The Zika virus isn’t unprecedented, epidemiologically speaking. What is unprecedented, however, is its associated birth defects, including microcephaly, as well as the fact that it can be sexually transmitted.
That’s according to Aravinda de Silva, professor of microbiology and immunology at the University of North Carolina at Chapel Hill School of Medicine, who was part of an RTI International-sponsored panel focused on Zika research and response in North Carolina on June 7. In addition to de Silva, who specializes in the research of dengue fever, panelists included a mosquito expert from N.C. State University, a virologist from Duke, and representatives from the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH).
There are more than 10 groups at UNC working on Zika research and response. Just this week, the UNC School of Medicine internally funded three $50,000 pilot grants to research Zika’s diagnostics, transmission and associated neurological disorders.
During the panel discussion, de Silva said some aspects of Zika are not so different from other viruses, while there are certain aspects of the virus that make Zika stand out.
Zika is a flavivirus, a group of viruses that include West Nile, dengue, tick-borne encephalitis and yellow fever, and, because this is the case, researchers like de Silva are already familiar with its basic virology and epidemiology.
“We know a lot about these viruses,” said de Silva, who is also a member of the UNC Institute for Global Health and Infectious Diseases. “As we think about dealing with Zika, a lot of the things that we can do, actually, will be based on knowledge we already have from other flaviviruses. There are things that are very similar between Zika and other flaviviruses like dengue.
“Zika showed up a few years ago in the Western hemisphere, but this [introduction of new flaviviruses to the Americas] is a trend that we’ve seen over the last three to four centuries.”
Aedes aegypti, a native African mosquito species, was introduced into the Americas in the 17th century. This mosquito is responsible for the transmission of yellow fever, dengue, chikungunya and Zika viruses to people.
Michael Reiskind, assistant professor of entomology at N.C. State University, also spoke during the panel discussion on Tuesday. Reiskind said an estimated 95 to 99 percent of worldwide cases of Zika were transmitted by mosquitoes. The fact that Zika is also transmitted sexually “is something different than we’ve seen in any similar other mosquito-borne virus,” Reiskind said.
“That being said, because most cases are going to be transmitted by mosquitoes – at least in the developing world – understanding the ecology of the mosquitoes provides assessment of risk and our most fruitful avenue for prevention of the disease,” Reiskind said.
Like yellow fever, dengue and chikungunya before it, Zika has now made its way to the United States, though no known cases here have been attributed to a mosquito vector. Known U.S. cases have either been contracted outside the U.S. or transmitted sexually.
“There are also things that are really unusual about Zika,” de Silva said. “And that’s why I think we are all here. It’s the sexual transmission and the birth defects. These are unprecedented.”
“And those are really new and unexpected findings that need to be studied.”
The main birth defect attributed to Zika is microcephaly, a rare neurological condition in which an infant is born with a much smaller head than other infants the same age – an effect of abnormal brain development.
“A critical issue is diagnostics,” de Silva said. “All these reports you see – so many cases of microcephaly, so many people being hospitalized with Zika – many of these are just a clinical diagnosis.” A reliable lab test for Zika has yet to be developed, he added.
“This is a huge problem,” de Silva said. “Seventy-five percent of people who are infected don’t show any symptoms, so if you’re only looking at the fraction of people who get very sick, you’re really unable to track the epidemic. We need diagnostic assays.”
Another variable that lends to the difficulty of diagnosing Zika is that it’s being transmitted in areas with many other flavivirus transmissions. Therefore, it is difficult to determine if a positive test is a result of infection with Zika or another related virus like dengue.
“The good news is, though the problem is complex, this is highly solvable,” de Silva said. “We know enough now about how to go about coming up with diagnostic tests.”
UNC researchers are currently working with state and federal health officials, including the CDC and NIH, which has supplemented current grants so researchers can broaden the scope of their work to expedite the research and response to Zika, de Silva said.
The UNC School of Medicine has a decades-long history of studying arboviruses – a term that refers to any virus transmitted by mosquitos, ticks or other arthropods.
“And so there’s real expertise here,” he said. “My group and others, we have been studying dengue viruses for many years. Dengue is very closely related to Zika, but distinct. And we have a program that includes epidemiology, human immunology and pathogenesis, and this work includes a lot of international work in South Asia, as well as in the Americas.”
A vaccine for Zika could be developed based on previous work to successfully develop yellow fever, Japanese encephalitis, and dengue vaccines, de Silva said. According to the World Health Organization (WHO), an estimated 390 million people are infected with dengue worldwide each year.
“There’s a tremendous amount of work going on right now on dengue vaccines,” he said.
Currently, there are three phase-three clinical trials for a dengue vaccine and UNC is collaborating with vaccine developers to understand data from these trials, de Silva said.
“Our group at UNC has been working very closely with all the leading vaccine developers,” he said. “And as these clinical trials are going on, for example, in South America, Zika is adding another level of complexity to our understanding of these vaccine trials.”
Good vaccines currently exist for yellow fever and Japanese encephalitis, while the first dengue vaccine was just recommended by the WHO for use in people over the age of 9 living in endemic countries.
“The good news is that there are already excellent vaccines against this class of viruses,” de Silva said.