Not only did male mice infected with the Zika virus have a tougher time getting females pregnant, their levels of sex hormones crashed, and their testicles shrunk by 90%, possibly permanently, according to new research by the Washington University School of Medicine in St. Louis.
Of course, these are mice, not men.
"We undertook this study to understand the consequences of Zika virus infection in males," said co-senior author Dr. Michael Diamond, associate director of the school's Center for Human Immunology and Immunotherapy Programs.
The study found that Zika not only crossed that barrier, it attacked and destroyed the Sertoli cells, which do not regenerate.
At three weeks after infection, according to the study, the male mice's testicles were one-tenth of their normal size. The organs showed no signs of healing when examined at six weeks, even though the virus had long cleared the bloodstream. Sperm counts and levels of testosterone in the male mice also dropped tenfold.
"We don't know for certain if the damage is irreversible, but I expect so, because the cells that hold the internal structure in place have been infected and destroyed," Diamond said.
Whether any of this damage will also occur in men is unknown, say the researchers, but it's worth studying in areas of the world with high rates of Zika infection, such as Central and South America.
"Wouldn't a man notice if his testicles shrank?" Moley asked. "Well, probably. But we don't really know how the severity in men might compare with the severity in mice. I assume that something is happening to the testes of men, but whether it's as dramatic as in the mice is hard to say."
"We don't know what proportion of infected men get persistently infected or whether shorter-term infections also can have consequences for sperm count and fertility," Diamond said. "These are things we need to know."