The term “cat lady” is often used as an online joke or insult. It’s also frequently tied to the conversation about declining birth rates. Now, some scientists are exploring whether there may actually be a connection between cats and fertility—but not in the way online trolls imagine.
A growing body of research is looking into Toxoplasma gondii, a parasite commonly spread by cats. This parasite may harm sperm in men, possibly leading to infertility.
The idea sounds unusual, but there may be some real science behind it.
What Is Toxoplasma gondii?
Toxoplasma gondii is a tiny parasite found all over the world. Experts believe it may infect up to one-third of people and animals globally.
Cats shed the parasite in their feces. The eggs, known as oocysts, can survive in soil, water, or litter boxes for months. People can become infected by touching contaminated soil, eating unwashed fruits or vegetables, or drinking unsafe water. Infection can also occur by eating undercooked meat from an infected animal.
Once inside the body, the parasite becomes active and quickly multiplies. It then forms cysts—tiny capsules that settle in muscles and organs, including the brain and heart. The infection is usually mild or unnoticed in healthy people, but it can be dangerous during pregnancy or for those with weak immune systems. That’s why pregnant women are told not to clean cat litter boxes.
Can Toxoplasma Cause Male Infertility?
Animal studies suggest the answer could be yes. In experiments on mice, rats, and rams, researchers found the parasite could:
−Lower sperm counts
−Damage testicular function
−Alter the shape and health of sperm
These consistent findings in animals give scientists a reason to believe there could be a similar effect in humans.
What Do Human Studies Show?
Human research so far has been limited but interesting. Studies have mostly been cross-sectional, meaning they looked at people at a single point in time to check for a link between infection and infertility.
−A 2021 study in Prague found fertility issues in 49% of infected men, compared to 42% of uninfected men.
−A 2002 study in China showed 36% of sterile men had the parasite, versus only 14% of fertile men.
−Another Chinese study of couples found 35% of infertile couples were infected, compared to just 12% of fertile ones.
These numbers suggest a possible connection, but they don’t prove the parasite causes infertility.
Why Don’t These Studies Prove a Link?
To show true cause and effect, scientists need stronger data. The best studies are prospective—they follow large groups of people over time to see what happens after infection.
Two key factors are still missing from current research:
Temporality: Did the infection come before the infertility?
Dose-response: Does more exposure to the parasite lead to worse fertility problems?
So far, neither has been proven in humans.
Is There Reason for Doubt?
Yes, there are reasons to be cautious. First, male infertility appears to be rising globally, while rates of Toxoplasma infection are not. Second, not all studies agree on the link.
This makes it harder to argue that the parasite is the main cause of the fertility problem.
Should Men Be Worried?
For now, the evidence is too limited to recommend testing or treatment for Toxoplasma gondii in men with infertility. However, scientists agree that more research is needed—especially long-term human studies that can better show whether the parasite really has an impact.
What is clear is that preventing Toxoplasma infection is a smart move for everyone. Simple precautions include:
−Washing fruits and vegetables
−Cooking meat thoroughly
−Wearing gloves when gardening
−Being careful when handling cat litter
These steps are easy and help protect against other infections, too.
The Bottom Line
So, is cat ownership somehow linked to childlessness through a hidden biological route? The idea is still under investigation.
There’s some evidence, mostly from animals and small human studies, that Toxoplasma gondii may affect male fertility. But for now, scientists say the connection remains unclear.
The mystery continues. As researchers look deeper, we may soon know whether this parasite is a quiet player in the global fertility crisis—or just another coincidence.
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