PITTSBURGH (KDKA) – Researchers already know the Zika virus is sexually transmitted, but now they say the virus can flourish inside a woman’s vagina.

A new study by Yale University finds that Zika reproduced in the vaginas of pregnant mice four to five days after infection.

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Researchers found that the virus then spread from the vagina to the fetal brain.

The Dallas News reports that studying the virus on mice is tricky because a mouse’s immune system fights off the infection, making it quite resistant to Zika.

Researchers reportedly had to tweak the animal’s immune system to make it more susceptible to the Zika virus.

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Even with an enhanced immune system the Zika virus managed to reproduce inside the vagina.

The study shows that not only did the Zika virus thrive inside the vagina, but it spread to the fetal brain and caused weight loss.

Previous studies have shown that Zika can persist in a woman’s vaginal mucus 11 days after infection, and the virus can linger up to six months after infection in semen.

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The paper also reports that Yale researchers say that since humans are more susceptible to Zika than mice, the virus may replicate more robustly.