How the U.S. Lost the War Against West Nile

A mosquito-control expert searches a New Hampshire marsh in July 2000 for mosquitoes that could carry West Nile.
Photo: Getty Images

For a brief time at the turn of the millennium, few things might have scared the average New Yorker more than the words “West Nile,” the name given to the mosquito-borne virus that, in 1999, began killing birds and eventually people for the very first time in the U.S.

Two decades later, the worst fears sparked by West Nile hysteria haven’t come to pass. The initial outbreak in New York, which infected at least 59 people and killed seven, wasn’t the work of bioterrorists. There were never massive outbreaks of West Nile that arrived on deadly wings like clockwork every summer, nor did droves of people horrifically die from having their brains infected and cooked from the inside out.

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But despite dedicated mosquito spraying and surveillance efforts, the virus has thrived exceptionally well here. First discovered in Uganda in 1937, it’s now the most common mosquito-borne disease in the U.S., with cases regularly seen in all 48 landlocked states. Along the way, it has periodically decimated bird and horse populations, sickened at least 50,000 people (millions of people have probably been infected, but only a minority experience symptoms), caused devastating neurological illness in 25,000 people, and killed over 2,000 people. And scientists have called West Nile’s arrival in the U.S. one of the most important events in the world of arbovirology (“arbo” meaning spread by an insect or arthopod) to have happened in the past two centuries.

In recognition of West Nile’s 20th anniversary in the U.S., Gizmodo interviewed Laura Kramer, director of the Arbovirus Laboratory at the New York State Department of Health. Kramer is one of many experts who have contributed to a retrospective on West Nile that is published today in the Journal of Medical Entomology. She was also one of the first scientists brought in by the local government to establish a surveillance team for West Nile, following the initial cases documented in the summer of 1999. The following conversation has been edited and condensed for clarity.

Gizmodo: As a lifelong New York City resident, the arrival of West Nile that year was one of the first truly frightening news events I can remember witnessing growing up. But what was it like for the researchers and scientists on the ground, trying to study and contain it?

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Kramer: At first, the idea that West Nile was here in the U.S. was sort of like, “what!?” Because the initial thought was that it was St. Louis encephalitis, but St. Louis doesn’t kill birds. So it took a little bit of time to sort that out, but not very long.

I never felt fear. I had questions. It was alarming that this virus could come to the U.S., but then the big question was, will it last? You know, will it make it through the winter? And if it makes it through, will it be able to establish itself? And if it establishes itself, what will happen when it gets to the southern states where there’s a much longer transmission season? I think when you’re in the middle of it, you don’t have fear. You just have these questions. What do we need to do? How can we accomplish it? Let’s get there.

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Gizmodo: Ultimately, the virus did spread eastward, southward, and eventually everywhere, through the help of Culex mosquitoes. Did we ever stand a chance of containing it in the beginning?

Kramer: For a zoonotic disease, once you have a receptive environment, susceptible hosts, and proper weather conditions, it’s really hard to contain it. I think they did everything that they could have done. You know, they sprayed heavily in the areas where West Nile had been identified, like in Queens. But once it got in the birds—and there’s so many species of birds that are susceptible, I think it’s over 300—every bird could have a role in keeping the virus going.

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In retrospect, they could have paid more attention to birds dying earlier. But that’s not a CDC thing, that’s USDA. Birds were dying, but people weren’t thinking in terms of public health. And I don’t think most people noted the birds were dying at first. So maybe if that had been noticed earlier, then spraying early could have stopped it much earlier. But I don’t know—it would have been hard.

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Gizmodo: What do you think might be the most lasting legacy of West Nile?

Kramer: I think we’ve learned a lot from West Nile. One thing that West Nile did was also prepare us for Zika. Not that Zika is in the country, and it’s a completely different virus, but having the stronger public health infrastructure that we did helped us get the testing for Zika up very quickly.

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I also think it taught us that we need to have a global perspective in order to be alert for invasive viruses and other pathogens. And not just the pathogens, but the mosquitoes. Culex pipiens was an invasive species; it was brought to the U.S. West Nile also really brought home the lesson of the one health concept, where we have to pay attention not just to human disease but animal health. And it taught us that we need to keep communication open between labs and other scientists. It definitely increased communication between veterinarians and public health practitioners, and veterinarians had sometimes been sidelined in the past.

The other major lesson is about the complexity of these disease cycles—that it’s not just the virus, or just the birds, or just the mosquitoes. There are different species of mosquitoes, and even within a species, there’s differences in populations. Similarly with the virus, West Nile has more than one lineage, and the lineage that came here evolved. It was very well adapted when it came, but it’s still evolving and adapting further.

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Gizmodo: It seems like you’re saying that we don’t have the tools, even today, to eradicate West Nile in this country.

Kramer: Oh, yeah, no. It’s out of the bag. It’s enzootic [the animal equivalent of an endemic disease in people] in the wildlife, the birds, the mosquitoes. The activity level can go up and down year to year, but it cannot be eradicated. Even if you had mosquito control that was really innovative, something like using Wolbachia [a bacteria that’s been used in other mosquito species to keep them from hosting and spreading diseases like Zika and dengue], there are enough birds, enough new birds every year that are susceptible and could keep it going.

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What we have to do is maintain public health infrastructure, which we have to do for many reasons besides West Nile, like for tick-borne diseases and other invasive diseases. And I do think surveillance has really improved. It’s more rapid, and we can do more specific testing. But I also think we need to rethink how we do surveillance.

There’s some of that thought going on now, with all the new technology we have. We need to be able to see things that we’re not looking for. Right now, we only test for what we know is here—and that’s fine, we can follow the activity of what’s here. But if something else comes in, and we miss it at first, because we’re just doing this very specific testing, we’re going to be in the same boat with the next invasive virus.

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About the author

Ed Cara

Science writer at Gizmodo and pug aficionado elsewhere