While careful to advise that nothing is certain for humans yet, researchers from the Washington University School of Medicine in St. Louis have found that West Nile virus–like Zika–has the ability to cross from a mouse to her fetuses, causing brain damage.
The two viruses are known to be closely related, but this could represent big news in the medical world. Up until now, Zika was fairly unique in its ability to cause miscarriages and birth defects and gained global attention to that end when Brazil was ravaged by its after-effects in the lead up to the Olympics in 2016.
“Millions of people were infected with Zika in a short time, and I think that made it easier to see, in people, that Zika virus could infect and cross the placenta and cause fetal damage,” Jonathan Miner, an assistant professor of medicine and the study’s senior author, said. “But our data show that other flaviviruses have the same capacity, at least in mice. It may be that it’s just more difficult to prove a link between West Nile and birth defects because the number of cases is smaller and infections are more sporadic.”
Miner previously developed mouse models of Zika infection during pregnancy. When he discovered no one had rigorously tested the possibility of comparing the virus with West Nile–despite some reports that it also transferred mother to child–he set out to do so with graduate student Derek Platt.
Together, they injected pregnant mice with one of multiple viruses and examined their placentas and fetuses a week after the fact. In all cases, the viruses infected the placentas and fetuses, but West Nile was found to have the most dramatic effect: levels 23 to 1,500-fold higher than those of the other three viruses in the placentas, and 3,000 to 16,000 times greater in the heads of fetal mice. It was severely damaged to brain tissue, whereas one of its competitors–chikungunya–left brain tissue appearing healthy. About half of those fetuses so infected by West Nile died within 12 days of infection. None died from chikungunya or Mayaro virus infections.
The researchers then infected human placentas similarly. Chikungunya and Mayaro viruses were found not to multiply in human placentas, but Zika, West Nile, and Powassan did.
Their findings were recently published in Science Translational Medicine.