Scientists Discover that A Common Parasite Decapitates Sperm

Understandably, its thought this violent behavior may contribute to the rise in male infertility.

Hiya!

We’re learning a lot about human health recently, including things specific to the female and male sexes. Today’s topic will focus on the latter of the two. I’ve written about several recent discoveries related to male health and reproduction, including the role of sperm during pregnancy, the disappearance of the Y chromosome as males age, and the fact that male sperm lack mtDNA.

And now, in addition to previous research supporting the claim, a new study discovered that a common parasite decapitates human sperm, which may be a new culprit in the rising rates of male infertility.

The Rise of Male Infertility

By now, you’re likely aware that human infertility is on the rise worldwide. Typically, when there’s a decrease in birth rates, all eyes turn to women. However, research over the last few years has found that male fertility is plummeting — and has been for the past half-century.

A decade ago, in 2015, a report found that male infertility accounted for over half of the cases of global childlessness, which affects about 186 million people worldwide.

More recently, a study published in November 2023 found that between 1990 and 2019, male infertility rates grew nearly 80 percent.

Meanwhile, other research has linked male infertility to a decrease in males’ sperm count and quality.

Understandably, people are concerned, and researchers are scrambling to figure out what’s going on. So far, experts know that some circumstances can create infertility in men, from obesity, poor diet, and environmental toxins, to genetics, drug use, hormonal imbalances, and cell phones.

Additionally, several infectious diseases, including chlamydia, gonorrhea, and genital herpes, have also been proposed as factors that affect fertility in men.

And now, evidence is accumulating that suggests a common single-celled parasite called Toxoplasma gondii may also contribute to male infertility — by decapitating sperm upon contact.

Toxoplasmosis

Saying that the Toxoplasma gondii (T. gondii) parasite is “common” is accurate, but also a bit of an understatement considering it’s estimated that between 30 and 50 percent of the global population is permanently infected with the tiny parasites, including between 40 million and 60 million people just within the United States.

Once infected, known as toxoplasmosis, the T. gondii parasite spreads to nearly every organ and skeletal muscle. Most people with toxoplasmosis are likely unaware they’re even infected, as people with healthy immune systems typically experience few, if any, symptoms.

Still, even without symptoms, the parasite will stay in the body for the rest of a person’s life — existing as seemingly dormant cysts in their muscle tissue, brain, and heart. And, unfortunately, even if the infection is initially symptomless, the parasite can reactivate for any given reason and cause all sorts of problems, from severe illness to damaging critical organs.

Meanwhile, some people do experience flu-like symptoms when infected, such as swollen lymph nodes, general pains, and muscle aches.

In severe cases, toxoplasmosis can result in damage to vital organs, including a person’s eyes and brain. Pregnant people can also pass the infection to their fetus, which may not experience any symptoms at birth, but may later in life if the parasite reactivates.

Given how widespread toxoplasmosis is, there must be a common source, right? Yup, several.

One of the most prominent transmitters of the T. gondii parasite is none other than our beloved felines. That’s right, infected cats, both wild and domestic, are ideal hosts that drop T. gondii eggs anywhere they defecate, whether in their litter box, a garden, or anywhere else, making it super easy to be accidentally picked up by other animals, including us.

The eggs are also commonly found on unwashed fruits and vegetables, in water, and within shellfish. Beyond the eggs, since the parasitic cysts like to nestle in the muscle tissue of warm-blooded animals, they’re also found in the meat we eat.

Eating meat from an animal that had toxoplasmosis can spread the infection to you unless it is destroyed by cooking the meat to proper temperatures. While you’ll still consume the cyst, the parasite will be dead and thus harmless.

I wish I could tell you we have simple cures for toxoplasmosis, but unfortunately, I didn’t find much. Generally speaking, treatment isn’t provided unless the infection causes symptoms, in which case a combination of anti-parasitic medicines and antibiotics can be prescribed.

However, such therapies only stop the parasites from growing and reproducing in your body — it doesn’t kill them completely, eliminate them, nor will they get rid of the cysts the parasites have already made in you.

Complicating matters further, the treatment for toxoplasmosis is only effective when the parasites are active.

Toxoplasma gondii and Male Infertility

I mentioned the T. gondii parasite can infect basically any organ or muscle, but, and I’m sorry guys, that includes your testicles, too.

Scientists first learned that the parasite can target human male reproductive organs in the 1980s, during the height of the AIDS pandemic, after it was found in the testes of some male patients — now referred to as testicular toxoplasmosis.

More recently, studies have found a link between testicular toxoplasmosis and sperm abnormalities. Thankfully, the condition is considered “extremely rare,” though immunocompromised male patients are most at risk.

Still, scientists are working to learn more about it.

Imaging studies involving infected mice have shown that in a matter of days, the T. gondii parasites can travel to the testes, eyes, and brain.

Bill Sullivan, a Professor of Microbiology and Immunology at Indiana University, whose lab focuses on the T. gondii parasite, wrote an article published by The Conversation. In it, he mentions a 2017 study by him and his colleagues in which they discovered that T. gondii can also develop cysts in mouse prostates.

Other research has found the parasites in the ejaculate of many animals, including humans, which indicates the infection may be sexually transmitted.

Naturally, scientists have sought answers by studying infected human males in addition to mice.

For instance, a study from 2002 by Chinese scientists compared the rate of testicular toxoplasmosis among 178 infertile couples to 190 fertile couples and found that the positive result of infection in the infertile couples was significantly higher (35 percent) than that in fertile couples (12 percent).

Similarly, a 2005 study by a different group of Chinese scientists compared infections between 100 sterile and 100 fertile males and discovered that the sterile males were more likely (36 percent) to test positive for testicular toxoplasmosis than fertile men (14 percent).

Yet another, more recent, study from 2021 by scientists in Prague discovered that of 163 infected males, over 86 percent of them had semen abnormalities.

Considering this growing pile of research, there appears to be a clear link between toxoplasmosis and male fertility. However, none of the evidence details what, precisely, the parasite is doing to cause it.

Remarkably, it appears we may finally have an answer, and it sounds like something straight outta science fiction.

New Research

An international team of researchers from Germany, Uruguay, and Chile didn’t set out to make the discovery they made.