Zika, Mosquitoes and the Plagues to Come

Zika, Mosquitoes and the Plagues to Come

Every time there is a major infectious disease outbreak that scares us — Ebola in West Africa in 2014, Middle East Respiratory Syndrome (MERS) on the Arabian Peninsula in 2012 and in South Korea in 2015, and now the Zika virus in South and Central America and the Caribbean — government leaders, the public and the news media demand explanations, guidance and predictions, and often express indignation that not enough was done to prevent it. Today everyone is asking about Zika: How did this crisis happen, and what do we need to do to make it go away? We immediately forget about the outbreak that came before it, and don’t plan for the ones we know are on the horizon. Almost no one wants to talk about Ebola or MERS now, or what we have or haven’t done to try to prevent an ugly recurrence.

When it comes to diseases, we have a very short attention span, and we tend to be reactive, rather than proactive. Instead of devoting ourselves to a comprehensive plan to combat microbial threats, we scramble to respond to the latest one in the headlines. There are lessons from previous infectious disease outbreaks that could and should have left us much better prepared than we are.

First, the mosquito that transmits this disease, the species Aedes aegypti, has never been more numerous or lived in more locations. Think of Aedes aegypti as the Norway rat of mosquitoes; it has evolved to live in close quarters with humans, and the trash that humans create. This is quite different from most other species of mosquitoes, like the ones that transmit West Nile virus, which tend to lay their eggs in marshes, rice fields, ditches, the edges of streams and small, temporary rain pools.

The world has changed dramatically in the past 40 years with regard to increasing the habitat for Aedes aegypti breeding. An explosion of plastic and rubber solid waste now litters virtually all parts of the globe, particularly in the developing world. Non-biodegradable containers, used tires and discarded plastic bags and wrappers — whether in the backyard, a roadside ditch or an abandoned lot — make ideal habitats for these mosquitoes to lay their eggs. All they need is a little rainfall.

This species is currently present in 12 states in the United States, mostly in the Southeast. But its close cousin, Aedes albopictus, known as the Asian tiger mosquito, came to the United States in the 1980s and is now in some 30 states, including the entire Eastern Seaboard up to New York City. For now, fortunately, this species does not appear to be a significant factor in the transmission of Zika to humans. What we in North America have to worry about is whether the Asian tiger mosquito can become a more effective transmitter of the virus to humans. If that happened, we would face a very serious risk of an outbreak here.

One of the solutions to this problem is called “vector control.” It involves both eliminating the places where these mosquitoes breed, or chemically treating those sites, and spraying chemical insecticides to kill adult mosquitoes, or at least keep them away from where humans live, work and play. We must clean up the garbage to have any hope of reducing Zika infections in humans.

From the 1950s through the 1970s, there was a major initiative to eradicate Aedes aegypti from the Americas by public health organizations, nonprofits and national governments. It almost succeeded. In part, that was because eliminating these mosquitoes’ breeding sites was much simpler before the spread of plastic and rubber waste. But governments and nonprofit agencies decided too early that the job had been done, and dismantled these programs to save money. Now the mosquito is back.

This is not new science or new policy. Now we’ve got an outbreak on our hands, and although the symptoms of Zika itself are absent to mild for most, for some there can be devastating consequences to infection. An increasing number of infected women have given birth to babies with microcephaly, which causes small heads and brain damage. We’re learning that Zika can lead to Guillain-Barré syndrome, a dangerous autoimmune disorder that can cause paralysis. Some believe we need more scientific data to confirm these more severe manifestations. I don’t agree; I believe the evidence is already compelling.

We shouldn’t have needed thousands of babies born with severe birth defects or people of all ages developing life-threatening autoimmune paralysis to remind us that mosquitoes pose a serious health threat. Dengue viruses, which are also transmitted by these two mosquito species, caused 2.3 million cases of dengue fever and far more serious dengue hemorrhagic fever in 2013 in the same countries in the Americas that have been, or will be, affected by Zika. These included more than 37,000 severe illnesses and 1,300 deaths. And yet these numbers hardly raised an eyebrow in the United States. If we had paid more attention then, we might be more prepared now.

Zika is here to stay in the Western Hemisphere; it will be part of life for many years to come. Even if we make vector control efforts a major initiative, it will only reduce, but not eliminate, the risk of Zika. What we need next, urgently, is a vaccine.

Some critics are suggesting that such vaccine research for Zika should have been done years ago, but this isn’t entirely fair. It was only in the past two years that there was any indication this virus could cause serious human disease. Now we have to catch up. But it’s going to be complicated. If Guillain-Barré syndrome is indeed caused by the patient’s immune response to the virus, as happens with other infectious diseases, could the vaccine itself put us at risk? This will take careful research to determine. And it will take time.

The point is, we should have anticipated that the large increase in mosquitoes would create a major health crisis. Just as we should have anticipated that a deadly hemorrhagic disease caused by the Ebola virus would emerge one day from the remote forests and threaten the vast slums of the rapidly growing megacities of Africa. We should now anticipate that the MERS virus will result in more deadly outbreaks outside of the Arabian Peninsula, as it did in Seoul, South Korea. We should anticipate that viruses such as Venezuelan equine encephalitis may spread from their jungle homes and be even more deadly than Zika.

Even more than these viruses, we should be afraid of a planet-wide catastrophe caused by influenza. The best way to avert a pandemic is to develop a game-changing universal influenza vaccine. All these crises are largely predictable and we can do much in advance to lessen the effects and diminish the spread. And believe me, the cost of acting now will be infinitely less than the cost of not acting in the long run.

Michael T. Osterholm, a professor and director of the Center for Infectious Disease Research and Policy at the University of Minnesota, is the author of the forthcoming book Common Enemy: Dispatches from the War with Deadly Pathogens — the Fight We Cannot Afford to Lose.

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