Undiagnosed chlamydia infection can harm male fertility, a new study suggests.

"Chlamydia infection has been associated with women's infertility but much less is known about its impact on male infertility, particularly if men do not experience symptoms, which is estimated to be in about 50% of cases," said study leader Ken Beagley, a professor of immunology at Queensland University of Technology in Australia.

"When people have no symptoms, they can unknowingly pass on the infection to sexual partners," Beagley added in a university news release.

The Australian research is the first to find the sexually transmitted disease in testicular tissue biopsies of infertile men with no identified cause for their infertility.

Chlamydia was found in fixed testicular biopsies from 43 of 95 men (45.3%) who had no defined cause of infertility.

Chlamydia was also found in 16.7% of fresh testicular biopsies (3 of 18 men) with no identified cause of infertility. Twelve of those 18 (66.7%) had chlamydia-specific antibodies, indicating they had been exposed to the bacteria, but none had symptoms of chlamydia or said they had been diagnosed with any STI.

"This is the first reported evidence of chlamydia infection in human testicular tissue, and while it can't be said that chlamydia was the cause of the infertility of the men, it is a significant finding," Beagley said.

"It reveals a high rate of previously unrecognized chlamydia infection and the potential role of infection in the failure of sperm to develop in the testes," Beagley explained.

"Animal studies by our group support these human findings. Those studies show that chlamydia infection in male mice establishes a chronic infection in the testes that significantly impairs normal sperm development," he said.

"We believe future studies with male patients should look at how chlamydia infection might cause damage to the male reproductive system and contribute to infertility," Beagley concluded.

The study was published recently in the journal Human Reproduction.