When the Pan American Health Organization put out an alert last May about the first confirmed cases of Zika virus infection in Brazil, the news barely registered. After all, compared with other mosquito-borne viruses, such as potentially life-threatening dengue and yellow fever, Zika seemed pretty harmless. Only 20% of people infected with Zika even become ill, and their symptoms tend to be mild—fever, rash, joint pain, and conjunctivitis.
But in January, nine months after the organization raised the alarm, doctors in Brazil reported a disturbing trend that coincided with Zika’s spread across the country. Since October 2015, more than 4,000 babies in Brazil had been born with abnormally small heads and brains—a rare condition known as microcephaly. Although further analysis lowered that figure by 462 cases, the sharp rise nonetheless has experts worried that Zika could be to blame. For comparison, Brazil reported just 147 cases of microcephaly in 2014.
With a treatment or vaccine for Zika potentially years away, countries are relying on mosquito control to curb the virus’ spread. Aedes aegypti mosquitoes, which inhabit tropical and subtropical regions, have been named as the culprit in transmitting the virus.
But getting rid of Aedes aegypti is extremely difficult because the mosquitoes don’t seem to be affected by most spraying regimens, says Joseph M. Conlon, an entomologist and technical adviser to the American Mosquito Control Association. The problem, Conlon tells C&EN, is that Aedes aegypti feed during the day, and pesticides must be sprayed at dawn or dusk to be effective. Also, the mosquitoes like to come indoors to feed. So, unless pesticides are sprayed inside homes, chances are good they’re not getting to the insects.
These mosquitoes are very small and you can’t feel the bites. “Oftentimes you don’t even know you’ve been bitten,” Conlon says.
To get rid of the biting bugs, it’s critical to eliminate any standing water. “I’ve seen Aedes aegypti breeding in discarded soda bottle caps,” Conlon says. “They’re survivors.”
Despite Aedes aegypti’s survival skills, the mosquitoes actually have a fairly limited flight range of about 150 m. That has made some scientists suspect that because Zika has spread so quickly, the more common Culex mosquito may be transmitting the virus as well. The theory is currently being investigated.
“If that is true, that brings this to a whole different level,” Conlon says. Culex mosquitoes have a much larger range, he notes, but they can usually be controlled through common mosquito abatement programs.
Zika is also being blamed for an uptick in cases of Guillain-Barré syndrome, a potentially life-threatening disorder in which the body’s immune system attacks the central nervous system and causes paralysis. As with microcephaly, the evidence connecting Zika and Guillain-Barré is still circumstantial. Nevertheless, the link is strong enough for the World Health Organization to declare the Zika outbreak a public health emergency of international concern.
Margaret Chan, WHO’s director-general, said earlier this month that the virus is “spreading explosively” through the Americas, with cases of active virus transmission in at least 26 countries and territories in the Americas. Panic over the virus has prompted health officials in some countries to take the drastic measure of advising women to delay pregnancy for months or longer. In El Salvador, Deputy Health Minister Eduardo Espinoza asked women to avoid becoming pregnant until 2018.
With Zika making headlines for the past month, scientists have been scrambling to get a handle on the virus. Industry, government, and academic scientists have all announced efforts to develop and test treatments and vaccines. But the path ahead for these researchers is long and full of pitfalls. Even though it’s been around for almost 70 years, surprisingly little is known about the virus and its basic biology. A PubMed search for “Zika virus” turns up mostly case studies.
What we do know is that Zika is a flavivirus, a member of the same family as dengue, yellow fever, and West Nile virus. Zika is primarily transmitted via bites from infected mosquitoes, but in recent weeks doctors have reported that the virus can be sexually transmitted as well.
It was first identified in a monkey in Uganda’s Zika forest in 1947, but only a handful of human Zika cases were reported until a 2007 outbreak in Micronesia’s Yap Island. An outbreak in French Polynesia followed six years later. Last November officials in that country reexamined the cases of microcephaly that followed the outbreak. Before the outbreak, about one case of microcephaly was reported each year. In 2014-15 officials found 17 cases of fetuses and infants with “central nervous system malformations,” which includes microcephaly.
As the case connecting Zika to serious health effects builds, the world would love a vaccine or treatment for the virus. But because so few have studied Zika, drug developers currently have few tools to work with. For example, there’s no commercially available, U.S. Food & Drug Administration-approved test to screen for Zika virus.
Tracking Zika in people is hard because it’s difficult to determine that they’re infected with Zika and not a related flavivirus or that they’re not infected with more than one virus, says Priscilla L. Yang, a flavivirus expert at Harvard Medical School. Simultaneous infection with Zika and another virus could cause health effects that haven’t been seen before.
Scientists can use polymerase-chain-reaction-based methods to distinguish Zika from other flaviviruses. But those tests are accurate only during the short window patients still have the virus in their system—about seven days after infection. By the time a patient has symptoms that warrant a visit to the doctor, the virus is no longer circulating in their bloodstream, Yang notes.
Another option is to look for antibodies against the virus. But Zika and dengue are closely enough related that antibodies to Zika also recognize dengue and vice versa. Making a definitive diagnosis based on antibodies is possible but becomes time consuming and laborious, Yang says.
For scientists who have compounds that might be effective against Zika, actually testing them has been tough. “We have small molecules that seem to be broadly acting against dengue and West Nile virus,” Yang says. “We want to test them, but getting access to the live virus has been hard.” She’s heard that certain labs known to have the Zika virus have been bombarded with hundreds of requests from researchers.
Even if someone manages to access the live virus and can find a compound that kills it in cells, the researcher will hit another roadblock: To date, no one has published practical animal models of Zika virus to screen potential therapies against. Yang points to a paper from the 1970s in which scientists did an intracranial injection of Zika virus in newborn mice, but she notes that is a poor model because many small molecules can’t slip past the blood-brain barrier.
“We’re basically starting from scratch on this one, unfortunately,” says Sina Bavari, chief scientific officer (CSO) at the U.S. Army Medical Research Institute of Infectious Diseases. Bavari and colleagues are currently working with pharma companies to see if they have any compounds that inhibit Zika replication in cells.
They’re primarily interested in compounds that have passed the hurdles of Phase I or Phase II clinical trials but are sitting idle for business reasons. That’s because it can take upwards of a year and a half just to get a new compound ready for Phase I. “My worry is that by the time we get something out the door, this outbreak will have already burned out,” Bavari says.
Scientists are also grappling with this question: If only 80% of people infected with Zika have symptoms, who would get the treatment? The most vulnerable patients are pregnant women, but Bavari points out, there’s a high bar when it comes to approving a medication that can be given to them. “They don’t even want to drink caffeine,” he says.
Other scientists are working to develop a vaccine against the Zika virus. Earlier this month President Barack Obama said he would ask Congress for $1.8 billion to combat Zika at home and abroad. Of those funds, $200 million would be used for vaccine development. The U.S. National Institute of Allergy & Infectious Diseases, Sanofi Pasteur, and NewLink Genetics are among the heavy-hitters in the vaccine field who’ve said they’ll step up to the plate.
Even so, it could take three to five years before a vaccine is ready, experts say. Thomas P. Monath, CSO of NewLink’s infectious disease division, led that firm’s efforts to develop an Ebola vaccine and was CSO at Acambis, where he worked on vaccines for dengue and yellow fever. Monath tells C&EN he thinks a large field trial of 10,000 to 20,000 people across multiple sites will be necessary to determine efficacy once a Zika vaccine is developed. “Only after those trials would you contemplate doing studies in pregnant women,” he says.
Monath also says because so many people who are infected with Zika never show any symptoms, it is more difficult to determine whether the vaccine has actually prevented infections. Still, he thinks a large enough trial should be conclusive.
But some scientists say the emphasis on vaccines is misplaced. “We just don’t know enough about Zika virus right now to run around and vaccinate people,” Bavari says. “Understanding the immunopathology and immunology behind it would be really prudent before starting a full vaccination program.”
Harvard’s Yang says developing a vaccine for every emerging virus is impractical. “Vaccines are, for the most part, specific. You have one virus and you have one vaccine for it,” she explains. “I don’t think we’ll ever have the luxury of enough resources to get a vaccine against every single possible emerging virus or enough time to do it in a reactive way.”
One area that’s not getting as much attention, she says, is development of broadly acting antivirals that could keep a virus in check while the immune system fights it off. Classical antivirals go after a single viral enzyme, but viruses are quick to develop resistance to them. “If people could identify targets that have the potential to be effective against multiple viral pathogens, it could be game-changing,” Yang says.
H. Alex Brown, a Vanderbilt University professor who works on antivirals, agrees. “There are so many viruses out there. We need to be working on a much more broad-spectrum approach to infectious disease,” he says. “If we can develop more tools to combat broad categories of viruses, I think we would be much better off than we are today.”
In the meantime, scientists agree that the research community needs to be more organized if it’s going to have a real shot at combating Zika. Yang thinks the first steps should be figuring out how to get the necessary reagents to the labs that need them and agreeing on standards so they can compare results and learn from each other’s work. “If you actually want to have some sort of impact, we all need to work together,” she says. In an encouraging sign, earlier this month, major scientific institutions and top research journals agreed to share data relevant to Zika virus.
Bavari agrees scientists need to be better at organizing their efforts, but he has doubts about the direction the community is taking. “The outbreak is moving so quickly that I am worried people will jump and we won’t do the correct research,” he says.