Zika virus infection causes infertility by shrinking the testicles and lowering the testosterone levels in male mice, reports a recent study.

Zika infection is known to affect pregnant women and cause birth defects in newborn but the recent study establishes a link between Zika and male infertility though it is not sure if the effects observed in mice translates to humans.

Previous reports have noted that Zika virus exists in men's semen for months and on account of which the Centers for Disease Control and Prevention has recommended men not to have unprotected sex for at least six months after travelling to Zika infected areas whether or not they experienced the symptoms of infection.

Michael Diamond, the study's co-senior author and Herbert S. Gasser Professor of Medicine said that the research was undertaken to study the effects of Zika infection in males. Though it is not certain if Zika affects fertility in men as in mice, the study suggests that there is also a possibility of low sperm count and low testosterone levels in men after Zika infection.

For the purpose of the study, the investigators injected healthy male mice with Zika virus. After one week of infection the virus was found to have entered the testes from the blood stream. At about two weeks of infection many cells were found to have died leading to the shrinkage of testes. The internal structure of the testes was also observed to have collapsed significantly.

Diamond noted that it is not clear whether or not the damage is reversible since the internal structures are damaged extensively. The Sertoli cells that act as the barrier between testes and bloodstream don't regenerate once damaged.

It was found six weeks after infection that the sperm count in infected mice has decreased ten-folds and the testosterone levels dropped significantly. The infected mice were four times less likely to impregnate healthy females when compared to their healthy male counterparts.

Kelle Moley, the study's co-senior author said that Zika is the first known virus to cause infertility as not many microbes cross the barrier between the bloodstream and the testes.

"People often don't find out that they're infertile until they try to have children, and that could be years or decades after infection," Moley said, in press release.

The researchers noted that to be able to find if Zika virus infection affects male reproductive system human studies should be carried out in highly infected zones.

The study published is in the journal Nature on Oct. 31.