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Here’s What We Now Know About Zika

And what American communities can do to prepare.

By Francie Diep


The Aedes aegypti mosquito larvae, photographed at a laboratory in San Salvador. (Photo: Marvin Recinos/AFP/Getty Images)

As predicted, the summer season has brought with it a spate of Zika virus infections throughout the United States. The illness’ spread comes at a time when scientists are finally learning more about how the virus works.

Researchers from the Centers for Disease Control and Prevention (CDC) published an essay on Monday, summarizing everything we know about the Zika virus, with recommendations for combating infections. Prevention is crucial, the researchers suggest. “The effects of brain damage due to microcephaly and consequences of other Zika-related birth defects are likely devastating, lifelong, and costly,” they write. These defects may also prove deadly: Just this week, officials reported a newborn baby girl died in Texas because of birth defects caused by the Zika virus. She was the first such death in the state.

It’s been 10 months since Brazilian doctors first reported they were seeing unusually high numbers of babies being born with microcephaly — a birth defect characterized by small heads and developmental delays — alongside a rise in the number of Brazilians infected with the virus. At first, scientists weren’t even sure whether Zika infections caused microcephaly, though they suspected it. Now, the connection is clear, and federal and local agencies have to decide what they’ll do to prevent the spread of Zika.

Below, some highlights from the essay, which appeared in the Journal of the American Medical Association:

What Zika Can Do

  • Although scientists initially weren’t certain whether Zika virus infections cause birth defects, now the science has come in — and indeed they do.
  • If a woman has a Zika virus infection early in a pregnancy, the likelihood the baby will be born with microcephaly may be between 1 percent and 13 percent.
  • Scientists have never seen anything that’s quite like this outbreak. “Never before, to our knowledge, has a mosquito-borne virus been associated with human birth defects or been capable of sexual transmission,” the CDC researchers write.

Where Zika and Zika-Caused Microcephaly Have Spread

  • Since January, more than 60 countries or territories have reported Zika virus spreading within their borders.
  • By August 4, almost 1,700 people in the continental U.S. have been reported as having Zika virus infections, including 479 pregnant women. Almost all contracted the virus while traveling outside the U.S.
  • In a six-block area north of downtown Miami, Florida, officials have confirmed 13 cases, including cases of local spread.
  • Northeastern Brazil has recorded more than 1,700 cases of microcephaly caused by Zika.

How Zika Spreads

  • The most efficient carriers of the virus are Aedes aegypti mosquitoes, which live in 30 states. Aedes albopictus mosquitoes, which live in 41 states, are also able to spread the virus, though less efficiently.
  • The virus can be transmitted sexually. It may live for several months in semen.
  • In Brazil, it has spread through blood transfusions, prompting American blood banks to screen their donations.
  • There’s one documented instance of an American getting Zika after caring for an infected elderly relative.

What to Do About Zika

  • The CDC recommends pregnant women don’t travel to regions where the virus is spreading among the population, including a small part of Miami. This is the first time the agency has made such a recommendation about a neighborhood within the U.S.
  • Women already living in Zika-endemic areas may use Environmental Protection Agency-registered insect repellents, including DEET. When possible, they should stay in air-conditioned rooms, or at least rooms with screened windows and doors.
  • For the nation as a whole, the CDC recommends “protection against mosquito bites; screening the blood supply; ensuring access to voluntary, effective contraception; and effective vector control” — which might mean campaigns to remove pools of stagnant water around people’s homes, as well as the use of insecticides.

What We Still Don’t Know

Some mysteries remain around the virus, which has never caused major public-health problems until recently. One lingering question: whether a seemingly healthy baby, born of a woman infected with the Zika virus, may develop neurological symptoms in the future. In addition, Zika infections are associated with other conditions, including Guillain-Barré syndrome and severe thrombocytopenia, but scientists are less sure about whether the virus actually causes those conditions.