It seems that with each new day, there’s more bad news to learn about the mosquito-borne Zika virus. The latest, published Thursday in Cell, suggests that the virus may be able to survive in the vagina of women for nearly a week after they're infected.

Yale researchers, led by Dr. Akiko Iwasaki, a professor of immunobiology and scientist at the university’s Howard Hughes Medical Institute, infected two groups of female mice with the virus through the vaginal canal. The animals were either perfectly healthy wild-type mice, or mice whose immune systems were weakened when researchers stopped their ability to produce type 1 interferon. They found that in either case, the virus survived and replicated in the vagina for several days. The finding is especially worrying given that Zika is known to be spread through sexual contact in addition to mosquito bites. Other research has indicated that it’s capable of surviving in sperm for at least 90 days.

"We saw significant virus replication in the genital tissue, up to 4-5 days. With other routes of infection, the Zika virus does not replicate unless you block type I interferons,” said Iwasaki in a statement. “What surprised us most was that the virus replicated in the vagina of wild-type mice with intact interferon response.”

Although up to 80 percent of adult Zika carriers don’t experience any symptoms when infected with Zika (and those who do usually suffer a mild flu-like illness for two to seven days), the results obtained by Iwasaki’s team carry deeper implications for the especially vulnerable — namely developing fetuses in the first trimester of pregnancy. In later experiments with infected pregnant mice, the team once again confirmed the virus’ influence on the very young. The virus was detected in the brains of mice fetuses, and fetal infection was linked to weight loss.

"Early during pregnancy, if the mother is infected, there is significant impact on the fetus, even in wild type mice," Iwazaki said.

The findings may also explain an earlier surprise about Zika. Earlier this July, the Centers for Disease Control and Prevention (CDC) reported for the first time that a woman from New York City had likely given Zika to her male sexual partner after having sex without a condom (she was originally infected during travel to a Zika-prevalent area of the world). Elsewhere, research has detected the virus’ presence in the vaginal fluid of both humans and other primates.

Taken as a whole, Iwazaki speculated that our genitals may very well serve as a “niche” for Zika, a reality that further emphasizes the need to prevent sexual transmission of the disease during pregnancy. Currently, the CDC has recommended that people traveling back from areas of the world where Zika is active avoid condomless sex for up to six months in the case of men confirmed to have Zika, and 8 weeks for women, as well as men without any symptoms.

Source: Yockey L, Varela L, Rakib T, et al. Vaginal Exposure to Zika Virus during Pregnancy Leads to Fetal Brain Infection. Cell. 2016.

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