Intestinal parasites in cats: Toxoplasma, Giardia, Toxocara, and pregnancy

How many newly pregnant women in the US still hear "you'll have to get rid of the cat" the moment they share the news? The number is hard to pin down, but most OB-GYNs and clinical veterinarians put it well above 30 percent. The fear traces to one disease, Toxoplasma gondii, and the epidemiology dismantles the reflex. In the countries where researchers have traced where pregnant women actually pick up a first-time toxoplasma infection, the large majority come from undercooked meat and poorly washed produce, not the cat on the couch.

That does not make feline intestinal parasites harmless. Toxocara cati and Giardia duodenalis carry real clinical impact, deworming schedules exist for good reasons, and litter box hygiene is a genuine tool in households with immunocompromised people or a pregnancy underway. Here is the full picture of feline intestinal parasites for US owners, following CAPC and CDC guidance.

The three parasites that matter

Toxoplasma gondii: the cat is the definitive host

Toxoplasma is a protozoan. The cat is the definitive host, the only species in which the parasite completes its sexual cycle and sheds infective oocysts in feces. Every other mammal (sheep, cattle, pigs, humans) is an intermediate host: the parasite cysts in muscle and brain without producing oocysts.

The cycle in the cat:

Primary infection: the cat ingests tissue cysts (by catching a mouse or eating raw meat) or sporulated oocysts from the environment.
Intestinal multiplication: for 3 to 10 days after infection, the cat sheds millions of oocysts in its feces. This is the only window in which the cat is a source of contagion.
Environmental sporulation: freshly shed oocysts are not infective. They need 1 to 5 days in the environment to sporulate and become contagious.
Lifelong immunity: after the first infection, the cat stops shedding oocysts. A later re-exposure produces minimal or no shedding. An adult cat that has already passed through toxoplasmosis does not transmit it.

What this means in practice:

An indoor cat that eats commercial food and never hunts has a very low probability of shedding oocysts at any given moment.
If it sheds at all, it does so for 1 to 2 weeks over its entire lifetime, usually as a young cat.
Oocysts freshly deposited in the litter box need at least 24 hours to sporulate. Scooping the box daily drops the risk close to zero.

Giardia duodenalis: the chronic-diarrhea parasite

Giardia is another protozoan, this one with a direct cycle and no separate definitive host. Resistant cysts in water, food, or on surfaces; ingestion by the cat; trophozoites that attach to the small intestinal lining; new cysts shed back into the environment.

The typical clinical picture:

Chronic, intermittent diarrhea in young cats, especially from catteries or multi-cat colonies.
Soft, bulky, foul-smelling stool, sometimes with mucus.
Weight loss or stunted growth in kittens.
Many infected adults stay asymptomatic.

Prevalence varies by source, but surveillance (CAPC in the US, ESCCAP in Europe) reports detectable Giardia in 5 to 15 percent of cattery and shelter cats. In single-cat homes the prevalence is lower.

There are cat-specific subtypes (assemblages). Assemblage F is predominantly feline with low zoonotic potential. Assemblages A and B do carry zoonotic capacity, but they are a minority in cats.

Toxocara cati: the feline roundworm

The most common nematode in young cats. Large, whitish larvae that owners sometimes spot in stool or vomit ("spaghetti"). Infection happens through:

Transmammary route: the queen passes larvae to her kittens through her milk. This is the dominant route.
Ingestion of eggs from the environment.
Ingestion of infected rodents (paratenic hosts).

Prevalence:

Kittens under 6 months: up to 30 to 50 percent in surveys.
Adults: under 10 percent in well-managed indoor cats.
Outdoor and hunting adults: intermediate figures.

Clinical signs in kittens:

Distended belly.
Stunted growth.
Dull coat.
Diarrhea, occasional vomiting with visible larvae.
In heavy burdens: intestinal obstruction.

There is a real zoonotic angle: Toxocara eggs in contaminated sand or soil can infect humans, especially children, and produce visceral or ocular larva migrans, rare but documented. The CDC tracks toxocariasis as a neglected parasitic infection in the US, with seroprevalence highest in children and in the Southeast.

Quick data

Parasite	US prevalence	Shedding period	Diagnosis	Treatment
Toxoplasma gondii	High seroprevalence in outdoor/hunting cats	1 to 2 weeks over a lifetime	Fecal exam plus serology	Usually none if asymptomatic
Giardia duodenalis	5 to 15 percent catteries, under 5 percent single home	Chronic, intermittent	Fecal antigen ELISA or PCR	Fenbendazole plus metronidazole
Toxocara cati	30 to 50 percent kittens, under 10 percent adults	Until treated	Fecal flotation	Fenbendazole, pyrantel, or milbemycin

Toxoplasma and human pregnancy: myth vs reality

Toxoplasmosis matters in pregnancy because a first-time infection during gestation can cross the placenta and cause congenital toxoplasmosis (hydrocephalus, brain calcifications, chorioretinitis). The real question is who actually infects the pregnant person.

Documented sources of human primary infection, per CDC and published European cohorts:

Eating raw or undercooked meat (lamb, pork, beef carrying tissue cysts): the dominant route in most studied populations.
Poorly washed vegetables and fruit contaminated with environmental oocysts.
Untreated water in rural areas.
Handling garden soil without washing hands afterward.
Contact with a contaminated litter box without hygiene: a minor but real route.

When you design real toxoplasmosis prevention for a pregnant person, the measures that work are:

No raw or undercooked meat. Cook meat to safe internal temperatures (the USDA lists 145 degrees F for whole cuts of beef, pork, and lamb with a 3-minute rest, 160 degrees F for ground meat). This rules out steak tartare, carpaccio, dry-cured charcuterie that has not been frozen, and a rare burger.
Wash fruit and vegetables carefully, especially produce eaten raw that has touched soil.
Gardening gloves and handwashing after any contact with soil.
Do not drink untreated water.
For the household cat: scoop the litter box daily (ideally someone other than the pregnant person), wear gloves, and wash hands. If the pregnant person handles it, gloves and rigorous washing.
Keep the cat indoors, fed commercial food, not raw meat.
Do not test the cat. Feline serology is poorly suited to managing risk: a seropositive cat has already shed and stopped, and a seronegative one could start. What does make sense is serologic testing of the pregnant person in the first trimester where indicated.

US obstetric guidance is consistent on this point. ACOG and the CDC do not recommend removing the cat from the home because of pregnancy. It is a measure with no medical justification.

Diagnosing intestinal parasites

A reasonable protocol for a cat with compatible signs (diarrhea, vomiting, poor growth, worms visible in stool) or at a routine exam:

Fecal flotation

The standard test. It detects Toxocara eggs, hookworm, other nematodes, and sometimes Giardia cysts. Sensitivity varies, so a three-day pooled sample improves detection.

Fecal antigen ELISA or PCR for Giardia

More sensitive than flotation for Giardia, which sheds intermittently. ELISA is available in-clinic as a rapid snap test.

Detecting Toxoplasma

Fecal exam: detects oocysts only during the acute shedding phase (1 to 2 weeks after first infection). A negative result does not rule out past infection.
Serology: IgG and IgM in serum. Positive IgG indicates past infection (the cat no longer sheds); positive IgM suggests recent infection.

When to do it

Kittens: fecal exam at the first vet visit (8 to 10 weeks), repeated before each early deworming.
Symptomatic adults: fecal exam plus a Giardia ELISA.
Annual screening for outdoor or hunting cats.
Before adopting a second cat: fecal exam on the newcomer, with Giardia ruled out.

Treatment

Toxocara cati

Fenbendazole 50 mg/kg/day orally for 3 to 5 days.
Pyrantel pamoate 20 mg/kg single dose, repeated in 2 to 3 weeks.
Milbemycin oxime single dose.
Combination spot-ons: imidacloprid/moxidectin, selamectin, eprinomectin.

For kittens: deworm at 3, 5, 7, and 9 weeks, then monthly through 6 months of age, per CAPC.

Giardia duodenalis

Fenbendazole 50 mg/kg/day orally for 5 days.
Metronidazole 25 mg/kg every 12 hours orally for 5 to 7 days (veterinary use; watch for neurologic signs in sensitive cats).
Ronidazole 30 mg/kg/day for 7 days in refractory cases (compounded, special use).
Bathe the cat at the start and end of treatment to remove cysts stuck to the coat.
Environmental hygiene: diluted bleach on surfaces, full litter box replacement, daily scooping.

Relapse is common when the environment is not cleaned.

Toxoplasma gondii

In an immunocompetent, asymptomatic cat, do not treat. Shedding is self-limiting and controlled with litter box hygiene.

In a symptomatic cat (rare), clinical toxoplasmosis with fever, uveitis, or neurologic or respiratory signs:

Clindamycin 10 to 15 mg/kg every 12 hours orally for 4 weeks.
Trimethoprim-sulfonamide as an alternative.
Supportive treatment of the affected clinical process.

US deworming schedule

CAPC sets the baseline schedule for US cats. A reasonable plan, adjusted to the cat's lifestyle:

Kittens (through 6 months)

3 weeks: pyrantel or fenbendazole against Toxocara.
5, 7, 9 weeks: repeat.
Monthly from 9 weeks through 6 months.
Fecal exam before adoption and at the first vet visit.

Strictly indoor adult cat

Internal deworming 2 to 4 times a year depending on contact with other cats.
Annual fecal exam at the wellness visit.
External parasite control (fleas, ticks) monthly if the cat accesses a balcony or porch, or lives with an outdoor dog.

Outdoor or hunting adult cat

Internal deworming monthly or every 2 months.
Strict monthly external parasite control.
Watch for tapeworm (Dipylidium, carried by fleas; Taenia taeniaeformis, by rodents).

Cat in a home with a pregnant person, young children, or immunocompromised members

Monthly deworming for the duration of the situation.
Daily litter box hygiene with gloves.
Fecal exam when the cat first joins the home.

Practical products available in the US

Oral tablet: Drontal (pyrantel + praziquantel), Profender oral options, Bayer/Elanco pyrantel products.
Combination spot-on: Profender (emodepside + praziquantel), Centragard (eprinomectin + praziquantel), Bravecto Plus (fluralaner + moxidectin), Revolution Plus (selamectin + sarolaner).
External-only spot-on: Revolution, Frontline Plus, Advantage II.

A combination spot-on simplifies the routine: one application covers internal and external parasites in a single monthly step. Several of these are prescription-only in the US, so the protocol runs through your veterinarian.

Prevention: what is actually in the owner's hands

Complete the kitten's full schedule without skipping doses.
Do not feed raw meat or raw organ meat. If you run a raw diet, freeze the meat at minus 4 degrees F (minus 20 degrees C) for at least 72 hours to destroy Toxoplasma cysts.
Scoop the litter box daily. This stops any oocyst present from sporulating.
Wash hands after handling the litter box or garden soil.
Limit hunting in outdoor cats where possible (a collar bell, restricted hours), though the behavior is hard to suppress.
Fecal exam on any new cat before mixing it with the others in the home.
Deep-clean the litter box weekly with diluted bleach (1:10) or boiling water to destroy resistant oocysts and cysts.

Common questions

Do I have to give up my cat if I become pregnant?

No. No US obstetric body recommends it. Keep up daily litter box hygiene, ideally have someone else scoop it, wear gloves, and wash your hands. The real risk of infection from an indoor cat is very low.

How do I know if my cat has toxoplasma?

Serology detects past infection (IgG) or recent infection (IgM). A fecal exam only catches it during a 1-to-2-week window across the cat's whole life. To manage pregnancy risk, testing the pregnant person is more useful than testing the cat.

My cat has chronic diarrhea and every test comes back normal. Could it be parasites?

Yes. Giardia is the most likely parasitic cause of chronic diarrhea with a negative conventional fecal exam. Ask for a fecal antigen ELISA or a Giardia-specific PCR.

Do the dewormers sold at pet stores and supermarkets work?

Products with the correct active ingredient and an adequate dose work, but many over-the-counter bargain products have the wrong dosing or ingredients with no real effect. Buy through a pharmacy or your veterinary clinic; the cost difference is small and the efficacy difference is not.

Does milk with garlic deworm a cat?

No. It is folklore. On top of that, garlic in any meaningful amount is toxic to cats (hemolytic anemia). Use a veterinary dewormer, with no home substitutes.

How often should I deworm a strictly indoor cat?

Two to four times a year is reasonable. If the cat lives alone, does not hunt, and does not share space with an outdoor dog, the lower frequency is enough. An annual fecal exam confirms the schedule is working.

Bottom line

Feline intestinal parasites are a real clinical problem with effective treatment, wrapped in a persistent myth about Toxoplasma and pregnancy that still costs many cats their homes for no reason. The sensible approach in 2026 is to follow the CAPC schedule, run at least an annual fecal exam, keep the litter box scooped daily, and stop thinking about rehoming the cat every time someone in the house becomes pregnant. A plate of dry-cured ham that was never frozen is more likely to transmit toxoplasma than an indoor cat fed commercial food. This is not an opinion; it is what the epidemiologic series have shown for decades.