What Medical Laboratories Need to Know About Zika Virus

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Infectious Disease Expert Talks about Diagnostic Tests in Q&A Podcast with ASCP’s Lab Medicine

What do pathologists and medical laboratory professionals need to know about the Zika virus? Michael Diamond, MD, Ph.D., Professor of Medicine, Molecular Microbiology and Pathology Immunology at Washington University School of Medicine, St. Louis, talked about the tests used to diagnose the Zika virus in a recent Q&A interview with Kelly Swails, MT(ASCP), Web Editor of ASCP’s Lab Medicine. To listen to the interview via podcast, go to http://labmed.oxfordjournals.org/page/zika-virus-podcast.

“ASCP is always looking out for pathologists and laboratory professionals. This educational podcast will provide our members with the knowledge they need,” Ms. Swails says. “We need to be on the forefront of the epidemic. If it spreads the way that health experts think it might, pathologists and lab professionals need to be prepared for it.”

Currently, there is no vaccine or medication to prevent the Zika virus. Outbreaks have been reported in many countries, particularly in the Americas, and health officials anticipate the virus will continue to spread and it will be difficult to determine how and where the virus will spread over time. Areas affected by Zika virus outbreaks have also reported an increased incidence of birth defects and Guillain-Barré syndrome.

There are a few different tests used to diagnose the virus. The gold standard of testing for the Zika virus—isolating the virus—is done at the Centers for Disease Control and Prevention and some federal labs. Most other labs lack the facilities and expertise to do this reliably, according to Dr. Diamond.

“Really, we’re dealing with two other types of tests,” he says. “One looks for the viral RNA. The sequence these viruses have of their RNA is unique. You can detect that sequence using specialized tests to amplify the viral RNA.”

This test works when someone has active RNA in their blood or other fluid health officials may be testing. The test is quite specific, but there is a narrow window when an individual might have the virus in a particular bodily fluid, in this case the blood. “So you may still be infected, but you may not have a lot of virus in the blood and you may not detect it. If you do detect it, it’s a very specific test and gives you a secure diagnosis,” Dr. Diamond says.

The other test detects antibodies against the virus. An individual’s immune system responds to the virus and generates antibodies. “This happens after the phase when the virus is in the blood. Over a period of time, you transition from being RNA positive and antibody negative to RNA negative and antibody positive,” Dr. Diamond says.

The challenge with the antibody test is that there is significant cross-reactivity with other viruses that circulate globally, such as dengue. In places such as Brazil, Central and South America, Mexico, and Puerto Rico, there is a high prevalence of dengue, and so it is difficult to distinguish if a patient’s antibodies were generated in response to an acute Zika infection, an acute Dengue infection, or a current Zika infection, but having been infected with Dengue in the past. “We need better diagnostic reagents which will be able better distinguish those,” Dr. Diamond says. “There are some tests that can be done that could give you a pretty definitive answer, but many times, it’s equivocal and so were not certain using antibody of serologic-based test.”

What are the next steps for pathologists and lab professionals? “There are a number of public and private sector groups that are trying to generate new tests,” Dr. Diamond says. “The other thing is to be aware for detection in the blood supply and monitor it very carefully. Think of the diagnosis. Whether you’re in a pathology lab in a certain part of the country which may not be a Zika epidemic but you have travelers going back and forth (to areas where the Zika virus is prevalent), and if you see a clinical history that is suspicious for the Zika virus but lab tests have not been ordered, ask if they have considered this diagnosis. Have an open dialogue with clinicians and let them know what we know.”

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Susan Montgomery
American Society for Clinical Pathology
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