Animal Research Yields Clues to Sexual Spread of Zika

THURSDAY, Aug. 25, 2016 (HealthDay News) -- New research in mice may offer insight into how the Zika virus is transmitted sexually and affects a fetus.

People typically get the virus through the bite of an infected mosquito, although Zika can also be spread through sex.

Since the Zika outbreak began last year in Brazil, thousands of babies whose mothers were infected with Zika early in pregnancy have been born with a devastating birth defect known as microcephaly, in which the head and brain are abnormally small.

To learn more about sexual transmission of Zika and how that might affect fetal development, scientists used mice to study vaginal Zika infection. Their findings were published Aug. 25 in the journal Cell.

"The Zika virus appears to have a niche within the vagina," study senior author Akiko Iwasaki, an immunobiologist at Yale University, said in a journal news release. "We see from our model that it's a place where the virus can replicate for an extended period of time, and in pregnant mice vaginal infection can lead to brain infection of the fetus and growth restriction."

Mice typically don't get sick from Zika, so the researchers bred mice that were genetically vulnerable to the virus. But even in normal mice, Zika was able to survive and replicate in the vagina for several days.

"That's the most surprising finding of this study," Iwasaki said.

When normal pregnant mice were vaginally infected with Zika, their fetuses developed more slowly and had the infection in their brains. In the mice bred to be vulnerable to Zika, the virus increased uncontrollably in the fetus and caused spontaneous abortions.

"The fact that a sexually transmitted virus can end up in the brain of the fetus is worrisome. We're investigating this rigorously," Iwasaki said.

Researchers are also investigating ways to block Zika in the vagina.

"We're cautious about any conclusions regarding human transmission at this point, but the vagina may be a place, in addition to the testes, where the Zika virus can replicate for an extended period of time," Iwasaki said.

"We need to be careful about advising the public about sexual exposure with infected women. This study adds a piece to the puzzle in terms of the vagina as a site for virus replication -- vaginal secretions may be a reservoir for the Zika virus in humans, but this requires more investigation," she added.

More information

The U.S. Centers for Disease Control and Prevention has more on Zika.