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Vaccinating the World's Top Predators May Be the Only Way to Save Them

A disease that began in domestic dogs is threatening carnivores the world over—and a desperate, difficult plan to vaccinate some of the planet's deadliest predators may be the only way to save them.
February 19, 2015, 3:21pm
​Lions may soon be the target of a global vaccination campaign. Kevin Pluck: Wikimedia

If we want lions and tigers to survive, it might be time to start vaccinating them. At least, that's the latest thinking of some of the world's leading wildlife vets, who are confronting one of the most devastating bouts of canine distemper virusever diagnosed.

"This is a high impact disease with the potential to cause local and possibly massive extinction," virologist Colin Parish, director of the Cornell Feline Health Center, told me.


It's a harrowing image: A gaunt tiger stumbles out of the forest, staggers across a snow-covered road into a quiet Siberian town. The animal, dazed and feverish from brain swelling, has not only lost its fear of humans—it's ravenous. Frightened residents may decide to shoot the beast before it decides to go after them.

A tiger stumbling across a Siberian highway.

Incidents like this have become tragically common over the past decade, as the virus that was first discovered in man's best friend now wreaks havoc amongst Earth's top predators. With charismatic animals like Siberian tigers facing possible extinction, wildlife vets from across the world convened last month at the Bronx Zoo to discuss an option that once sounded absurd.

"The most logical approach for protecting threatened carnivores from canine distemper virus may be to target the vaccine on the endangered species itself," virologist Edward Dubovi of Cornell's Animal Health Diagnostic Center told his colleagues at the Vaccines for Conservation International Meeting.

If the idea gains traction, we may soon bear witness to one of the largest global vaccination campaigns ever targeted toward wild animals—and some of Earth's most deadly, to boot.

While best known for afflicting our beloved pets, the promiscuous CDV, a close cousin to the measles, infects a range of wild carnivores large and small. In addition to causing fever, diarrhea, and dehydration, the virus can induce deadly brain swelling and neurological disorders. Even if afflicted individuals recover, they can be behaviorally impaired for life, making them easier targets for poachers.


The rare Ethiopian wolf is another predator now facing extinction at the hands of CDV. Image: Wikimedia

While it doesn't garner the attention of a Disneyland measles outbreak, CDV has been the bane of conservationists and wildlife vets for decades. It nearly annihilated the black footed ferret in the 1980's, slaughtered thousands of Caspian seals in the 1990s, and in recent weeks, has killed four giant pandas in Chinese zoos. Giant cats were thought to be immune until a 1993 outbreak in Serengeti National Park wiped out over a third of the park's lion population in one deadly spate.

As the situation grows dire for some of the world's most endangered predators, the conservation community has sounded a call to arms. At the Vaccines for Conservation meeting, ecologists, epidemiologists, virologists, and policymakers came together to discuss options for containment.

Previous attempts to control the spread of CDV into wild populations focused on stopping the virus at the presumed source—domestic dogs. Unfortunately, research now shows that top predators are probably contracting CDV from smaller wild animals that act as intermediaries. The simplest solution, then—ensuring that humans vaccinate their pets—may no longer be an effective option.

Which is where vaccinating the afflicted carnivores directly comes in. While immunizing wild animals is not unheard of—it's common practice, for instance, to administer rabies vaccines to foxes and raccoons—targeting dispersed populations of large and dangerous predators isn't standard fare.

"The general feeling is that the dangers associated with capturing and anesthetizing these animals are very high," Parrish said. "If a vaccine strategy is going to be implemented, it would be much better if we could come up with a passive delivery mechanism."

Oral and aerosol vaccines, planted in baits or on marking posts, have been successfully deployed to contain rabies. Whether scientists are able to cook up a CDV vaccine that's safe, effective, and packaged inside something that halfway resembles dead gazelle remains to be seen, but researchers are hot on the problem.

At least when it comes to wildlife, all parties involved agree that vaccination is a good thing.