Zika is notorious for devastating parents. The virus seized worldwide attention last year by mercilessly causing birth defects, leaving thousands of babies with malformed brains. But the insidious virus may have another, subtler way of terrorizing families: wreaking havoc on the male reproductive system.

At least that’s the concern raised by a new study that finds that the virus causes severe damage to the testes of mice. In the course of a few weeks, the virus damaged reproductive tissue, spurred inflammation, hampered hormone production, shrunk testicles, and reduced sperm counts of the animals, researchers report Monday in Nature. Subsequent mating trials showed that the infected male mice had lower fertility, producing fewer pregnancies and viable offspring.

It’s unclear if the mosquito-borne Zika would cause the same injuries in men as it does in mice, the authors and other experts caution. However, the study begs for follow-up research—particularly given the fact that the virus is known to persist in men’s semen for weeks and cause pain and bleeding.

"Don't jump to the conclusion right off that this is definitely what is happening to the human," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases told ABC News (Fauci was not involved with the study). But, he added, the finding is a "red flag” that researchers need to pursue.

It's not the only new red flag, either. As scientists dive deeper into Zika research, they're finding more and more potential health effects of the cunning virus. In addition to neurological conditions and the birth defect microcephaly (marked by babies born with malformed heads), which first drew worldwide attention to Zika, new research suggests that the virus can infect bone and cartilage and cause eye and hearing problems in developing fetuses, in addition to attacking the male reproductive system.

For the new study, scientists at Washington University used a Zika infection mouse model to track the effects of the virus in males. As in humans, the virus set up shop in the male reproductive tract. By two weeks, mice infected with Zika had shrunken testicles. Researchers also noted signs of inflammation and damage to the tissue structure along the reproductive tract. As a control, mice infected with dengue virus—a relative of Zika—saw no change in their testicle size and condition.

By two weeks, the Zika-infected mice also had lowered levels of two hormones important for the production of sperm: testosterone and inhibin B. At 42 days after infection, the mice had three times less motile sperm than at the start of the study. Unsurprisingly, when the mice were allowed to mate with healthy females, Zika-infected mice produced fewer pregnancies than healthy, uninfected mice. Of those successful pregnancies from infected fathers, there was a higher rate of non-viable fetuses than those from healthy fathers.

“The extent to which these observations in mice translate to humans remains unclear,” the authors concluded, “but longitudinal studies of sperm function and viability in [Zika virus]-infected humans seem warranted.”

Nature, 2016. DOI: 10.1038/nature20556 (About DOIs).