Infections
Zika-virus IgM
Antibodies that may point to a recent infection with the Zika virus; hard to interpret because of cross-reaction with dengue.
Everything about this testWhat it measures
The Zika virus is transmitted by a mosquito and occurs in parts of Central and South America, the Caribbean, Asia and Africa. During an infection, the immune system first makes IgM antibodies (defense proteins), which disappear again after a few weeks to months. IgM is therefore a sign of a recent infection. According to the LCI guideline (RIVM), serology is only useful from about six days after the start of symptoms; in the first week, a PCR on blood is the appropriate test, and in urine the virus can be detected up to about thirty days.
- A possible recent infection with the Zika virus, usually after a stay in an area where the virus occurs
Positive
IgM antibodies were found that fit a recent infection with the Zika virus. A positive result is not proof on its own: the Zika virus closely resembles other viruses from the same family, such as dengue and yellow fever virus, and a vaccination against yellow fever or a previous dengue infection can also make the test positive. According to the LCI guideline (RIVM), a neutralization test in a specialized laboratory is needed to confirm the diagnosis. A Zika infection causes no symptoms in about 75 to 80 in 100 people; those who do get symptoms usually have a mild fever, rash, red eyes and pain in the joints and muscles, for two to seven days.
Negative
No IgM antibodies were found. That makes a recent Zika infection less likely, but does not rule it out: in the first days after the start of symptoms IgM is often not yet detectable, and according to the LCI guideline (RIVM) a negative result does not rule out an infection. With symptoms in the first week after returning, a PCR on blood or urine is the appropriate test. After a few months IgM disappears again, even if there has been an infection.
If your result is abnormal
With a positive result, a neutralization test is done in a specialized laboratory to distinguish it from dengue and other related viruses; with symptoms in the first week, a PCR on blood and urine is also done. In pregnancy, referral to a gynecologist follows for extra ultrasound scans. There is no treatment against the virus itself. Zika is notifiable (group C) in a number of situations: in pregnancy, with complications such as Guillain-Barré syndrome or a birth defect, and with hospital admission within four weeks after the start of the infection.
Reliability
According to the LCI guideline (RIVM) on Zika virus infection, serology is hard to interpret because of cross-reaction with other viruses from the flavivirus family, such as dengue and yellow fever virus. A positive result must be confirmed with a neutralization test; a negative result does not rule out an infection. In the first week after the start of symptoms, a PCR on blood and urine gives a clearer answer. The test is intended for people with symptoms or a specific question after travel, not as a general check-up.
Limitations
- Cross-reaction with dengue, yellow fever virus and other related viruses, including after a vaccination against yellow fever, can give a falsely positive result.
- In the first days after the start of symptoms, IgM is often still negative.
- IgM disappears after a few weeks to months; after that, a negative result says nothing about a past infection.
- The result does not say when the infection took place, which is especially important around a pregnancy.
How common is this
The Zika virus is not transmitted in the European Netherlands, because the mosquito that spreads the virus does not occur here; infections are picked up while traveling. In the Caribbean Netherlands there was an outbreak in 2016 and 2017. Since November 2016, a Zika infection has been diagnosed in fourteen pregnant women in the Netherlands, with one child born with an abnormally small head and one case of Guillain-Barré syndrome.
Who is this useful for
The result says the most with symptoms that fit Zika (fever, rash, red eyes, joint pain) after a stay in an area where the virus occurs, and with a pregnancy or a wish to become pregnant after such a stay. In people without symptoms and without a pregnancy question, the result is hard to interpret and falsely positive results due to cross-reaction are relatively common.
Downsides and risks
- A falsely positive result due to cross-reaction with dengue or a yellow fever vaccination can cause a lot of worry, especially during pregnancy or when planning a pregnancy.
- A negative result can give false reassurance, because IgM may still be absent early in the infection and disappears again after a few months.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results