Death By Hyperdisease

It took less than a decade for native rats to become extinct on the Indian Ocean's previously uninhabited Christmas Island once Eurasian black rats jumped ship onto the island at the turn of the 20th century. But this story is more than the typical tale of direct competition.  According to new genetic research published in PLoS One on November 5, black rats carried a pathogen that exterminated two endemic species, Rattus macleari and R. nativitatis. 

http://www.sciencedaily.com/releases/2008/11/081105081955.htm