Toxoplasmosis: IgG-positive cat and a pregnant owner
Healthy 6-year-old Domestic Shorthair cat that went into the garden when young and now lives exclusively indoors on commercial food. Its owner is pregnant and wants to know whether the cat poses a risk.
| Parameter | Result | Reference |
|---|---|---|
| Toxoplasma gondii IgG | 1/1,024 | < 1/64 |
| Toxoplasma gondii IgM | Negative | < 1/64 |
Which statement is correct?
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A. The cat was infected in the past and is very unlikely to shed oocysts again
Correct. Positive IgG with negative IgM indicates past infection. Cats shed oocysts for 1–3 weeks after primary infection, usually before seroconversion, and rarely shed again. A seropositive cat poses less risk than a seronegative cat that hunts.
B. The high IgG titre indicates active toxoplasmosis and clindamycin is needed
IgG can remain high for years. Only a fourfold rise in paired samples or a high IgM suggests recent infection, and the cat is also healthy.
C. Faeces must be examined for oocysts to rule out the risk
Shedding is brief and almost always occurred years ago; a negative faecal test adds no useful information and a positive one is almost never seen in chronically seropositive cats.
D. She should rehome the cat during the pregnancy
This is not justified. The main sources of human infection are undercooked meat and contaminated vegetables or soil. It is enough for someone else to clean the litter tray daily and to wash hands.
lightbulb Key takeaway
Oocysts need 1–5 days to sporulate and become infective: cleaning the litter tray daily breaks the risk. In a sick cat (uveitis, pneumonia, neurological signs), a high IgM or a fourfold rise in IgG supports active toxoplasmosis; IgG alone only indicates exposure.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.