Nina Fedoroff – TRANSCRIPT
Zika fever: our newest dread disease. What is it? Where’d it come from? What do we do about it? Well for most adults, it’s a relatively mild disease — a little fever, a little headache, joint pain, maybe a rash. In fact, most people who get it don’t even know they’ve had it. But the more we find out about the Zika virus the more terrifying it becomes. For example, doctors have noticed an uptick of something called Guillain-Barré syndrome in recent outbreaks. In Guillain-Barré, your immune system attacks your nerve cells it can partially or even totally paralyze you. Fortunately, that’s quite rare, and most people recover. But if you’re pregnant when you’re infected you’re at risk of something terrible. Indeed, a child with a deformed head.
Here’s a normal baby. Here’s that infant with what’s called microcephaly. a brain in a head that’s too small. And there’s no known cure. It was actually doctors in northeastern Brazil who first noticed, just a year ago, after a Zika outbreak, that there was a peak in the incidence of microcephaly. It took medical doctors another year to be sure that it was caused by the Zika virus, but they’re now sure. And if you’re a “bring on the evidence” type, check out this publication.
So where did it come from, and how did it get here? And it is here. Like many of our viruses, it came out of Africa, specifically the Zika forest in Uganda. Researchers at the nearby Yellow Fever Research Institute identified an unknown virus in a monkey in the Zika forest which is how it got its name. The first human cases of Zika fever surfaced a few years later in Uganda-Tanzania. The virus then spread through West Africa and east through equatorial Asia — Pakistan, India, Malaysia, Indonesia. But it was still mostly in monkeys and, of course, mosquitoes.
In fact in the 60 years between the time it was first identified in 1947 and 2007 there were only 13 reported cases of human Zika fever. And then something extraordinary happened on the tiny Micronesian Yap islands. There was an outbreak that affected fully 75 percent of the population. How did it get there? By air. Today we have two billion commercial airline passengers. An infected passenger can board a plane, fly halfway around the world before developing symptoms — if they develop symptoms at all. Then when they land, the local mosquitoes begin to bite them and spread the fever. Zika fever then next surfaced in 2013 in French Polynesia. By December of that year, it was being transmitted locally by the mosquitoes. That led to an explosive outbreak in which almost 30,000 people were affected.
From there it radiated around the Pacific. There were outbreaks in the Cook Islands, in New Caledonia, in Vanuatu, in the Solomon Islands and almost all the way around to the coast of South America and Easter Island. And then, in early 2015, there was an upsurge of cases of a dengue-like syndrome in the city of Natal in northeastern Brazil. The virus wasn’t dengue, it was Zika, and it spread rapidly — Recife down the coast, a big metropolitan center, soon became the epicenter. Well people have speculated that it was 2014 World Cup soccer fans that brought the virus into the country. But others have speculated that perhaps it was Pacific Islanders participating in championship canoe races that were held in Rio that year that brought it in.
Well today, this is only a year later. The virus is being locally transmitted by mosquitoes virtually throughout South America, Central America, Mexico and the Caribbean Islands Until this year, the many thousands of cases that have been diagnosed in the US were contracted elsewhere. But as of this summer, it’s being transmitted locally in Miami. It’s here.
So what do we do about it? Well, preventing infection is either about protecting people or about eliminating the mosquitoes. Let’s focus on people first. You can get vaccinated. You can not travel to Zika areas. Or you can cover up and apply insect repellent. Getting vaccinated is not an option, because there isn’t a vaccine yet and there probably won’t be for a couple of years. Staying home isn’t a foolproof protection either because we now know that it can be sexually transmitted. Covering up and applying insect repellent does work until you forget.
So that leaves the mosquitoes, and here’s how we control them now: spraying insecticides. The protective gear is necessary because these are toxic chemicals that kill people as well as bugs. Although it does take quite a lot more to kill a person than to kill a bug. These are pictures from Brazil and Nicaragua. But it looks the same in Miami, Florida. And we of course can spray insecticides from planes. Last summer, mosquito control officials in Dorchester County, South Carolina, authorized spraying of Naled, an insecticide, early one morning, as recommended by the manufacturer. Later that day, a beekeeper told reporters that her bee yard looked like it had been nuked. Oops. Bees are the good guys. The citizens of Florida protested, but spraying continued. Unfortunately, so did the increase in the number of Zika fever cases. That’s because insecticides aren’t very effective.
So are there any approaches that are perhaps more effective than spraying but with less downsides than toxic chemicals? I’m a huge fan of biological controls, and I share that view with Rachel Carson, author of “Silent Spring,” the book that is credited with starting the environmental movement. In this book she tells the story, as an example, of how a very nasty insect pest of livestock was eliminated in the last century. No one knows that extraordinary story today.
So Jack Block and I, when we were writing an editorial about the mosquito problem today, retold that story. And in capsule form, it’s that pupae — that’s the immature form of the insect — were irradiated until they were sterile, grown to adulthood and then released from planes all over the Southwest, the Southeast and down into Mexico and into Central America literally by the hundreds of millions from little airplanes, eventually eliminating that terrible insect pest for most of the Western Hemisphere. Our real purpose in writing this editorial was to introduce readers to how we can do that today — not with radiation but with our knowledge of genetics. Let me explain.
This is the bad guy: Aedes aegypti. It’s the most common insect vector of diseases, not just Zika but dengue, Chikungunya, West Nile virus and that ancient plague, yellow fever. It’s an urban mosquito, and it’s the female that does the dirty work. She bites to get a blood meal to feed her offspring. Males don’t bite; they don’t even have the mouth parts to bite. A little British company called Oxitec genetically modified that mosquito so that when it mates with a wild female, its eggs don’t develop to adulthood. Let me show you.
This is the normal reproductive cycle. Oxitec designed the mosquito so that when the male mates with the wild female the eggs don’t develop. Sounds impossible? Well let me show you just diagrammatically how they do it. Now this represents the nucleus of a mosquito cell, and that tangle in the middle represents its genome, the sum total of its genes. Scientists added a single gene that codes for a protein represented by this orange ball that feeds back on itself to keep cranking out more of that protein. The extra copies, however, go and gum up the mosquitoes’ genes, killing the organism.
To keep it alive in the laboratory they use a compound called tetracycline. Tetracycline shuts off that gene and allows normal development. They added another little wrinkle so that they could study what happens. And that is they added a gene that makes the insect glow under UV light so that when they released it they could follow exactly how far it went how long it lived and all of the kinds of data for a good scientific study. Now this is the pupal stage, and at this stage the females are larger than the males. That allows them to sort them into the males and the females and they allow only the males to grow to adulthood.
And let me remind you that males don’t bite. From there it’s pretty simple. They take beakers full of male mosquitoes, load them into milk cartons, and drive around the city, releasing them guided by GPS. Here’s the mayor of a city releasing the first batch of what they call the “friendly Aedes.” Now I wish I could tell you this is an American city, but it’s not. It’s Piracicaba, Brazil. The amazing thing is that in just a year it brought down the cases of dengue by 91 percent. That’s better than any insecticide spraying can do.