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  • Zika virus is transmitted to people primarily through the bite of an infected Aedes species mosquito (A. aegypti and A. albopictus). These are the same mosquitoes that spread dengue, chikungunya, and yellow fever viruses.
  • The mosquitoes typically lay eggs in and near standing water in things like buckets, bowls, animal dishes, flower pots and vases. 
  • They prefer to bite people, and live indoors and outdoors near people.
  • Mosquitoes that spread Zika are aggressive daytime biters.They can also bite at night.
  • Mosquitoes become infected when they feed on a person already infected with the virus. Infected mosquitoes can then spread the virus to other people through bites.

Sexual Transmission

  • What we know
    • Zika can be passed through sex from a person who has Zika to his or her sex partners. Sex includes vaginal, anal, oral sex, and the sharing of sex toys.
    • Sexual exposure includes sex without a condom with a person who traveled to or lives in an area with Zika.
    • Zika can be passed through sex, even if the person does not have symptoms at the time. It can be passed from a person with Zika before their symptoms start, while they have symptoms, and after their symptoms end. It may also be passed by a person who has been infected with the virus but never develops symptoms.
    • Current research shows that Zika can remain in semen longer than in other body fluids, including vaginal fluids, urine, and blood.
  • What we don't know
    • We don’t know if Zika can be passed through saliva during kissing.
    • We don’t know if Zika passed to a pregnant woman during sex has a different risk for birth defects than Zika transmitted by a mosquito bite.

Vertical Transmission

  • A pregnant woman can pass Zika virus to her fetus during pregnancy. Zika is a cause of microcephaly and other severe fetal brain defects. Infection during pregnancy has also been linked to adverse outcomes including pregnancy loss and eye defects, hearing loss, and impaired growth in infants. The full range of other potential health problems that Zika virus infection during pregnancy may cause is still under investigation.
    • Birth defects could include microcephaly, calcium deposits in the brain indicating possible brain damage, excess fluid in the brain cavities and surrounding the brain, absent or poorly formed brain structures, abnormal eye development, or other problems resulting from damage to the brain that affects nerves, muscles and bones, such as clubfoot or inflexible joints.
    • Pregnancy losses could include miscarriage, stillbirths, or terminations with evidence of the birth defects mentioned above.
  • To date, there are no reports of infants getting Zika virus through breastfeeding. Because of the benefits of breastfeeding, mothers are encouraged to breastfeed even in areas where Zika virus is found.
  • No evidence exists to suggest a non-pregnant woman who is infected with the Zika virus, whether symptomatic or not, will run risks of Zika related birth defects with future pregnancies.
  • To understand more about Zika virus infection, CDC established the US Zika Pregnancy Registry and is collaborating with state, tribal, local, and territorial health departments to collect information about pregnancy and infant outcomes following Zika virus infection during pregnancy.

Accidental Exposure

  • CDC is assisting in the investigation of a case of Zika in a Utah resident who is a family contact of an elderly Utah resident who died in late June of unknown causes but was subsequently confirmed to have had a Zika virus infection. The deceased patient had traveled to an area with Zika and lab tests showed he had uniquely high amounts of virus—more than 100,000 times higher than seen in other samples of infected people—in his blood. Laboratories in Utah and at the Centers for Disease Control and Prevention (CDC) reported evidence of Zika infection in both Utah residents. The living family contact has fully recovered from the Zika infection.
  • A University of Pittsburgh lab worker accidentally stuck herself with a needle on May 23, 2016 while working with the Zika virus, resulting in what appears to be the first known Zika infection through accidental needle stick. The employee subsequently exhibited symptoms associated with Zika. Whether she was pregnant at time of exposure was not indicated.


  • On October 20, 2016 news sources reported that the FDA has confirmed several units of donated blood in Florida have tested positive for Zika. As of this date, no transmission of the virus in the United States has been confirmed through transfusions.
  • On August 26, 2016 the Food and Drug Administration (FDA) issued a revised guidance recommending universal testing of donated Whole Blood and blood components for Zika virus in the U.S. and its territories.
    • Because all blood donations are now screened, donor screening as previously outlined in FDA’s February 2016 guidance can be discontinued.
    • If a donor volunteers a recent history of Zika infection, blood or blood components from that individual must not be collected. Such a donor should wait 120 days after a positive viral test or the resolution of symptoms, whichever timeframe is longer before donating.
  • The American Red Cross is following FDA blood donation guidance.

Zika and Animals

  • Nonhuman primates (apes and monkeys) have shown the ability to become infected with Zika virus, either naturally or experimentally.
  • At this time, there is no evidence that Zika virus is spread to people from contact with animals.
  • There have not been any reports of pets or other types of animals becoming sick with Zika virus.

Zika and Guillain-Barré Syndrome (GBS)

  • An increase in GBS has been observed in areas where a Zika virus epidemic has been documented (e.g., in French Polynesia and Brazil).
  • A direct causal relationship, however, has not been established between Zika viral infection and GBS.
  • Prior infection with dengue or genetic factors could contribute to or increase cases of GBS.

US States (CDC, 05/03/2017):

  • Locally acquired vector-borne cases reported: 224
  • Travel-associated Zika virus disease cases reported: 4973
  • Other:
    • Laboratory acquired cases reported: 1
    • Sexually transmitted: 46
    • Congenital infection: 29
    • Unknown: 1
  • Total: 5274

US Territories (CDC, 05/03/2017):

  • Locally acquired cases reported: 36431
  • Travel-associated cases reported: 143
  • Total: 36574 (In local Zika endemic areas, cannot determine mosquito vs sexual transmission)

Pregnant Women with Any Laboratory Evidence of Possible Zika Virus Infection (CDC, 04/25/2017):

  • US states and DC: 1793
  • US territories: 3700

Estimated range of Aedes aegypti and Aedes albopictus mosquitoes in the United States, CDC

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Symptoms, Diagnosis, Treatment


  •  Only about 1 in 5 people infected with Zika virus are symptomatic.
  • The illness is usually mild with symptoms lasting for several days to a week.
  • Common characteristic clinical findings are acute onset of fever with maculopapular rash, arthralgia, or conjunctivitis. Other commonly reported symptoms include myalgia and headache.
  • The incubation period (the time from exposure to symptoms) for Zika virus disease is not known, but is likely to be a few days to a week.
  • Rarely has Zika proven fatal.
  • Zika virus usually remains in the blood of an infected person for about a week but it can be found longer in some people.


  • Based on the typical clinical features, the differential diagnosis for Zika virus infection is broad. In addition to dengue, chikungunya, and yellow fever, other considerations include leptospirosis, malaria, rickettsia, group A streptococcus, rubella, measles, and parvovirus, enterovirus, adenovirus, and alphavirus infections.
  • In 2016, Zika virus disease became a nationally notifiable condition.
  • There are currently no commercially available diagnostic tests for Zika virus disease. The FDA has issued an Emergency Use Authorization (EUA) for a diagnostic tool for Zika virus that will be distributed to qualified laboratories and, in the United States, those that are certified to perform high-complexity tests.
  • During the first week after onset of symptoms, Zika virus disease can often be diagnosed by performing reverse transcriptase-polymerase chain reaction (RT-PCR) on serum. In addition, now urine samples should be collected less than 14 days after onset of symptoms for rRT-PCR testing. Virus-specific IgM and neutralizing antibodies typically develop toward the end of the first week of illness; cross-reaction with related flaviviruses (e.g., dengue and yellow fever viruses) is common and may be difficult to discern.
    • Due to concerns of microcephaly associated with maternal Zika viral infection, fetuses and infants of women infected with Zika virus during pregnancy should be evaluated expeditiously for possible congenital infection and neurologic abnormalities. Reporting through the CDC’s US Zika pregnancy registry is also strongly encouraged.


  • No vaccine is currently available nor are there specific medicines to treat Zika infections.
  • Treat the symptoms:
    • Get plenty of rest.
    • Drink fluids to prevent dehydration.
    • Take medicine such as acetaminophen (Tylenol®) to relieve fever and pain.
    • Do not take aspirin and other non-steroidal anti-inflammatory drugs; if dengue and not Zika, could potentiate Dengue Shock Syndrome.
    • If you are taking medication for another medical condition, talk to your healthcare provider before taking additional medication.
    • If you have Zika, prevent mosquito bites for the first week of your illness.
      •  During the first week of infection, Zika virus can be found in the blood and passed from an infected person to a mosquito through mosquito bites.
      • An infected mosquito can then spread the virus to other people.

Additional Resources

For Women Who Are Pregnant or Wish to Conceive

Zika Virus & Pregnancy

What we know

  • Pregnant women can be infected with Zika virus. 
  • The primary way that pregnant women get Zika virus is through the bite of an infected mosquito. 
  • Zika virus can be passed to a pregnant woman by a male or female sexual partner.
  • Pregnant women can pass Zika virus to her fetus. 
  • Zika virus can be passed from a pregnant woman to her fetus during pregnancy or at delivery.

What we do not know

  • If a pregnant woman is exposed, we don’t know how likely she is to get Zika.
  • If a pregnant women is infected:
    •  We don’t know how the virus will affect her or her pregnancy.
    • We don’t know how likely it is that Zika will pass to her fetus.
    • We don’t know if the fetus is infected, if the fetus will develop birth defects.
    • We don’t know when in pregnancy the infection might cause harm to the fetus.
    • We don’t know whether her baby will have birth defects. 
    • We don’t know if sexual transmission of Zika virus poses a different risk of birth defects than mosquito-borne transmission.

Healthcare Provider Evaluation

CDC recommends that pregnant women not travel to an area with active Zika virus transmission.

  • If a pregnant woman must travel to one of these areas, she should talk to her healthcare provider. If she travels, she should be counseled to strictly follow steps to avoid mosquito bites and prevent sexual transmission during the trip.
  • Use EPA-registered insect repellent; EPA-registered repellents including DEET are considered safe to use in pregnant and lactating women
  • Wear long-sleeved shirts and long pants to cover exposed skin
  • Wear Permethrin-treated clothes
  • Stay and sleep in screened-in or air-conditioned rooms
  • Aedes mosquitoes that transmit the Zika virus bite mostly during the daytime; however, practice mosquito prevention strategies throughout the entire day.
  • Obtain recent travel history from pregnant women.
  • If history of travel to an area with ongoing Zika transmission during pregnancy is present:
  • Evaluate for symptoms of Zika virus and other related viruses (dengue and chikungunya) during or within 2 weeks of travel.
  • If a pregnant woman has a partner (male or female) who lives in or has traveled to an area with Zika, she should use a condoms or other barrier protection every time she has sex or should not have sex with that partner for the duration of her pregnancy. Sex includes vaginal, anal and oral sex, and the sharing of sex toys. Barrier protection includes male or female condoms for vaginal or anal sex, as well as dental dams for oral sex.
  • The type of testing recommended varies depending on the time of evaluation relative to symptom onset or last date of possible exposure.
  • Testing of serum and urine by rRT-PCR is recommended for pregnant women who seek care up to 2 weeks after symptom onset or last date of possible exposure. A positive rRT-PCR test confirms the diagnosis of recent maternal Zika virus infection.
  • For pregnant women who seek care 2-12 weeks after symptom onset or last date of possible exposure, serologic assays can be offered to detect Zika virus-specific IgM antibodies.
  • Immediate rRT-PCR testing is now recommended for women who have a positive or equivocal Zika virus IgM result, because it provides the potential for a definitive diagnosis of Zika virus infection.
  • Negative rRT-PCR results should be followed up with plaque reduction neutralization testing to measure virus specific neutralizing antibodies to confirm the presence of an immune response to a flavivirus infection and to differentiate Zika infection from other similar illnesses.

For Women of Reproductive Age

  • In the context of Zika virus transmission, it is important for women and their partners to plan their pregnancies. Health care providers should discuss reproductive life plans, including pregnancy intentions and timing with women of reproductive age.
  • Healthcare providers should ensure that women who want to delay or avoid pregnancy have access to safe and effective contraceptive methods that best meet their needs. Women and their partners who do not want to get pregnant now should use the most effective birth control correctly and consistently.
  • Healthcare providers for women and men residing in areas with active Zika virus transmission who have Zika virus disease should recommend they wait to attempt conception until the risk of viremia or viral shedding in semen is believed to be minimal.
  • For women and men who have been diagnosed with Zika virus or who have symptoms of Zika, like acute onset of fever, rash, joint pain or conjunctivitis after possible exposure to Zika virus, CDC recommends:
  • Women to wait at least 8 weeks after their symptoms first appeared before trying to get pregnant.
  • Men to wait at least 6 months after their symptoms first appeared. Men should be counseled to also correctly and consistently use condoms for vaginal, anal, and oral (fellatio) sex or abstain during this time period if they are concerned about the possibility of transmitting Zika virus to their sex partners.
  • For men and women without symptoms of Zika virus but who had possible exposure to Zika who do not reside in an area with active Zika virus transmission, healthcare providers should recommend their patients wait 8 weeks after their possible exposure before trying to get pregnant. Men should correctly and consistently use condoms for vaginal, anal, and oral sex or abstain from sex during this time period if they are concerned about the possibility of transmitting Zika virus to their sex partners.

Additional Resources:

Prevention & Vector Control

Zika virus is transmitted primarily to people through the bite of an infected Aedes species mosquito. Hence, mosquito control and bite prevention remains the best methods for minimizing viral spread.

When traveling to countries where Zika virus or other viruses spread by mosquitoes are found, take the following steps:

  • Wear long-sleeved shirts and long pants.
  • Stay in places with air conditioning or that use window and door screens to keep mosquitoes outside.
  • Sleep under a mosquito bed net if you are overseas or outside and are not able to protect yourself from mosquito bites.
  • Use Environmental Protection Agency (EPA)-registered insect repellents. All EPA-registered insect repellents are evaluated for effectiveness.
  • Always follow the product label instructions
  • Reapply insect repellent as directed.
  • Do not spray repellent on the skin under clothing.
  • If you are also using sunscreen, apply sunscreen before applying insect repellent.

If you have a baby or child:

  • Do not use insect repellent on babies younger than 2 months of age.
  • Dress your child in clothing that covers arms and legs, or
  • Cover crib, stroller, and baby carrier with mosquito netting.
  • Do not apply insect repellent onto a child’s hands, eyes, mouth, and cut or irritated skin.  Adults: Spray insect repellent onto your hands and then apply to a child’s face.
  • If you use both sunscreen and insect repellent, apply the sunscreen first and then the repellent.
  • Treat clothing and gear with permethrin or purchase permethrin-treated items.
  • Treated clothing remains protective after multiple washings. See product information to learn how long the protection will last.
  • If treating items yourself, follow the product instructions carefully.
  • Do NOT use permethrin products directly on skin. They are intended to treat clothing.

If you have the Zika virus, protect others from getting sick

  • During the first week of infection, Zika virus can be found in the blood and passed from an infected person to another mosquito through mosquito bites. An infected mosquito can then spread the virus to other people.
  • To help prevent others from getting sick, avoid mosquito bites during the first week of illness.

Community Efforts

Before mosquito season

  • Conduct public mosquito education campaigns focusing on reducing or eliminating larval habitats for the Ae. aegypti and Ae. albopictus vectors
  • Conduct surveys to determine abundance, distribution, and type of containers; large numbers of containers may translate into high mosquito abundance and high risk
  • Initiate a community wide source reduction campaign – the goal of the campaign is to motivate the community to remove and dispose of any water holding containers
  • Cover, dump, modify or treat large water-holding containers with long-lasting larvicide

Beginning of mosquito season

  • Continue public education campaigns focusing on reducing or eliminating larval habitats for Ae. aegypti and Ae. albopictus vectors
  • Develop and distribute mosquito education materials about Ae. aegypti and Ae. albopictus and personal protection measures
  • Initiate Ae. aegypti and Ae. albopictus community-wide surveys to:
  • determine presence or absence
  • estimate relative abundance
  • determine distribution
  • develop detailed vector distribution maps
  • evaluate the efficacy of source reduction and larvicide treatment
  • Continue/maintain community source reduction efforts.
  • Initiate adult sampling to identify or confirm areas of high adult mosquito abundance
  • Initiate preventive adult control to reduce adult populations targeting areas of high mosquito abundance
  • Concentrate control efforts around places with high mosquito density

Additional Resources:

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