CHAPEL HILL, NC – Researchers at the UNC School of Medicine are working to develop a test for the Zika virus that they hope will provide accurate results for a wide range of time between when an individual is potentially exposed to when he or she is tested for the virus.
Currently, much Zika testing is conducted via molecular diagnostics that look for the actual virus in the individual, according to Aravinda de Silva, PhD, professor of immunology and microbiology at the UNC School of Medicine and a member of the UNC Institute for Global Health and Infectious Diseases. These tests are most accurate in cases where someone was recently exposed, and, in most cases, is symptomatic. But because approximately 80 percent of people infected with Zika are asymptomatic, there is a critical need for better, more accurate diagnostics for people who are asymptomatic or whose potential exposure goes back weeks, months, or even years.
De Silva's lab, along with colleagues at Duke University, the University of Vermont, and the University of Nicaragua-León, has been awarded a federal contract for $3.2 million to work in close partnership with the Centers for Disease Control and Prevention (CDC), to develop improved serological tests to bolster public health efforts for Zika. A serological test measures the level of antibodies produced by the body, rather than relying on detection of the viral components or the virus itself.
This new approach could be particularly beneficial in differentiating cases of Zika from related flaviviruses such as dengue fever, de Silva said.
Like most flaviviruses, Zika is transmitted by mosquitoes. But unlike similar viruses, Zika can also be transmitted sexually, as well as by crossing the placenta. This places pregnant women at the highest risk, given the associated birth defects, which include microcephaly, blindness, seizures, deafness, and other problems referred to collectively as the congenital Zika syndrome, de Silva said.
"The virus seems to clear out of the system rather quickly, but it does leave behind clues in the form of antibodies that can be identified in a serological test," de Silva said. This is particularly important for pregnant women who live in flavivirus-endemic areas and for those who have traveled to Zika-endemic areas or who have had unprotected sex with a partner who has potentially been exposed, according to Matt Collins, MD, PhD, a fellow in the UNC Institute for Global Heath and Infectious Diseases, and an OIA Global Health Scholar.
"The serological diagnostics we're developing are potentially more effective because individuals can be tested farther out from a potential exposure, making it more useful," Collins said.
Early in the epidemic, several researchers hypothesized that it would be "impossible" to distinguish Zika from other similar viruses, like dengue, de Silva said.
"When you move away from the molecular test to the serological test, you really have a very large window of opportunity that starts as early as the first week of infection once the person's body starts mounting an immune response to an infection, and that can last, really, for life, but definitely for years beyond an exposure," Collins said. "We think this kind of test will be an important tool for public health because it gives us the ability to diagnosis people who have had a recent or remote exposure. That would include a pregnant woman in the middle of her pregnancy who may have been exposed very early on – two or three months prior to her first prenatal appointment, for example.
A serological test could also be helpful in assessing populations for surveillance and tracking purposes.
"It could help in the case of a country that was trying to determine if Zika was recently introduced to the population or if the numbers were up or down from recent years," Collins said.