I tried to be calm during the toxoplasmosis blood draw.



Officially known as T. gondii, toxoplasmosis (toxo) is a single-celled protozoa transmitted by contact with cat excrement and eating raw meat. We can also get a toxo infection when gardening, eating unwashed fresh fruit and veggies, and walking barefoot on feces-rich soil.



My obstetrician tests all pregnant women for toxo, as do many doctors in Europe. Infection rates hover around 12 percent in the United States. In Brazil, about 67 percent of pregnant women are infected (due to warm climate), in Hungary 59 percent, and in France about 45 percent (for these countries, blame all that steak tartare and pink lamb).



For decades, scientists have known that rats that are infected by toxo act a bit strange. While a rodent in his right mind is afraid of the smell of a cat, a toxo-infected rat is strangely aroused by it. And because toxo-infected rats seek out cats, they're often eaten, which in turn infects the cat, whose feces infects more rats, completing toxo's lifecycle. The parasite manipulates rodents to sacrifice themselves to spread the infection. It perpetuates itself by puppeteering.



Terrifyingly, toxo also infects the human brain, which, anatomically speaking, has a lot in common with the rat brain. There's no evolutionary pressure on the parasite to have a deliberate effect on human behavior because we don't spread the disease like rats do. For instance, it doesn't make us into cat lovers.

But, generally speaking, people infected with toxo -- even if the infection is not active -- behave slightly differently from those who are not infected.

Paristologist Jaroslav Flegr of Charles University in Prague found that people with a latent infection tend to be more apprehensive, -prone, self-doubting, and insecure. They have slower reaction times, especially if they also lack a certain blood protein, and are three times as likely to get into traffic accidents due to impaired or reflexes. Infected women tend to be warmer-hearted, dutiful, conforming, easy-going, persistent, and more and promiscuous. Infected men tend to be more , rigid, slow-tempered, rule-flaunting, emotionally unstable, impulsive, and more dominant.



Researchers have a theory about how toxo may cause these shifts in and behavior: Infection with the parasite causes slight brain inflammation, which alters its host's levels of , the neurotransmitter associated with reward and anticipation (and also movement). The parasite does this by producing an enzyme called hydroxylase, which makes dopamine.



Dramatic as this sounds, most infected people are completely oblivious that toxo haunts their cells. Only pregnant women are commonly tested. And I'm one of them. Because I'm a often-barefoot, life-long cat owner who once worked on a farm, travels extensively, and doesn't always scrub her veggies vigorously, I'm convinced I've been infected.



The nurse doesn't think it's an issue. "Not much happens if you're positive," she says, and shrugs. Her suggests it's a silly test. "Unless it's a recent infection it doesn't matter. We can tell by the antibodies if you've been infected in the last few months. If so, we give you antiparasitic drugs."



Simple as that.



From a medical perspective, what she says is true. The risk to a fetus depends on the timing of infection -- and only recent infection is a risk. If you happen to become infected with toxoplasmosis while pregnant, or soon before, the parasite or its toxins may cross over the placenta to infect your baby's . Babies born to mothers infected in the first half of often have shrunken or swollen brains and mental retardation. If infected in the second half, babies may not show symptoms at birth yet central nervous system problems may emerge years later. These babies are at a higher risk of developing -- delusions, , and so on -- later in life, likely due to altered levels of dopamine triggered by the parasite.



The reassuring news is that if you've been infected for years before pregnancy you probably won't pass toxo to your baby, nor will you likely have any obvious signs of infection (although cysts form in the brain). Dr. Flegr told me that only an active infection in the mom suggests a causal link between infection and her baby's risk of mental disorders. This is because the maternal immune system usually keeps the parasite in check.

That's not to say that a silent toxo infection doesn't affect pregnancy is subtle ways.



In the past decade or so, studies have found that moms with dormant, "asymptomatic" toxo infections are significantly more likely to have sons (up to two boys for every girl), and those fetuses develop more slowly than average. Perhaps there are other side effects that are undocumented.



Reading up on the science of prenatal infection, I get reflective. Viruses, bacteria, and other parasites have always entered us -- and some, such as our mitochondrial DNA (originally a bacterium), have become part of us, and we can not live without them. Ancient viruses exist deactivated or defanged in our genome (in fact, many from the placenta are thought to be a legacy of ancient viruses). Some viruses may be reactivated, like semi-reformed villains released from prison, and are thought to be a cause of cancer. Some dangerous invaders have converted to communalism -- for instance, the thousands of good-guy varieties of healthy gut bacterial that make digestion possible. There are more bacterial than human genes in our bodies.



In a way, pregnancy made me less fixed on the notion that my self is a singular over which I have total control. But as philosophical as I was about self and other, me and microbe, my heart raced when I called the nurse for my test results.



Negative for toxoplasmosis.



I was relieved. Truth is, the only parasite I really didn't mind carrying is the baby.

*If you like this blog, click here for previous posts (where this article was originally published) and here to read a description of my most recent book, Do Gentlemen Really Prefer Blondes?, on the science behind love, , and . If you wish, check out my forthcoming book, Do Chocolate Lovers Have Sweeter Babies?: The Surprising Science of Pregnancy.

