To control rabies in wildlife, the USDA drops vaccine treats from the sky

In the early 1900s, more than 100 people died annually from rabies in the United States.

These days, that number is five or less.

And although hundreds of domestic animals and livestock still contract the disease every year, their numbers were historically much higher too. All species of mammals are susceptible to rabies infections. But only a few of those species act as reservoirs, or hosts that allow the virus to spread.

And so, since 1995, the U.S. Department of Agriculture has run a yearly campaign that aims to keep rabies at bay in one population in particular: raccoons.

How they vaccinate is somewhat unique.

Vaccines from the sky

Every year, the USDA drops millions of oral rabies vaccines across fourteen states, mostly along the eastern seaboard. (Texas also has a program.) In urban and suburban areas, this usually means officials drive around, depositing bait where raccoons are likely to find it and eat it, like around dumpsters.

In rural areas, though, there's a more efficient way to distribute the bait.

"They're scattered by these low flying planes. And the planes have a tube and a conveyor belt that just drops these vaccines to make sure they're sort of evenly dispersed," says Emily Mullin, a staff writer for WIRED who covered the USDA raccoon vaccination program for Undark.

The program covers tens of thousands of square miles. So far, the program has been a big success. It has essentially stopping the geographic spread of rabies in the eastern U.S., according to Jordona Kirby, a USDA wildlife biologist and field coordinator for the National Rabies Management Program.

Long term, she hopes the program will stomp out raccoon rabies for good. That would require "marching it from its current extent, which is essentially along the Appalachian Mountains running from Maine to Alabama ... all the way back to the ocean," she says. "That is our long term vision."

A vaccine, but make it tasty

The oral rabies vaccine was developed in the 1960s and '70s. The first field trials targeted red foxes in Switzerland.

By the 1990s, the U.S. began its first field trial on an uninhabited Atlantic barrier island off the coast of Virginia. And in the mid '90s, the USDA started partnering with states to begin oral rabies vaccination programs for wildlife.

One key to the success of the raccoon vaccination effort was making the bait palatable to a raccoon. "So we've got the fish flavor and then the other one is a sweet flavor ... both of which work quite well for raccoons," says Kirby.

Turns out, raccoons love a vanilla oral vaccine. Go figure!

But these flavors don't only attract raccoons. "Our feelings are absolutely not hurt if skunks, foxes or coyotes pick them up. And they do," Kirby notes. "So, although raccoons are the reservoir and spread rabies primarily in the east, those other animals, just like any mammal, can contract rabies."

If another animal, like a dog, finds and eats the bait, it won't harm them.

Why tasty vaccines are not enough

Kirby thinks that with more resources, the U.S. could eradicate raccoon rabies in the coming decades.

But eradicating all rabies in the U.S. is a tall order.

Raccoons aren't the only reservoir. Skunks and bats also circulate the disease, with the latter being the leading cause of rabies deaths in people in the country.

Bats pose a particular challenge to any larger eradication effort.

How do you get an oral vaccine to an animal that flies?

Kirby says there have been some studies into aerosol vaccines or coating a few bats that will take it back to their colonies through grooming, "but it's still sort of in the infancy stages."

In the interim, Kirby says education around bats as rabies carriers is important. For example, knowing that people can't always feel a bat bite and that immediate treatment in the case of an exposure is the best tool for keeping people safe.

Further Reading:

• Emily Mullen's story on USDA's raccoon rabies vaccination program, which inspired this episode

• Emily Mullen's story on rabies in vampire bats, which are moving toward the southern border of the U.S.

Listen to Short Wave on Spotify, Apple Podcasts and Google Podcasts.

Curious about an infectious disease? Email us at shortwave@npr.org.

This episode was produced by Berly McCoy, edited by Rebecca Ramirezand fact checked by Anil Oza. Ko Takasugi-Czernowin was the audio engineer.

Copyright 2023 NPR. To see more, visit https://www.npr.org.

• The science and art of breeding, growing and tasting fruit
• Helen Scales advocates for the ocean in ‘What the Wild Sea Can Be’
• Stargazers can see the final supermoon of the year this weekend
• Taurid meteor shower to light up the night sky. Here's how you can see it