Yale: Zika in mice shows risk of sexual transmission

NEW HAVEN » The Zika virus has been found to reproduce in the vaginas of pregnant laboratory mice for several days after an infection, and it then spreads to the brain of the fetus, causing birth defects, according to a Yale University-led study.

This suggests that sexual transmission may be a significant source of Zika infection. The virus, which causes microcephaly — abnormal small heads and underdeveloped brains — in human fetuses, also is spread by mosquitoes.

“We saw significant virus replication in the genital tissue, up to 4-5 days,” said co-author Akiko Iwasaki, professor of immunobiology at Yale and investigator at the Howard Hughes Medical Institute, in a press release. Researchers found the virus reproduced even in mice with intact immune systems. They compared non-genetically modified mice with those without an intact immune system because they lack genes that regulate proteins known as type I interferons.

“What surprised us most was that the virus replicated in the vagina of wild-type mice with intact interferon response,” Iwasaki said.

The immune response to the Zika virus differs between mice and humans, but the study raises concerns about sexual transmission of the virus, the release said. “The finding may be important for women, not only pregnant women,” said Iwasaki. “The vagina is a site where the virus can replicate and possibly transmit to partners. In pregnant women, vaginal transmission of Zika virus may have a significant impact on the developing fetus.”

Other studies have found that Zika can stay active in semen for 180 days after infection, Iwasaki said. Another report found female-to-male transmission of Zika after intercourse. She called reproductive organs a “niche” for Zika and called for further study of sexual transmission of the virus during pregnancy.

The study was published online Thursday in Cell.

The Zika virus is most common in Latin America, the Caribbean and in some Pacific islands, according to the Centers for Disease Control and Prevention. Cases of mosquito-borne transmission also have been identified in the Miami area.