Zika Virus Update: Epidemiology, Sexual Transmission, Pregnancy

By Betsy Todd, MPH, RN, CIC, clinical editor

A close view of a repellent product being sprayed on a person's hand in Brasilia, Brazil, 27 January 2016. The Brazilian government announced that repellent products will be given for free to pregnant women registered in the assistance programs to avoid Zika contagion. EPA/FERNANDO BIZERRA JR.

Mosquito repellant being sprayed on a person’s hand in Brazil. EPA

Zika virus is now being actively transmitted in 42 countries, primarily in the Americas and on islands in the South Pacific. As of April 13th, there had been 358 travel-associated cases reported in the U.S., including 31 pregnant women.

While there are as yet no locally acquired U.S. cases, local transmission has been established in several U.S. territories (primarily, Puerto Rico). Travel-associated cases are expected to continue in the U.S., almost certainly leading to eventual limited local transmission.

Transmission. Most cases of Zika virus infection have been vector-borne—that is, they resulted from the bite of an infected mosquito. Other modes of transmission have been documented, including intrauterine, perinatal, sexual, and via exposure to lab specimens

Transmission may be possible during blood transfusion, organ or tissue transplantation, breast feeding, or fertility treatments, but thus far there have been no reports of infection acquired in this way.

Immunity after infection with Zika virus is currently thought to be lifelong. There have been no known cases of reinfection after a primary Zika infection, nor of “relapsing” cases of the disease (as seen after Ebola virus infection).

Serologic testing can be done via reverse transcription–polymerase chain reaction (RT-PCR) for viral RNA, or immunoglobulin M (IgM) testing for antibodies. Information regarding the accuracy of tests done on infected but asymptomatic people is limited, and Zika virus disease should  not be ruled out on the basis of a negative test. As with other infectious diseases, the decision to test is guided by the patient’s symptoms, travel history, and current geographical location.

Sexual transmission of Zika. The virus has been detected in semen. All reported cases of sexual transmission involved men who had or developed symptoms of infection, and who did not use condoms. Both female and male partners have been infected. There has been no known transmission from infected women to their partners.

The CDC’s newest recommendations regarding sexual transmission of Zika virus suggest time periods during which men potentially exposed to or diagnosed with Zika infection abstain from sex or consistently use condoms in order to prevent transmission. The length of time varies from eight weeks to six months, depending on the circumstances.

The CDC does not recommend testing semen for Zika virus in an effort to determine the risk of sexual transmission. These tests are not widely available and it’s still not clear how to interpret the results.

There are still many unanswered questions about sexual transmission, and studies of semen, vaginal fluids, and saliva are ongoing.

  • Can women transmit the infection to their sex partners?
  • Can asymptomatic infected individuals transmit the disease sexually? (The majority of infected people have no symptoms.)
  • How long does the virus remain infectious in semen? Live virus has been cultured from semen at least 14 days after the start of symptoms; virus particles in semen have been detected at least 62 days after symptom onset.
  • Can other fluids in addition to semen transmit Zika virus?
  • Does sexual transmission pose a different risk than mosquito-borne transmission for microcephaly and other congenital conditions.

Zika and pregnancy. The CDC has posted updated recommendations about Zika for women trying to conceive during the epidemic (including couples seeking infertility treatment).

In addition, the CDC offers ideas for a “Zika prevention kit” for pregnant women and a “Doctor’s Visit Checklist” for pregnant women who have travelled to an area where there is active Zika transmission.

For clinicians, the CDC has devised algorithms to assist in determining whether a pregnant woman (or, eventually, her new baby) should be tested for Zika virus, and in order to monitor pregnancies and outcomes during the epidemic, the CDC has instituted a Zika Pregnancy Registry. Clinicians should help to ensure that the following patients are referred to the Zika Pregnancy Registry:

  • pregnant women with lab evidence of Zika virus infection
  • babies born to these infected women, even when the babies are born with no evidence of Zika infection
  • babies with evidence of Zika virus infection or complications, even when their mothers were not known to be infected with Zika during the pregnancy (mothers of babies in this last category should be added retrospectively to the Registry)


Clinical editor, American Journal of Nursing (AJN), and epidemiologist


  1. Vianney R July 14, 2017 at 4:55 pm

    Ms. Todd,
    I am glad that your article depicts an update of the Zika virus in the United States as well as in the other 41 countries. Many were not aware of Zika in the United States until it affected the state of Florida specifically South Florida. We know how it can be contracted and few tests are available to be done to accurately find the virus in patients. I work in a NICU and we had cases of mothers exposed to Zika and children were being tested to see if they had contracted it. Also, we did have a case of a microcephaly child whose mother was from overseas test positive for Zika and had her child in South Florida. This is something commonly seen unfortunately in Zika zones like Brazil. That’s why prevention is key. The examples given how to protect people from contracting Zika either through mosquito bites or a partner need to be a constant reminder to people. The CDC removed Miami Dade County as a yellow zone for Zika as of June 2, 2017. This does not mean we should put our guard down. We can have latent mosquitoes or cases are yet to hear about. Meanwhile, third world countries are still battling this virus.
    Advice for people living in or traveling to South Florida. (2017, June 30). Retrieved July 14, 2017, from https://www.cdc.gov/zika/intheus/florida-update.html

  2. Angel A July 14, 2017 at 4:12 pm

    The spread of the Zika virus in the last few years has sparked great concerns in all of the dozens of countries that is has reached, initially it was thought to be a vector borne virus. Unfortunately, it is sad to see that mosquitos are not the only means of spreading the disease; sexual intercourse and bodily fluids has also been added as a possible transmission means of the virus, making it easier for the virus to spread across a wider audience.
    It is shocking to see the CDC’s recommendations for men, they call for men to abstain from having sexual intercourse from 8 weeks to 6 months after a potential exposure to the virus unless protection is used in the form of wearing a condom. It is interesting to see think how future research on the virus will help humanity fully understand Zika, and how is can be eradicated.

  3. Jennifer April 18, 2017 at 11:58 pm

    The Zika virus is very scary, you have to be very careful when going outside now days. It is incredible how the zika virus has spread so fast. reading this article, it is very interesting that zika virus can be spread from semen, and every man had symptoms. it was very interesting to to read about that there has not been any relapsing. This article is very knowledgeable as well as very educational.

  4. Lissa April 18, 2017 at 11:01 pm

    Dear Ms.Todd,
    The Zika virus has been a rapidly growing global health threat. What I found most concerning about this article are the teratogenic effects to fetuses and the various routes of transmission. Several cases have been identified in my home state, Florida. Per the Florida Department of Health in 2016 there were 276 cases of locally acquired Zika infections which has since decreased. As of 2017 only one case of locally acquired Zika has been identified. In 2016, out of the 1,384 cases identified 264 of the cases consisted of pregnant women. Are there any measures that can be taken to prevent transmission to the unborn fetuses similar to ways HIV transmission can be prevented from mother to child? Your blog has definitely expanded my knowledge of how the disease is transmitted, however I still have many unanswered questions. Since the virus has been detected in semen for at least 62 days, how long should one wait before attempting to conceive, men and women? What suggestions would you make to civilians in Zika infected areas to prevent contracting the disease?

    Florida Department of Health, Office of Communications. (n.d.). Department of Health Zika Update. Retrieved April 18, 2017, from http://www.floridahealth.gov/newsroom/2017/03/030217-zika-update.html

  5. David Ferrell April 18, 2017 at 5:55 pm

    Ms. Todd,
    I live in South Florida where there was an outbreak of Zika. I am very concerned with the teratogenic effects of Zika and how many ways it can be spread. South Florida is a hub that sees millions of visitors from many of the countries and territories that have a prevalence of Zika. I was not surprised when it showed up here, and when it was found in mosquitos on Miami Beach. What did surprise me is how quickly the spread has seemed to be controlled. There must be hundreds of visitors that carry Zika who are bitten by mosquitos here in Miami. Those mosquitos can then bite people who live here and therefore spread the virus. With the added complication of it also being able to be spread sexually as well, why aren’t we seeing an epidemic of Zika here?

  6. Nathalie Duran April 17, 2017 at 9:50 pm

    Ms. Todd,

    Unfortunately, Zika is still of concern across the globe without clear answers as to what it may cause in the long run. Your post stated many facts about the virus that I previously did not know about. As a nurse in a NICU setting it has been interesting to see how many infants have come through with Zika-like anomalies and yet test negative for the virus, I was not aware that although one tests negative it should not be ruled out.

  7. Ana Duran April 13, 2017 at 2:29 am

    Mrs. Todd,

    I found your update regarding ZIKA very informative. Globally, this pandemic is difficult to contain as it is spread by mosquito bite and sexual contact. The CDC guidelines and reccomendations for infection provention include simple articles such as mosquito repelent and condoms. Unfortunately, in rural countries or lower economic countries these simple items are not easily attainable. Lack of these basic articles allow opportunity for ZIKA to be spread which subsequently represents a global crisis. Hopefully with our continued global health efforts, transmission of this virus can be better contained.

  8. Alexander Collazo November 29, 2016 at 11:10 pm

    Zika, as time moves forward, is becoming less and less relevant to the lives of many living in infected areas. However, the reality remains that Zika is still a prominent issue, and one which we know little about. While the actual Zika virus was first discovered 69 years ago in Uganda, it has most recently become a global issue, infecting humans with a total of 14 cases in 2007 (Al-Abdely, 2016). As an extremely dangerous teratogenic viral infection, from what we know so far Zika is mainly through a mosquito bite, and as we all know mosquitos are everywhere. Working in a hospital, I have come to see the reality of Zika, as we are constantly drawing labs to check for Zika on many patients entering the ICU. Unfortunately, Globalization and urbanization has broken the barriers that limit epidemics to isolated areas and this has caused many viral outbreaks to run chaotically out of control. We can only hope that the CDC, amongst other major organizations in the world can continue to work together for the better of humanity.

    Al-Abdely, H. M. (2016). Zika: An emerging teratogenic virus. Saudi Medical Journal, 37(8), 831–833. http://doi.org/10.15537/smj.2016.8.15676

  9. Leah Pacheco November 29, 2016 at 7:00 pm

    The Zika virus has posed as a threat to several countries and it has hit close to home as numerous people have reported to be infected with the virus in South Florida. I think there are many unanswered questions regarding this virus, which causes people to have mixed feelings about this issue and, therefore, not take it seriously. Many women who have become infected have had to make difficult decisions during their pregnancy due to the likelihood of her child being born with severe birth defects such as microcephaly, which is when the infant is born with an abnormally small head. It’s important to remain safe and stay protected from mosquito bites especially if you live in areas that have reported cases.

  10. Vanessa L. November 29, 2016 at 4:27 pm

    The Zika virus is growing global health issue that has affected over 40 countries. What I found interesting about this topic is that not many know that the virus can be transmitted sexually. The Zika virus is not new however there is a lot of questions still unanswered about the virus. I think that as the years progress we will hopefully have more questions answered. I am surprise to learn that the length of infection is also still unknown. So far, the virus is thought to be lifelong. The virus was first discovered in the 1940’s and hopefully in the near future there will many new discoveries regarding treatment and transmission.

  11. Sandra Duran July 29, 2016 at 11:59 pm

    I believe that the Zika Virus poses a large threat to the United States, especially in the Eastern Coast. Some threats have already been documented in the Florida area. Working as a nurse in a pediatric ER setting it is definitely something I must be aware off. It’s important to keep ourselves informed, and educate the population in decreasing their risks. The Zika virus can definitely have devastating consequences to the pregnant woman, and developing fetus. I hope we are able to minimize the threat of infection in the population.

Comments are moderated before approval, but always welcome.

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