Toxoplasma gondii, a widespread parasite, has been found to cause direct damage to human sperm, resulting in decapitation and potential male infertility. An April 2025 study demonstrated that human sperm lose their heads upon direct contact with the parasite.

This discovery adds to growing evidence linking Toxoplasma gondii to reproductive issues. Previous research has shown the parasite's presence in male reproductive organs and its association with decreased sperm quality and count.

Approximately 30% to 50% of the global population is permanently infected with Toxoplasma gondii, often without symptoms, raising concerns about its silent impact on male fertility.