Photo: Author, road crossing jungles through central Uganda, 2011.
The Zika virus has been grabbing headlines for nearly a year now with reports of its rapid spread in Latin America and its possible links to serious birth defects and illnesses in children and adults. However, the Zika virus itself is not new. Zika is named after a forest near the Uganda Virus Research Institute in Entebbe where the virus was first isolated from monkeys in 1947. Then, as indeed today, infection generally produced mild symptoms in humans, with many asymptomatic cases. The mosquito-borne virus thus garnered little attention until a series of minor outbreaks in Oceania in the last decade. Now, the large-scale, ongoing outbreak in the Americas that began in 2015 heralds Zika as the latest threat to human health around the world. The nature of the virus and the populations it affects are likely to make it extremely challenging to combat; a solution is going to require significant time and effort.
Concerns about Zika stem not from typical symptoms of infection—if these appear, they include mild headaches, rash, fever, conjunctivitis, and joint pain. Rather, two sets of potential complications are the source of growing alarm. The first of these is a link, strengthening as medical and epidemiological evidence mounts, between Zika infection in a mother and the development of microcephaly, a debilitating inhibition of growth in the brain and head, in unborn children. The second possible complication, still only weakly established, is between infection by Zika and an autoimmune disorder known as Guillain-Barre Syndrome. Both of these complications lie at the root of growing panic in Latin America and rising public fear in the United States, where, as mosquito season approaches, it seems likely the virus will spread to the southern states and the mid-Atlantic region where the Aedes mosquito vector is endemic.
The disease is already spreading with some speed in US territories in the Caribbean. A recent article in the Washington Post reports on the spread of Zika in Puerto Rico, where the CDC expects the virus to infect up to 20% of its 3.5 million people by the end of 2016. Travel back and forth between the mainland United States and Puerto Rico, the US Virgin Islands, and countries such as the Dominican Republic, Haiti, and the states of Central and South America is continuous. The intermixing of significant numbers of infected people from these areas with populations in the mainland United States is inevitable, and where appropriate mosquito vectors exists, local self-sustaining chains of infection will emerge. Because Zika fever is normally so mild, the virus is likely to become well-entrenched in a community before cases are first diagnosed, greatly complicating efforts at disease surveillance and prevention.
As in other cases of emerging diseases, such as HIV in the 1980s, West Nile and SARS in the early 2000s, and MERS, Ebola, and Chikungunya in the 2010s, globalization has provided the opportunity for Zika’s rapid spread into new regions. Formerly isolated disease agents travel on ships and planes to claim new home ground. It is unknown whether the pace at which new diseases emerge will accelerate in the near future, or if it will stabilize after the last corners of the world become connected to the rest. As a disease spreads it can sometimes become more aggressive, as seems to be the case with Zika and the new strains of the virus that have emerged in Oceania and the Western hemisphere.
What can be done to arrest the spread of Zika? Policy options are, unfortunately, few in the short and even medium-term. In the short-term, governments are limited to public education campaigns and vector-control measures. Public education would inform populations of the dangers of Zika infection, and encourage them to take measures to protect themselves from mosquito bites through the use of repellents, installation of screens to cover windows and doors, and eliminating backyard breeding sites for the Aedes mosquito. Community vector-control measures include spraying insecticide and eliminating breeding sites in public areas. These measures can be effective in reducing mosquito populations but are costly and require significant manpower. Brazil, for example, has found it necessary to mobilize its military to help public health officials reach the public and conduct vector-control operations. New vector-control techniques, such as the introduction into the wild of genetically modified mosquitoes carrying a heritable kill-gene which prevents offspring from reaching maturity, may also be effective, but are likely to be controversial. In any case, public education and vector-control efforts can only be expected to mitigate, not wholly prevent, the spread of the disease. Hopes, therefore, have turned toward the eventual development of a Zika vaccine.
A vaccine would be the preferred solution to the spread of the Zika virus, as it has been for many other infectious disease agents. And, it is quite possible initial candidate vaccines will not be difficult to develop, at least not from a technical point of view. The Zika virus is a member of the Flavivirus genus, and there has been significant success in the past developing vaccines for other viruses in this group, such as for Yellow Fever and Japanese Encephalitis. Vaccines against other members of the genus, however, such as West Nile and Dengue, have, for different reasons, proven more difficult to develop. It is not yet known whether the development of a Zika vaccine will pose a great challenge, but, we are likely to find out soon: with media attention being directed at the virus and concern increasing among governments and the public, the race to develop a vaccine is on.
If all goes well, a candidate vaccine could be tested as early as the next two to three years. However, many hurdles lie between development of a possible vaccine and its deployment. Human trials take time, as does getting a vaccine to market and to at-risk populations. If recent experience in drug development is any guide, this is likely to take the better part of a decade. In the case of Zika, other factors complicate the road to delivering a vaccine. Firstly, the population most at-risk by Zika, that is, the population where the consequences of Zika infection are likely to be the highest, is that of pregnant women – which happens to be one of the most sensitive populations when it comes to conducting medical trials. Both the health of the mother and the fetus must be taken into account and, until a trial is conducted, reactions by either to the trial vaccine will be unknown. This calls for particular caution in both the vaccine development and trial processes. The second factor complicating vaccine development is posed by the possible link between Zika and the paralyzing auto-immune disorder known as Guillain-Barre Syndrome. Auto-immune disorders are caused when one’s immune system attacks one’s own cells— in the case of Guillain-Barre, the cells being attacked are neurons of the peripheral nervous system, which connects the brain and spinal cord to the rest of the body, including to muscle tissues. When the immune system first breaks down a virus like Zika, and identifies molecular targets to finish off the infection and combat new ones, it may end up targeting viral molecules that happen to be similar to molecules already in the body, in this case, on the surface of neurons. The immune system is “tricked” into attacking the body, and an auto-immune disorder results. Because vaccines work by eliciting these types of immune responses, a Zika vaccine, if it is not tested properly, may well prompt the very auto-immune disorders it was developed to prevent. Both of these issues, that is, the special challenge posed by the virus’ effects on fetuses, and its potential link to an auto-immune disorder, are likely to complicate human trials, lengthening the time needed and cost required to approve a final vaccine for Zika.
It may well be that the current wave of Zika infections will have receded by the time a vaccine becomes available. Prudence, however, dictates that efforts to develop a vaccine continue unabated. Zika outbreaks may become a fixture in regions where the Aedes mosquito vector exists, occurring every five or ten years, making a vaccine likely the only permanent solution. In the meantime, robust prevention and vector-control efforts will be critical for achieving some measure of control over the virus. The $1.9 billion President Obama requested from Congress to combat Zika will be essential for these efforts, not only to support basic research, vaccine development, as well as education and vector-control efforts within the United States, but also to aid poorer countries which may find it difficult to muster the resources required to mount a comprehensive anti-Zika campaign. The United States remains the regional, and indeed, global leader in public health expertise, with disease detection, surveillance, and response capabilities which are a standard and reference for most countries across the world. With its response to the recent Ebola crisis, the United States proved it could mount a massive and, in the end, successful effort, an ocean away, against one of the most feared infectious disease agents in modern memory. Many fear the impact of Zika could prove more severe than that of Ebola. The United States should respond with all the tools at its disposal to support efforts to combat Zika within its borders and lead the effort internationally to rein in this latest threat to global public health.
Carlos A. Salazar is a PhD Candidate in Global Theory and History at the Johns Hopkins University School of Advanced International Studies (SAIS), and a Research Associate at the SAIS Foreign Policy Institute. He is interested in infectious diseases and their effects on power and security in the international system.