Scientists from Spain and Mexico have warned that chlamydia, a sexually transmitted infection which usually passes undetected, can make men infertile by damaging the quality of their sperm.
In a study, the researchers have found that men with chlamydia have three times the normal number of sperm with genetic damage, which can reduce their likelihood of becoming fathers.
Britain's national screening programme has revealed that 10.2 per cent of both men and women aged 18 to 25 carry the bacteria, and that the infection rates are as high as 5 per cent among older groups with a lower risk.
So far, this infection has been considered to be a threat only to female fertility. However, the new study suggests that untreated chlamydia infections also have direct consequences for men.
Allan Pacey, senior lecturer in andrology at the University of Sheffield and secretary of the British Fertility Society, said the new insight into how chlamydia affects male fertility might lead to a change in the way that society approaches the condition. "We might think of chlamydia as a disease that damages female fertility, but we need to think again. It does damage female fertility, but it appears to damage male fertility, too," Timesonline quoted him as saying.
"Previously, it was thought that the most worrying thing about chlamydia infections in men was as a conduit for the infection of women. The thing that drives most men to sexual health clinics is symptoms, and chlamydia is often symptom-free. Chlamydia is getting out of control. We have got to encourage men as well as women to go for screening," he added.
During the study, a team of researchers led by Jose Luis Fernandez of the Juan Cana-lejo University Hospital in La Coruna examined sperm samples taken from 193 men seeking fertility treatment with their partners in Monterey, Mexico.
Among the subjects, 143 were infected with both chlamydia and mycoplasma, another common sexually transmitted bacterium, while 50 were uninfected and served as healthy controls. Upon examining the men's sperm for a form of genetic damage called DNA fragmentation, which can cause sperm to die, the researchers found that an average of 35 per cent of the infected men's sperm was damaged, a proportion 3.2 times higher than in the healthy controls.
"We found there was a three-fold increase in the fragmentation of DNA in sperm cells compared with controls, and this could have a potential role in subfertility," Dr Fernandez said.
The researchers treated both partners in the infected group with antibiotics. During the early stages of treatment, just 12.5 per cent of the couples conceived, but the number of conception rose to 85.7 per cent when therapy was complete. Successful treatment of the male partners is more likely to have been responsible for this effect, say the researchers.
"After four months of treatment, there was a significant decrease in DNA damage that could improve pregnancy rates in these couples. It seems related to an improved pregnancy rate. It's a very dramatic difference, but this is a small number of couples, so the results are only preliminary," Dr Fernandez said.
The researchers suggest that infertility patients of both sexes should be routinely screened for chlamydia. "I would advise couples trying for a baby to be screened for chlamydia. The difficulty is that a positive diagnosis carries implications of infidelity, but of course as it can be asymptomatic the infection could have been there for many years," Dr Pacey said.