ASK THE VET: Cat little threat to pregnancy

Every now and then, a client comes to me in distress because she is pregnant and has heard that somewhat persistent myth that a cat will cause you to end a pregnancy. Now her mother is insisting that she get rid of the cat or risk losing the baby.

The concern about cats and pregnancy involves transmission of a one-celled parasite called Toxoplasma gondii. Toxoplasma can infect most warm-blooded animals and is widespread across the country. The parasite makes a home inside many tissues.

Carnivores become infected from eating prey that has the parasite.

Eating raw or undercooked meat, especially pork, is by far the most common way that humans get the parasite. Herbivores tend to get the infection from browsing in areas where an infected cat has passed stools with the parasite in it.

Most people and animals that have been infected with Toxoplasma have no idea because it rarely causes symptoms. Severely immunity-compromised patients are more likely to have problems because they have reduced ability to keep the organism in check.

Unfortunately Toxoplasma has the ability to cross the placenta, especially during the first two trimesters of pregnancy, and can cause an infection in a developing fetus that can result in severe birth defects or fetal death.

Cats have a unique place in the life cycle of Toxoplasma. They are the only animals in which the parasite undergoes the part of its life cycle in which it can develop oocysts, which are like little microscopic eggs passed out of the cat in its stool and left in the environment to be picked up by other animals. Oocysts can live in the environment for up to a year.

When a cat eats prey infected with Toxoplasma, the parasite finds its way to the cat's digestive tract, where it starts producing oocysts that are shed in the cat's stool within two or three days. After the oocysts are passed, however, they still need to mature for two to three days before they can cause an infection in another animal that ingests them. Cats will shed oocysts in the stool for only one to two weeks after they have been infected, and then they will stop.

What this means for a pregnant woman is that it takes a fairly unlikely - but not impossible - convergence of factors for her to get Toxoplasma from the cat. The cat has to have been infected within a two-week window, and the woman would have to have contact with that cat's stool after it has been sitting for at least two days, get some on her hands, and perhaps eat a sandwich without washing her hands first. All the same, the consequences of getting Toxoplasma during early pregnancy are severe enough to warrant some simple precautions.

1. Don't let the cat hunt outside. If he isn't eating wildlife, he isn't getting exposed.

2. Be careful about digging in the soil and eating produce grown in the backyard. Roaming cats will use your garden for a litter box, and it is possible that one could have deposited oocysts that remain infective. Gloves and good hand and food washing go a long way for safety.

3. Cook all meats thoroughly. Of course you should do this anyway, but it is especially important during pregnancy.

4. Somebody other than the pregnant woman should clean the cat's litter box every day.

But if a pregnant woman has to clean the litter box, she should use gloves and wash her hands thoroughly.

If you take these precautions you should be just fine - and there will be no reason to get rid of the cat.
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Anne Pierce is a Colorado Springs veterinarian and co-owner of High Plains Veterinary Hospital, a Colorado Springs small-animal clinic. Reach her at petdocs@highplainsvet.com.