The Zika Virus: A Pandemic Like No Other?

Editor's Note:

Sonia Shah is a science journalist and prizewinning author, and has written for The New York Times, The Wall Street Journal, Foreign Affairs, Scientific American, and elsewhere. She’s most recently the author of Pandemic, and joins Signature to contextualize the role of the Zika virus in the ongoing battle between us and evolving viruses.

The Zika pandemic exploded seemingly out of nowhere, unleashing fear and confusion in its wake. But the circuitous journey of the mysterious virus currently spreading across the Americas is anything but singular.

Over the past fifty years, more than 300 infectious diseases have newly emerged or re-emerged in new places where they’ve never been seen before, from Ebola in West Africa to MERS in the Middle East and novel forms of avian influenza in Asia. These newcomers had been pummeling the Americas for years before Zika arrived. In 2009, a novel form of influenza, H1N1, erupted in Mexico, causing a global pandemic; that same year, dengue emerged in Florida, where it hadn’t been seen in seventy years. In 2010, Haiti was hit by an unprecedented epidemic of cholera, where it hadn’t been reported in over 100 years. In 2013, the mosquito-borne virus Chikungunya started spilling across the Caribbean and South America. It had never been seen there before either.

Go back a couple more decades and HIV, Lyme disease, and West Nile virus extend the list of never-before-seen pathogens that have washed over the Americas. All three are now prevalent across the United States. And that’s just counting new infectious diseases in humans. Our wildlife and livestock have been hit hard too. In recent years, chytrid fungus has driven amphibian species to the brink of extinction, white nose syndrome has decimated North American bats, and colony collapse disorder has devastated bees. In 2014, a newly emerged flu virus from Asia emerged on turkey and chicken farms in the U.S. Midwest, sparking the most deadly epidemic of animal disease in U.S history.

All of these pathogens, Zika included, follow a well-worn path. They cross over into our bodies from wild animals, as our populations and industrial developments increasingly invade and destroy wildlife habitat, pushing humans and wild species into novel, intimate contact. More than sixty percent of our new pathogens originate in the bodies of the furred and winged creatures among us; seventy percent come from wildlife. From bats, we got Ebola and SARS. From rodents, monkeypox and Borrelia burgdorferi, which causes Lyme disease. From birds, West Nile virus and avian influenza. From our fellow primates, we got HIV.

Lucky ones are able to hitch rides on our flight travel network, allowing them to reach the growing hordes of people and livestock crowded into expanding cities and factory farms. That’s the good fortune that befell Zika. For decades, Zika was primarily a virus of monkeys in the equatorial forests of Africa and Asia. In 2007, it broke out in small, remote populations in Micronesia and French Polynesia. Then, in August 2014, a flight carrying French Polynesian paddlers to an international canoe race in Rio de Janeiro likely deposited Zika virus amidst the massive, urbanizing populations of Brazil, in the heart of the teeming Americas. It’s been accelerating across the continent ever since, expanding exponentially. Our belated defenses, hollowed out by years of under-investment in public health, struggle to scale up, linearly at best.

Experts have been bracing themselves for the next big pandemic, an outbreak of disease that spreads like a wave across continents and global populations, for years. In a 2006 survey, two-thirds of pandemic experts predicted that a pandemic that would cost the global economy $3 trillion would occur sometime in the next two generations. Their biggest fear? A contagion that would sicken 1 billion people and kill 165 million.

But, infernally, each new pathogen exploits the opportunities we provide them and circumvents our defenses in novel ways.

Zika doesn’t kill people. But it could still exact a heavy toll on human populations. A growing body of evidence suggests that it causes a brain-damaging birth defect in the children of infected women. (It is also associated with serious but seemingly short-term neurological effects in some victims.) Yet despite its ability to deform unborn babies, it moves among us almost imperceptibly. The overwhelming majority of infections pass without anyone noticing, causing only mild, forgettable symptoms. There’s no easy way to detect the pathogen inside the body, even when we look. Only a few people experience symptoms, and by the time they do, it’s too late to accurately pinpoint the cause.

Confounded, public health authorities in El Salvador, Jamaica, and elsewhere have made an unprecedented suggestion: that couples delay pregnancies until the epidemic is under control. That  could take years. Scores of fearful couples in affected countries — over twenty and counting — may well try. If birth rates fall as a result, human populations under Zika’s thrall will contract.

The Zika pandemic, in other words, could alter our demographics and the shape of our economies without killing a soul. If it does, it will join a rarefied group of pathogens that have caused pandemics in modern history. But like each of its predecessors, from the plague to influenza to HIV and cholera, it will be a pandemic like no other.