In 2016 the Centers for Disease Control verified that Zika virus caused birth defects such as microcephaly. This shocked the world. We witnessed the first mosquito-borne disease known to result in birth defects. Recent research, however, shows that two Zika-related viruses may also cause similar effects. Keep reading to learn more, or follow the original story here.
Researchers named West Nile, and Powassan viruses in their study. Both resulted in fetal death in mouse studies. The study’s senior author, Dr. Jonathan Miner (an assistant professor at Washington University School of Medicine in St. Louis) reports that both of these diseases are carried by insects. Furthermore, both disease exist in America and are actively spreading.
Scientists categorize West Nile and Powassan as flaviviruses. This places them in the same group as Zika. Ticks, and mosquitoes account for transmission of these viruses.
Dr. Miner and his team selected four viruses alongside Zika for their study. The group included West Nile, Powassan chikungunya, and Mayaro. The latter two primarily exist in Brazil and are categorized as alphaviruses rather than flaviviruses.
Researchers tested the viruses by injecting them into pregnant wild mice. After an incubation period of one week, researchers went back to examine the fetuses and placentas of the mice.
All fetuses and placentas showed signs of viral infection. West Nile, however, presented most dramatically. In placentas, West Nile levels were 23-1500 times higher than other viruses. In placentas, West Nile existed at a rate 3000-16000 times higher than other viruses.
Using microscopes, researchers identified that West Nile caused traumatic brain damage to fetuses. By comparison, fetuses infected by chikungunya seemed healthy. Researchers observed no fetal deaths in association with either chikungunya or Mayaro.
Both West Nile and Powassan resulted in fetal death in mice. Dr. Miner explains that the results are very familiar when compared to the effects of Zika.
Differences exist, of course, between humans and mice.The study’s co-author Carolyn Coyne set out to determine how threatening these viruses would be to humans. She based the next series of test on the fact that a virus must cross the placenta in order to reach a human fetus.
Coyne’s team utilized explants to study this question. Scientists source explants from human mothers and fetuses, maintaining the tissue in a nutrient medium. Infecting these explants with the five viruses being studied allowed the team to reach a conclusion. Flaviviruses (like Zika) reproduce in the placenta. Alphaviruses fail to do so.
Coyne emphasizes that this means the flavivirus group may be able to penetrate the placental barrier. This allows the viral group to reach the fetus and cause harm.
Chief medical officer at the nonprofit March of Dimes, Dr. Paul E. Jarris indicated the helpfulness of the study. “It’s, of course, not conclusive with regards to humans,” Dr. Jarris continued, “and so I think we have to keep that in mind — not to overstate what it says.”
Indeed, researchers still have many questions. Either way, Dr. Jarris points out, mosquitos and ticks are still bad actors. He cautions about the other diseases they spread – like dengue – and advises people to avoid bites and allowing areas for the creatures to breed.
Other researchers outside the project such as Yale School of Public Health professor emeritus of epidemiology Durland Fish desire to see this research furthered. Fish describes the virus study as “interesting…with enough significance” to merit human study.
One question remains for now though. If both West Nile and Powassan affect people in the US, why has no one reported birth defects or miscarriages as a result?
Coyne responds that the incidence may simply be too low. With such small numbers of incidence, it is possible that the diseases have been overlooked. Furthermore, complications may not be as obvious as imagined. When we think of disease, we think of something big. Sometimes developmental delay related to disease may take several years to be noticed. “It is unlikely that [the delays] would ever be linked with an infection that occurred in utero,” says Coyne.
Fish advocates that, for now, most people should not worry about West Nile or Powassan. They’re both relatively rare. He cautions, however, that should their rate of occurrence increase, both could become more demanding of our attention.
“These disease threats are out there, and because of globalization and environmental change, there will most certainly be more,” Fish explains. “We should be much better prepared for such ‘natural’ epidemics, as they probably pose a more serious threat to human health than bioterrorism.”