A common virus may be linked to infertility in men, say German scientists. They analysed semen samples from almost 100 men and found that 38 per cent of abnormal samples were infected with adeno-associated virus (AAV), compared with only 4.6 per cent of normal samples.
AAV infects 40 per cent of people by the age of 20 and most people are infected by middle age.
鈥淭he virus was not thought to be pathogenic,鈥� says J枚rg Schlehofer of the German Cancer Research Centre in Heidelberg, who led the new research. 鈥淏ut our research raises the issue of whether sperm cells used in ICSI or other reproductive techniques should be checked for AAV prior to fertilisation.鈥� ICSI involves injecting a single sperm directly into an egg.
Advertisement
Christopher Barratt, an expert on sperm biology at Birmingham University, says: 鈥淭he idea that infection with certain viruses 鈥� such as HIV 鈥� can cause sperm abnormalities is not new. But AAV is not generally thought to be pathogenic and that鈥檚 what makes this finding interesting.鈥�
AAV is used in gene therapy, to shuttle new DNA into a cell. It has recently been used to introduce DNA into mice sperm stem cells. 鈥淭he virus is a very good vector system. But nobody has really looked at what tissues it targets in humans,鈥� says Schlehofer. More work is needed to investigate whether AAV infection really does cause infertility, he says.
Strong bond
Schlehofer鈥檚 team analysed semen samples from 73 men who were participating in a fertility programme and 22 men with no history of infertility.
They used standard DNA analysis techniques to look for traces of the virus. Earlier work by the team on a small number of infertile men had found evidence of a high AAV infection rate. This work also showed that the viral DNA bound strongly with the sperm, but not with other constituents of semen. 鈥淏ut these were very few men, and we did not look at normal samples,鈥� says Schlehofer.
In the new study, they found that men with either very low sperm concentrations or defects in sperm motility were most likely to be infected with AAV.
There is some evidence that the virus can interfere with cell differentiation. 鈥淚t could be that important cells associated with the production of sperm and sperm maturation could be affected, and this results in the malformations,鈥� says Schlehofer.
Early miscarriage
AAV infection has previously been linked to very early miscarriage.
鈥淚t is possible that if an embryo is infected through an infected sperm, for example, the very sophisticated immunotolerance between the embryo and the mother is affected, and this could trigger miscarriage. But this is speculation 鈥� much more work needs to be done to investigate,鈥� says Schlehofer.
There is no 鈥渃ure鈥� for AAV, since it was not thought to be harmful to health, he adds. 鈥淏ut with ICSI, for example, there is not a very high baby take-home rate. Maybe this is due to infected sperm. If we could screen samples or get rid of the virus in assisted reproduction techniques, perhaps we could improve this rate,鈥� Schlehofer says.
It is not clear how AAV infection of the testis could occur, the team says. But it appears that the virus does 鈥渢arget鈥� genital tissue in particular.
Journal reference: Human Reproduction (vol 16, p 2333)