
Toxoplasmosis
It is thought that around 30% of women in the UK are immune to toxoplasmosis, but it is unusual to test for immunity in this country. If the mother has an illness or experience in very early pregnancy, which could damage her baby, then usually it will cause miscarriage rather than abnormalities in the baby.
The toxoplasmosis scare with regard to cats has limited foundation.
Even if you do change cat litter, it would be extremely hard for
you to catch toxoplasmosis from it - not impossible, but hard. You are much more likely to catch toxoplasmosis from eating rare or lightly cooked meat, and poor food hygiene generally.
Toxoplasmosis is caused by the parasite Toxoplasma gondii. It is only a danger to the unborn child if the mother contracts it during pregnancy for the first time. The infection can only cross the placenta in the acute phase of the illness, i.e. in the mother's first attack. After this the mother is usually immune, but even if she does have another dose, it will not harm the baby.
By the age of 25-30, it is estimated that around 30% of people in the UK will have had toxoplasmosis and so will be immune. In France and many other countries, it is routine to screen for toxoplasmosis antibodies in antenatal blood tests, so that the mother knows if she has to be careful or not. This is not considered cost-effective here, and if you do ask for a blood test, you have to make sure that the laboratory staff know that they are testing for toxoplasmosis *immunity* and not for a current infection. Normally when any test regarding toxo is requested here, it is to see if the mother has a current infection and so that is what lab staff will be expecting to look for.
So assuming you are not immune to toxoplasmosis, how do you go about catching it? Here's what you'd have to do with cats:
First, find a cat which is allowed outdoors and which hunts - as they
usually catch toxoplasmosis from eating rodent prey. Housebound cats will not be able to catch it. In cats generally, about 20-60% have been infected. The prevalence is highest in feral cats although domestic cats can catch it too. However, very few of these cats will actually be infectious themselves, as usually they will only transmit the disease during their primary infection. After the cat is first infected, it will shed oocysts (eggs) in its faeces for 10-14 days. It will not normally shed them after this period, and only around 1% of infected cats have been found to be infectious in surveys. However, the oocysts can survive for a year or more, so old cat faeces are potentially dangerous - e.g. ones that have been mouldering in your garden and which you stumble upon while weeding the borders.
So, having found your cat during its rare infectious period, you then have to actually ingest some of these oocysts to get infected. We are not talking about changing cat litter with basic hygiene precautions here. You actually have to ingest cat faeces somehow. If you are washing your hands after changing cat litter then this will be very unlikely. However, wearing gloves while gardening, and not touching your face or mouth while gardening, is probably a sensible precaution.
Just looking at the numbers here, if around 1% (and this is probably a high estimate) of cats are shedding oocysts at any particular time, and around 30% of women are immune anyway, then only around 0.6% of women who come into contact with one cat are at even a *theoretical* risk of catching toxoplasmosis from their cat while pregnant. And this would be assuming that they actually went out of their way to try to catch it, i.e. deliberately ate cat faeces! Bringing in basic hygiene precautions will mean that the proportion of that 0.6% of women who stand any realistic chance of being infected is miniscule.
Without being complacent about toxoplasmosis as it is a dreadful disease for a baby to catch in utero, it appears ridiculous that many pregnant women are paranoid about going near cats, when they should be concentrating their attentions on food hygiene and caution while gardening.
If you do catch toxoplasmosis in pregnancy, estimates of the likely
percentage of babies affected vary, as do estimates of the likely severity of the illness. For example: "there is approximately a 40% chance that the foetus will acquire the infection, and in around 10% of these cases, severe neurological or ocular disease is present at birth" or "The transmission rate from a maternal infection is about 45%. Of these 60% are sub-clinical infections, 9% result in death of the foetus and 30% have severe damage such as hydrocephalus, intracerebral calcification, retinochoroiditis and mental retardation."