When people first learn about toxoplasmosis, they typically wonder how they have not heard of it before. This parasitic brain infection affects approximately 2.4 billion people worldwide (about 30% of the population), and all you need to do to get it is be a bit careless when washing your food around cats. If you have spent significant time around cats, you have likely been exposed to the brain parasite Toxoplasma gondii. While active infection can be lethal, most people develop a “latent” infection without immediate symptoms, which is why it is often overlooked. Both the World Health Organization and Centers for Disease Control consider toxoplasmosis one of the most understudied parasitic infections globally. We are only beginning to understand the consequences of latent infection, which are numerous. Research shows that infected individuals experience neurotransmitter imbalances (dopamine, serotonin) and hormonal changes (testosterone), and face higher risks of psychiatric disorders, including depression and anxiety. They are more likely to engage in risky behaviours (smoking, drinking), have traffic accidents, and commit suicide. Evidence increasingly suggests that the parasite alters human behaviour, making people more prone to taking disproportionate risks. An astounding piece of research showed that people with latent toxoplasmosis are even more likely to engage in entrepreneurship, and several studies have shown that they are more likely to study business- and economicsrelated majors. WORLDWIDE EFFECTS While it may be difficult to accept that a tiny brain parasite influences billions of people’s behaviour, this aligns with the parasite’s life cycle. Toxoplasma gondii reproduces in cats’ intestinal tracts and is excreted in their faeces. After it produces spores, it infects mice, whose brains it inhabits. Infected mice become more curious and lose their fear of cats, making them easier prey. The parasite then returns to cats’ intestines, completing its cycle. As fellow mammals, humans experience similar effects to the mice, although research has not conclusively shown that the infection causes increased attraction to cats. Many people with latent toxoplasmosis do not exhibit obvious behavioural changes – they might just appear slightly more risk-seeking, which rarely prompts medical consultation. However, our research suggests these alterations can likely have negative economic consequences. HARD TO DIAGNOSE Diagnosing toxoplasmosis requires clinical testing of blood or saliva samples. While not extremely expensive (around £100), the cost makes large-sample studies prohibitively costly. My co-authors and I have developed an indirect test that requires no biological samples and can be administered online. How accurate is our test? In a clinical study comparing it with blood tests, our method showed 97% agreement. While not precise enough for individual medical diagnoses, this means our test is suitable for large-scale research studies at minimal cost. We incorporated the test into an online survey with a representative UK population sample. This allowed us to classify participants as “imputedinfected” or “non-infected.” Though we cannot be 100% certain about individual classifications, the method is valid for studying population-level effects. NEW INSIGHTS Our UK survey reproduced all previously known effects: imputedinfected individuals reported higher frequencies of psychiatric disorders, increased drinking and smoking, greater risk propensity, and lower patience. For the first time, we were able to estimate the economic consequences of infection, finding that people with imputed latent toxoplasmosis had an 11% higher probability of unemployment and suffered an average economic loss of £2,500 annually. 36 |
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