FrançaisInfection is common, disease is rare
“Infection is common in cats, but the clinical disease is rare” [1]. The European ABCD guideline estimates that around one third of cats become infected, yet few develop clinical toxoplasmosis [2]. In Finland, 48.4% of cats had IgG antibodies, while 3.1% of 193 cats examined after death had generalized toxoplasmosis [3].
Disease usually comes from the parasite waking up in a cat whose immune system is weakened. Listed triggers include FIV or FeLV infection, high-dose steroids, ciclosporin, oclacitinib and chemotherapy [2]. See FeLV and FIV in cats.
- Common signs: fever, depression, poor appetite, neurologic signs, eye inflammation (uveitis), jaundice, lameness, painful muscles, breathing difficulty, diarrhea and weight loss [2].
- Lungs: pneumonitis is the most common finding and can be rapidly fatal [2].
- In 100 confirmed cases: fever in 73% and eye inflammation in 81.5% of the cats checked; the parasite was found in 76.7% of lungs and 70.0% of livers [4].
Antibody tests: what each result means
All infected cats make IgG and IgA antibodies, and about 80% also make IgM [1, 2]. IgG can take 4–6 weeks to appear [1, 2]; the same ABCD text also says antibodies need two to three weeks to develop [2]. A positive test shows infection, not disease: 31.6% of 12,628 sick cats tested in the US were seropositive [2].
| Result | What it means |
|---|---|
| IgG positive, healthy cat | Past infection. The cat is extremely unlikely to shed oocysts; re-shedding has never been shown in naturally infected cats [2]. |
| IgG negative | No antibodies yet. This cat could be shedding oocysts, or will likely shed them if exposed for the first time [2]. |
| IgM positive | Points to a recent infection, but can occasionally be found in healthy cats [2]. |
| Very high or rising IgG or IgM, sick cat | Raises the suspicion of toxoplasmosis, but does not prove it on its own [2]. |
How to read the Toxoplasma IgG line
Here is an example line from a healthy adult cat tested before a family pregnancy.
- Abbreviation Toxo IgG or T. gondii IgG. An IgM line is sometimes reported next to it.
- Result 1:256 in this illustrative line: antibodies are present.
- Unit A titre is a dilution of the serum. Some laboratories report units instead, or simply “positive”.
- Laboratory interval An example cut-off only. Each laboratory sets its own, so compare with the interval printed on your report.
- Flag H or “positive”: in a healthy cat, a past infection. Such a cat is extremely unlikely to shed oocysts [2]. It does not prove disease [2].
What the blood work shows in a sick cat
Little is published about blood findings in feline toxoplasmosis [2]. What is known:
- ALT (liver enzyme): a raised ALT was the main abnormality [2]. See high liver enzymes in cats.
- Albumin: low in two reports, but raised in another [2].
- White blood cells: neutrophil and lymphocyte counts fell for a short time after experimental infection [2].
- Muscle enzyme (CK): the ABCD guideline notes that one would expect creatine kinase to rise when muscles are inflamed; this is an expectation, not measured data [2].
- Jaundice can be one of the signs [2].
These changes are not specific: other diseases cause them too. See cat blood work explained.
How toxoplasmosis is confirmed
- Antibodies (IgG, IgM) support the suspicion, especially very high or rising titres, but a positive result does not prove clinical toxoplasmosis [2].
- Finding the parasite is needed for a definitive diagnosis: tachyzoites (the active form) seen by cytology or immunohistochemistry, or detected by PCR [2].
- Looking for a trigger: because FIV, FeLV and immune-suppressing drugs are listed triggers, they are part of the picture [2].
Fever, eye inflammation and breathing signs have other causes in cats, including FIP, so tests are read together.
Oocyst shedding and your family
A cat sheds oocysts once in its lifetime, for a short time after its first infection: usually 3–10 days [1], or days four to eleven in the ABCD update [2]; experimentally between 4 and 13 days [5]. In experiments, re-infected cats sometimes shed again, briefly and in small numbers: 4 of 9 cats re-challenged 77 months later [2, 5].
Freshly passed oocysts are not infective. They need 1–5 days [1], or 2 days according to the ABCD update [2], to become infective. This is why scooping the litter every day helps. Oocysts can survive over 100 days in soil and water [2].
For people, the main sources are undercooked meat and unwashed vegetables. A European case-control review found that contact with cats was not a risk factor [2]. If you are pregnant or immunosuppressed, ask your doctor about your own risk.
Related articles
En français : toxoplasmose du chat.
Questions to ask your veterinarian
- Is the test IgG, IgM or both, and what is the laboratory’s cut-off?
- Is this result a past infection or a recent one?
- Is the ALT raised, and are other values abnormal?
- Is a cytology or PCR test needed to find the parasite?
- Should my cat be tested for FIV and FeLV?
Get your cat’s results explained together.
AI DiagAnimals reads antibody results, liver enzymes, albumin and the blood count together with your laboratory’s intervals, and prepares the questions for your vet. The service opens soon: leave your email to be told first.
Frequently asked questions
Do vets check for toxoplasmosis?
In a sick cat with suggestive signs, a vet can test for IgG and IgM antibodies. A definitive diagnosis needs the parasite itself, found by cytology, immunohistochemistry or PCR [2].
Can you tell if a cat has toxoplasmosis?
Not by looking at it, and not from antibodies alone: a positive test shows infection, and many infected cats are healthy. In one US study, 31.6% of sick cats were seropositive [2].
How long does toxoplasmosis last in a cat?
The shedding of oocysts happens once in a lifetime and lasts only days: usually 3–10 days [1], or days four to eleven after infection [2].
Is my IgG-positive cat a danger to my family?
A healthy antibody-positive cat is extremely unlikely to shed oocysts [2]. A seronegative cat is the one that could shed them if infected for the first time [2].
How do people usually catch toxoplasmosis?
Mainly from undercooked meat and unwashed vegetables. In a European review, contact with cats was not a risk factor [2].
Sources
- Hartmann K et al. Toxoplasma gondii infection in cats: ABCD guidelines on prevention and management. J Feline Med Surg. 2013;15(7):631-637. doi.org/10.1177/1098612X13489228
- ABCD Europe. Guideline for Toxoplasma gondii infection (update by D. Addie; last updated 08/02/2024). abcdcatsvets.org/guideline-for-toxoplasma-gondii-infection
- Jokelainen P et al. Feline toxoplasmosis in Finland. J Vet Diagn Invest. 2012;24(6):1115-1124. doi.org/10.1177/1040638712461787
- Dubey JP, Carpenter JL. Histologically confirmed clinical toxoplasmosis in cats: 100 cases (1952-1990). J Am Vet Med Assoc. 1993;203(11):1556-1566. pubmed.ncbi.nlm.nih.gov/8288479
- Dubey JP. Duration of immunity to shedding of Toxoplasma gondii oocysts by cats. J Parasitol. 1995;81(3):410-415. pubmed.ncbi.nlm.nih.gov/7776126
Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.