1 in 100: New study gives clues on rate of Zika-related birth defects

Scientists and bug spray manufacturers continue to seek ways to prevent Zika's spread

Pregnant women who are infected with Zika virus during their first trimester of pregnancy could face about a 1 in 100 chance that their fetus will develop microcephaly, according to a new study published in the journal Lancet.

While most people infected with Zika virus develop no symptoms, the spread of the virus has coincided with a massive increase in the number of women giving birth to infants with microcephaly, a neurological disorder characterized by an abnormally small head and potentially fatal developmental issues.

The study analyzed fetuses born with birth defects during a Zika virus outbreak in French Polynesia between September 2013 and July 2015. Before the Zika virus outbreak, the rate of microcephaly in French Polynesia was about two per 10,000 newborns.

During the outbreak, there were eight total cases of microcephaly, seven of which occurred over the last four months of the two-year period. The cluster of microcephaly cases toward the last four months "strongly supports the proposed association" between Zika virus and microcephaly, the researchers write.

However, the researchers cannot know if the mothers of the microcephalic fetuses were infected with Zika virus because the mothers were not tested.

While the odds of a fetus developing microcephaly are low, "if you apply a 1 percent risk to a large number of women, it's still a large public health problem," lead author Simon Cauchemez tells the New York Times. Since Zika virus is carried by mosquitoes, it can spread easily. During the Zika virus outbreak in French Polynesia, 66 percent of the population was infected.

The researchers also caution that the 1 percent risk of microcephaly in French Polynesia may differ from the risk in other countries experiencing a Zika outbreak. According to a study published in New England Journal of Medicine, 29 percent of ultrasounds performed on pregnant Brazilian women who tested positive for Zika virus showed fetuses with abnormally small heads and nerve damage.

Fighting Zika: Scientists pursue vaccine research, and bug spray manufacturers ramp up production

There is currently no vaccination or cure for Zika virus, but researchers are exploring a number of possible ways to prevent the virus.

An experimental vaccination against dengue fever, another mosquito-spread virus, could illustrate a path forward. In a new randomized, placebo-controlled trial, volunteers inoculated against dengue fever with an experimental vaccination were protected against dengue virus when it was introduced into their bloodstream six months later.

The study was "the closest that it can be to what may happen in natural infection," says Nikos Vasilakis, a virologist at University of Texas Medical Branch in Galveston, who was not involved in the study.

Some are hoping that the dengue study, and in particular its technique for deliberately infecting volunteers to test vaccine effectiveness, could help guide the development of a Zika virus vaccine.

With no treatment available, how can hospitals and health agencies prepare for Zika?

"We think that this is a tool that can really accelerate vaccine development," says Anna Durbin, study co-author and associate professor at John Hopkins School of Public Health.

In the meantime, others are working on ways to protect against mosquitos. In the United States, bug repellent is one of the few ways that people can protect themselves from mosquito-borne illness.

"We're doing anything you can imagine," says Kelly Semrau, spokesperson for S.C. Johnson & Son, the maker of two bug repellent products. "We've seen what has happened in Latin America; we are preparing for the eventuality that it will be here."

One of the company's factories that produces bug repellents is effectively operating 24/7, while others have added overnight and weekend shifts.

 Sales of bug repellents last month increased up to 200 percent compared with last year, according to market research firm IRI. The EPA is also working to expedite the pesticide approval process, which covers personal bug repellents, says an EPA spokesperson (Vincent, The Verge, 3/17; Saint Louis, New York Times, 3/15; Neergaard, AP/Washington Times, 3/16; Smith, MedPage Today, 3/16; Terlep, Wall Street Journal, 3/16).

A global look at disease outbreaks: It's not just Zika and Ebola

Hundreds of thousands of people worldwide are suffering from infectious disease—and it's not all Zika virus and Ebola. The Daily Briefing takes a look at some of the outbreaks affecting communities right now.

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