Cat then! A recent study published in the FBS Journal indicates that our domestic feline would harm male fertility via a bacteria from which it can be a carrier. This is toxoplasma gondii, the parasite responsible for toxoplasmosis. This parasite can reach the testicles and beheads sperm, thus making them unproductive.
It is often said that the best friend of the man is the dog. It is true, by its loyalty and its dedication. But if there is a domestic animal for which most humans crack, it is the cat. This hair ball is so cute, even by its meowing, that we want to hold it in our hands all the time. However, this animal would represent a danger for its masters and its masters because carrying a bacteria that can cause infertility. It is the toxoplasma gondii, the parasite responsible for toxoplasmosis and well known for women.
Since the 2000s, the cat has been suspected of being one of the causes of male infertility
Studies, notably conducted in China in the 2000s, had already suggested the possibility that this parasite affects male fertility, without ever clearly highlighting this thesis. New works conducted in April 2025 by German, Uruguayan and Chilean researchers provide additional proof to this hypothesis. These scientists have found that in mice, Toxoplasma can reach the testicles and the epididymis (the canal where sperm ripen and stored) two days after infection, then practically destroy sperm.
Toxoplasma, the cat parasite, beheads almost a quarter of the sperm
To find out what it was in humans, the team of German, Uruguayan and Chilean researchers has undertaken to put the parasite in direct contact with human sperm, in an in vitro experience. Result: after only 5 minutes of exposure to the parasite, almost 22.5 % of sperm were beheaded by toxoplasma gondii. And this percentage continued to increase in the minutes that followed. In addition, even the sperm that managed to keep their heads were affected by the parasite. Some presented morphological problems or small holes in the head, suggesting that Toxoplasma Gondi had tried to penetrate them.
Infection promotes chronic inflammation of male reproductive paths
Researchers also note that direct attack is not the only way by toxoplasma can damage sperm. Indeed, they also found that infection promotes chronic inflammation of the male reproductive pathways. However, this inflammation harms the production and proper functioning of sperm. According to the authors, the deleterious effects exerted by Toxoplasma on sperm could participate in the global problems of male fertility.
Toxoplasma does not always affect the reproductive organs
Scientists are therefore concerned about toxoplasma gondii infection. And all the more since when this infection takes place, it is no longer possible to get rid of it. He persists for life in our organism. Researchers also think that due to the many modes of transmission of this parasite, 30 % to 50 % of the world’s population hosts it permanently in the body.
Fortunately, they put it into perspective, toxoplasma does not always affect the reproductive organs. A Romanian pilot study conducted in 2015 on male volunteers revealed that 25 % of them had toxoplasmosis and that there was no difference in quality between their sperm and that of other participants.
The cat expels toxoplasma eggs in the litter and the garden
But it will take a more general study to draw a conclusion to this minor contamination. Also, we have still not studied infection in humans in situation. While waiting for these important steps, note that the cat expels the eggs (oocysts) of toxoplasma in the litter, the garden or any other place of the environment where human beings and other animals can ingest them.
Hygiene measurements must therefore be applied to avoid an infection. In particular to delegate the cleaning of the cat’s litter or do it with gloves, wash your hands carefully with hot water after this cleaning, eat meat cooked to heart, wash your fruits and vegetables well or avoid raw animal products.