“Will Zika return? What pregnant women and others need to know about this frightening disease”
“1 in 7 babies exposed to Zika in the womb have health problems”
“A ‘perfect storm’ for the future spread of the Zika virus”
Viruses like Zika have been the subject of intense media attention, particularly since the widely publicized outbreaks in South America began. It’s well-known that fetuses and newborns who carry the virus are at risk of permanent health issues – but how can doctors conclusively identify those infected?
Felix Drexler, Head of the Virus Epidemiology Group at the Charité – Universitätsmedizin Berlin, explains that current diagnostic methods for Zika and similar viruses face one common denominator: low sensitivity. “This applies to molecular methods, because viremia is super low and super short-lived, and also antibody tests – the latter in particular in tropical areas,” he says. “People with multiple flavivirus infections mount weaker IgM responses, and these people are so full of antibodies against common flavivirus epitopes that serological test specificity diminishes greatly.”
These complications can lead to false-positive results – a dangerous situation in general, but especially so for patients in outbreak regions or those without quality health care. Women may choose to terminate a pregnancy that might otherwise be healthily carried to term – and, in cases where safe reproductive care is difficult to access, such choices can be fatal.
Why are false positives so prevalent? Partly laboratory contamination and partly low test specificity. Drexler and his colleagues experimented with using IgA as a marker for acute infection (rather than the standard IgM approach) and saw markedly increased sensitivity (1). “At least 50 percent in our study,” says Drexler. “IgM and IgA may jointly allow high sensitivity and specificity. IgG increases in paired sera add significantly to this.”
Combined antibody testing offers new diagnostic options for not only Zika, but also for other viruses, such as Middle East Respiratory Syndrome (MERS) coronavirus. If laboratory medicine professionals can distinguish between infections caused by different viruses, it helps patients and primary care providers to understand how best to proceed after diagnosis – hopefully, saving lives.
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References
- FA Bozza et al., “Differential shedding and antibody kinetics of Zika and chikungunya viruses, Brazil”, Emerg Infect Dis, 25, 311 (2019). PMID: 30666934.
