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Health Effects of Zika Virus

Zika Health Effects

The majority of people who become infected with Zika virus will have no symptoms at all. For those who do experience symptoms, fevers and rashes are most common and the results are typically mild.

Nonetheless, according to the World Health Organization (WHO), Zika-related defects are an international public emergency. Additionally, research suggests a connection between Zika infections and higher rates of an autoimmune disorder known as Guillain-Barré Syndrome, which causes muscle weakness and paralysis. These health effects are discussed further below.

Asymptomatic Individuals

Up to 80% of people who contract Zika virus will experience no symptoms at all (i.e., asymptomatic). While these individuals will feel normal, the virus is still in their body and can be transmitted to other people through sexual contact or infected blood. Zika can also be picked up by uninfected mosquitoes that eventually bite an infected human. For this reason, people who travel to Zika-affected areas should use insect repellant for at least 3 weeks after returning home, even if they do not feel sick, to prevent mosquito bites and the potential transfer of the virus to the local mosquito population. Additional ways that infected but asymptomatic individuals can spread the virus can be found under Preparation and Protection.

Pregnancy Risk: Birth Defects

Zika virus can be passed from an infected mother to her unborn child during pregnancy. While the symptoms may be mild for adults, the unborn child is at risk for a number of birth defects, including:

  • Microcephaly (underdeveloped brain)
  • Other severe fetal brain defects
  • Eye defects
  • Hearing loss
  • Impaired growth

The Centers for Disease Control and Prevention (CDC) reported that more than 23 babies have been born in the U.S. with confirmed Zika-related birth defects. Although Zika infection has been linked to the birth defects described above, more research is needed to fully understand the risk the virus poses during pregnancy. For example, it is still unclear how likely a child will be born with birth defects if their mother was infected with Zika during pregnancy, or if there is a specific time during pregnancy that the fetus is most susceptible to Zika infection.

Based on the available evidence, Zika virus infection in a woman who is not pregnant will not threaten the health of future pregnancies if the virus has cleared from her blood.

Guillain-Barré Syndrome (GBS)

Guillain-Barré Syndrome (GBS) is an autoimmune disorder where the immune system attacks healthy nerve cells in your peripheral nervous system. It is normally very rare, only occurring in 1 or 2 people for every 100,000. However, current research suggests GBS is strongly associated with Zika infection—several countries that have experienced Zika outbreaks have also reported an increased incidence of GBS. In Brazil, where there is an ongoing Zika outbreak, the incidence of GBS is estimated to be approximately 7.5 people per 100,000 cases. The proportion of people with Zika who get GBS, however, is still small.

In GBS, the immune system attacks healthy nerve cells and starts to destroy the myelin sheath, which protects the nerve cells and is necessary for the nervous system to function properly. Symptoms of GBS include:

  • Weakness or tingling in the legs, spreading to the upper body
  • When severe, may cause total paralysis and interfere with breathing, heart rate, and blood pressure

Although GBS can be a devastating disorder, most individuals recover and can return to their normal lives. However, some continue to experience a certain degree of weakness.

Additional Resources

IEM Zika Perspective

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CBS’s 60 Minutes Features
the Fight Against Zika

On CBS’s 60 Minutes the country’s top scientists talk about the fight against Zika and the U.S. government’s efforts to control it.  IEM scientist, Dr. Jenn Kruk, comments on the lack of attention and general dismissal the virus gets from the majority of people who aren’t directly impacted. Read more.


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Dr. Rashid Chotani answers the question "Why is Zika spreading so rapidly, and why now?" in blog post in the Zika series, "Is Zika Here to Stay?" Read now.


 Additional Zika Perspectives

Zika Classified as an STD: What You Need to Know (November 2, 2016)

Hurricane Matthew’s Potential Impact on the Spread of Zika (October 19, 2016)

Zika: Protecting Yourself Protects Those Around You (October 7, 2016)

All Mosquitos Are Not The Same When It Comes To Zika (Sept 23, 2016)

Zika and the Brain: A Public Health Game Changer (Sept 16, 2016)

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IEM is providing this website for informational purposes only.  Information regarding Zika is evolving rapidly.  Accordingly, you should not use this website as a substitute for professional advice provided by a qualified healthcare provider. IEM encourages you to consult with a physician if you have specific questions about the Zika virus or its potential effect on you.