Hold still, big cat: Vaccination could save Siberian tigers

If you think getting your cat to the vet is tricky, think about this: New research has revealed that vaccination of endangered Siberian tigers is the only practical strategy to protect these big cats from a deadly disease in their natural habitat.

The disease, canine distemper virus (CDV), causes serious illness in domestic dogs and infects other carnivores. These include threatened species like the Siberian tiger, also known as the Amur tiger, of which there are fewer than 550 in the Russian Far East and neighboring China. It is often assumed that domestic dogs are the primary source of CDV.

But a team led by Martin Gilbert of the Cornell Wildlife Health Center found that other local wildlife was instead the primary source of CDV transmission to tigers; the team’s study published Nov. 23 in the Proceedings of the National Academy of Sciences.

“Understanding how tigers are catching distemper is absolutely crucial to helping us design effective measures to minimize the conservation impact of the virus,” Gilbert said. “Vaccinating tigers is hard to do, but our research shows that immunizing just two tigers within a small population each year can reduce the risk that CDV will cause extinction by almost 75%. At least in the Russian Far East, vaccinating local domestic dogs would not be an effective strategy to protect tigers.”

The research, led by Cornell, the Wildlife Conservation Society and the University of Glasgow, relied on several lines of evidence to build a picture of CDV epidemiology in the tigers’ habitat.

Using samples from domestic dogs, tigers and other wild carnivores, they compared viral genetic sequence data and used antibodies to assess patterns of exposure in each population.

“The taiga [snow] forest where the tigers live supports a rich diversity of 17 wild carnivore species,” said study co-author Dr. Nadezhda Sulikhan, a researcher from the Federal Scientific Center of East Asia Terrestrial Biodiversity, part of the Russian Academy of Sciences. “Our findings suggest that more abundant small-bodied species like martens, badgers and raccoon dogs are the most important contributors to the CDV reservoir.”

Controlling CDV in these abundant wild carnivore populations is not possible, as there are no CDV oral vaccines that could be distributed to these populations through baited food.

That left only one viable option – using an injectable vaccine on the tigers themselves. To determine whether currently available CDV vaccines could protect wild tigers, the researchers showed in the laboratory that serum from tigers vaccinated in captivity was able to neutralize the strain of CDV that they had detected in Russia. They then developed a computer model showing that even a low rate of vaccination (two tigers per year) could reduce the tigers’ risk of extinction significantly.

Gilbert and colleagues contend that vaccination can be a valuable conservation strategy. As wildlife populations become more fragmented through the effects of habitat destruction, poaching and climate change, they become increasingly vulnerable to local extinctions caused by infectious diseases, such as distemper.

Said study contributor Sarah Cleaveland, professor of comparative epidemiology at the University of Glasgow: “This work shows that CDV in the Amur tiger is a solvable problem – a rare piece of good news for the tiger conservation community.”

Lauren Cahoon Roberts is assistant director of communications at the College of Veterinary Medicine.

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