School of Medicine

Other viruses cause Zika-like damage to fetuses, study finds

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From the CNN Newsroom…

(CNN) — In 2016, the US Centers for Disease Control and Prevention confirmed that the Zika virus caused birth defects in babies born to women who had been infected while pregnant. This was the first mosquito-borne disease known to cause birth defects.

Since then, images of babies with underdeveloped heads, born to pregnant women infected with Zika virus, have touched hearts around the world.

Now, a study suggests that two viruses that are related to Zika can cause similar birth defects.

West Nile and Powassan viruses caused fetal death in infected pregnant mice, the researchers say.

“All of these viruses are spread by insects, and all of these viruses are currently spreading in the Americas,” said Dr. Jonathan Miner, senior author of the study and an assistant professor at Washington University School of Medicine in St. Louis. The study was published in the journal Science Translational Medicine.

“Powassan and West Nile virus are flaviviruses, in the same family as Zika virus,” he said. These viruses are transmitted by infected ticks and mosquitoes.

Miner and his colleagues decided to experiment on an assortment of four viruses plus Zika to “determine whether certain traits of these viruses may be unique to one family or another,” Miner said.

Damage to fetuses

Miner and his colleagues studied the effects of four emerging viruses that are spread by either mosquitoes or ticks: West Nile, Powassan, chikungunya and Mayaro. Found in Brazil, chikungunya and Mayaro can cause arthritis and are classified as “alphaviruses,” a category separate from flaviviruses.
The researchers injected each one of a group of wild female mice with one of the four viruses during the sixth day of their pregnancies. One week later, the researchers examined all the rodent fetuses and placentas.
Signs of viral infection were seen in all the placentas and fetuses. However, West Nile virus levels were 23 to 1,500 times higher than levels of the other viruses within the placentas.
In the fetuses, West Nile levels surpassed the other viruses by even more: 3,000- to 16,000-fold.
Through a microscope, the researchers also saw severe damage in the brain tissue of the West Nile-infected fetuses. By comparison, the brain tissue of chikungunya-infected fetuses appeared healthy.
No fetal deaths occurred in mothers infected with chikungunya or Mayaro, but the same could not be said of the mice infected with the flaviviruses.
“We found that West Nile virus caused injury to the fetal brain and intrauterine growth restriction, and that both West Nile virus and Powassan virus led to fetal death in mice. This is similar to what has been observed after congenital Zika virus infection in mice,” Miner said. Nearly half of the fetuses of mice infected with West Nile or Powassan died within 12 days of infection.
“We cannot say for certain whether these infections would lead to a birth defect in mice,” he said. “However, what we found is consistent with what we and other scientists have observed with congenital Zika virus infection in mice.”
Mice are by no stretch of the imagination human, as the researchers acknowledge.
Could West Nile or Powassan virus penetrate the placenta and infect a human fetus?