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Zika Virus Infection Update—Commentary

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

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

Diagnosis of Zika virus infection: Previously, testing for Zika virus infection was available only at the CDC. Currently, a few state health departments also have capability of testing for Zika virus. Rapid screening tests are being developed; some are available commercially outside of the US.

Travel and Zika virus: In addition to previous recommendations that pregnant women postpone visiting areas of active virus transmission (including most of Latin America and the Caribbean), the CDC now recommends:

  • Pregnant women consider not attending the Summer Olympics in Rio de Janeiro, Brazil, scheduled for August 5 through August 21, or the Paralympic Games, scheduled for September 7 through September 18 (
  • Men who travel to the Olympics should abstain from vaginal, anal, or oral sex with a pregnant partner, or else use condoms for the duration of the pregnancy.

Sexual transmission of Zika virus: There is increasing evidence of sexual transmission of Zika virus. The CDC reported on 14 suspected cases (

  • 2 cases confirmed by testing
  • 4 cases probable by testing
  • 6 cases still under investigation
  • 2 cases excluded based on additional information

Cases all involved men who had traveled to an area of active Zika virus transmission and developed symptoms. Their female sexual partners (who had no other risk factors for infection) became ill within 2 weeks. In all cases where type of sexual contact was documented, the contact included condomless vaginal intercourse and occurred when the male partner was symptomatic or shortly after symptoms resolved.

Thus, CDC advises men who have visited or lived in a Zika transmission zone and who have a pregnant partner to use a condom or practice abstinence for the duration of the pregnancy (

Men whose partner is not pregnant may still consider abstaining from sexual activity or using condoms consistently and correctly during sex; the duration of transmission risk is not known because Zika might persist in semen longer than it does in blood (about 1 wk). Routine testing of male travelers for Zika infection solely to assess risk for sexual transmission is not recommended.

Pregnancy and Zika virus infection: The CDC reported on outcomes in 9 pregnant women with laboratory-confirmed symptomatic Zika virus infection. Outcomes varied depending on trimester in which symptoms occurred.  (  

  • 3rd trimester: 1 healthy infant
  • 2nd trimester: 1 healthy infant, 1 pregnancy continuing
  • 1st trimester: 2 miscarriages, 2 elective abortions, 1 live birth with microcephaly, 1 pregnancy ongoing

In the 2 miscarriages, Zika virus was detected in fetal specimens. In the 1 abortion with results reported, fetal MRI showed severe brain atrophy.

Ten additional pregnant women with Zika virus infection are being observed.

In a similar study from Rio de Janeiro, Brazil, fetal abnormalities were detected by fetal ultrasound in 12 of 42 pregnant women (29%) who had developed acute laboratory-confirmed (by RT-PCR) Zika virus infection in the 8th to even as late as the 35th week of gestation. The abnormalities included stunted fetal growth, microcephaly, brain calcifications, and fetal death (

In 2 other studies, experiments with early fetal brain cells grown in test tubes showed that the Zika virus specifically targets and destroys fetal cells that eventually form the brain’s cortex, the outer brain layer responsible for many higher functions ( and However, the fetus in the uterus may not respond in the same way that cultured cells do.

Blood transfusion and Zika virus: During the 1st week of symptomatic Zika virus infection, patients have virus in their blood. During Zika virus outbreaks, the virus has been found in 3% of asymptomatic blood donors (80% of people infected with the Zika virus don’t show any symptoms). There have been several reports of blood transfusion transmission of Zika virus in Brazil, although none in the US.

The FDA now recommends screening blood donors by history (

  • Known Zika virus infection or symptoms and signs of Zika virus infection: self-defer for 4 wk after resolution of symptoms
  • History of sexual contact with a man who has been diagnosed with Zika virus infection or who traveled to or resided in an area with active transmission of Zika virus in the previous 3 months: Self-defer for 4 wk after last sexual contact

For areas of the US with active Zika virus transmission (eg, Puerto Rico), the FDA recommends transfusing only blood and blood components obtained from areas of the US without active transmission of Zika virus (until donor screening tests for Zika virus become available).

The American Red Cross also asks donors who develop symptoms consistent with Zika virus infection within 14 days of donation to immediately notify the Red Cross so that they can quarantine the product (

Guillain-Barré syndrome (GBS) and Zika virus infection: Clusters of cases of GBS are now occurring in 8 countries and territories affected by Zika virus infection. However, only a few cases have had Zika virus infection confirmed by laboratory testing (, GBS has also been described in association with other arbovirus infections (dengue and chikungunya), which are currently circulating in regions with ongoing Zika virus transmission. 

Dr. Levison is The Manuals' Editorial Board reviewer for Infectious Diseases.