By Guest Blogger,
The emergence of Zika virus in the Americas has prompted swift actions by public health authorities to forestall a growing regional epidemic of potentially serious infections (1). Because no vaccines or specific anti-viral treatments for Zika virus infections are available, proactive protection efforts focus on breaking the chain of transmission of this mosquito-borne virus to humans. That involves getting rid of standing water and removing trash to eliminate mosquito breeding sites, careful use of repellents and insecticides and keeping window screens in good repair. These simple actions are proven mosquito-borne disease prevention measures.
The Zika virus threat has produced an interesting opportunity for opinion leaders seeking to advance the acceptance and use of some new mosquito control methods (2). Field tests have confirmed that mass releases of genetically modified mosquitoes can dramatically suppress disease vector populations and the use of GMO mosquitoes to control transmission of viruses like Zika and Dengue in Key West, Florida, is now being evaluated. Proponents suggest this new technology is tested, scalable and ready to roll, if only regulators would simply expedite approval. The mosquito makers are anxious to go, but the problem is that this specific method has not yet been proven to suppress the transmission of any human disease. Whether this approach will actually stop Zika infections under the conditions present in Key West is not an established fact, it is a hypothesis that must be tested. Although the field trials were enormously encouraging, at this moment it is premature to imply GMO mosquitoes are a sure means to halt Zika virus transmission or that this technology represents our best hope to control the menace now facing us. Some groups may find it frustratingly slow, but there is no urgent need to short circuit the efficacy study processes.
The new, transformative genetic engineering technologies offer alluring prospects for a better future. However, we cannot be certain concepts like controlling diseases with GMO mosquitoes that look absolutely unbeatable on the drawing board will actually work as advertised and intended until they are tested. In addition, it is important to determine through objective assessments whether new technologies have any adverse environmental impacts. Releasing GMO mosquitoes may have a theoretically low level of risk, but more aggressive environmental manipulation approaches such as gene drives may be difficult or impossible to reverse if they produce adverse events. However, until these promising new strategies are evaluated fully, estimates of their true benefits and risks are little more than opinions.
Fully assessing environmental risks of proposed actions may be challenging because some adverse events unfold over long periods in unanticipated ways. Paralytic poliomyelitis (‘polio’) was once an extremely rare disease of infants. However, mass epidemics of polio paralysis began to appear in the twentieth century as communities improved their water supplies. Cleaning up municipal water sources decreased deaths due to typhoid fever and cholera, but unexpectedly replaced those scourges with something new. When water supplies were typically contaminated with sewage, babies were infected with polioviruses during the lifespan period when they were least likely to be paralyzed. Cleaning up the water meant that poliovirus infections came later in life when paralysis was a far more likely outcome. A simple and obviously beneficial change in living conditions had literally set the stage for the great polio epidemics to come. This unanticipated adverse event took years to become apparent and was impossible to predict before the fact of its emergence. Poliomyelitis epidemics were finally controlled through the implementation of mass vaccination programs (3).
Sometimes even simple changes without any obvious human health implications turn out to become enormously significant and threatening. Salvaging slaughterhouse waste products and feeding them back to cattle led to a massive epidemic of bovine spongiform encephalopathy (BSE), sometimes called mad cow disease, in Great Britain. This re-feeding practice is believed to have unwittingly amplified pathologic prions (infectious proteins) to the point at which cattle started to exhibit obvious signs of neurologic disease. Almost simultaneously in the same geographic region a new prion disease, new variant Creutzfeldt-Jakob disease (vCJD), appeared in humans. These striking correlations suggest the pathologic prions causing the mad cow epidemic had somehow invaded human populations. The ultimate consequences of these events on human health remain uncertain.
Clearly, every adverse consequence of change cannot be readily predicted or easily mitigated. Genetic engineering technologies are novel and still in the trial-and-error phases. Not even all the laboratory experiments have turned out as expected (4). As new environmentally aggressive concepts like gene drives are touted as solutions to challenging problems it is important to bear in mind that our world can be unpredictable and inhospitable to human manipulations (5). Hard experience confirms that comprehensive efficacy testing coupled with long-term surveillance to reveal any consequential negative changes must remain part of the decision making processes necessary for regulatory agency approvals.
The promise of genetic engineering technology is immense. Whether or not it ultimately proves to be titanic depends on how wisely we manage it.