I would go with something more exotic: Puma. No other species, just pure viral infection.
Long fangs and claws, and like any feline it could hide claws to move without a sound on any surface.
Despite rotting hairless body with all vertebras sticking out from it's back - and larger cranium - it would still be very agile, fast with short distances and capable of performing long leaps.
Very sharp sense of hearing and smelling. Improved tapetum lucidum granting sharp sense of sight in dark but alot worse than human's in daylight, nearly nonexistent. Would also have reduced depth and colour perception.
It would hunt like before mutation; waiting for pray, taking advantage of higher ground.
Most vulnerable part of body would be legs, to slow it down and take away it's capability to leap. Also easy to befuddle with high-pitched sounds and with direct bright light to it's eyes.
I would name it after feline goddess in ancient Egypt, Bastet.
Now THAT is my monster !