Parasite Profile: Toxoplasma

T. gondii cysts under microscope

Life Cycle

Toxoplasma gondii is a protozoan parasite that infects most species of warm blooded animals, including humans, and can cause the disease toxoplasmosis. The only known definitive hosts for toxo are domestic and wild cat species. Unsporulated oocysts are shed in the cat’s feces. Although oocysts are usually only shed for 1-2 weeks, large numbers may be shed. Oocysts take 1-5 days to sporulate in the environment and become infective. Intermediate hosts in nature (including birds and rodents) become infected after ingesting soil, water or plant material contaminated with oocysts. Cats become infected after consuming intermediate hosts harboring tissue cysts. Cats may also become infected directly by ingestion of sporulated oocysts.

In the human host, the parasites form tissue cysts, most commonly in skeletal muscle, myocardium, brain, and eyes; these cysts may remain throughout the life of the host. Diagnosis is usually achieved by serology, although tissue cysts may be observed in stained biopsy specimens. Diagnosis of congenital infections can be achieved by detecting T. gondii DNA in amniotic fluid.

CDC- Toxoplasma life cycle

Pregnancy and Toxoplasmosis

A common misconception is that pregnant women must give up their cats because of the risk of Toxoplasma gondii infection. First-time infection of women in early pregnancy can have significant effects on the fetus, potentially leading to abortion, neonatal death, or congenital effects. Similarly, infection in immunocompromised individuals (particularly AIDS patients) can cause encephalitis and other very serious complications. Children may ingest infectious oocysts from soil during play, but infection is not known to cause significant issues as long as they are immunocompetent. Although cats are the definitive hosts of this parasite, keep these points in mind:

  1. Almost all cats are infected with T gondii at some point, but very few are shedding Toxoplasma oocysts at any one time. Most cats shed significant numbers of oocysts only for a couple of weeks after initial infection, typically at an early age. The likelihood of a healthy mature cat shedding T gondii oocysts is generally low.1
  2. The oocysts shed in cat feces generally become infective at least 24 hours after they are passed. Cleaning the litter box daily will greatly reduce the client’s risk of infection.
  3. Depending on a woman’s location and lifestyle, she may also be exposed to T gondii from eating certain undercooked meats, or from contact with contaminated soil. The parasite must be swallowed to cause infection—contact alone is not enough, but contamination and poor hygiene of the hands can lead to oral transmission.

The bottom line: Pregnant women can keep their cats, but should take precautions to reduce the risk of T gondii exposure. Most cat owners have already been exposed to toxo (though it is not guaranteed! Our pregnant vet and technician have both tested negative!), and only new infections contracted during pregnancy cause problems for the fetus. Ask your doctor for a ‘toxoplasmosis titre’ blood test to determine if you already have the parasite. De-worming during pregnancy or breastfeeding is not advised.

Reducing Risk of Transmission

  • avoid adopting a cat younger than 1 year
  • have someone else clean the litter box daily while pregnant (or wearing gloves and mask while cleaning), and clean the box often with disinfecting soap and scalding water
  • cooking meat properly (visit for information about proper temperatures)
  • thoroughly wash all produce to remove potentially contaminated soil
  • washing hands thoroughly after working in soil or handling cat litter
  • Keep long haired cats trimmed around the anus to avoid feces from being carried around the house
  • Do not feed your cats raw food
  • Keep cats inside. Indoor cats without an opportunity to hunt have little chance of contracting toxo
  • Keep outdoor sandboxes covered, and teach children to wash hands after playing outside



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