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Zika Virus Explained: An Update—Commentary

16/03/16 Matthew E. Levison, MD, Drexel University College of Medicine|Drexel University;

This is an update to a previously published Commentary on Zika virus infection.


As the number of cases of Zika virus infection continues to grow, scientists are working to learn more about the virus, including developing tests for the virus, identifying ways to reduce risk of infection,  and studying the disorders it causes.

Testing for Zika virus: Previously, testing for the virus was available only through the Centers for Disease Control and Prevention. Now, some state health departments are also able to test for the virus. Tests that can rapidly identify the infection are being developed, and some are already available outside the United States.

Travel and Zika virus: The CDC has previously advised pregnant women to avoid travel to areas where Zika virus transmission is occurring. The experts at the CDC have now expanded their advice, recommending that pregnant women consider not attending the Summer Olympic games (August 5-21) or the Paralympic Games (September 7-18) in Rio de Janeiro, Brazil (

Sexual transmission of Zika virus: There is increasing evidence that Zika virus can be transmitted by sexual intercourse. The CDC is investigating several suspected cases, and two cases have been confirmed by testing. The cases all involved female sexual partners who had vaginal sex without the use of a condom with men who had symptoms of Zika virus infection and had recently returned from an area of Zika virus transmission.

Because Zika virus infection has been linked to birth defects, including microcephaly, the CDC advises men who have traveled in areas of Zika virus transmission (including those who are attending the Olympics) and whose partner is pregnant to either use a condom or abstain from sex during the remainder of the pregnancy.

Men whose partner is not pregnant may still consider abstaining from sexual activity or using condoms consistently and correctly during sex because it is not known how long the Zika virus can be transmitted in semen. Routine testing of male travelers for Zika infection solely to assess risk for sexual transmission is not recommended.

Women whose male partner has traveled to an area of Zika virus transmission and who are trying to get pregnant should talk with their doctors. Further information is here:

Blood transfusions and Zika virus: There have been several reported cases of Zika virus transmission due to blood transfusions, although none have occurred in the United States. Because 80% of people infected with Zika virus do not show symptoms of infection, the federal Food and Drug Administration has recommended that blood donors be asked about their travel history and asks that donors defer blood donations for a period of 4 weeks after return from an area in which Zika virus transmission is occurring. The American Red Cross also asks that people who have donated blood and later develop symptoms of Zika virus infection notify the Red Cross so their donation will not be given to a patient who needs blood. (

Disorders caused by Zika virus: A number of cases of Guillain-Barre syndrome (GBS) have occurred in areas of Zika virus transmission. GBS is a rare disorder of the nerves that sometimes occurs after certain infections. GBS causes muscle weakness that can be severe. Most people recover but a few continue to have some weakness for years. Although laboratory confirmation of Zika virus infection has been obtained in only a few of the people with GBS, GBS does occur in people who have had infections similar to Zika virus (such as dengue), so it is likely that Zika can cause GBS.

Doctors in France have linked another neurologic disorder, meningoencephalitis, an infection and swelling of the brain, to Zika virus infection.
Dr. Levison is The Manuals' Editorial Board reviewer for Infections.