Is your cat trying to kill you?

Warning – if you’re at all squeamish, or have a pet cat, it might be better to stop reading now!

Studies have estimated that in Europe, somewhere between 43% and 67% of cats are infected with Toxoplasma Gondii. Toxoplasmosis is a disease caused by a parasitic protozoan known as Toxoplasma gondii (big ‘T’ little ‘g’). A parasitic protozoan is a ‘single celled organism that feeds on organic matter. Toxoplasma gondii are able to infect almost any warm-blooded animal but can only sexually reproduce in cats. Toxoplasma gondii (often abbreviated to T. gondii) is one of the most common parasites in humans in developed countries with estimates of between 50% and 64% of the population of some countries currently infected with this parasite.

Infections in humans are most common from raw or undercooked meats, gardening where cats have been ‘doing their business’, or changing your cat’s litter tray. This is why you should probably consider wearing gloves for gardening or changing the litter tray, and if you do insist on eating meat, make sure it’s cooked properly!

A T. gondii infection can be serious for pregnant women or those with a weakened immune system, but for most other people, you may not notice even notice the symptoms. At worst, you might feel like you have the flu. However, this parasite has actually developed a very devious way of getting back to a cat – it attempts to change you behaviour to make its host more likely to be eaten by a cat.

The parasite also changes your behaviour

It has been found that the parasite has the ability to change the behaviour of its host – including humans – reducing their inhibitions and making them more likely to take risks. Infected rats and mice become less fearful of cats and therefore more likely to be caught & eaten by a cat. In fact, in these studies, some of the infected rats actively sought out cat-urine-marked areas, appearing to have become sexually attracted to the scent.

Of course, unless you’re a zookeeper, you’re probably unlikely to get eaten by a cat… but the parasite doesn’t know that – it simply wants to get back to the place where it can reproduce, which is more likely to happen when you’re not being as cautious as normal.

Increased risk-taking behaviour in humans due to T. gondii infection is real

In humans, the increased risk taking behaviour has been found to be a very real thing! A relationship was discovered between Toxoplasmosis infection and motorcycle ownership. Apparently, the percentage of populations infected with T. gondii in a country is proportional to the number of motorcyclists, and the number of road deaths from speed. A study from 2010 reported that in France, the human infection rate from Toxoplasmosis was around 45% (compared to 6.6% in the UK at the same time), and in 2021, over 11% of the French population reported they intended to buy a motorbike. Road deaths were at that time 68% higher in France than in the UK. The author of the study goes on to say that motorcyclists have a ‘high probability of having Toxoplasmosis infections’, and that ‘infected people are 3 to 4 times more likely to be killed in accidents involving reckless speeding’. This suggests that the condition may increase our appetite for speed and taking risks.

But it gets worse

Although infections in humans are normally asymptomatic, there is no treatment that is 100% effective. The parasite infects the hosts body and brain, which really complicates the delivery of treatments such as pyrimethamine, sulfadiazine, and folinic acid. You’d hope that your immune system would be able to get rid of the infection. However, this clever little parasite has another crafty trick up its sleeve. As your immune system tries to fight it off, the parasite forms ‘cysts’ in the host and goes dormant. Your immune system therefore can’t eradicate the infection completely, and your infection may re-emerge again at some point in the future. Most infections from meat are from the ingestion of T.gondii cysts.

But it gets even worse than that!

In a study published on 2nd December 2023 ‘Cat Ownership and Schizophrenia-Related Disorders and Psychotic-Like Experiences: A Systematic Review and Meta-Analysis’ found ‘an association between broadly defined cat ownership and increased odds of developing schizophrenia-related disorders’.

The findings support an association between cat exposure and an increased risk of broadly defined schizophrenia-related disorders. You’ve heard of the term ‘crazy cat-lady’? Maybe the basis for the cliche has it’s roots in this infection!

A study published 2013 in the PCM also linked T. gondii to affective and neurological disorders in humans such as OCD, Parkinson’s disease, Alzheimer’s disease, bipolar disorder, and suicide

There is also the ever growing and convincing body of evidence concerning a potential relationship linking T. gondii with that of some forms of affective and neurological disorders in humans. Correlations have been found for OCD (Miman et al., 2010b), Parkinson’s disease (Miman et al., 2010a), Alzheimer’s disease (Kusbeci et al., 2011), suicide (Arling et al., 2009) and bipolar disorder (Pearce et al., 2012).

T. gondii may also be influencing the gender of human babies

Women who had had a T. gondii infection have also been found to be much more likely to give birth to boys. In 2006 a Czech research team discovered that women with high levels of toxoplasmosis antibodies had a 72% chance of giving birth to a boy, as opposed to an average of around a 51% chance in women without the presence the antibodies.

Symptoms and treatment

If you’re worried you may have Toxoplasmosis, but you’re otherwise healthy and not showing serious symptoms, there’s probably not a lot you can do about it. The NHS has a useful page describing who is most at risk from this illness, the common symptoms, and what you should do if you’re ill.

However, the best thing you can do is avoid getting it in the first place – using gloves when gardening or changing cat litter trays, not eating meat (or at least making sure it’s properly cooked if you do eat it), washing your hands properly, and washing fruit & veg properly

So is my cat really trying to kill me?

The short version however is ‘no’, of course not! Although cats tend to, in general, feel quite indifferent about most humans, they’re normally not actively trying to kill you. Yes, people have died from Toxoplasmosis both directly and indirectly, however, unless you’re pregnant, or immunocompromised, you most likely be OK. In fact, you may not even know you’re infected. Toxoplasmosis certainly wants you to be eaten by a cat – after all that’s the only way it’ll be able to reproduce – but will its affect on your inhibition actually kill you? That’s unlikely too. Just don’t buy yourself a motorbike!