A new threat has emerged that could finally push tigers to extinction, wildlife experts have warned.
Canine distemper virus (CDV) has been identified by scientists as responsible, at least in part, for the decline in the Amur tiger population in Russia's Sikhote-Alin Biosphere Zapovednik (SABZ).
The study, by the Wildlife Conservation Society, found that CDV was the cause of death in two dead tigers found on the reserve between 2007 and 2012 – over the five years the population fell from 38 tigers to just nine.
Researchers believe CDV played a role in the overall decline of the population.
CDV is fatal in about 50% of cases. It infects the brain, spinal cord, respiratory tract and gastrointestinal tract. Symptoms include vomiting and diarrhoea, seizures, paralysis and watery-discharge of the nose and eyes.
In the study, published in PLOS One, computer models showed how smaller populations were more at risk from CDV –populations of 25 tigers were 1.65 more likely to decline over the next 50 years if the disease was present.
Martin Gilbert, a vet with WCS, said: "Although we knew that individual tigers had died from CDV in the wild, we wanted to understand the risk the virus presents to whole populations. Tigers are elusive, however, and studying the long-term impact of risk factors is very challenging. Our model, based on tiger ecology data collected over 20 years in SABZ, explored the different ways that tigers might be exposed to the virus and how these impact the extinction risk to tiger populations over the long term."
Researchers simulated the effects of CDV on isolated tiger populations through a series of scenarios, including tiger-to-tiger transmission and transmission through preying on CDV-infected domestic dogs and/or infected wild carnivores.
Findings showed CDV increased the chance of tigers going extinct in SABZ over the next 50 years by 55% compared with CDV-free populations.
WCS Russia programme director Dale Miquelle said: "Tigers face an array of threats throughout their range, from poaching to competition with humans for space and for food. Consequently, many tiger populations have become smaller and more fragmented, making them much more susceptible to diseases such as CDV."
Researchers said they must now identify the animals that spread CDV and other sources of the disease.
"While we must continue to focus on the primary threats of poaching and habitat destruction, we now must also be prepared to deal with the appearance of such diseases in the future," Miquelle said.