Toxoplasmosis: Myth vs Reality
January 23, 2013
Toxoplasmosis is a parasitic disease that I love to talk about. I am a doctor of veterinary medicine. I am also a mother. In playing both of these roles it is very rewarding to be able to offer strong scientific medical data to debunk misinformation and superstition. This is especially true when it affects our feline patients and the mothers and children who love them.
When toxoplasma, a protozoan parasite, is mentioned in conversation it almost always involves a story about a pregnant woman and her family cat. This is because the toxoplasma organism can, if ingested by a woman at a very specific time during her pregnancy, cause abortion. Toxoplasma organisms can also be shed in cat feces. It is because of this that many family physicians will recommend that women give up litter box duty during their pregnancies. Still, some physicians will cruelly and unnecessarily recommend surrendering the family’s beloved cat to a shelter.
It has been known for decades that there is no correlation between infection with toxoplasmosis and cat ownership. Two studies in the New England Journal of Medicine and the Journal of the American Medical Association from the 1960s demonstrate this very nicely.* In fact, even in severely immunocompromised individuals such as AIDS patients, there is no correlation between toxoplasma exposure and cat ownership.**
So, where are people getting exposed, and why are cats the target of so much misinformation?
The most common ways in which people ingest toxoplasma organisms are through handling and ingestion of raw or undercooked meat, microwaved pork, and not properly washing hands after gardening (toxoplasma is found in the soil).
Because our beloved feline companions are hunters, they ingest the organism when they eat the raw meat they catch (rodents). After their very first exposure to the organism and during a very small-time frame (2–3 weeks) cats can shed the toxoplasma organism in their feces.
In order for a human to be exposed to the organism from a cat, that person would have to have a cat who is indoor/outdoor, actively hunting, and has never been previously exposed to the organism. Then, the human would have to, rather unhygienically, clean the litter box, wash their hands poorly, and ingest the cat’s fecal material during the two to three-week time frame the cat is shedding once in that individual cat’s life.
The Centers for Disease Control & Prevention has excellent information about toxoplasmosis on its website.
The most important message I pass along to expectant mothers who are worried about this organism is to wash their hands at every opportunity they get. Be very careful when handling raw or undercooked meat, thoroughly cook the meat in any meal, and wash every surface thoroughly if you do eat meat. Do not microwave any pork products. Wear gloves when gardening. Pass litter box duty along to another family member for a while (you deserve the break).
Finally, give every non-human animal in the house an appropriate dose of strategic parasite control. The biggest zoonotic (infectious disease spread between non-human and human animals) risk to human children is not toxoplasmosis, it is the common roundworm. This easy-to-kill intestinal parasite can cause eye disease in children and, as we all know, getting kids to wash their hands is a lot more challenging than we would like!
* Warren K.S., Dingle J.H.: A study of illness in a group of Cleveland families, XXII. Antibodies to Toxoplasma gondii in 40 families were observed for 10 years. New England Journal of Medicine 274:993–997. 1966.
Lamb G.A., Feldman H.A.: Risk in acquiring toxoplasma antibodies; a study of 37 “normal” families. Journal of the American Medical Association 206: 13005-1306, 1968.
** Wallace MR, Rosetti RJ, Olsen PE: Cats and toxoplasmosis risk in HIV-infected adults. Journal of the American Medical Association 269:76–77, 1993.