Toxoplasmosis is caused by a parasite called toxoplasma gondii. This is found in different forms in raw meat, within cats who eat raw meat and their faeces. Toxoplasmosis infection is common in both men and women outside of pregnancy, however it is infection during pregnancy that is of most concern as it can lead to infection being passed to the baby causing congenital toxoplasmosis.
Who is at risk?
Once you have had toxoplasmosis, the body develops immunity and new exposure during pregnancy is not an issue. Peak incidence of infection is between ages 25 and 30 years and by this time, about 30% of people will have had toxoplasmosis, hence will not be at risk of any problems during pregnancy. In the US, about 30-35% have antibodies and in France more than 65% of women will have already had toxoplasmosis. Because infection is more common in France, congenital toxoplasmosis occurs at over twice the rate in other countries.
It is not known for sure how many women catch toxoplasmosis during pregnancy, but some research suggests it is of the order 1 in 500.
What are the symptoms of toxoplasmosis?
It is unusual for otherwise healthy people to be ill when infection occurs. The most common symptoms are a viral, glandular fever-like illness or swollen glands in the neck with malaise and muscle aches. The life-cycle of toxoplasma gondii includes an oocyst which originates in the digestive tract of members of the cat family.
There are 3 main ways of catching toxoplasmosis:
- Eating inadequately cooked meat
- Inadvertently eating the toxoplasmosis oocyst that cats have passed in their faeces, either from a cat litter box, infected soil or unwashed vegetables from infected soil
- Congenital infection from mother to baby
You cannot catch toxoplasmosis by human-to-human transmission apart from the pregnancy-associated congenital infection mentioned above.
Although some research has found cleaning a cat litter box or owning a cat to be a risk factor for infection, other studies including two in pregnancy did not find this. Cats generally only shed oocysts for several weeks during their life if they do catch toxoplasmosis. Cats that do not hunt prey and are not fed raw meat are unlikely to catch toxoplasmosis and so are of minimal concern. Because of their grooming habits, faecal matter is not present on the fur of normal cats and the risk posed by stroking or living with a domestic cat is minimal to non-existent.
How is it diagnosed?
A blood test can indicate whether you are susceptible to getting an infection, hence at risk. It can also diagnose new infection in the mother. In France all women are screened at the beginning of pregnancy to see if they are susceptible to infection. In other countries, including New Zealand and the UK, this is not the case as the incidence of infection is low.
In any case, risk can be avoided through simple measures, and although knowing your antibody status may reassure you if you are immune, it's not as though there is a vaccine to prevent infection, as is the case with other congenital infections, such as Rubella.
What are the risks to the baby?
In only about 30-40% of women who catch toxoplasmosis during pregnancy, does the infection pass to the unborn baby. The actual risk appears to be related to the stage of pregnancy at which the infection is acquired. It is greatest in the third trimester at 70%, whereas in early pregnancy only 15% of infants will become infected when their mother has toxoplasmosis.
Toxoplasmosis infection may lead to miscarriage, stillbirth, or survival with growth problems, blindness, water on the brain (hydrocephalus), brain damage, epilepsy, or deafness. This often develops after birth, so even normal infants of women with known infection should be kept under observation for some time.
If a woman is found to have acquired toxoplasmosis during pregnancy, she will be offered an ultrasound scan to look for signs of fetal infection. After 20 weeks gestation, she may be offered a definitive test by sampling the amniotic fluid (amniocentesis). This involves a scan and the sample of liquor being tested for toxoplasma gondii DNA.
What is the treatment?
The evidence that treatment can help to prevent some of the sequelae of toxoplasmosis infection is unfortunately contradictory. The usual treatment is a drug called spiramycin started once an infection is confirmed in the mother, and pyrimethamine/sulfadiazine if fetal infection is confirmed by amniocentesis. If a scan suggests severe damage, there may be an option to terminate the pregnancy.
There are no particular risks or procedures needed for labour and delivery, and the mother nor baby requires isolation either during labour or after the birth. The paediatrician will carry out appropriate testing for neonatal infection. Congenital infection can be ruled out if the blood test for toxoplasmosis does not persist in the baby for longer than one year.
How can I avoid catching toxoplasmosis?
Although toxoplasmosis is quite serious when it occurs, as you will see from the figures above, it is relatively rare. Women with cats do not need to disown them when they become pregnant; it is just necessary to take a few precautions.
Be sure to only eat meat which has been cooked right through. Wash your hands, cooking utensils and food surfaces after preparing raw meat and wash all the soil from fruit and vegetables before eating. Keep raw meat and cooked foods on separate plates. If possible get someone else to clean out the dirty cat litter or use gloves and wash your hands afterwards. Always use gloves when gardening and wash your hands afterwards.
Try not to worry excessively or become paranoid about this - if you take these precautions, chance of infection is practically eliminated - you can still pet your cat, without fear!!
Finally, it is important for pregnant farmers to be aware that toxoplasmosis can be caught from sheep at lambing time.