White rhinos wiped out?

So apart from majoring in journalism in my Arts degree I am also majoring in Zoology in Science so the recent story about the death of the white rhinos at Dubbo zoo really sparked my interest. If you haven't read the story here is a link:

http://www.news.com.au/national/dubbo-zoo-mourns-loss-of-four-white-rhinos/story-e6frfkwi-1226306101785

Basically four rhinos died for unknown reasons at the Western Plains Zoo, Dubbo. Scientists and vets are still trying to figure out exactly why. With only 14,500 of these animals left this is a real scare for everyone. Could there be a new disease spreading that will wipe out the population? Rhinos in other zoos, like the ones up here at Australia Zoo, are now being closely monitored.