The Language of Zika Virus Testing

The language of Zika virus testing


When a new virus emerges or an old one re-emerges, one of the earliest conversations is about whether there exist good tests to detect it. Laboratory testing takes different forms but remains key to understanding whether an emerging virus is or was present in a suspected case of infection. Testing is the first step in understanding how many cases have occurred, how long they have been occurring, the range of disease outcomes possible or whether there really is any link between detection of the virus and disease. Virus tests have indeed kept pace with the latest emerging virus outbreaks, but perhaps virus testing has not.

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If a disease is thought to be caused by a virus, laboratory testing is usually needed to confirm the virus is there. Which patients are sampled for testing, what samples are collected, what tests are used and whether and how the results are reported are all affected by the same politics of life that are found in any human decision making process.

In recent years there have been lots of news stories about scary-sounding outbreaks of new viruses we knew about, but ignored. Sometimes the commentary describes the lack of any test for the virus. This may be true when the outbreak occurs in a region of the world with few resources, limited experience or testing expertise. Sometimes the message is just confused, misleading or plain wrong.

A primer on human virus testing

Laboratory virus testing usually involves the polymerase chain reaction (PCR) which can detect small amounts of the virus’ genetic code in a sample from a sick person. Different testing involves finding evidence that the person was infected previously, by showing a change in their immune response (antibodies) to the virus. A “routine” lab can return a single result in six to eight hours if the specimen is appropriate, no technical problems occur, no repeat or add-on testing is required, and if result reporting is straightforward. There is a third group of tests – which can cover virus, antibody or other chemistry – that can be done at the point of care (POC) – these aim to be fast, inexpensive and more simple to interpret.

Routine lab tests can be performed in the clinic, as they are created or assembled by the laboratory, or they may come in ready-to-use commercial kits. Which type of test is used depends on local guidelines and regulations (which vary around the world) and on the skills and capacity of the laboratory to create, optimise, validate and oversee in-house testing. A major benefit of using a commercial kit is that reliability is assured. All the hard work of validating the test for a range of different sample types and conditions has already been done by the company. There can still be a few issues with kits. For example, supply when demand is high, cost, and requirements for supporting reagents and equipment. Kit validation should also (but sometimes does not) consider and account for the impact of region-specific co-circulating pathogens. For example dengue and chikungunya viruses in areas where Zika virus (ZIKV) transmission is active.

Recent testing times

When Middle East respiratory syndrome (MERS) emerged, the narrative often focussed on the absence of good testing for its causal coronavirus (MERS-CoV). In reality, a reliable and robust PCR-based test, still widely used today, was described almost immediately.[1] Testing was available, but understanding of the importance of testing may have been the more critical shortfall.[2] Faster POC testing may have helped contain early spread from the very first, or index, case that triggers an outbreak in a healthcare setting.[3]

understanding of the importance of testing may have been the more critical shortfall

The Zaire ebolavirus (EBOV) epidemic took place in a part of the world where modern testing was not resourced and unable to cope with the unexpected speed and ferocity of EBOV transmission.[4] Many good PCR-based tests were in use or in readiness around the world, but could not be used in West Africa, which lacked the supporting infrastructure of laboratories, equipment and trained personnel. Here, ready-to-go rapid, inexpensive, sensitive and specific POC tests would have been very useful for improved triage of suspected cases.[5]

Zika virus tests us more than we test for it

Forty countries have confirmed local ZIKV transmission since 2015 and once again we see claims that testing is inadequate.[6, 7] But precisely what about the testing is inadequate?

Whether because of limited resources, habit, mindset or simply the scale of the epidemics, some countries have reported ZIKV-positive lab results on only a small fraction of suspected positive patients. It is presumably hoped that these limited data will accurately represent the rise and fall of the epidemic. Clinical assessment is relied upon to document ZIKV presence. Clinical diagnosis is not accurate because the symptoms are indistinguishable from those due to other co-circulating viruses such as dengue, chikungunya and others that can cause rash and fever. We also know from a study in 2007, that up to 80% of ZIKV infected people may not have any signs of acute disease.[8]

ZIKV persists for a shorter time in serum than other viruses, yet serum is the commonly used sample for ZIKV testing. ZIKV is reportedly found for longer periods in whole blood and urine.[9] So PCR tests need to be performed fairly early on in the infection. There are good, highly specific ZIKV PCR tests that can detect infection [10, 11] and new ones that are being developed.[12]

There is a known issue of cross-reactivity in testing antibody responses to infection by flaviviruses, the family of viruses that ZIKV is part of.[13]  A person who has high levels of antibodies against dengue virus [14] or West Nile virus [8, 15] for example, may show a positive result in a ZIKV antibody test.  It is often hard to be sure whether that is because of true cross-reaction (the antibodies to different viruses both bind the same substrate used in the test) or because the person has been infected by both of the viruses, either at the same time, or consecutively. Collecting two serum samples, two weeks apart is essential. Different antibody detection tests, protocols, laboratories and approaches all perform differently. Specific ZIKV antibody test results are possible, but they require a good quality method that has been well validated, ideally with additional testing for other mosquito-borne viruses likely to be in the same geographic region.[16]

It is hard to tell how often or exactly which of these tests are being used in the current epidemics because testing methods or findings are not always reported. There is no POC testing available for ZIKV.

What we need more of

When we read about a lack of tests or testing, what can be meant is that the tests we have are not easily available in sufficient quantities for the demand, they are not in kit form, they are not rapid, sensitive and specific, competitively priced or are simply not used. POC testing is a tool ideally suited to help contain outbreaks because it can be used when and where needed, to inform public health decisions and to aid infection control; for viruses the reality of POC testing has to date fallen far short of the promise.[17, 18]

That said, we do have the technology for slower but very sensitive and specific testing and a world of expertise in that space. The major roadblock to improve testing is us; humans make the call as to whether innovative new or trusted traditional tests for a new or emerging virus are developed, deployed and funded for sufficient use to make it possible to truly understand a new or emerging disease.


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  2. Pereyaslov D, Rosin P, Palm D, Zeller H, Gross D, Brown CS, et al. Laboratory capability and surveillance testing for Middle East respiratory syndrome coronavirus infection in the WHO European Region, June 2013. Euro Surveill. 2014;19(40):20923. PubMed PMID: 25323078.
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  6. Pan American Health Organization. HomeHealth TopicsProgramsMedia CenterPublicationsDataCountries and CentersAbout PAHO Regional Zika Epidemiological Update (Americas) – 14 July 2016: Pan American Health Organization; 2016 [updated 14/7/201616/7/2016]. Available from:
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  9. Lustig Y, Mendelson E, Paran N, Melamed S, Schwartz E. Detection of Zika virus RNA in whole blood of imported Zika virus disease cases up to 2 months after symptom onset, Israel, December 2015 to April 2016. Euro Surveill. 2016;21(26). doi: 10.2807/1560-7917.ES.2016.21.26.30269. PubMed PMID: 27386894.
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Katherine Arden
Katherine was awarded her PhD on the control of replication of HIV-1, from the University of Queensland (UQ) in 1999. She has completed postdoctoral research including promoter studies of ion channels in the Department of Physiology and Pharmacology, UQ; trafficking of iron-related proteins in haemochromatosis at the Queensland Institute of Medical Research; and the detection, culture, characterisation and epidemiology of respiratory viruses while working at the Qpid laboratory, Sir Albert Sakzewski Virus Research Centre. She has since left the bench and is working as a freelance science and medical writer, while gaining greater hands-on experience of respiratory viruses from her children.
Ian M Mackay, PhD
Ian completed undergraduate studies in Medical Laboratory Science at the Queensland University of Technology, Australia. Between 1992 and 2015 he was a Research Assistant, PhD student, post-doctoral group leader, Chief Investigator and Associate Professor in virology at the Royal Children’s Hospital and The University of Queensland. Ian left research for a Supervising Scientist role detecting viral threats to the public’s health, for Queensland Health. Ian designs, validates and conducts investigations which support clinical and public health need, helping to discover and characterize known, new, newly identified and rare viruses. Apart from several editorial roles, he reviews for journals and granting bodies. He enjoys spending time with his family, cat and writing for his blog and is an avid Star-anything fan.


  1. Katherine and Ian

    Thanks for the very insightful article on Zika testing. As the number of reported cases in the Miami Florida area from mosquito-borne Zika infection has grown to 30 reported cases as 8/15/16, both the CDC and the Governor of Florida announced plans last week for the need for more robust Zika testing in the area, especially among pregnant women.

  2. Zika Testing News Story 9/28/16

    The Washington Post ” CDC whistleblower: CDC is using wrong Zika test”
    Robert Lanciotti is one of the leading experts on the Zika virus and is Chief of the CDC lab responsible for developing tests to diagnose viral diseases such as Zika that are transmitted by mosquitoes, ticks and fleas.

    Lanciotti was actually demoted in May after he raised fears inside and outside the agency when the CDC recommended a new test for Zika. He stated publically that the new test was less effective and missed 40% of Zika infections. The scientist was reinstated after a whistleblower lawsuit. The CDC has now acknowledged testing for Zika is “difficult and needs to be improved.”

    Amazing but true-DM