The virus is most common in poor Israeli-Arab neighborhoods with open sewers ■ The average infection rate in Israel is 88 people per year
Gustavo Henrique, who has microcephaly due to the Zika virus, undergoing medical treatment in Recife, Brazil, in 2016. West Nile virus is related to Zika and may also infect fetuses in the womb.\ REUTERS
Four viruses in the same family as Zika can also infect fetuses in the womb, and two of them cause fetal defects and death in mice, scientists warned Wednesday in the journal Science Translational Medicine. One of the four is West Nile virus, which is endemic to Israel.
WNV particularly affects families living in impoverished areas with open sewage systems, which encourage the proliferation of the mosquito vector that spreads the disease. The Health Ministry told Haaretz that the average infection rate in Israel is 88 people a year.
Zika has been proven to cause – as opposed to just being associated with – profound nervous system damage in unborn children exposed to the virus during pregnancy. “Unfortunately, Zika virus may not be unique in its ability to afflict fetal damage,” writes the team from the Washington University School of Medicine in St. Louis and the Pittsburgh Medical Center, Pennsylvania.
The four flaviviruses related to Zika that were tested in the new study were WNV, Powassan, chikungunya and Mayaro.
Most of the WNV infections in Israel originated in poorer areas with inferior sewage service, a 2017 study showed. In other words, WNV is most common in the Arab neighborhoods of Israel (“There was a significant association between seropositivity and the Arab population group vs. Jews and others,” the scientists reported in Plos One).
Flaviviruses are transmitted by insects: WNV, chikungunya and Mayaro (and Zika) are transmitted by mosquitoes; Powassan (detected in the Great Lakes region of North America and in Russia) by ticks. In Israel, WNV is transmitted chiefly by two species of mosquito – Culex pipiens and Culex perexiguus.
The capacity of the four viruses to infect fetuses in the womb, like Zika, was tested in mice. But it was shown that the four can replicate in human maternal and fetal tissues, the scientists report.
The requisite question is whether, like Zika, the four viruses could be associated with fetal damage or death, without modern medicine yet noticing.
Since all four of the flavivirus types checked were found to pass the placenta (i.e., from mother to fetus), all could have the capacity to cause birth defects, the scientists suspect. Two of the four, WNV and Powassan, also turned out to lead to fetal death.
Because the study was done on mice, it is not clear at this stage what effect WNV or Powassan would have on pregnant women or their newborns.
The Health Ministry confirmed there are no warnings associated between WMV in pregnant women and possible birth defects or fetal death.
Though Zika has been known for at least 70 years, it was only in 2015 its role was first recognized in causing grave birth defects involving the nervous system, including microcephaly.
The virus apparently originated in or around Uganda, but the trigger to discovering the devastating effect on newborns was a massive Zika epidemic in Brazil and other South (and Central) American countries that sickened more than 1.5 million people.
The belated discovery of Zika’s dangers begged the speculation that other insect-transmitted germs could cause more harm than realized. So, Washington University’s Derek Platt and colleagues tested the ability of its four relatives to infect the placenta and fetus in healthy, pregnant mice.
All four viruses crossed the placenta and replicated inside the fetal brain, they report.
Like Zika, WNV and Powassan could replicate in maternal and fetal tissues obtained from healthy pregnant human donors in their second trimesters. Also, the two killed the developing fetuses. Chikungunya was not observed to cause this.
In conclusion, West Nile and the other three viruses could be causing birth defects, possibly even serious ones, but medicine hasn’t noticed yet.
While WNV is endemic to Israel, Zika is not. So far, there have been 27 confirmed cases in Israel, the Health Ministry said, all of which were contracted abroad.
As for why Zika suddenly turned so virulent in Brazil and South America, nobody knows yet. The ministry explained, “The world is struggling with that question. The Zika virus did undergo genetic changes over the years,” as viruses do, but it isn’t clear whether those mutations caused the change in its virulence.
“The virus may have been vicious to brain tissue in the fetus all along, but that fact may have been revealed only upon [spreading and] reaching a large population without immunity. Or other factors may be involved,” the ministry continued. “Could the same happen with WNV? The world of microbiology is dynamic. Pathogens undergo frequent mutation. Most have no effect on human beings, but a minority does. As of today, we have no way to predict the changes to come, or their ramifications.”
It is precisely this rapid rate of mutation that leads to, for example, viral flu epidemics.
What can be done to prevent the dangers of flaviviral infection? Not much. Don’t let mosquitoes bite you, say the experts, helpless to provide better advice: Use repellents and clothing that covers the skin.