Sunday, June 8, 2014

What is the connection among Toxoplasma, cats, and pregnant women?

by Amanda L. Maus DVM
Catalina Pet Hospital
Tucson, AZ

Toxoplasma gondii is a parasite that can infect birds and mammals, including humans.  Cats become infected by eating the parasite "egg" or infected small mammals or birds.  Cats are the only animal in which Toxoplasma reproduces, with the "eggs" being found in cat feces.  However, most cats can clear the infection and do not continue to pass infected feces after a few weeks.  Other cats are infected with Toxoplasma for life, with the organism living in their organs or tissue.

In addition to direct exposure to Toxoplasma in cat feces and litter, humans can be exposed when handling raw meat or eating undercooked meat, handling or eating raw vegetables, and handling garden soil without gloves.

The symptoms of Toxoplasma in cats and people can vary from no signs in most patients with a strong immune system to severe diarrhea, heart or lung disease, liver disease, neurologic disease, eye disease, etc in patients with a weak immune system. 

A human mother who has been exposed to Toxoplasma prior to pregnancy, who already has antibodies against Toxoplasma which she will pass to her offspring, has a very low risk for her baby to become infected.  A human mother with a first time, new exposure and infection due to Toxoplasma has the highest risk for her baby to become severely affected, especially during first trimester.  A blood test can be performed by a obstetrician to look for Toxoplasma antibodies in the mother.

While pregnant, in conjunction with passing the litter box duties to another family member, wearing gloves while gardening, hand washing, rinsing produce, and safely handling raw meat and properly cooking meat help prevent exposure to Toxoplasma. 


  1. Thanks for this informative piece. If I could offer a few scattered thoughts...

    First, while likelihood of a pregnant woman passing on her infection is higher in the first trimester, the severity of disease in the baby is worse when infection happens later in pregnancy.

    Second, indoor cats aren't likely to become infected at all, so I don't think avoiding kitty litter is necessary in that case. (I guess unless you also have a rodent infestation...)

    Third, it takes oocyst "eggs" 1-5 days to sporulate (become infective), so cleaning the cat box twice a day is likely to mitigate those risks if a partner or family member isn't around.

    Fourth, freezing meat is effective at killing Toxo, but the time it takes to do it depends on temperature -- 24 hours at 10F should do it, but at 20 F it likely takes two weeks, and above that much longer.

    1. Dear misterbatz,
      Thanks for your comments. The most important thing a woman can do is to be tested for antibodies against toxoplasma and then follow precautions based on her risk factors discussed with her doctor. Following those precautions will help protect her and the fetus during the entire pregnancy.
      Indoor only cats can become infected with toxoplasma in various ways, such as interactions with newly acquired cats, encountering prey in the house such as mice or small reptiles, escaping outside and becoming exposed, etc.
      Cats can release millions of unsporulated oocysts and that is the main reason for avoiding scooping the litterbox when pregnant, since not all of the oocysts will be removed with scooping alone, regardless of frequency. The active oocysts can survive in the litterbox for months if it is not properly sanitized.
      Due to the variability of freezing temperatures on toxoplasma, I believe following safe meat handling procedures is a better general guide, since it will also help limit exposure to Salmonella, E. coli, and other potentially harmful diseases as well.