Cortex Leech
Cortex Leeches are loathsome creatures resembling Rippers that leap onto the face of their victims and insert long feelers into their ears, nose and eyes. These feelers are capable of manipulating the new host's brain, forcing them to become a dribbling puppet under the sway of the Hive Mind.
Tyranid zombie-makers.Allegedly, under the right conditions can infect things up to and including titans.