West Nile Virus May Pose Zika-Like Threat to Fetus

WEDNESDAY, Jan. 31, 2018 (HealthDay News) -- Zika may not be the only virus that can harm a fetus, a new study in mice suggests.

"We found that West Nile virus and Powassan viruses shared with Zika the ability to infect the placenta and cause fetal death," said senior researcher Dr. Jonathan Miner, who's with Washington University School of Medicine in St. Louis.

Both of those viruses are spread by the bites of insects and are in the same family of viruses as Zika, called flaviviruses.

So far, the researchers have only confirmed this in mice, although they have found these viruses have the ability to replicate in human placental tissue.

Does that mean pregnant women should be concerned every time they get a mosquito or tick bite?

Miner said this study definitely shouldn't be the cause of "mass hysteria." Research done in animals doesn't always turn out the same when done in people.

"The work we do is basic science. We try to understand what may be possible. Our work is not done to make a claim about what is occurring in the human population," he explained.

He's an assistant professor in the departments of medicine, pathology and immunology and molecular microbiology.

Miner said no one can know for sure yet if these other viruses can cause the same types of problems in a developing human fetus as the Zika virus can. He noted that with Zika, which has been linked to microcephaly, a condition that causes undersized brains and heads, it was relatively easy to make the statistical link needed because the outbreak was so large. These other viruses have only had smaller outbreaks, he explained.

Dr. Amesh Adalja, a senior scholar at Johns Hopkins Center for Health Security, said the findings aren't surprising, particularly given the findings of older studies on other flaviviruses.

"It will be important to assess how frequently this occurs and whether any human congenital syndromes with Powassan and West Nile have gone unnoticed," said Adalja, who wasn't involved with the study.

"In general, mosquito-borne viruses of this family should be considered as a potential danger to a developing fetus based on all the historical and emerging evidence," he said.

The basis for the latest study was the idea that Zika likely wasn't the only insect-transmitted virus that could affect a developing fetus.

The researchers looked at four viruses to assess their ability to cause fetal harm in pregnant mice. Three of the viruses are spread by mosquito bites: West Nile, chikungunya and Mayaro. The fourth virus, Powassan, is transmitted by ticks.

All of the viruses were able to cross the placenta. All replicated inside fetal brains. But only West Nile and Powassan caused fetal death.

The researchers also found that West Nile and Powassan were able to replicate in human maternal and fetal tissue.

"Our study underscores that there may be other viruses like Zika that could cause outbreaks in the future, and that's one reason why basic science like this is so important. No one was really looking at Zika before the outbreak. Basic discovery allows us to be prepared," Miner said.

Asked if he had any advice for pregnant women or women thinking about becoming pregnant, Miner suggested that women "take reasonable precautions." He said most women are probably already doing what they can to avoid mosquito and tick bites, and it's a good idea to continue to do so.

The study was published Jan. 31 in the journal Science Translational Medicine.

More information

To learn more about Zika and pregnancy in humans, visit the U.S. Centers for Disease Control and Prevention.