The ominous shadow of the Zika virus continues to spread, but scientists warn that it’s not the only lurking threat.
Some researchers are saying more could have been done sooner to anticipate the outbreak. Now that the world is mounting its counterattack to the Zika virus, they caution against losing sight of other looming plagues stretching their tendrils through the Americas as the climate warms.
The Centers for Disease Control and Prevention reported that the Zika virus is circulating in 37 countries and that Puerto Rico may see hundreds of thousands of infections this year.
However, at the same time, the Pan American Health Organization reported that there have been more than 29,000 suspected cases of Chikungunya infections and 364,000 probable cases of dengue in the Americas this year to date.
"Given the emergency status, I don’t think we should move resources from dengue and Chikungunya to Zika," said Pei-Yong Shi, a professor of human genetics at the University of Texas Medical Branch.
Zika virus, with its growing list of effects, has nonetheless captured the public’s fears.
Health officials warn that the disease can spread via sex, and as evidence builds linking the virus to Guillain-Barré syndrome and a devastating birth defect known as microcephaly, researchers are starting to learn that the virus can harm brain development in infants without any outward signs. These effects may not manifest themselves for years.
The tricky work of preparing vaccines
Marcos Espinal, director of the Department of Communicable Diseases and Health Analysis at the Pan American Health Organization, told reporters at the American Association for the Advancement of Science meeting last month that he wouldn’t be surprised to see 2 million to 3 million infections in the Americas this year.
Though it’s not spreading in the United States yet, several travelers have brought the virus with them to the country after visiting afflicted regions.
As a result, health officials are aggressively pushing for the prevention and treatment of these viruses after being ambushed again, but there are steps they could take to be better prepared for future epidemics.
One of the most important weapons in a fight against a virus is a vaccine, a treatment that provides immunity to the disease.
Shi explained that developing a vaccine is slow and tedious, so fighting an outbreak with these treatments requires planning far in advance.
Vaccine development happens in two main phases. In the preclinical phase, researchers have to decide what kind of path to take, whether to use a dead virus, a blend of virus components, a weakened form of the virus or a hybrid vaccine that mixes parts of the target virus with an existing vaccine.
Each technique has its advantages and drawbacks. Dead viruses tend to be safer but have a harder time generating an immune response compared with a virus that can replicate to a small degree and provoke a stronger reaction from the body.
"Given the current situation, I think all of these approaches should be pursued simultaneously, in parallel," Shi said.
Starting vaccine development early
Fortunately, Zika belongs to a well-studied family of viruses called flaviviruses, which include the yellow fever virus and the dengue virus.
"We have a very rich experience in developing flavivirus vaccines," Shi said.
After testing in animals, the vaccine then moves into the clinical phase, where human tests begin. It can take months, if not years, before a vaccine is approved for human use, but given the intense policy focus on the Zika virus, progress may be swift, at least in drug development time scales.
"I’m quite optimistic with such an intensity of research," Shi said.
The Obama administration has requested an additional $1.8 billion in supplemental funding from Congress to fight Zika in the United States and in other afflicted countries with vaccines and vector control. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said last month that he expects a Zika vaccine to enter clinical trials by the end of the summer.
However, even an approved vaccine isn’t a guaranteed blow against the disease. Shi noted that viruses can mutate, rendering a vaccine ineffective, or the immunity can wear out over time. And a vaccine for Zika is still more than a year away.
Therefore, scientists should begin developing vaccines ahead of outbreaks, drawing on surveillance, human migration and climate variables that affect vectors, according to Shi. The Zika virus has been circulating in sporadic outbreaks for more than 50 years, so more rigorous study of the infection in earlier epidemics could have foretold the current devastation.
Pre-outbreak research ‘a hard sell’
Keeping the research machinery greased up and running even in years without an outbreak will help make sure health officials aren’t caught off-guard when another virus strikes, Shi said.
As the climate changes, researchers warn, the risk of new diseases spilling over into humans will likely increase as infected organisms move around and cross paths with humans (ClimateWire, Feb. 20, 2015).
Scientists have also observed that the Aedes aegypti mosquito — which spreads Zika, dengue and Chikungunya — is moving to higher latitudes and altitudes as the climate warms (ClimateWire, Feb. 8). This means new populations are likely to be exposed to these viruses.
But in a world of finite resources and limited time, attacking a disease before it becomes an epidemic in a region is a tough sell. Some lawmakers were hesitant to draw links between climate change and the risk for Zika virus transmission (ClimateWire, March 4).
House Republicans proposed paying for the president’s Zika virus funding request with leftover money from the fight against the Ebola virus epidemic. The Department of Health and Human Services has $1.4 billion left of the original $2.8 billion to fight the 2014 Ebola outbreak.
Reps. Nita Lowey (D-N.Y.), the ranking Democrat on the House Appropriations Committee, and Rosa DeLauro (D-Conn.), the ranking Democrat on the Labor, Health and Human Services, and Education Appropriations Subcommittee, issued a statement last month opposing this idea.
"The majority’s suggestion to shift unobligated Ebola funds to confront Zika would rob Peter to pay Paul, and it would increase health risks both at home and abroad," they wrote. "It is penny wise and pound foolish to tell our public health professionals they can be prepared to respond to only one life-threatening pandemic at a time."
Vaccine research just one piece of the puzzle
However, given the scale of the potential threat, some scientists argued that the United States is not investing enough in countering vector-borne diseases in general.
"The overall problem is there is too little money for all of these tropical diseases," said Peter Hotez, dean of the National School of Tropical Medicine at the Baylor College of Medicine. "The problem isn’t that we’re spending too much money on one at the expense of the other."
He pointed out that vector-borne diseases emerge from many variables, including climate, human movement and ecology. Though it’s hard to blame any one variable, it’s also important not to draw a false sense of security from them, either.
This is particularly true for economics. Many epidemiologists have observed that dengue outbreaks occur often on the Mexican side of the U.S.-Mexico border but not often in the United States, since Americans spend more time indoors and spend the cash to keep public areas free of the standing water that makes active breeding grounds for disease-carrying mosquitoes (ClimateWire, Nov. 15, 2013).
Yet not everyone in the United States has a share of this wealth, and many poor communities in the country with substandard living conditions, particularly around the Gulf Coast, are vulnerable to creeping tropical infections.
"One of the interesting observations I’ve made now is that most of the world’s neglected diseases are occurring in wealthy economies," Hotez said. "It’s the poor living among the rich that account for these diseases."
What this means, according to Hotez, is not that there isn’t enough money to go around in these instances, but that it’s not spread in the right way. While vaccine research is important, immediate benefits may come from controlling vectors by spraying or even cleaning up garbage in poor neighborhoods to fight the Zika virus.
"Right now, [vaccine] R&D is not going to have any impact on the Zika epidemic in the United States," he said.
