Winter 2016
As US and world health authorities ramp up efforts to control the Zika virus, an emerging threat linked to hundreds of thousands of illnesses in Central and South America, they will use every resource in the public health toolkit. One asset, however, stands out: surveillance data documenting confirmed human cases and the spread of infected Aedes aegypti mosquitoes, the primary source of transmission to people.
Without surveillance data, authorities could not zoom in on the virus’s location—for example, in the US Virgin Islands and Commonwealth of Puerto Rico, where there is active transmission—and thus, would not know where to target resources for mosquito control and other interventions.
From where does surveillance data come? Public health laboratories.
How easy is it to come by? Not very.
In fact, the Zika virus is new to the Americas—with no confirmed local transmission in any US state so far—there is no commercially available, off-the-shelf diagnostic test for Zika virus disease. The tests used in the United States were developed by CDC and have been performed mostly at the CDC Arbovirus Diagnostic Laboratory in Fort Collins, CO.
APHL is working to change that, by helping to disseminate the testing technology to public health laboratories across the country—a critical preparedness measure. The association has convened a number of “laboratory alert calls” to explain the complexities of Zika testing and to provide information about test performance, viable specimen types, laboratory biosafety guidelines and whom to test (for example, pregnant women with a history of travel to endemic areas).
As of March 11, 2016, 23 US public health laboratories can conduct testing for Zika virus using a combination of RT-PCR, IgM ELISA and PRNT assays. RT-PCR testing can detect Zika virus RNA in blood specimens collected during the first days of illness-onset. After this period, Zika virus RNA is no longer detectable, and public health laboratories must rely on IgM ELISA testing to detect IgM antibodies to the virus, which may be present in blood ≥4 days after illness onset. The antibody test, however, is complex and laborious; Zika is a flavivirus and the test cross-reacts with antibodies from previous flavivirus infections, such as West Nile virus, yellow fever and dengue infection.
This cross-reactivity necessitates a follow-up procedure to screen out false-positive IgM results—a labor-intensive plaque reduction neutralization test, which requires growing the virus in culture.
In the end, it doesn’t matter if Zika virus surveillance data are difficult to generate. Without this data, health authorities are operating blind; they can’t be sure where the virus is. And inaccurate data are arguably worse than none at all. That’s why APHL efforts to expand testing capacity and assure rigorous quality control are so important. And why the association will continue to be a conduit of information and technical support as the Zika outbreak evolves.
For more information, contact Kelly Wroblewski, MPH, MT(ASCP), director, Infectious Diseases, at
240.485.2728, kelly.wroblewski@aphl.org