Update: A recent study suggests that Toxoplasma gondii may not be as harmful as once thought. It found little to no connection between the parasite and schizophrenia, depression, or poor memory — in fact, there was essentially no difference in the personalities of those who tested positive for it and those who did not. However, while the effects of Toxoplasma gondii seem to be much slighter than previous studies suggest, it still poses a real danger to pregnant women and people with weak immune systems. This article was originally published on September 22, 2015. Yesterday we learned an important lesson from Martin Shkreli, the dude whose start-up raised the price on a much-needed medication by more than 5,000%. The lesson is: Don't do that. But even crazier than the cost (and Shkreli's questionable assurance that this is the right thing to do) is the illness that drug is needed to treat — a personality-altering parasitic infection called toxoplasmosis. If you know anything about toxoplasmosis, it's probably that you can get it from your pet cat. It's estimated that nearly a quarter of us in the States have been infected with the parasite, Toxoplasma gondii, which your kitty may unintentionally eat in animals she's killed. Then, you can get a whiff of it in his or her feces when you clean out the litter box and accidentally inhale litter dust (or if it gets on your hands and you don't wash them: bad idea). But you can also get it from contaminated soil and undercooked meat. Once you've been exposed, the parasite can affect your brain, lungs, liver, and heart. For most of us, symptoms are either nonexistent or mild, consisting mainly of flu-like body aches and a fever. According to the Centers for Disease Control and Prevention (CDC), these symptoms usually last for a few weeks and resolve with or without treatment, sometimes leaving the parasite dormant inside your body indefinitely. However, for people with weakened immune systems (often pregnant women or those with HIV/AIDS), toxoplasmosis can become a much more serious — even deadly — problem. Symptoms here can include seizures as well as vision and lung problems. And, although the infection isn't normally transmitted between people, pregnant women can pass it on to their babies. This can cause some scary stuff for the child, including diseases affecting the nervous system. So, to beat the infection, doctors usually give patients a combination of antibiotics and Daraprim (generic version: pyrimethamine). Which is why the aforementioned price hike on Daraprim is such a big deal — the drug can save the lives of some of our most medically vulnerable patients. Perhaps the craziest thing about toxoplasmosis, though, is that it may cause subtle changes in your personality even after the infection is gone. In one 2012 study, both men and women who had been infected were more outgoing and less conscientious than their uninfected peers. Other research has linked toxoplasmosis infections to mental illnesses like bipolar disorder and schizophrenia as well as, weirdly, a higher incidence of car accidents. But most of this work is based on correlations, and researchers don't have a solid idea yet of how the parasite could be causing all of this. Chances are, toxoplasmosis isn't something you need to worry about. But if you're pregnant or your immune system is compromised (or you've noticed yourself being a little extra reckless recently), you might want to consider a chat with your MD. Just cross your fingers you don't have to pay through the nose for an Rx.