Seems that it always exists in the animal population in some form, but can't discover why it flares up.
In Asia and in parts of the Americas and Africa, dogs remain the principal host. In 2010, an estimated 26,000 people died from rabies.[54] The majority of the deaths occurred in Asia and Africa.[3] India has the highest rate of human rabies in the world, primarily because of stray dogs,[55] whose number has greatly increased since a 2001 law forbade the killing of dogs.

But sounds serious. Apparently it is fatal to humans in almost 100% of cases if not treated before symptoms manifest.