownership altogether based on fears that are largely disproportionate to the actual risk. The science of toxoplasmosis is nuanced, and getting to grips with it means separating what is genuinely important from what has been overstated.
What Is Toxoplasma gondii?
Toxoplasma gondii is an obligate intracellular protozoan parasite with a complex life cycle that can involve almost any warm-blooded animal — but cats hold a unique and critical role. Cats, both domestic and wild, are the definitive host of T. gondii, meaning they are the only animals in which the parasite can complete its sexual reproductive cycle and produce the environmentally resistant oocysts that drive transmission.
The life cycle works as follows: a cat ingests tissue containing Toxoplasma cysts — typically by eating infected prey such as mice or birds. Inside the cat's intestinal cells, the parasite undergoes sexual reproduction, producing oocysts that are shed in the faeces. These unsporulated oocysts are not immediately infectious; they require one to five days in the environment to sporulate and become capable of infecting a new host. Once sporulated, however, they can remain infectious in moist soil for up to eighteen months.
Intermediate hosts — including rodents, birds, livestock, and humans — become infected by ingesting sporulated oocysts from contaminated soil, water, or unwashed produce, or by eating tissue containing bradyzoite cysts in undercooked or raw meat. In these intermediate hosts, the parasite forms cysts in muscle and neural tissue that persist for the host's lifetime.
How Do Cats Become Infected?
Cats most commonly acquire toxoplasmosis by hunting and eating infected prey animals, particularly rodents. Indoor cats fed commercial diets and with no access to raw meat or prey have very low rates of infection. In surveys of cat populations, higher Toxoplasma seropositivity is consistently associated with outdoor access and hunting behaviour.
A cat typically sheds oocysts only once in its lifetime — during the initial acute infection, which lasts approximately one to three weeks. After this period, the immune response suppresses the intestinal phase of the parasite's life cycle, and shedding ceases. Severely immunocompromised cats, such as those with FIV or FeLV, may shed again, but this is not common in otherwise healthy individuals.
This means that the window during which a cat is actually a transmission risk — through its faeces — is relatively narrow. A cat that was infected months or years ago and is now seropositive is not currently shedding oocysts and does not represent a faecal transmission risk.
Toxoplasmosis in Humans: Who Is Actually at Risk?
Toxoplasma infection is extremely common in humans globally — estimates suggest that up to one-third of the world's population has been exposed, with seropositivity rates varying markedly between countries. In most immunocompetent adults, infection produces either no symptoms or a mild, self-limiting flu-like illness that resolves without treatment. The immune system then keeps the parasite in a latent state, and no further harm results.
The two groups for whom toxoplasmosis carries genuine clinical risk are:
- Pregnant women who have not previously been infected — primary infection during pregnancy can result in congenital toxoplasmosis in the foetus, potentially causing miscarriage, stillbirth, or serious neurological and ocular damage in the newborn
- Severely immunocompromised individuals — including those undergoing chemotherapy, organ transplant recipients, and people with advanced HIV — in whom latent infection can reactivate and cause life-threatening encephalitis or other systemic disease
For the general population of healthy adults, contact with cats carries minimal meaningful risk from toxoplasmosis, particularly when basic hygiene is practised.
The Truth About Indoor Cats and Transmission Risk
Here is the statistic that puts the entire conversation in perspective: studies consistently identify contact with cats as a minor risk factor for human toxoplasmosis, far outweighed by consuming undercooked meat, unwashed raw vegetables, and contaminated water. In one large European study, eating undercooked or cured meat products was identified as the primary risk factor, with cat contact playing a comparatively minor role.
Indoor cats that do not hunt and are not fed raw meat have extremely low rates of active infection. Even in cats that are infected, the oocysts require one to five days outside the body before becoming infectious — meaning that daily litter tray cleaning eliminates virtually all faecal transmission risk from a household cat.
Recommendations for pregnant women are therefore appropriately targeted:
- Have another person empty the litter tray daily where possible
- If this is not possible, wear gloves and wash hands thoroughly afterwards
- Avoid handling stray cats or cats with unknown histories during pregnancy
- Wear gloves when gardening, as soil can contain oocysts from outdoor cats
- Wash hands thoroughly before eating, and wash all raw produce before consumption
- Avoid undercooked or raw meat during pregnancy
Clinical Toxoplasmosis in Cats
While most cats infected with T. gondii show no clinical signs, disease can occur in immunocompromised cats or in those with heavy exposure. Clinical signs in affected cats can include fever, lethargy, loss of appetite, respiratory signs, neurological symptoms, and uveitis — inflammation within the eye, which may manifest as cloudiness, dilated pupils, or apparent changes in eye colour.
Diagnosis in cats involves antibody testing to detect IgM (indicating recent infection) and IgG antibodies. Treatment with clindamycin or trimethoprim-sulphonamide combinations is effective when initiated promptly. Ocular toxoplasmosis may require corticosteroids alongside antiprotozoal treatment to manage inflammation.
Toxoplasmosis deserves to be taken seriously, but in proportion to actual risk rather than speculation. For the vast majority of cat owners, sensible hygiene practices are all that is required to manage whatever small risk exists. Rehoming a pet over this concern, in most circumstances, is a significant overreaction to a manageable situation — and one that the evidence simply does not support.