I try to be calm as the obstetrician draws my blood to test for toxoplasmosis.

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

My doctor 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 are infected (due to warm climate), in Hungary 59 percent, and in France about 45 percent (for the latter, blame all that steak tartare and pink lamb).

We’ve known for decades that toxo does weird things to the brain because rats infected with the parasite act a bit strange. By strange I mean they’re not only afraid of cat scents, they’re strangely aroused by them. And because they seek out cats, they’re often consumed, and in being consumed they infect the cats, completing toxo’s lifecycle. This is how the parasite perpetuates — by puppeteering. It manipulates rodents to sacrifice themselves to infect other cats and other rats, and so on.

Toxo may also invade and manipulate the human brain, which shares much of the same anatomy and neurotransmitters with rats — although mind control here is different (cats don’t usually eat humans, so there’s no evolutionary pressure on the parasite to tweak its effect on people). Paristologist Jaroslav Flegr of Charles University in Prague found that people with a latent infection tend to be more apprehensive, guilt-prone, self-doubting, and insecure. They have slower reaction times, especially if they also lack a certain blood protein, and three times as likely to get into traffic accidents due to impaired attention or reflexes. Infected women tend to be warmer-hearted, dutiful, moralistic, conforming, easy-going, persistent, and more outgoing and promiscuous. Infected men tend to be more jealous, rigid, slow-tempered, rule-flaunting, emotionally unstable, and impulsive.

Correlation is not causation, as scientists say when fascinating associations like this arise. But toxo may have an impact on personality and behavior because causes slight brain inflammation and alters its host’s levels of dopamine, 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 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 hypochondriachal 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 body language 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 recent infection has the most disastrous consequences. 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 nervous system. Babies born to mothers infected in the first half of pregnancy 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 schizophrenia — delusions, hallucinations — later in life, likely due to altered levels of dopamine triggered by the parasite.

The nice 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). According to Dr. Flegr, only an active infection in the mom suggests a causal link between infection and her baby’s temperament. This is because your immune system usually keeps the parasite in check. But don’t think it’s completely asymptomatic.

In the past decade or so, studies have found that moms with dormant toxo infections have more sons (up to two boys for every girl), and those fetuses develop slightly more slowly than other babies. 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 now exist deactivated or defanged in our DNA (in fact, genes from the placenta are thought to be a legacy of ancient viruses) Some viruses may be reactivated, like half-cured villains released from prison, and are thought to be a cause of cancer. Some invaders, initially dangerous, have converted to communalism, such as the thousands of good-guy varieties of healthy gut bacterial that make digestion possible. Strange but true: there are more bacterial than human genes in our bodies.

In a way, pregnancy has made me less fixed on the notion that my self is a singular identity over which I have total control. The fetus is me but not me, and she has changed me in ways I can’t yet fathom. The line between self and other is getting fuzzier.

But as philosophical as I get about self and other, me and microbe, my heart still races when I call the nurse to read my test results.

Negative for toxoplasmosis.

I’m relieved. Truth is, the only parasite I really don’t mind carrying is the baby.