Toxoplasma Gondii is a small protozoa – a single celled organism that acts as a parasite. It is, in my opinion, one of the most interesting critters that causes disease. It can only sexually reproduce in felines, so it has evolved unbelievable abilities to help it get into cats. It wants to be in a cat so much that if it gets into the wrong species, such as a mouse or rat, it can change the behaviour of the mouse so that it loses its fear of cats. It does this by altering the genes in nerve cells in the rodent’s brain so that it stops the rodent from being afraid of predators. Most bizarrely, there is also evidence that people with Toxoplasma infection have behaviour changes similar to those seen in rodents. They may take more risks (one study in the USA showed that victims of road traffic accidents were three times more likely to be infected than the general population), and be less grossed out the smell of cat urine. It is estimated that somewhere between 33-50% of the UK population is infected.
Once an animal or human eats the eggs (called oocysts), they hatch in the gut and they tunnel out of the gut into the blood, and hide in the liver, heart, brain and muscle tissue where they replicate, and form tiny cysts. Healthy individuals make a strong immune response against these bugs, and they are not generally found in the blood after this first exposure. Infection is probably life long, you are not infectious, and isn’t a problem in healthy people. Toxoplasmosis is only a problem if you first contract the disease during your pregnancy, especially in the early stages. If you are already infected by the time you get pregnant there is no risk to your baby so don’t worry!
There are two ways to get toxoplasma, and they are: eating the eggs that have been shed from a cat, or eating cysts containing the parasite in undercooked meat. Toxoplasma can only sexually reproduce and lay eggs in a cat’s intestine. The eggs are shed in cat poo, and can last for a long time in the environment in spores. To prevent contracting this disease for the first time during your pregnancy, get someone else to deal with the litter tray, and don’t eat vegetables from your garden if you know that your (or someone else’s) cat does its business there.
The actual risk of contracting the disease from undercooked meat isn’t known, and research is ongoing to work out just how many farm animals are infected with Toxoplasma. The good news is that freezing your meat for a week has been shown to be completely effective at killing any Toxoplasma cysts that may be present.
The last study done in 1990 found that 29% of sheep carry the disease, but a new study is currently underway and preliminary results suggest that around 70% of sheep are now testing positive. Lamb is the meat that is most likely to cause infection, so do avoid eating pink lamb unless you know that it has been frozen first.
Pigs are less likely to be carriers, but there is no data from the UK to say just how common it is. Pork is usually cooked well, so as long as you avoid uncooked products there isn’t a risk here.
One of the questions we are asked a lot is: can I eat a rare steak during pregnancy? It’s a tricky one to answer. Not much is known about Toxoplasmosis in cattle. There have been no published cases where viable tissues cysts have been found, even after experimental infection. There has been some evidence of infection based on the presence of antibodies in the blood, but these don’t seem to translate to the presence of the parasite in the muscle or in the milk. Based on this, the risk of contracting Toxoplasmosis from beef is extremely low, so, while I might avoid a truly rare steak, I may allow myself to have it medium rare rather than well done!