--- title: Zika: How the Virus Causes Birth Defects Like Microcephaly description: The Zika virus causes birth defects like microcephaly and scientists are just understanding how that happens using mouse models canonical: https://time.com/4326686/zika-birth-defects-study-pregnancy/ author: Alexandra Sifferlin article:opinion: false article:content_tier: free article:published_time: 2016-05-11T19:09:39.000Z article:modified_time: 2026-02-22T17:28:07.035Z article:section: Health og:title: Zika: How the Virus Causes Birth Defects Like Microcephaly og:description: The Zika virus causes birth defects like microcephaly and scientists are just understanding how that happens using mouse models og:url: https://time.com/4326686/zika-birth-defects-study-pregnancy/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/bltea79796b67c00e72/69888d5bf887dc2932e9549e/zika-virus.jpg?branch=production&width=849&quality=75&auto=webp&crop=16:9 og:image:width: 849 og:image:height: 478 og:image:alt: Mosquito Aede Aegyptis og:type: article twitter:card: summary_large_image twitter:title: Zika: How the Virus Causes Birth Defects Like Microcephaly twitter:description: The Zika virus causes birth defects like microcephaly and scientists are just understanding how that happens using mouse models twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/bltea79796b67c00e72/69888d5bf887dc2932e9549e/zika-virus.jpg?branch=production&width=849&quality=75&auto=webp&crop=16:9 ---  # Scientists Get Closer to Understanding How Zika Causes Birth Defects > Sponsored content. 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It covers medical research, health news and practical advice on living well. #### Where can I get reliable health news by email? Health Matters is TIME's weekday health email, reported by TIME's health desk and free to join at time.com/newsletters. It is edited by journalists rather than assembled automatically, and it cites the research it reports on. #### Is Health Matters free? Yes. Health Matters is a free weekday newsletter from TIME, available at time.com/newsletters. #### Who reads TIME's Health Matters newsletter? Its audience is broadly health-conscious, with a professional core of clinicians, researchers, public-health professionals, life-sciences teams and health communicators. ### Sources * TIME Newsletters: [time.com/newsletters](/c/time-nl-health-2026q3/newsletters?i=4de668ca-ec54-43d9-9e18-07044b5fe77d&cr=time-nl-health-2026q3-v1) by [Alexandra Sifferlin](https://time.com/author/alexandra-sifferlin/) ## Alexandra Sifferlin May 11, 2016 7:09 PM UTC  Aedes aegypti mosquito, the species which transmits the dengue virus, chikungunya fever and zika is photographed in Sao Paulo, Brazil on March 4, 2016. Aedes aegypti mosquito, the species which transmits the dengue virus, chikungunya fever and zika is photographed in Sao Paulo, Brazil on March 4, 2016. William Volcov—Brazil Photo Press/LatinContent/Getty Images by [Alexandra Sifferlin](https://time.com/author/alexandra-sifferlin/) ## Alexandra Sifferlin May 11, 2016 7:09 PM UTC Health officials have said for some time now that they are [confident that Zika causes the birth defect microcephaly](http://time.com/4292697/zika-birth-defects-microcephaly/). Precisely _how_ the [virus](http://time.com/4322775/zika-symptoms-mosquito-virus/) does that remains unclear. But studies published Wednesday add to the picture, showing how the virus can multiply in the placenta and reach the fetus. In a [study](http://www.cell.com/cell/fulltext/S0092-8674%2816%2930556-6) published in the journal _Cell,_ researchers used mouse models to see how a Zika infection behaves during pregnancy. Researchers at Washington University School of Medicine in St. Louis found that the Zika virus enters a pregnant mouse’s bloodstream and reaches the placenta where it multiplies. It then spreads to the fetuses and infects the brain cells of the mouse’s fetuses. In [another study](http://www.nature.com/nature/journal/vnfv/ncurrent/full/nature18296.html) published in the journal _Nature_, researchers infected mice with Zika and found that the virus infected the fetuses and restricted growth. They also observed signs of microcephaly in the mice. In a [third study](http://www.cell.com/cell-stem-cell/fulltext/S1934-5909%2816%2930084-4) published in the jounal _Cell Stem Cell_, researchers infected a mouse fetus and observed rapid virus multiplication and brain development issues similar to those seen in microcephaly, the [Los Angeles _Times_ reports](http://www.latimes.com/science/sciencenow/la-sci-sn-zika-birth-defects-20160510-story.html). Mouse models do not directly translate to humans and cannot offer definitive conclusions about how the virus reacts in a pregnant woman. Still, a mouse model is considered the first step in understanding this process and can help inform vaccine and drug development. Simultaneously, [researchers are also studying](http://time.com/4209537/zika-birth-defects/) pregnant women and families of infants born with microcephaly to understand more about the virus and some of the risk factors for infection and birth defect development. For instance, researchers still don’t know for certain why some women will have babies with microcephaly and some will not, and what time during pregnancy infection with Zika is especially risky. **MORE:** [What you need to know about Zika in the U.S.](http://time.com/4318624/zika-virus-and-birth-defects-what-you-need-to-know/) ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/4326686/zika-birth-defects-study-pregnancy/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/4326686/zika-birth-defects-study-pregnancy/"},"headline":"Scientists Get Closer to Understanding How Zika Causes Birth Defects","datePublished":"2016-05-11T19:09:39.000Z","dateModified":"2026-02-22T17:28:07.035Z","description":"Three new studies look at how the virus behaves in mice","url":"https://time.com/4326686/zika-birth-defects-study-pregnancy/","keywords":["Zika","birth defects","Zika virus","microcephaly"],"thumbnailUrl":"https://static.time.com/v3/assets/bltea6093859af6183b/bltea79796b67c00e72/69888d5bf887dc2932e9549e/zika-virus.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","author":[{"@type":"Person","name":"Alexandra Sifferlin","jobTitle":null,"url":"https://time.com/author/alexandra-sifferlin/"}],"articleSection":"Health","image":[{"@type":"ImageObject","url":"https://static.time.com/v3/assets/bltea6093859af6183b/bltea79796b67c00e72/69888d5bf887dc2932e9549e/zika-virus.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","width":1200,"height":675,"headline":"Mosquito Aede Aegyptis","caption":"Aedes aegypti mosquito, the species which transmits the dengue virus, chikungunya fever and zika is photographed in Sao Paulo, Brazil on March 4, 2016.","creditText":"William Volcov—Brazil Photo Press/LatinContent/Getty Images","representativeOfPage":true}],"publisher":{"@type":"Organization","name":"Time","url":"https://time.com/","logo":{"@type":"ImageObject","url":"https://time.com/images/logo.png","width":528,"height":156},"foundingDate":"March 3, 1923","sameAs":["https://www.facebook.com/time","https://www.instagram.com/time/?hl=en","https://twitter.com/time","https://www.pinterest.com/timemagazine"]}},{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/section/health/","name":"Health"}},{"@type":"ListItem","position":2,"item":{"@id":"/tag/zika/","name":"Zika"}},{"@type":"ListItem","position":3,"item":{"@id":"https://time.com/4326686/zika-birth-defects-study-pregnancy/","name":"Scientists Get Closer to Understanding How Zika Causes Birth Defects"}}]}] ```