Toxoplasmosis

Toxoplasmosis is a widespread infection of humans and many other species of warm-blooded animals. It is caused by a parasitic organism called Toxoplasma gondii. The definitive host is the cat, domestic or wild. The major public health importance of the parasite is that it is capable of being transmitted via the placenta from mother to unborn child.

MEANS OF INFECTION

Cats become infected in one of three ways: during gestation through the placenta, by ingesting oocysts (eggs) of the parasite shed in the feces of other cats, or by eating small prey animals (birds, mice, etc.). Cats are the only animal that can shed the organism into the environment after infection; in other animals and humans the parasite remains in the body, encysted in various tissues.

Humans also may become infected in one of several ways. The major source of human infection in this country seems to be through ingestion of under-cooked meat, especially pork or lamb. Cows are resistant to infection, but beef is frequently contaminated by being cut by equipment previously in contact with infected pork. Raw goats' milk has been shown to be the source of some human infection. Another source of infection is from soil, as in gardening and other yard work. The oocysts shed by infected cats can survive in the soil for several months to a year even under adverse environmental conditions.

The least common means of infection for humans is by having a cat in the home. Toxoplasmosis is much less common in housecats than in those who roam outside. The oocysts are not able to cause infection until one to five days after being shed. Since the average litter box is cleaned of solids more frequently than every five days, few oocysts will be left in the box to become infective. The grooming habits of cats make it unlikely for oocysts to be present on the coat.

CLINICAL SIGNS

Cats infected with Toxoplasmosis may show no illness at all, or they may have diarrhea, fever, enlarged lymph nodes, inflammation of the eye, and/or respiratory problems. Some infections are fatal. Cats may shed the oocysts so early in the course of the infection that the disease is not yet detectable by the usual blood tests. After infection, most cats develop immunity to the organism and will not shed oocysts again unless they are severely stressed or in some other way their immunity is suppressed.

In adult humans, Toxoplasmosis is not a serious disease. Many people have no signs at all. Others report such things as headache, muscle ache, enlarged lymph nodes, and sore throat. However, if a pregnant woman is infected with Toxoplasmosis, especially in the first half of the pregnancy, there is a 20% to 50% chance of the fetus becoming infected, with severe consequences including blindness and mental retardation. This is the basis for the many questions we receive from pregnant women who have cats and who have been frightened by well-meaning but sometimes misinformed friends or relatives.

DIAGNOSIS

Although T. gondii is an intestinal parasite of cats, the oocysts are shed for such a brief period of time that routine fecal exams are rarely diagnostic. Testing the blood for antibodies to the organism will indicate whether a cat has been exposed to it, but will not give information about whether the cat is contagious to others. In fact, since antibodies to Toxoplasma develop after the period of oocyst shedding, a positive cat may be less likely to spread the disease than a cat who has recently become infected but still tests negative.

For women, the time to be tested for Toxoplasmosis is BEFORE becoming pregnant. A woman with a positive test before pregnancy is considered to have previous exposure to the organism, to be immune to it, and unlikely to pass it on to her fetus. A woman with a negative test before pregnancy must be especially cautious not to become exposed after the pregnancy begins.

Our recommendations are as follows:

All women should be tested before becoming pregnant. Check with your physician about having this done.
Testing of cats is optional and depends upon several factors, including the results of the woman's test and whether the cat's lifestyle leads to a high likelihood of exposure. We will be happy to discuss your particular situation.

PREVENTION AND CONTROL

TO PREVENT INFECTION

IN CATS

If possible, keep cats indoors at all times to prevent hunting and scavenging.
Do not feed raw meat, viscera (i.e. liver) or bones.
Cover trash cans to prevent scavenging.

IN CHILDREN

Do not feed undercooked meat, especially pork products.
Do not feed unpasteurized milk, especially goats' milk.
Cover all children's sandboxes when not in use to prevent use as a litter box by outdoor cats.
Enforce washing of hands after playing on the ground or with outdoor cats and before eating.

OF PREGNANT WOMEN AND THEIR UNBORN CHILDREN

Wash hands thoroughly with soap and water after handling meat.
All cutting boards, counters, sink tops, knives, and other material coming into contact with uncooked meat should be scrupulously washed with soap and water.
All meat should be completely cooked before being tasted or eaten. (At least to 155° F).
Wash vegetables carefully before eating to remove soil.
Wear gloves while gardening and clean hands with soap and water afterwards.
Remove cat feces from the litter box at least once daily, being very careful not to touch the box or its contents with your hands. Better yet, get someone else to do this chore.
Also have someone else do the major litter box emptying and disinfection. If this is impossible, wear gloves (i.e. Playtex type).
Stay away from unknown cats, especially those outside. Wash hands after petting or otherwise handling any cat, including housecats.

In summary, Toxoplasmosis is NOT a reason for eliminating the pleasure and comfort of a cat's company from your home. With common sense and reasonable precautions, the disease is not difficult to prevent.