The facts of the Zika outbreak have left people terrified, and understandably so. Lies and hysteria about the source of the virus aren’t helping. Photograph by Felipe Dana / AP

Late last month, Margaret Chan, the director of the World Health Organization, announced that the Zika-virus outbreak in Latin America had moved from being a “mild threat to one of alarming proportions.” This week, the Centers for Disease Control and Prevention made that threat palpable. The agency said it was investigating fourteen reports in which the virus appears to have been transmitted through sex, in addition to being spread by mosquitoes.

In most cases, Zika is so mild that people can become infected and never know it. But the virus has also been associated with an otherwise-rare birth defect in which babies are born with abnormally small heads and underdeveloped brains, a condition known as microcephaly. It is also suspected of having caused Guillain-Barré syndrome, which leads to (an almost always temporary) paralysis. It is too soon for epidemiologists to have proven those links beyond question, but few, if any, experts doubt them.

These facts have left many people terrified, which is understandable. There is no treatment for Zika, and no vaccine. This is a serious virus, and we don’t know much about it yet. But we do know a few things: Zika is not caused by vaccines, despite persistent rumors spread by anti-vaccine zealots, including the willfully uninformed Vaccine Information Network. Or by pesticides, or larvicides, or the Gates Foundation, or the Rockefeller Foundation. It is not even caused by Monsanto. Nor is it new. As David Quammen pointed out in a post for National Geographic, the virus, which, like dengue fever, is transmitted by the Aedes aegypti mosquito, was first recognized in 1947, in Uganda.

But conspiracy theories flow constantly across the Internet. An endless stream of anti-single-bullet theories seems to be a price we pay to have human knowledge at our fingertips. And conspiracy theories are part of American life. The leading Republican candidate for President has at various times supported the idea that vaccines cause autism (they don’t), that Barack Obama wasn't born in America (he was), and that climate change is a non-crisis invented by the Chinese to capture market share.

At least one Zika conspiracy, by far the most damaging, may be hard to ignore. More than a third of the Americans surveyed in a poll, out this week, from the University of Pennsylvania’s Annenberg Public Policy Center believe that genetically modified mosquitoes caused the spread of Zika. This is a particularly dangerous misapprehension, because, for now, controlling mosquitoes may be the only way we can hope to control Zika.

This myth seems to have grown out of a Reddit post, which was then repeated and tweeted. “This seems like a case to me where mankind's arrogance may have backfired on us,’’ the post says, before going on to suggest, with no regard to the facts, that Oxitec, a British company that modifies mosquitoes to fight the spread of another disease, dengue fever, might be at the root of this epidemic. The post notes that there were cases of microcephaly not far from Juazeiro, Brazil, where Oxitec introduced modified mosquitoes, in 2012. Actually, those cases are more than a thousand miles away. (I was in Juazeiro when Oxitec released mosquitoes there, and I wrote about it for this magazine.)

There is no treatment or vaccine for dengue, which affects as many as fifty million people every year. It is a debilitating disease, and the current approach is to use chemicals to kill the mosquitoes that spread it. As I wrote in the piece, the Oxitec mosquitoes are modified so that one gene carries instructions to manufacture far too much of a protein required to maintain healthy new cells; the results are lethal. Scientists keep the gene at bay, and the mosquitoes alive, by placing the antibiotic tetracycline in the insects’ food. The drug latches on to the protein and acts as a switch that can turn it on or off. As long as tetracycline is present, the mosquitoes live and reproduce normally and can be bred for generations. Once they are released from the lab, however, the antidote is gone; the lethal gene goes unchecked. Within days, the males, along with any eggs they help create, will perish.

It is worth pointing out that Aedes aegypti don’t fly far or live long; a major traveller would move a few hundred yards and, on average, survive as an adult for ten days or two weeks.

The logic of the genetically-modified-mosquitoes conspiracy theory is hard to grasp: it has been four years since they were first released in Brazil. Human pregnancies last nine months. Surely some babies must have been born in the intervening three years. Why were they spared the microcephaly if the genetically modified mosquitoes are to blame? Moreover, the altered mosquitoes had previously been released in the in the Cayman Islands, Malaysia, and Panama without causing problems. Viruses constantly spread and mutate, and that began long before humans arrived on Earth.

Not long ago, Americans were naïve enough to think the days of infectious disease were over in this country. By the end of the nineteen-sixties, vaccines had been developed to prevent smallpox, polio, measles, pertussis, and rubella, among other serious maladies. We had even managed to almost vanquish malaria, which in the developing world continues to kill hundreds of thousands of children, and sicken tens of millions, every year.

Then, in 1981, people in our biggest cities, most of them, at first, gay men, began to die in the prime of their lives, and our delusions about infectious diseases ended. In the age of AIDS, there has also been a resurgence of tuberculosis, which came back in a more resistant form. We are threatened by avian flu, swine flu, SARS, MERS, and Ebola, to name just a few. The number of people with Lyme disease has also grown exponentially.

Now we have Zika. Next year or month or week, it will be something else, because climate change and the fast pace of travel in a global economy have all but guaranteed that emerging infectious diseases are everywhere to stay. What happens in Malaysia or Uganda no longer stays in Malaysia or Uganda. Lies and hysteria are never going to help.