The Zika virus, a tropical disease that has triggered an epidemic in Brazil and other parts of South and Central America, poses real risks of spreading to the U.S., infectious disease experts warn.
On Friday, the U.S. Centers for Disease Control and Prevention issued an alert telling travellers to watch out for mosquito bites in 14 South and Central American nations, including Brazil, where birth defects in thousands of babies have been linked to Zika infections during early pregnancy. Pregnant women and those considering getting pregnant are advised to postpone travel.
“I think the warning was appropriate and it’s balanced, given what we now know,” infectious disease expert Daniel Lucey of Georgetown University told BuzzFeed News. (This so-called level 2 alert is less serious than calls to totally avoid travel to a region, as was seen in the recent Ebola crisis in Western Africa.)
So far in Brazil, the Zika virus has infected perhaps 1.5 million people and has been linked to some 3,500 infants born with microcephaly, an abnormally small brain. That is a 20-fold increase in the birth defect there since 2014. “I would say the suspicions are very strong about the birth defect link at this point,” Lucey said.
It appears that Zika virus damages nervous system development during the early stages of pregnancy, similar to rubella or cytomegalovirus. This is surprising to public health officials because Zika doesn’t seem to act like other tropical viruses in its family, such as Dengue or West Nile, which don’t seem to cause birth defects.
“We have to be cautious, because much of the evidence for a link from the Zika virus to microcephaly is indirect,” infectious disease expert Nikos Vasilakis of the University of Texas Galveston Medical Branch told BuzzFeed News. “At the same time, we have seen a wave of tropical diseases spread widely. And there is a real chance of this disease spreading here.”
That’s because Zika, like West Nile virus, is carried by mosquitoes. Between 1999 and 2003, West Nile was linked to 1,100 deaths across the U.S. It likely entered the country inside an infected traveller who had been bitten by a mosquito that transmitted the disease, and in turn, passed it to other people and to birds via subsequent mosquito bites.
“Public health officials are very aware of this threat,” Lucey said, which is particularly concerning because it can’t be screened for at airports, and is generally reported by doctors after patients are diagnosed with symptoms. “Maybe the only good thing about Ebola is we do know how to screen travellers.”
Zika is hosted by the Aedes aegypti mosquitoes that also carry Dengue fever and which are found widely across southern U.S. states. But Asian tiger mosquitos, found as far north as the Great Lakes states, could also carry the Zika virus, according to a New England Journal of Medicine analysis released on Wednesday by Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases.
On the other hand, widespread air-conditioning, window screens and mosquito abatement measures make U.S. homes less hospitable to these mosquitoes, raising some expectation that spread of Zika isn’t inevitable.
“We don’t want to scare people, but awareness and education doesn’t hurt anyone,” Vasilakis said. “This is all the more reason to avoid mosquitoes, wear long pants and shirtsleeves, wear mosquito repellant, and stay where it’s air-conditioned.”
Zika virus was first discovered five decades ago in Uganda in an infected monkey. One mystery in the current outbreak is why a link to birth defects has not been observed sooner, given how long the disease has been around. It’s possible that in Africa the disease generally infects people with an unremarkable flu-like disease during childhood, before they ever can become pregnant. That allowed its birth defect effects to escape detection until its recent spread around the equator, where it infected a large population in Brazil that included many fertile women without any childhood immunity to the disease.
Aside from overcoming an infection, there is no vaccine or treatment for Zika virus, which usually causes mild flu symptoms, and was not viewed as a major concern until the reports of birth defects in Brazil. Spurred by the Brazilian reports, public health officials in French Polynesia have since gone through their health records of an earlier Zika outbreak there affecting about 8,000 people, and reported in November at least 17 cases of brain birth defects tied to infections.
“We may have to cast a wider net now looking at more than microcephaly to find more cases in more places,” Vasilakis said.
All of that said, Lucey also worries that American panic over Zika may be similar to what happened during the Ebola outbreak, which claimed more than 28,00 lives in Africa, but also led to excessive fears of its spread in the United States.
“I was in Africa during the Ebola crisis and it was the worst thing I have ever seen, just unimaginable,” Lucey said. “That is not what we are facing here in any way.”
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