The Zika virus has been linked to microcephaly, or shrunken heads, in the infants of pregnant women who contract the virus, but it also decimates the testicles of males—at least in mice, report researchers in the journal Nature. Little is currently known about the impact of an infection on the male reproductive system, and while what happens to mice doesn't necessarily translate to humans, it's "a red flag you need to pursue," as the director of the National Institute of Allergy and Infectious Diseases, which helped fund the study, tells ABC News. Researchers infected male mice with a mouse-adapted African or Asian Zika virus strain and found that they showed signs of infection by day seven, per a press release; by day 14, their testes had shrank visibly, while the seminiferous tubules where sperm form began to break down, too. Overall, ABC notes that testicles shrank by 90% of their weight.
The mouse's own inflammatory cells piled on their own attack, and by day 42 sperm motility was slashed threefold, while testosterone levels were down, too—all signs of greatly reduced fertility. To wit, infected males impregnated females at a quarter the average rate, and those who did conceive had half the normal number of pups. The lead researcher in the study tells ABC that he thinks the damage is permanent. Interestingly, the mice were most affected by the African strain, while those infected with the related dengue virus didn't suffer similar effects. It's time, researchers conclude, to see what happens to the reproductive health of men who've been infected with the Zika virus. (Zika proved to be a no-show at the Olympics.)