Could Vaccines Save Wild Populations of Endangered Animals?

This was the idea first proposed to protect the Siberian or Amur tiger (Panthera tigris)…

This was the idea first proposed to protect the Siberian or Amur tiger (Panthera tigris) from canine distemper virus, which showed up in the early 2000s. Though the disease, which plagues the respiratory system and, later, the brain, appeared to affect only two tiger populations in Siberia, wildlife managers grew greatly concerned; in 1994, an outbreak of CDV killed roughly one-third of the Serengeti’s lion population.

Gilbert found that if small tiger populations, like the one in southwest Primorski, are exposed to even modest levels of CDV, it’s 65% more likely the population will go extinct within 50 years.

“Initially, we thought this was going to be a dog issue — tigers eat dogs regularly,” Gilbert says of the origin of the virus. Veterinarians, therefore, assumed that vaccinating domestic dogs in Siberian villages and controlling their movement would mitigate the threat to wild tigers. But Gilbert’s latest research reveals that, surprisingly, dogs aren’t the reservoir population of canine distemper in Siberia. Instead, when Gilbert and his colleagues sampled wildlife carcasses found in fur traps and along roadsides, they found high levels of CDV antibodies in the brain tissue of everything from raccoon dogs (Nyctereutes procyonoides) to badgers (Meles leucurus) to Siberian weasels (Mustela sibirica).

Canine distemper is likely transmitted to tigers from their prey, Gilbert says. “In late summers, tigers will sit along badger runs and kind of pop them like candy as they come running along their trails through the forest.” Such findings indicate that “the only feasible approach to mitigating the impact of distemper on the tigers would be to vaccinate the tigers themselves.”

The logistics are daunting. Many people living in Siberia have never even seen a tiger. And no wild tigers have ever been vaccinated for any disease.

“We’re never going to be able to vaccinate the whole population of tigers,” Gilbert says. But he adds it’s possible inoculation could be done on a passive basis: conservationists could vaccinate tigers captured due to conflicts, or orphaned cubs in rehabilitation. He’s found that if veterinarians were able to vaccinate just two tigers per year, they would reduce the extinction risk by 75% in Russia’s Primorye population.

The other challenge is that there is no dedicated CDV vaccine for big cats. Today, they only exist for ferrets and dogs. To repurpose a vaccine for a different species, clinical trials may need to be conducted anew.