Lessons from tigers in the Russian Far East: drawing principles from puzzles

Following the deaths of several Amur tigers Panthera tigris altaica in the Russian Far East from canine distemper virus (CDV), research has been directed at understanding the need for, and design of potential mitigation... [ view full abstract ]

Following the deaths of several Amur tigers Panthera tigris altaica in the Russian Far East from canine distemper virus (CDV), research has been directed at understanding the need for, and design of potential mitigation strategies. An individual-based stochastic, SIRD (susceptible-infected-recovered/dead) model showed that the 50-year extinction risk in populations consisting of 25 individuals was 1.65 times greater when CDV was present than control populations. Extinction was also disproportionately more likely for small populations. One such population exists in Southwest Primorskii Krai and represents the source for tiger recovery in China, and successful reintroduction attempts in the Pri-Amur region represent another emerging isolated population with high risk of CDV infection. Existing recommendations to improve connectivity between disjointed tiger populations would reduce extinction risk, but are not being implemented. Field epidemiological studies determined that CDV was circulating over a wide spatial scale, and involved both domestic and wild carnivore hosts. The widespread involvement of wild carnivores in CDV transmission suggests that vaccination of domestic dogs would be unable to eliminate infection of tigers. Vaccination strategies that target tigers would reduce mortality from CDV, but are challenging in such a cryptic species, particularly as available products are not designed for oral delivery. The SIRD model was modified to assess the impact of tiger vaccination using several low coverage strategies with two hypothetical vaccine efficacies. Simulations suggested that 50-year extinction risk could be reduced from 43.2% to 5.4%, depending on vaccination method. A preventive control program that vaccinated 2-4 tigers annually provided better protection than a responsive protocol that vaccinated up to 50% of tigers when outbreaks were detected. While these findings suggest that vaccination of tigers would benefit their conservation, further studies are required to assess vaccine safety and efficacy in Panthera spp., and development of orally available products could enhance program feasibility.