The Institute of Tropical Medicine in Antwerp (ITM) has developed a test that can confirm an infection with the Zika virus even after the acute infection phase. A correct diagnosis is especially important for pregnant women because of the potential risks for the unborn baby if the mother is infected. With the neutralization test, the ITM Reference Laboratory, which analyses all suspicious Zika samples in Belgium, can confirm Zika virus infections in case of doubt.

This is a transmission electron micrograph (TEM) of Zika virus/Cynthia Goldsmith
This is a transmission electron micrograph (TEM) of Zika virus/ Cynthia Goldsmith

Zika is a flavivirus related to the dengue, yellow fever and West Nile viruses. The virus causes fever and is transmitted by the Aedes mosquitoes that bite mostly during the daytime. Only one in five people infected with the Zika virus become ill. About 80% will present no symptoms.

In order to establish a Zika infection with certainty, the virus itself has to be detected in blood or other body fluids. At ITM, the virus is detected using a molecular test called PCR (polymerase chain reaction). Unfortunately, this test is only useful for a limited period, about five to seven days after infection. After that period, the presence of antibodies indicates exposure to the virus, but currently used tests do not allow drawing firm conclusions. The new ITM test helps to diagnose a Zika infection with certainty even in the later, post-acute phase. The test was developed in less than two months.

“In the neutralization test in the laboratory, the virus is added to a blood sample of the patient. That way we can see if antibodies against Zika virus are present and we can distinguish them from antibodies against related viruses,” said Prof. Kevin Ariën, Head of the Unit of Virology at the ITM.

The new test is fairly complex, but it provides significant added value, especially for pregnant patients.

“Due to the potential risk of abnormalities in the foetus, a precise diagnosis is crucial for pregnant women. With the neutralization test, we can eliminate all doubt,” according to Dr. Marjan van Esbroeck, Head of the Clinical Laboratory and the National Reference Centre for Arboviruses at ITM.

The laboratory analyses between 20 and 40 suspected Zika blood, urine and semen samples each week. A total of 12 Zika infections have been diagnosed so far in returning travelers, three of which were confirmed using the new neutralization test.

ITM advises pregnant women, or women trying to become pregnant during or after their stay abroad, to postpone all travel to areas where a Zika virus outbreak is ongoing (South and Central America, the Caribbean, some islands in the Pacific). If the trip cannot be postponed, travelers are advised to consult a doctor in advance to discuss preventive measures.