Zika Virus: An Update and Review of the Risk

In January, we released a most-important-facts sheet about Zika and the current status based on reports and information from the CDC and World Health Organization. Today we give you an in-depth discussion on the current status of the Zika outbreak, its presence in the United States, and how to gauge Zika as a risk factor in pregnancy. Certified Nurse Midwife and public health specialist Rebekah Wheeler -- who is also currently pregnant -- shares with us her insight and collected research on the disease and its relative risk to pregnant families in the United States. The following article is a condensed version of the complete two-part article that appears this week on our sister blog, Science & Sensibility

mosquito-542156_640.jpgAlthough Zika is everywhere in the news these days, confusion about what it is, what it does, and what to do about it is widespread.  As one tries to follow the news on Zika, they encounter advice for pregnant people ranging from “avoid travel to affected areas” to “everyone who can become pregnant anywhere are at risk.” It can feel alarming to families and professionals alike.  I am a Certified Nurse Midwife (CNM) who has been faced with terrified patients, and I want to help you have a realistic sense of how much risk Zika might pose to your babies’ health.  I am also a former public health researcher with a background in international women’s health, dedicated to examining the data closely to figure out what we really know about Zika and pregnancy.  Lastly, I am a pregnant woman, and I want to know whether and how much to worry myself.

What We Know About Zika

The Zika virus was first identified nearly 70 years ago in Uganda, and has never previously been thought to pose a major public health threat.  Over the decades, there have been numerous outbreaks infecting tens of thousands of people across the world, and no cases of microcephaly (babies born with abnormally small heads and corresponding learning and developmental problems) have ever previously been reported.  The most recent outbreak in Brazil is the first time we’ve seen a significant rise in microcephaly among babies born to women who also had Zika in their bloodstream.

Zika is a mild viral infection, and the CDC states that 80% of those who get it never feel any symptoms. Part of why most have never heard of it before is that it has been thought to be relatively harmless. When people do show effects from the virus, they are usually quite mild, present up to two weeks after exposure, and last less than a week. Severe disease requiring hospitalization is uncommon. No evidence exists to suggest that pregnant people are more likely to get the Zika virus or experience the disease more severely.  Documented symptoms of Zika, when symptoms are even present at all, are:

  • Mild fever (100-102 F)
  • Rash (usually not itchy)
  • Joint and muscle pain (known as arthralgia)
  • Red eyes (known as conjunctivitis, usually without the discharge of pus we usually associate with this)

Almost all known cases of Zika infection have occurred in Central America, South America, the Caribbean and the Pacific Islands.  Go the CDC website for the most up to date list of affected countries.  A few cases have been documented in other places, including Florida, Texas and Hawaii, but it is believed that all of these individuals were infected in one of the above countries before flying back to the US.  When reviewing the CDC list of affected countries and territories, know that it doesn’t mean that the whole country is crawling with Zika.  For example, cases in Mexico have thus far been confined to very rural areas not frequented by tourists, with zero cases reported in beach resort towns US visitors are more likely to visit.  Virtually every case of Zika was spread by a well-known specific species of mosquito known as the aedes aegypti.

There have now been confirmed cases of a woman getting Zika from her male partner through sexual contact, but each was within the initial two weeks after the male partner’s exposure to the disease, while the virus is active in the bloodstream.  No cases of sexual transmission have been documented beyond the acute exposure period (2 weeks), so we don’t currently think Zika can be dormant in the bloodstream and spread to others, like HIV can be.

Zika and Microcephaly

Here’s why Zika has been linked to cases of microcephaly all of a sudden.  There was a Zika outbreak in Brazil in 2015, with between 500,000 and 1,500,000 Brazilians getting the virus (FRAMEWORK, S. R. 2016).  At the same time, local health officials in northern Brazil noticed that there was a sharp increase in rates of microcephaly. Brazil usually sees about 150 cases of microcephaly each year, but in 2015 that number was above 3,000, a massive increase (FRAMEWORK, S. R. 2016).  Researchers began to suspect, due to the fact that the Zika outbreak happened at the same time as the increase in microcephaly cases, that perhaps contracting Zika during pregnancy might be the cause of microcephaly in the fetus. What they don’t know, and may never know, is how many of the babies with microcephaly were exposed to Zika in utero.  This may never be possible to measure, as Zika does not stay in the bloodstream for more than about 12 weeks (FRAMEWORK, S. R. 2016).

In one study out in late February, two pregnant women with fetuses with microcephaly were found to have Zika in their amniotic fluid (Calvet, G. et al, 2016).  The study authors note that while this confirms that Zika can pass through the placenta, it does not actually do anything to prove a relationship between Zika and microcephaly, and that finding this is only two fetuses thus far is actually a very small number. The relationship between fetal microcephaly and the Zika virus remains unclear, and the quality of this evidence is poor.

It is very important to know that the link between Zika infection and microcephaly is a suspected link, not a proven one. In fact, experts from the World Health Organization are being very careful to say that the link between Zika virus and microcephaly is a suspected one, but has not been confirmed in any scientific study.  Microcephaly has historically been known to have multiple non-Zika causes, including Down Syndrome and other genetic disorders, exposure to toxic chemicals, smoking in pregnancy, maternal malnutrition and some severe maternal infections. Further cause for caution in assuming a causative link comes from Colombia, where they have had more than 3,000 cases of Zika but no increase in microcephaly rates.

Here is how I think it makes sense to think about this: There was a Zika outbreak and a large increase in microcephaly cases at the same time.  That is potentially scary, but assuming one causes the other without a clear biological pathway and hard evidence is a recipe for causing potentially unnecessary panic. Studies are being conducted to evaluate whether the link might have to do with other factors instead of, or in addition to Zika infection, such as concurrent infections with other diseases and viruses, poor nutrition, toxin exposure (including exposure to chemicals that kill baby mosquitoes), or other unknown environmental factors.

“Should Expectant Families Worry About Zika in the US?” Probably Not.

Even if it is determined that there is a direct link between Zika infection and microcephaly during pregnancy, does this mean pregnant people should worry about becoming infected?  If you live in the US, probably not. To understand why the risk to Americans is so low, it helps to understand a little about how Zika is spread.  Almost every case of Zika ever recorded was transmitted by the mosquito aedes aegypti, the same mosquito species that transmits dangerous but rare infections like Dengue Fever, Yellow Fever, and Chikungunya, all of which are considered more dangerous than Zika.  The typical American probably has not even heard of these because the aedes aegypti mosquito is not common here.  While they have been seen in small numbers in the warmer US states such as Texas, Florida, Hawaii and Southern California, the number of outbreaks of these diseases has been very few. Furthermore, occasional outbreak is isolated and eradicated very quickly because of our excellent public health and disease control infrastructure.  Should an outbreak of Zika suddenly occur in the US, it would also likely be contained and controlled quickly and effectively.     

The fact that people don’t sit around fearing infection with Dengue, Yellow Fever, or Chikungunya in the US is a reminder that we need not fear Zika here either.  Instead, I think of the Zika outbreak as very similar to there being an outbreak of either of these diseases in another country: I would not travel there unless I absolutely had to, and I would cover up and use lots of repellent if I did go (more on that below).  What I wouldn’t do is panic (lots more on that below).

Reasonable Steps to Avoid Zika

If a family feels a little concerned about Zika exposure, here or abroad, they could

  • Consider using mosquito repellents that are effective against aedes aegypti. Per the EPA, it is safe to use insect repellents containing DEET, picaridin, and IR3535 in pregnancy.  NPR recently published an article summarizing research on which repellents most effectively keep aedes aegypti away. For complete list of products and their EPA ratings, check out this article. ·         
  • Cover up or stay inside. The aedes aegypti species typically bites during the day and at dusk.  Because of this, mosquito nets for sleeping aren’t useful.
  • Use air conditioners and window screens to keep mosquitoes out of the home. Sleep in an air-conditioned room (mosquitoes hate cold).
  • Try to eliminate mosquito-breeding grounds near the home.  Mosquitoes breed in standing water, even tiny puddles like the dish under a house plant.  Get rid of this standing water and there will be fewer mosquitoes around, period.
  • Those who are pregnant or considering pregnancy should consider postponing travel to areas with Zika virus transmission.

Further info on avoiding mosquito bites is available at this CDC web page.

If a Pregnant Person Believes They May Have Been Exposed to Zika

  • If someone traveled to any of the affected areas during pregnancy, or do so in the future, they should tell their prenatal provider.  The blood tests for Zika seem only to be accurate within two months of infection, so if it was more than three months ago, guidelines suggest monthly ultrasounds to measure the baby’s head (Peterson, E.E. 2016).  If the baby’s head was already measured at an anatomy scan or another ultrasound, this should be reassuring.  If the test is negative, the CDC still recommends ultrasounds (they are erring on the side of extra surveillance and caution).
  • If someone might have Zika, they should avoid getting more mosquito bites.  This way, they can avoid risk of transmitting Zika within the US.
  • If their partner went to an area with Zika, it seems prudent to avoid unprotected sex for at least two weeks. While the CDC does recommend condoms throughout pregnancy for all those with potentially-exposed partners, there has never been a documented cases of transmission more than a week after exposure.

To Get The Most Up-To-Date Info and Recommendations

Go to the CDC’s most concise and helpful site (and do all you can to avoid media reports): to find out what the current recommendations are and to read the most recent reports and information on this topic.

The Big Picture: Pregnancy and Risk

The truth is, we live with risk all the time.  Pregnant people are regularly warned about threats to their fetus’ well-being, from smoking to sushi.  Providers say “don’t do xxx” in pregnancy, and people fear it and avoid it, even without knowing the real size or severity of the risk.  I believe that it is highly problematic that the majority of prenatal care providers in the US don’t take the time to differentiate between common risks with proven, causal, significant impacts and rare risks with unusual or unproven negative outcomes.

Breaking down the “smoking to sushi” phrase I used above, for example, illustrates the vast difference in scale and severity of different risks in pregnancy.  Smoking has been proven to increase risks for poor fetal growth, preterm delivery, cerebral palsy, asthma and SIDS (Tobacco Use and Pregnancy. 2015). The impact is studied, proven, real, and severe.  Sushi, on the other hand, is warned against for its possible risk of increased exposure to listeria bacteria, and the severe food-borne illness that can result in hospitalization, miscarriage and fetal malformations (Janakiraman, V., 2008).  The last time that freshly-made sushi was implicated in a case of listeriosis in pregnancy in the US, however, was more than eight years ago (The Prevalence of Listeria in Food and the Environment)).  The advent of faster and safer fast-freezing methods for raw fish have dramatically decreased the likelihood of listeria exposure, implicating prepackaged and processed foods far more often than fresh foods  (CDC. 2013), (Miya, S., et al.2010), but providers aren’t keeping us up to date on size or severity of risk.

As a prenatal care provider, I regularly talk about risk with my patients and their partners.  I think every patient deserves to be given real data on the frequency of a risk and the severity of the conditions that might arise if they are exposed to this risk.  Some risks are rare but severe, like getting a first exposure to the Herpes Virus in pregnancy.  Some are common but have small impact and are reversible, such as having anemia.  In flu season, for example, I want pregnant patients to know that influenza infection in pregnancy results in much more severe illness than in non-pregnant adults.  This can mean hospitalization, possible miscarriage or fetal loss, or in some cases even fetal abnormalities.  Similar conversations should be had about CMV, Parvovirus, Toxoplasmosis, Rubella and others. As with Zika, we know our risks of contracting them is rare, and we go about our lives without any sense of overwhelming fear.  Many of these are actually airborne or food borne, making them much easier to transmit and contract than a mosquito-vector virus such as Zika.  In order to avoid undue risk, we make loose rules that could help avoid most exposures, and we’re comfortable with that.

When counseling about exposure risk, I talk about the relative risks of vaccination versus contracting flu, and then I let my patients make the decision they think is best for them.  I respect that different sets of parents will have different comfort levels when it comes to abstract and rare risks.  Each individual or couple will interpret risk differently, and have different values around risk exposure and avoidance.

Pregnancy is a period of practice in making choices around risk versus benefit.  This is practice for being a parent, for risk doesn’t end when a child is born.  Quite to the contrary, parents are now thrown into a world of decisions about breast vs bottle-feeding, vaccination schedules, preschool vs daycare…the list goes on and on.  Parents are constantly calibrating risks and benefits and making decisions based on the best data available to them.  Part of learning to think about risk is to check in with themselves about whether doing or not doing something will cause more anxiety.  In choosing whether or not to screen for genetic abnormalities such as Down Syndrome, for example, I see many families who decide that the emotional risk of a false positive outweighs their worries about having a baby with any genetic problem.  They opt against testing.  Other couples know that the reassurance of a negative test is important to them, and choose to screen.  Risk means different things to different people.

Consider the Zika virus in the greater context of risk.  It is a new risk, in that most of us had never heard of it before last month, and the frequency and impacts are unknown, which is scary.  But there are many factors about Zika that make it unlikely to be a frequent risk, and that also point to a very small likelihood of it causing microcephaly in most cases. Consider approaching Zika the way we do other risks in pregnancy: avoid the behaviors that maximize risk of exposure and practice behaviors that would minimize risk.

The great challenge to parents is to live full lives without being incapacitated by the fear of risk. Parenting means making an unending series of decisions about risk, and learning to make them without undue anxiety or loss of a sense of the fullness and potential of life. The media love this story, because it is intense and full of unknowns.  It is hard to keep perspective when the media is in a frenzy, but remember that there is much we do not know, and what we do know so far points toward a low personal risk.  If we start to see an uptick in cases of Zika in this country, invest in bug spray, turn on your air conditioner, and cover up. 


Calvet, G., Aguiar, R. S., Melo, A. S., Sampaio, S. A., de Filippis, I., Fabri, A., … & Tschoeke, D. A. (2016). Detection and sequencing of Zika virus from amniotic fluid of fetuses with microcephaly in Brazil: a case study. The Lancet Infectious Diseases.

FRAMEWORK, S. R. (2016). ZIKA. (http://who.int/emergencies/zika-virus/strategic-response-framework.pdf?ua=1)

Petersen, E., Staples, E., Meaney-Delman, D., Fischer, M., Ellington, S., Callaghan, W., & Jamieson, D. (2016). Interim Guidelines for Pregnant Women During a Zika Virus Outbreak – United States, 2016.  Centers for Disease and Control: Morbidity and Mortality Weekly Report (MMWR).

Janakiraman, V. (2008). Listeriosis in pregnancy: diagnosis, treatment, and prevention. Rev Obstet Gynecol, 1(4), 179-85.Centers for Disease Control and Prevention (CDC. (2013). Vital signs: Listeria illnesses, deaths, and outbreaks–United States, 2009-2011. MMWR. Morbidity and mortality weekly report, 62(22), 448.

Miya, S., Takahashi, H., Ishikawa, T., Fujii, T., & Kimura, B. (2010). Risk of Listeria monocytogenes contamination of raw ready-to-eat seafood products available at retail outlets in Japan. Applied and environmental microbiology,76(10), 3383-3386.

The Prevalence of Listeria in Food and the Environment. (n.d.). Retrieved February 29, 2016, fromhttp://www.about-listeria.com/listeria_prevalence/#.VtONWvIrLIU

Tobacco Use and Pregnancy. (2015). Retrieved February 29, 2016, fromhttp://www.cdc.gov/reproductivehealth/maternalinfanthealth/tobaccousepregnancy/index.htm

About Rebekah Wheeler© Rebekah Wheeler

Rebekah Wheeler, RN, CNM, MPH, works as a full-scope Nurse-Midwife in San Francisco.  She moved to the Bay Area in 2011, after completing her MPH and MSN at Yale University.  Before becoming a midwife, she worked in international women’s health programming and research in Tanzania, Malawi, South Africa and Mexico. She is the founder of the Malawi Women’s Health Collective, a small non-profit she created while on a Fulbright scholarship. Rebekah has served on the boards of the California Nurse-Midwifery Association, Planned Parenthood of Rhode Islandand the Women’s Health and Education Fund of Southeastern Massachusetts.   

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