Tyger

The Tyger were a race of shape-shifters who reproduced by introducing a nano-virus into their victim's bloodstream that would eventually turn the victim into a Tyger.

History
The Tyger landed a spaceship in India in the early 20th century and took the form of tigers to blend into their environment. The Tygers were however bigger then Earth tigers and stood on two legs. They attacked a nearby British-occupied village and turned many of the townsfolk into Tygers. A British scout party helped by the Eighth Doctor managed to track down the last of the Tygers and kill them. (TN: The Eye of the Tyger)