In June 2010, an emaciated and disorientated female Amur tiger (Panthera tigris altaica) named Galia wandered into the Russian town of Terney seeking any prey she was still strong enough to kill. Authorities were forced to put her down, a sad day for a subspecies that numbers maybe 250 to 300 animals in the wild.

The story got worse as all three of Galia's 3-week-old cubs were also found nearby, dead, their bellies empty.

Galia was the fourth similar death of a radio-collared Amur (or Siberian) tiger in the 10 months leading up to her shooting. At the time, there was no indication of what caused the tigers' illness, and the Wildlife Conservation Society (WCS), which has been heavily involved in Amur tiger conservation, voiced fears of a mystery illness, possibly an epidemic spreading through the species.

Now, thanks to a cross-continental team of experts from the WCS and Russian health and veterinary organizations, we have an answer: Galia was infected with canine distemper, a viral disease which causes fever, diarrhea, labored breathing, dehydration and seizures, among other symptoms. It is usually fatal in the wild. The virus likely left Galia too weak to hunt, either for herself or for her young, and she probably entered the village looking for domesticated dogs, which would be easier to kill than wild game. The team presented their findings in September at a Russian symposium on wildlife diseases.

"With all the threats facing Siberian tigers—from poaching and habitat loss—relatively little research has been done on diseases that may afflict tigers," WCS Director of Russia Programs Dale Miquelle said in a prepared statement. "There are no records of tigers entering villages and behaving so abnormally before 2000, so this appears to be a new development and new threat. Understanding whether disease is a major source of mortality for Siberian tigers is crucial for future conservation efforts."

Now that canine distemper has been identified, the next step, according to WCS Chief Pathologist Denise McAloose, is to identify the source of the infection, which could be coming from domesticated dogs or other local carnivores such as wolves, badgers, red foxes or raccoon dogs. "From a vaccination perspective, vaccinating dogs would be a good first step," she says. "If this were to be a recommended strategy, decisions about the safest vaccine for dogs and tigers that might eat the dogs would need to be made." Distemper vaccinations are required for most pet dogs in the U.S., but not in Russia.

Vaccinating the tigers themselves would be next to impossible, Miquelle told me. "Siberian tigers live at extremely low densities (generally less than one in 100 square kilometers) and are very elusive. We are lucky to catch two to three tigers in two months of trapping effort when we are attempting to radio-collar tigers."

Even catching a tiger and vaccinating it once wouldn't do the trick, as a tiger could require multiple boosters over several weeks to properly vaccinate it against the disease, according to 2002 vaccination recommendations from the Siberian Tiger Species Survival Plan at the Henry Doorly Zoo in Omaha, Neb. Captive tigers are often routinely vaccinated for canine distemper, as well as the related feline distemper virus and other diseases.

One method used to vaccinate other wild carnivores, such as Ethiopian wolves, is leaving out bait injected with vaccines, but in that wouldn't work in Russia, where "it is more likely that any bait put out would be eaten by other carnivores (fox, sable, badgers, bears) before it was found by tigers," Miquelle says. Instead, he suggests it would be "better to focus on the source population."

Vaccinating local dogs to protect wild big cats has precedence. In Africa, dog-vaccination campaigns around the Serengeti appear to have reduced the impact of canine distemper on lions.

In addition to coming up with a vaccination program in Russia, WCS and Primorskaya State Agricultural Academy hope to set up a wildlife lab in Ussurisk to facilitate local diagnostic testing and help identify sick tigers faster. "Currently," McAloose says, "samples can be shipped to the US for histology and PCR (polymerase chain reaction) testing," but she says this takes "considerable time and is problematic in outbreak situations." Setting up a lab in Russia will take several years, though, as it requires not only funding and equipment but also trained staff.

It's uncertain how many Amur tigers, one of six living tiger subspecies on Earth, remain in the wild. The last official survey, conducted in 2005, estimated the population at between 430 and 500 animals. "Since then," Miquelle says, "nearly all experts agree that tiger numbers have declined in Russia, but nobody agrees on the extent of the decline." At 2009 report from WCS estimated the population at just 300 tigers.

Photo: A camera trap image of an Amur (Siberian) tiger in the Russian Far East. Courtesy of WCS Russia Program