Science

Why the Capitol Hill Fox Had to Die

It had to be put down before it tested positive for rabies.

A greyed-out image of a fox in front of the US Capitol building with "ELIMINATED" stamped in red over it. RIP Capitol Fox.
Gone but not forgotten. Photo illustration by Slate. Photos by lucky-photographer/iStock/Getty Images Plus, GlobalP/iStock/Getty Images Plus, and Aquir/iStock/Getty Images Plus.

I come bearing unfortunate news: The Capitol Hill Fox, which Slate covered with adoration, has been euthanized. I know, tough to hear. But the fox was responsible for nine (!) bites, so it had to be tested for rabies. And in order to be tested for rabies, the fox needed to be put down.

I did wonder, however, if it had to go like this. In this case, the fox did have rabies, officials confirmed Wednesday afternoon; rabies is lethal anyway. But why was killing the animal immediately the way to go? Couldn’t they have tranquilized the fox, and tested it, while it was still alive? And then—had it been negative—released it far, far away from humans? The answer to that is no, for a few reasons.

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The common cultural idea of rabies is an animal foaming at the mouth, ready to bite whoever is unfortunate enough to cross paths with them. This had me thinking that some kind of mouth swab could do the trick. Foaming mouth, biting—these things all seem to point to an oral disease. But rabies is a virus that is primarily found in the host’s nerves and brain.

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Here’s how catching rabies works: After an animal or person is bitten, if no post-exposure measures are taken, the virus seeps in through the puncture wound and infects the nerves close to the bite. From there, it takes advantage of the communication system between  neurons to hitch a ride to its final destination: the brain. There, it wreaks havoc on the brain cells. It also makes its way to the salivary glands, where it’s excreted in saliva, and ready to start the whole process over again.

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When it comes to testing, though, saliva samples are unreliable: a swab of saliva won’t always contain the virus. (In humans, you can do a skin biopsy, but this isn’t typically done for animals.) A test might return a negative result for the particular bit of saliva you tested, even if the animal is secreting saliva that does contain the virus.

Instead, the “gold standard” of rabies testing is testing the animal’s brain, including its cerebellum and brain stem, Dr. Leyi Wang, a veterinary virologist at the University of Illinois, told me. If an animal has rabies, you will definitely find the virus in its brain. This test, called a direct fluorescent antibody test, is thought to have never failed to detect rabies in an animal. And you need to be 100 percent sure if an animal has rabies or not, because rabies is nearly 100 percent fatal in humans once an infection has established itself. This is not a situation where we can afford to risk false negatives. If someone has been bitten, they have to go get a series of shots that will prevent the virus from making itself at home in their brain. But once the infection has taken hold, there is currently no reliable treatment. (Options like the Milwaukee Protocol, which saved one person’s life in 2004 by way of inducing a coma, do not usually work.)

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In order to test the animal’s brain, you have to euthanize it. (In the state of New York, it also may have to be  decapitated so the  head  can be sent in for testing.) For pets, there is an exception: if a pet is unvaccinated against rabies and it bites someone, its owner can elect to quarantine it for a few months. But foxes are not pets, cute as this one was (until it started biting people). Wang told me that foxes as a group are a “rabies reservoir,” meaning that it made a lot of sense to test that fox because it’s not uncommon to find rabies in foxes. So there was no getting around it: that fox had to be tested.

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Rabies infections in humans are very rare. That’s a huge win for public health. That success is thanks to a number of factors: that series of shots immediately after exposure works exceedingly well, pet vaccination programs have curbed transmission and because we use surveillance methods like testing wild animals … after we kill them. So I’m sorry, animal lovers, but the fox did indeed have to be euthanized. When you’re dealing with something as serious as rabies you have to be sure—and in this case, since the fox actually had rabies, it paid off directly. It sucks for the fox, but preventing rabies is more than worth it.

Correction, April 7, 2022: This article originally misstated that the fox had to be tested for rabies specifically because the bites were unprovoked. Foxes always have to be tested for rabies after they bite people.

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