To diagnose a Zika virus infection
Zika Virus Testing
When you develop a fever, rash, joint pain, and conjunctivitis (pink eye) after traveling to an area where Zika virus is endemic or have symptoms and had sexual contact with someone who recently traveled from an area where Zika is present; if you are pregnant and have traveled to an area where Zika is active, regardless of symptoms; or when a baby is born with microcephaly (small head)
A blood sample drawn from a vein in your arm and/or a urine sample collected in a clean container; less commonly cerebrospinal fluid (CSF) or amniotic fluid
Zika is a viral infection that is spread primarily by the bites of infected Aedes mosquitoes and less commonly by sexual transmission. Testing detects the genetic material (RNA) of the Zika virus in blood, urine, cerebrospinal fluid (CSF), or amniotic fluid or detects antibodies in the blood produced in response to Zika virus infection.
About 80% of individuals infected with Zika virus will have no symptoms at all, while others will have only mild illness. For people who do develop symptoms, prognosis is very good for full recovery. The most common initial symptoms of Zika include fever, rash, joint pain, and conjunctivitis (pink eye) lasting from a few days to a week. These symptoms are similar to other mosquito-borne illnesses like dengue fever and chikungunaya. The similarities between Zika symptoms and other diseases mean that laboratory testing is essential to diagnosing Zika virus.
Zika virus infection is typically diagnosed with blood and urine tests. Laboratory tests may include either molecular tests for Zika virus (PCR), which detect the presence of the virus itself, or an antibody test that detects antibodies produced by the immune system after a person has been exposed to the virus.
Since the first human case of Zika virus in 1952, outbreaks have been reported in Africa, Southeast Asia, and the Pacific Islands. Zika was found in Brazil in May 2015, representing the virus' first introduction to the Americas. Since then, it has rapidly spread through the Americas. Check the Centers for Disease Control and Prevention (CDC) web page for updates and more information about Zika virus status in the U.S.
While most people infected with the Zika virus do not develop noticeable or severe symptoms, it can cause risk of serious complications for a pregnant woman and her unborn child, including miscarriage and birth defects. Starting in May 2015, Brazilian health officials reported an increase in Zika infections along with an uptick in babies born with microcephaly (smaller than expected heads). Since the outbreak that started in Brazil, the CDC has confirmed that Zika virus infection during pregnancy can cause severe microcephaly and other birth defects.
Babies with microcephaly have much smaller heads than normal and severe microcephaly causes a range of lifelong problems, including developmental disabilities, seizures, hearing loss, and vision loss. Scientists are still learning about other impacts of Zika infection during pregnancy. If you are pregnant or considering pregnancy, the CDC web page has up-to-date recommendations on how to protect yourself.
In rare cases, Zika virus is also linked to the development of Guillain-Barré syndrome (GBS). GBS is an autoimmune disorder that causes the body to attack its own nervous system, causing muscle weakness and paralysis. Researchers are still working to understand what causes GBS, but most people with GBS develop it after a viral or bacterial infection. The CDC is still investigating the relationship between Zika and GBS.
In January 2016, the CDC issued a travel alert for areas of the world where Zika virus is circulating. The alert recommends that pregnant women avoid travel to certain areas with Zika, and that women considering pregnancy consult their healthcare providers before traveling to those areas. There is currently no vaccine or treatment for Zika virus. Avoiding Aedes mosquito bites is the best way to prevent a Zika infection.
Since information about Zika is changing quickly, check the CDC's web site for the latest on the virus.
A blood sample is collected by inserting a needle into a vein in the arm. A urine sample is collected by voiding into a clean container. Sometimes, a healthcare practitioner may collect a sample of cerebrospinal fluid or amniotic fluid.
No test preparation is needed.
- How is it used?
Zika virus testing is used to detect a Zika infection in a person without signs and symptoms and to determine whether a person with signs and symptoms of Zika has been infected after exposure in a region with Zika virus. It may also be used to test people who have had sexual contact with a recent traveler to a country with Zika.
Zika infection may be difficult to diagnose without laboratory tests because symptoms may resemble those of other diseases, such as dengue fever or chikungunya infection, or the patient may be asymptomatic. Currently, two types of testing are available:
Molecular tests for Zika virus (PCR)—these detect the presence of the RNA of the virus and can diagnose Zika infection if tested within a week after the onset of symptoms. One type of Real Time RT-PCR test can detect Zika and the two other mosquito-borne viruses, dengue and chikungunya, and distinguish between the three. This test can be used on blood, cerebrospinal fluid (CSF), amniotic fluid, or urine samples.
Molecular tests of blood are not likely to detect Zika after 7 days of illness. Urine testing can detect Zika RNA for at least two weeks after symptoms begin. According to a recent study, urine may be the preferred specimen for detecting Zika RNA during the first three weeks of illness. If urine and blood specimens are taken less than 7 days after the onset of illness, the Centers for Disease Control and Prevention (CDC) recommends testing both samples.
If the result of a PCR test is negative, an antibody test can be used to help establish a diagnosis, according to the CDC (see below).
Antibody blood tests—these detect the IgM class of antibodies produced by the immune system when a person has been exposed to the virus. An antibody test may be used following a negative result on a PCR test or as alternative test for individuals who may have been infected but the length of time has passed when PCR can be performed. IgM antibodies appear in the blood 4 to 5 days after the start of the illness and last for about 12 weeks. Performing the test outside this window can yield false-negative results.
IgM antibody tests can be positive if a person has been infected with a similar virus, such as dengue (called cross-reaction). If an initial IgM antibody test is positive, a second test called the Plaque Reduction Neutralization Test (PRNT) is used to confirm the presence of antibodies to Zika virus and to help rule out other viral infections.
The amount of time that it takes for test results to become available can vary depending on where the person being tested is located and whether the state public health laboratory is performing Zika testing. Some samples may need to be sent to the CDC for testing. In general, it may take about three weeks for results, according to the CDC.
- Molecular tests for Zika virus (PCR)—these detect the presence of the RNA of the virus and can diagnose Zika infection if tested within a week after the onset of symptoms. One type of Real Time RT-PCR test can detect Zika and the two other mosquito-borne viruses, dengue and chikungunya, and distinguish between the three. This test can be used on blood, cerebrospinal fluid (CSF), amniotic fluid, or urine samples.
- When is it ordered?
Zika testing may be ordered when an individual has signs and symptoms associated with Zika infection and recently traveled to areas where the virus is actively spread by mosquitos or had sexual contact with someone who recently traveled from an area where Zika is present.
Signs and symptoms of Zika typically last between 2 and 7 days. Some of the main signs and symptoms include:
- Joint pain
- Conjunctivitis (pink eye)
According to CDC guidelines, asymptomatic pregnant women who have recently traveled to an area with active Zika transmission may be offered the antibody test. Pregnant women who have had sexual contact with a recent traveler to a country with Zika may also be tested.
Testing may be performed when a newborn has microcephaly (an abnormally small head). If a person has Guillain-Barre syndrome and is at risk for Zika virus, that person may be tested.
- What does the test result mean?
- A PCR test that detects the RNA of the virus is generally considered the most reliable means of diagnosis. A positive PCR result for Zika is considered conclusive. All positive results should be reported to the state public health department.
A negative PCR result may indicate that no infection is present or that the level of virus is too low to detect. This can happen if the blood test is performed after the 7-day window and/or the urine test is performed after the 2 to 3-week window during which the virus is present in the sample. The CDC recommends that antibody testing be done following a negative PCR result (see below).
- A positive IgM test for Zika antibodies is followed by a second test called the Plaque Reduction Neutralization Test (PRNT), which is used to confirm the presence of antibodies to Zika virus. No patient management decisions should be made based on IgM blood tests (serology) alone until the PRNT is completed because of the risk of false-positive results. A PRNT positive for Zika virus and negative for dengue virus is indicative of recent Zika virus infection.
Negative tests for IgM antibodies do not rule out the possibility of Zika virus infection. A negative result may mean that the individual tested does not have a Zika infection and symptoms are due to another cause. It may also mean that the level of antibody may be too low to measure. The person may still have a Zika infection; it may just be that it is too soon after initial exposure to the virus to produce a detectable level of antibody. Early in the infectious process before the production of antibodies, PCR testing (above) may be performed when testing is done within 7 days of illness.
Since information about Zika is changing quickly, check the CDC's web site for the latest on the virus and testing.
- Is there anything else I should know?
Tests for the Zika virus or antibodies do not provide any information about fetal health in pregnant women with Zika virus.
Physical symptoms like rash or aching joints are not a reliable means for diagnosing Zika because the symptoms are not specific to Zika.
The U.S. Food and Drug Administration (FDA) has directed blood collection facilities to screen all donated blood and blood components for the Zika virus. The FDA approved two investigational tests for this purpose. The tests were approved under an "investigational new device (IND)" protocol and did not go through the standard regulatory process prior to implementation, which can be time-consuming. The tests screen for the presence of the virus by detecting its genetic material (RNA). Units of blood that test positive for the virus are removed from the supply and not used for transfusions.
- How long does it take to get results?
The amount of time that it takes for results to become available can vary depending on where you are located and whether your local or state public health laboratory is performing Zika testing. Some samples may need to be sent to the Centers for Disease Control and Prevention (CDC) for testing. Test results may be available within 3 weeks. However, it may take longer during the summer when arbovirus (viruses spread by bites of mosquitos and ticks) activity is high.
- Can Zika virus be passed from person to person?
Yes. It can be spread from a pregnant woman to her developing baby. In rare cases, it can be spread from person-to-person through sexual contact. The CDC recommends that until more is known about Zika and pregnancy, pregnant women use condoms with male sexual partners who have lived or traveled to areas with Zika. In rare cases, Zika may be transmitted through blood transfusion or organ donation. Health officials are still investigating reports of Zika transmission via blood transfusion in Brazil.
- Can Zika be prevented?
Currently, there is no Zika vaccine available and no treatment for the virus. Limiting exposure to the virus primarily depends upon protecting against mosquito bites. To avoid mosquito bites:
- Wear long-sleeved shirts and long pants, preferably light-colored.
- Use EPA-registered insect repellents containing DEET, picaridin, oil of lemon eucalyptus (OLE), or IR3535m and only used as directed, including precautions for pregnant women and children.
- Treat shoes, socks, pants, and tents with permethrin, a repellant.
- Sleep in rooms that are screened against insects or sleep under a mosquito net.
Empty water from mosquito breeding sites, such as buckets, pots, or old tires.
Since Zika can be spread through sexual contact, you can help protect yourself by using a condom correctly and consistently when you have sex. The only way to be sure to avoid getting Zika through sexual contact is by abstaining from sex.
- If I have had a Zika infection, can I get it again?
If you've been infected with Zika once, it's unlikely that you will be infected again.