While I’ve focused a lot on the poaching risks to tigers, the fact is that their small populations make them vulnerable to other risks as well. For instance, one of the tiger reserves I visited in the Hun Chun area of Jilin, had a grand population of two Siberian tigers.
This was brought home recently when a wild Siberian tiger (Panthera tigris altaica) was caught in a stuporous state in a village in the Russia. Russian has most of the world’s wild Siberian (or Amur) tiger population, with numbers ranging between 400 to 500 animals. China has around 20 wild Siberian tigers and North Korea. Well, let’s just say while nobody has really looked, nobody really expects that North Korea will have done any work conserving any relic tiger populations that may be left.
The tiger suffered massive systemic infection and starvation, and subsequently died. The autopsy result showed the animal was suffering from a morbillivirus infection (canine distemper) . This is the first documented case of such an infection in the wild Siberian tiger population. The animal also tested positive for feline panleukopenia and feline coronavirus.
The disease risk in small populations can be catastrophic. Local tiger populations are simply not robust and do not cope with shocks well. This is one area where captive-breeding is actually very useful. It provides a backup population source- a kind of insurance policy against disasters.
 Kathy S. Quigley, James F. Evermann, Charles W. Leathers, Douglas L. Armstrong, John Goodrich, Neil M. Duncan and Dale G. Miquelle (2010). Morbillivirus Infection in a Wild Siberian Tiger in the Russian Far East.
Journal of Wildlife Diseases, 46(4), pp. 1252-1256