Toxoplasma is a protozoal (simple single-cell organism) infection, which can affect all mammals. The adult stage of Toxoplasma is found in cats only, and can transmit to other mammals or people.

Many people worry that their cats will infect them. Pregnant women, in particular, are concerned about Toxoplasma infection, as it can cause abortion or illness of the baby.

It is important to understand that the risk from cats in Hong Kong is minimal. Most cats live indoors, use litter trays and are fed commercial cat foods. The lifecycle of Toxoplasma will explain the minimal risk:

Cats can be infected by the following methods:

• Exposure to the oocysts (eggs) found in soil which is contaminated by an infected cat’s stool;
• By eating meat containing Toxoplasma cysts.

The toxoplasma organism invades the cat’s intestinal wall. They then produce huge numbers of oocysts themselves, which are excreted in the stool for 2-3 weeks. THIS IS THE ONLY PERIOD THAT CATS ARE INFECTIVE TO PEOPLE. It takes 5 days before the oocysts in the stool develop to become infective, so oocysts in fresh stool cannot transmit to people. However, oocysts in stool remain infective for many months in moist soil. People are not at risk if their cats are using littertrays which are cleaned daily.

After invading the intestine, the Toxoplasma organism will invade the cat’s body and form cysts in the muscles and brain. These remain dormant and seldom cause symptoms or disease. If other mammals or people are infected, the organism also invades muscle and the brain to form these cysts. This seldom causes disease unless the immune system is compromised, for instance in AIDS patients or people on chemotherapy. The cysts are then infective to cats eating raw meat, or people eating poorly cooked meat

In people, affected mothers will pass the disease onto their unborn babies through the placenta. This does not happen in cats. Cats are almost always infected by cysts in raw meat, so cats fed commercial cat foods are not at risk. Other Mammals or people do not pass oocysts in their stool.

Summary

It is only possible for a pregnant woman to contract Toxoplasma from a cat for 2-3 weeks after the cat’s infection, via stool that is more than 5 days old. The cat would have to eat infected raw meat, or be in contact with other infected cat stool more then 5 days old, to become infected. Once a cat has been infected, it becomes resistant and will not get infected again. People will also only become infected once.

So people are not significantly at risk from pet cats, but care should be taken when handling soil, which has been used by street cats or wild cats as their toilet. We are at risk from eating undercooked meat or drinking unpasteurised milk. It is, however, estimated that 30-50% of the world’s population has been infected by Toxoplasma, mainly in developing countries.

So what testing can be done by women planning a baby?

She can have herself tested. If she already has antibodies against Toxoplasm, she will have previously been infected and will be resistant to new infections.

Her pet cat can be tested. There are three possibilities:

• The cat has not antibodies, and this means that the cat has not previously been infected. If it becomes infected during the owner’s pregnancy, it could be a potential source of infection to the owner;
• The cat has antibodies, and this means the cat has already been infected previously. If this was very recent then the cat could be infective. If this is suspected, a second test three to four weeks later will have a much higher antibody level. It is therefore important to repeat tests if they are positive initially.
• If the antibody levels remain consistent for both tests, the cat will be resistant to re-infection and poses no threat to people.

Symptoms of Toxoplasmosis in cats

Few cats will show disease symptoms even if infected. If they do, it is usually kittens or young adults that show symptoms. Initially signs are not specific, such as poor appetite, fever and depression. Some cats will develop pneumonia with difficult breathing. Occasionally hepatitis (with vomition, diarrhoea and jaundice), pancreatitis and swollen lymphnodes may develop. Some cats develop signs of infection of the brain and eyes, with signs of brain damage, seizures and blindness developing. Inflammation of the inside of the eye with blood and pus present is seen. Note that these symptoms are the same as for the dry form of FIP virus, a common disease in Hong Kong.

Treatment with a specific antibiotic should show rapid improvement – if there is no improvement within two to three days, this is probably not Toxoplasmosis.

So women who are pregnant need not fear that their cat can infect them, if they take simple precautions and you should be very safe:

1. Feed the cat only cooked food – all commercial cat foods are cooked.
2. Clean the litter tray daily, using gloves and washing their hands afterwards.
3. Don’t introduce new cats, especially street cats or wildcats, to your home during your pregnancy.
4. Cook your own food well and wash fresh vegetables well. Drink only pasteurized milk.
5. Do not handle soil where cats have access.