Were you a little rat going about your daily ratty business, sniffing, nibbling, grooming and exploring, you natural rat self would we terrified, repulsed and would get the hell away from any space smelling of cat pee. A generous amount of fear and skittishness keeps the beings, which are in the natural food chain labelled as pray and dinner, alive. The ones who have greater reserves towards a potential danger, because if there is fresh kitty pee here the kitty is not far away, survive for longer. But we don’t live only in the world of macro things we can see with the naked eye such as cats, rats and humans. There is a whole sub macro, micro world coexisting with us and is full of pretty crafty organism who’ve managed to pull some of the nature’s greatest magic tricks and take control of their host, albeit not hosted willingly for a lovely dinner party. These things are parasites.

They are a strange bunch and play a high stakes game where if you win in this biochemical private warfare you get to complete your life cycle and propagate. Parasites are far more adaptable and “smarter” than a roomful of humans trying to figure out the bits and pieces of their survival mechanisms. You may be disgusted with the word parasite itself but you’ve got to give them credit for their ingenuity and what they accomplish with zero brain power. Life finds a way, no matter which form it appears in. One of these parasites is toxoplasma gondii, an intercellular one celled eukaryote aka the thing that causes the wide spread toxoplasmosis. The only place it can reproduce is the GI tract of a cat. The rat eats the faeces, and in order to complete the cycle the parasite needs to get back into the cat’s stomach. So it “decides” to be a stowaway in the rat and hijack its system, changing behaviours and the way the rat responds to danger. What it does is it plays a trick – migrates to the rat’s brain and overrides millions of years of inbuilt fear from cats. The rat loses its ability to detect cat pheromones as sign of a dangerous predator nearby, and begins to even like it and go closer, increasing its risk of it being eaten.

Nature already knows our strongest drivers and it even made sure that not only the rat doesn’t mind the smell of cat pee, but it actually starts secreting more testosterone, meaning the cat pee is somewhat arousing and well… sexy. Somewhere along the evolutionary arrow toxoplasma gondii picked up a gene which lets it manipulate dopamine receptors and adapt behaviour of the hosts through the dopaminergic reward system for every time they are reckless and fearless, a sort of joy in risky behaviour from a biological standpoint. Interestingly enough it’s so sophisticated to leave the fear of other predators intact since their GI tracts are of no use to toxoplasmosis. So a rat will run away from a snake but not a cat. Its hosts shorter lifespan is irrelevant. The original strand goes back into the cat while in the meantime the infected rat is more likely to propagate since, instead of being deemed as infected and unsuitable for mating by female rats as it usually is with sick ones, toxoplasmosis makes the male rat smell better and more attractive to females, enhancing the spreading the disease and spawning a new generation of rats with a death wish.

So why is this relevant? Because toxoplasmosis can be transmitted to humans as well by eating infected uncooked meat, exposure to contaminated cate waste products or from mother to child during pregnancy, where it can cause damage to the baby’s developing brain. Toxoplasma gondii is one of the most common parasites infecting almost half of the planets population at one point of their lives and for the most part we’re not aware of it. Even if you’ve overcome it, there is a chance you have the dormant cysts in you. If they do no damage it is not a problem but there is a growing body of evidence that they affect human behaviour, just as they effects the behaviour of rats, introducing changes into the neurobiology and personality, resulting in behavioural changes such as being prone to risky behaviours, reckless fearlessness and enhanced aggression – so you may have more success playing an aggressive sport, but you’re also more likely to engage in behaviours that will result by you dying. There is a higher rate of deaths in car accidents caused by speeding or motorcycle accidents in those affected by toxoplasmosis. They can trigger and exacerbate mental conditions such as schizophrenia or depression and make suicidal people more prone to take their life. Just as in rats, it seems to blunt fear responses in us as well.

So, if you feel a sudden onset of disregard for safety or see a significant personality change in someone usually cautious, it may be a good idea to test for this parasite, and keep in mind that the effects are more visible in male behaviour. There is no lab on earth which could with our current knowledge construct something so disgusting and brilliantly manipulative as toxoplasmosis did for itself.